0001741830-21-000018 | 10-K | XBRL Viewer

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2020	Mar. 22, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-39592
Entity Registrant Name	Kronos Bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1895605
Entity Address, Address Line One	1300 So. El Camino Real
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	San Mateo
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94402
City Area Code	650
Local Phone Number	781-5200
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	KRON
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	No
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 0
Entity Common Stock, Shares Outstanding		56,047,683
Entity Central Index Key	0001741830
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission (SEC) subsequent to the date hereof pursuant to Regulation 14A in connection with the registrant's 2021 Annual Meeting of Stockholders, are incorporated by reference into Part III of this Annual Report on Form 10-K. Such proxy statement will be filed with the SEC not later than 120 days after the conclusion of the registrant's fiscal year ended December 31, 2020.

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 248,009	$ 32,570
Short-term investments	165,052	59,614
Prepaid expenses and other current assets	6,741	1,119
Total current assets	419,802	93,303
Long-term investments	49,001	4,762
Total property and equipment, net	13,646	3,721
Operating lease right-of-use assets	27,322	473
Restricted cash	2,027	0
Other noncurrent assets	166	427
Total assets	511,964	102,686
Current liabilities:
Accounts payable	4,550	1,506
Accrued expenses	4,974	818
Current portion of operating lease liabilities	937	285
Current portion of other liabilities	2,395	88
Total current liabilities	12,856	2,697
Noncurrent operating lease liabilities	31,120	211
Other noncurrent liabilities	2,469	74
Total liabilities	46,445	2,982
Commitments and contingencies (Note 13)
Convertible preferred stock, $0.001 par value; zero and 21,506,977 shares authorized as of December 31, 2020 and 2019, respectively; zero and 21,504,893 share issued and outstanding as of December 31, 2020 and 2019, respectively; zero and $123,016 liquidation preference as of December 31, 2020 and 2019, respectively.	0	122,907
Stockholder's equity:
Common stock, $0.001 par value, 200,000,000 and 40,000,000 shares authorized as of December 31, 2020 and 2019 respectively; 54,073,901 and 5,660,391 shares issued and outstanding as of December 31, 2020 and 2019, respectively.	54	6
Additional paid-in capital	577,390	271
Accumulated deficit	(111,906)	(23,462)
Accumulated other comprehensive loss	(19)	(18)
Total stockholders' equity (deficit)	465,519	(23,203)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 511,964	$ 102,686

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	0	21,506,977
Convertible preferred stock, shares outstanding (in shares)	0	21,504,893
Convertible preferred stock, shares issued (in shares)	0	21,504,893
Convertible preferred stock, liquidation preference	$ 0	$ 123,016
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	40,000,000
Common stock, shares issued (in shares)	54,073,901	5,660,391
Common stock, shares outstanding (in shares)	54,073,901	5,660,391

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 43,250	$ 13,446	$ 5,033
General and administrative	14,794	3,370	1,612
Total operating expenses	58,044	16,816	6,645
Loss from operations	(58,044)	(16,816)	(6,645)
Other Income and Expenses [Abstract]
Change in fair value of convertible notes payable	(27,408)	0	0
Interest expense	(3,890)	(3)	(76)
Interest and other income, net	898	702	0
Total other income (expense), net	(30,400)	699	(76)
Net loss	(88,444)	(16,117)	(6,721)
Other comprehensive income (loss):
Net unrealized loss on available-for-sale securities	(1)	(18)	0
Net comprehensive loss	$ (88,445)	$ (16,135)	$ (6,721)
Net loss per share, basic and diluted (in dollars per share)	$ (5.43)	$ (3.05)	$ (1.38)
Weighted-average shares of common stock, basic and diluted (in shares)	16,277,247	5,278,748	4,856,774

Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2017	0
Convertible preferred stock, beginning balance at Dec. 31, 2017	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A convertible preferred stock, net of issuance costs (in shares)	7,806,977
Issuance of Series A convertible preferred stock, net of issuance costs	$ 17,985
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2018	7,806,977
Convertible preferred stock, ending balance at Dec. 31, 2018	$ 17,985
Common stock, beginning balance (in shares) at Dec. 31, 2017		4,844,551
Beginning balance at Dec. 31, 2017	(610)	$ 5	$ 9	$ 0	$ (624)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from common stockholder	4		4
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock (in shares)		121,676
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	1		1
Stock-based compensation expense	30		30
Net unrealized loss on available-for-sale securities	0
Net loss	(6,721)				(6,721)
Common stock, ending balance (in shares) at Dec. 31, 2018		4,966,227
Beginning balance at Dec. 31, 2018	$ (7,296)	$ 5	44	0	(7,345)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A convertible preferred stock, net of issuance costs (in shares)	13,697,916
Issuance of Series A convertible preferred stock, net of issuance costs	$ 104,922
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2019	21,504,893
Convertible preferred stock, ending balance at Dec. 31, 2019	$ 122,907
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock (in shares)		694,164
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	115	$ 1	114
Stock-based compensation expense	113		113
Net unrealized loss on available-for-sale securities	(18)			(18)
Net loss	(16,117)				(16,117)
Common stock, ending balance (in shares) at Dec. 31, 2019		5,660,391
Beginning balance at Dec. 31, 2019	$ (23,203)	$ 6	271	(18)	(23,462)
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2020	0
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of preferred stock into common stock (in shares)	(21,504,893)
Conversion of preferred stock into common stock	$ (122,907)
Convertible preferred stock, ending balance at Dec. 31, 2020	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock (in shares)		795,026
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	645		645
Stock-based compensation expense	3,753		3,753
Net unrealized loss on available-for-sale securities	(1)			(1)
Issuance of common stock upon initial public offering, net of issuance costs of $23,775 (in shares)		15,131,579
Issuance of common stock upon initial public offering, net of commission and issuance costs of $23,775	263,725	$ 15	263,710
Conversion of preferred stock into common stock (in shares)		22,687,625
Conversion of preferred stock into common stock	122,907	$ 23	122,884
Issuance of common stock upon conversion of convertible notes and change in fair value of convertible notes at time of conversion (in shares)	186,137	$ 10	186,127
Issuance of common stock upon conversion of convertible notes		9,799,280
Net loss	(88,444)				(88,444)
Common stock, ending balance (in shares) at Dec. 31, 2020		54,073,901
Beginning balance at Dec. 31, 2020	$ 465,519	$ 54	$ 577,390	$ (19)	$ (111,906)

Statements of Convertible Preferred Stock and Stockholders' Deficit (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 7.67	$ 2.31
Preferred Stock \| Convertible preferred stock
Payments of stock issuance costs	$ 78	$ 31

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (88,444)	$ (16,117)	$ (6,721)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	839	356	91
Net amortization/accretion on available-for-sale securities	326	(4)	0
Change in accrued interest on available-for-sale securities	265	45	0
Change in fair value of convertible notes payable	27,408	0	0
Debt issuance costs on convertible notes payable	3,889	0	0
Acquired in-process research and development	3,565	0	0
Stock-based compensation expense	3,753	113	30
Noncash lease expense	4,027	249	69
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,226)	(607)	5
Other long-term assets	261	(153)	(247)
Accounts payable	2,807	716	(28)
Accrued expenses	3,229	620	193
Right-of-use operating assets and liabilities, net	685	(252)	(43)
Other liabilities	4,704	(48)	210
Net cash used in operating activities	(37,912)	(15,082)	(6,441)
Cash flows from investing activities:
Purchase of property and equipment	(9,568)	(2,948)	(1,075)
Purchase of available-for-sale securities	(229,328)	(64,633)	0
Maturities of available-for-sale securities	78,661	0	0
Net cash used by investing activities	(160,235)	(67,581)	(1,075)
Cash flows from financing activities:
Proceeds from initial public offering, net of commission and issuance costs	263,725	0	0
Proceeds from issuance of convertible notes, net of issuance costs	151,275	0	0
Principal payments on finance lease	(32)	(30)	(72)
Proceeds from issuance of common stock upon exercise or vesting of stock options	645	115	5
Proceeds from issuance of preferred stock, net of financing fees	0	104,922	16,285
Net cash provided by financing activities	415,613	105,007	16,218
Net increase in cash and cash equivalents	217,466	22,344	8,702
Cash, cash equivalents and restricted cash at beginning of period	32,570	10,226	1,524
Cash, cash equivalents and restricted cash at end of period	250,036	32,570	10,226
Supplemental disclosures of non-cash activities:
Common stock issued on conversion of convertible preferred stock	122,907	0	0
Common stock issued on conversion of convertible notes payable	186,137	0	0
Property and equipment additions included in accounts payable and accrued expenses	1,280	116	104
Right-of-use asset obtained in exchange for operating lease liability	28,839	4	810
Property and equipment obtained in exchange for finance lease liability	0	0	139
Issuance of convertible preferred stock upon conversion of convertible notes	$ 0	$ 0	$ 1,700

Nature of Operations and Basis of Presentation	12 Months Ended
Nature of Operations and Basis of Presentation	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Basis of Presentation	NATURE OF OPERATIONS AND BASIS OF PRESENTATION Kronos Bio, Inc. (Kronos or the Company), a Delaware corporation, was incorporated on June 2, 2017. The Company is a clinical-stage biopharmaceutical company dedicated to the discovery and development of novel cancer therapeutics designed to transform patient outcomes through a precision medicine strategy by targeting dysregulated transcription. The Company operates in one business segment, the development of biopharmaceutical products. Basis of Presentation The accompanying financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and accounting principles generally accepted in the United States of America (GAAP). Initial Public Offering In October 2020, the Company completed an initial public offering (IPO) of its common stock. In connection with its IPO, the Company issued and sold 15,131,579 shares of its common stock, which included 1,973,684 shares of its common stock issued and sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $19.00 per share. As a result of the IPO, the Company received $263.7 million in net proceeds, after deducting underwriting discounts and commissions of $20.1 million and offering expenses of $3.7 million payable by the Company. At the closing of the IPO, 21,504,893 shares of outstanding convertible preferred stock were automatically converted to 22,687,625 shares of common stock and the 2020 Notes (See Note 15) were automatically converted into 9,610,713 shares of common stock. At the closing of the IPO, the Gilead Note (See Note 13) was also converted into 188,567 shares of common stock. Following the IPO, there were no shares of convertible preferred stock outstanding. Forward Stock Split On October 2, 2020, the Company filed an amendment to the Company’s amended and restated certificate of incorporation to effect a forward split of shares of the Company’s common stock on a 1.055-for-1 basis (the Forward Stock Split). In connection with the Forward Stock Split, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionally adjusted such that the common stock issuable upon conversion of such preferred stock was increased in proportion to the Forward Stock Split. The par value of the common stock was not adjusted as the result of the Forward Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these financial statements have been retrospectively adjusted to reflect the effect of the Forward Stock Split for all periods presented. Need for Additional Capital The Company has sustained operating losses and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities. The Company had cash, cash equivalents and investments of $462.1 million as of December 31, 2020. Since inception through December 31, 2020, the Company has incurred a cumulative net operating loss of $111.9 million. Management expects to incur additional losses in the future to fund its operations and conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan. The Company intends to raise additional capital through the issuance of equity securities, debt financings or other sources in order to further implement its business plan. However, if such financing is not available when needed and at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its product candidates. The Company expects that its cash and cash equivalents and investments will be sufficient to fund its operations for a period of at least one year from the date the accompanying financial statements are filed with the Securities and Exchange Commission (SEC). The Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 pandemic will have on its financial condition and operations, including ongoing and planned clinical trials. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments, including the duration and spread of the pandemic and related governmental advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected. The future viability of the Company is dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a material adverse effect on its financial condition and ability to pursue business strategies. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaboration arrangements or obtain government grants. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce, or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. In the event that the Company requires additional funding, there can be no assurance that it will be successful in obtaining sufficient funding on terms acceptable to the Company to fund its continuing operations, if at all.

Significant Accounting Policies, Estimates and Judgments

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Significant Accounting Policies, Estimates and Judgments

SIGNIFICANT ACCOUNTING POLICIES, ESTIMATES AND JUDGMENTS

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual of research and development expenses, the fair value of investments, income tax uncertainties, the valuation of equity instruments and the incremental borrowing rate for determining the operating lease assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Research and Development Expenses

Research and development (R&D) expenses consist primarily of personnel costs, including salaries, benefits and stock-based compensation, discovery and development research performed by contract research organizations (CROs), materials and supplies, licenses and fees and overhead allocations consisting of various support and facility-related costs. The Company expenses R&D costs as the services are performed or the goods are received. Research and development expenses for the year ended December 31, 2020 included $6.6 million related to acquired intangible assets as research and development costs pursuant to the Asset Purchase Agreement with Gilead (See Note 13) as, at the time of acquisition of the asset, the technology was under development; was not approved by the U.S. Food and Drug Administration or other regulatory agencies for marketing; had not reached technical feasibility; or otherwise had no foreseeable alternative future use. There were no acquired intangible assets expensed for the years ended December 31, 2019 and 2018.

CRO costs are a significant component of R&D expenses. The Company monitors levels of performance under each significant contract through communications with its CROs. The Company accrues costs for discovery research and development performed by CROs over the service periods specified in the contracts and adjusts its estimates, if required, based upon its ongoing review of the level of effort and costs actually incurred by the CROs. All of the Company’s material CRO contracts are terminable by the Company upon written notice and it is generally only liable for actual services completed by the CRO and certain non-cancellable expenses incurred at any point of termination.

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.

Restricted Cash

The Company has deposited cash of $2.0 million as of December 31, 2020 to secure a letter of credit in connection with the lease of the new Cambridge facility (See Note 14). The Company has classified the restricted cash as a noncurrent asset on its balance sheets.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents and investments. The primary objectives for the Company’s investment portfolio are the preservation of capital and the maintenance of liquidity. The Company does not enter into any investment transaction for trading or speculative purposes.

The Company’s investment policy limits investments to certain types of instruments such as certificates of deposit, money market instruments, obligations issued by the U.S. government and U.S. government agencies as well as corporate debt securities, and places restrictions on maturities and concentration by type and issuer. The Company maintains cash balances in excess of amounts insured by the FDIC and concentrated within a limited number of financial institutions. The accounts are monitored by management and management believes that the financial institutions are financially sound, and, accordingly, minimal credit risk exists with respect to these financial institutions. As of December 31, 2020 and 2019, the Company has not experienced any credit losses in such accounts or investments.

The Company is subject to a number of risks common for biopharmaceutical companies, including, but not limited to, dependency on the clinical and commercial success of its product candidates, ability to obtain regulatory approval of its product candidates, the need for substantial additional financing to achieve its goals, uncertainty of broad adoption of its approved products, if any, by physicians and patients, significant competition, and untested manufacturing capabilities.

Investments

Investments are available-for-sale and are carried at estimated fair value. The Company’s valuations of available-for-sale securities are generally derived from independent pricing services based upon quoted prices in active markets for similar securities, with prices adjusted for yield and number of days to maturity, or based on industry models using data inputs, such as interest rates and prices that can be directly observed or corroborated in active markets. Management determines the appropriate classification of its investments in debt securities at the time of purchase. Investments with original maturities beyond three months at the date of purchase and which mature at, or less than 12 months from, the balance sheet date are classified as short-term investments.

Unrealized gains and losses are excluded from earnings and are reported as components of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not that it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in interest and other income, net. The cost of investments sold is based on the specific-identification method. Interest income on investments is included in interest and other income, net on the Company’s statements of operations and comprehensive loss.

Fair Value Measurement

Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.

Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active.

Level 3— Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The fair value estimates are made at a discrete point in time based on relevant market information and information about the financial instruments. Fair value estimates are based on judgments regarding future expected loss experience, current economic conditions, risk characteristics of various financial instruments, and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and, therefore, cannot be determined with precision. Changes in assumptions could significantly affect the estimates.

As of December 31, 2020, the Company recorded financial assets requiring fair value measurement. The financial assets include cash equivalents and investments. The financial liabilities recorded during the year ended December 31, 2020, consisting of the convertible promissory note (Gilead Note) from the Gilead Asset Purchase Agreement (See Note 13) and the convertible promissory notes (2020 Notes) sold in August 2020 (See Note 15), were settled upon the closing of the IPO. As a result, there were no financial liabilities requiring fair value measurement as of December 31, 2020.

As of December 31, 2019, the Company recorded financial assets, including cash equivalents, and investments, requiring fair value measurement. There were no financial liabilities requiring fair value measurement as of December 31, 2019.

Fair Value Option

Under U.S. GAAP, the Company has the irrevocable option to report most financial assets and financial liabilities at fair value on an instrument by instrument basis, with changes in fair value reported in the statements of operations and comprehensive loss. The option was elected for the treatment of the Company’s convertible promissory note from the Gilead Asset Purchase Agreement entered into in July 2020 (See Note 13) and the convertible promissory notes (2020 Notes) sold in August 2020 (See Note 15) in order to more accurately reflect the economic value of the notes at the time of issuance and again upon settlement.

Property and Equipment, Net

Property and equipment is stated at cost less accumulated depreciation and amortization. Depreciation and amortization are recognized using the straight-line method over the estimated useful lives of the respective assets. Leasehold improvements are amortized over the lesser of their useful lives or the remaining life of the lease. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the statements of operations and comprehensive loss in the period realized. Repairs and maintenance costs are expensed as incurred.

Estimated useful lives in years are generally as follows:


Description						Estimated Useful Life
Lab equipment						3 to 7 years
Leasehold improvements						Shorter of useful life or lease term
Furniture and fixtures						5 to 7 years

Deferred Offering Costs

Offering costs, including legal, accounting, and filing fees related to the IPO, were deferred and were offset against the offering proceeds upon the completion of the IPO. Prior to the IPO, all deferred offering costs were capitalized in other noncurrent assets. Upon the completion of the IPO in October 2020, $3.7 million of deferred offering costs were reclassified to additional paid in capital on the accompanying statement of convertible preferred stock and stockholders’ equity (deficit). There were no deferred offering costs recorded as of December 31, 2019.

Leases

The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use (ROU) assets, current portion of operating lease liabilities, and noncurrent operating lease liabilities on the Company’s balance sheet. Finance leases are included in property and equipment, current portion of other liabilities, and other noncurrent liabilities on the balance sheet.

ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The operating lease ROU asset also includes any lease payments and initial direct costs incurred, net of lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company elected to exclude from its balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases.

Impairment of Long-Lived Assets

Long-lived assets, including property and equipment, are reviewed for impairment whenever facts or circumstances either internally or externally may suggest that the carrying value of an asset or asset group may not be recoverable. Should there be an indication of impairment, the Company tests for recoverability by comparing the estimated undiscounted future cash flows expected to result from the use of the asset or asset group and its eventual disposition to the carrying amount of the asset or asset group. Any excess of the carrying value of the asset or asset group over its estimated fair value is recognized as an impairment loss.

Stock-Based Compensation

The Company has an equity incentive plan under which various types of equity-based awards are granted, including stock options, restricted stock awards (RSAs), and restricted stock units (RSUs). Prior to the year ended December 31, 2020, only stock options had been issued under the plan. The Company measures stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes stock-based compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company calculates the fair value measurement of stock options using the Black-Scholes option-pricing model. Forfeitures are accounted for as they occur. The fair value of the RSA and RSUs is equal to the fair value of the Company’s common stock on the grant date of the award.

Income Taxes

The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on differences between the financial statement carrying amounts and the tax bases of the assets and liabilities using the enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2020 and 2019, other comprehensive loss consisted of unrealized gains and losses from available-for-sale securities. There was no difference between net loss and comprehensive loss for the year ended December 31, 2018.

Net Loss Per Share

Basic net loss per share is computed using the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed using the sum of the weighted-average number of shares of common stock outstanding during the period and the effect of dilutive securities.

In periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive shares of common stock are not assumed to have been issued if their effect on net loss per share is anti-dilutive.

Recently Adopted Accounting Pronouncements

In August 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2018-13, Fair Value Measurement (Topic 820) Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement (ASU 2018-13). The Company adopted ASU No. 2018-13 on January 1, 2019. This standard modifies certain disclosure requirements on fair value measurements. The adoption of this standard did not have a material impact on the Company’s financial statements.

In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (ASU 2018-07). The new standard involves several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. Early adoption is permitted for any entity in any interim or annual period for which financial statements have not been issued or made available for issuance, but not before an entity adopts Accounting Standards Codification (ASC) 606, Revenue from Contracts with Customers. The Company elected to early adopt ASU 2018-07 on January 1, 2018 and has reflected the adoption in its financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Section A—Leases: Amendments to the FASB Accounting Standards Codification (ASU 2016-02 or ASC 842). The new standard revised guidance related to leases to increase transparency and comparability among organizations by requiring the recognition of ROU assets and lease liabilities on the balance sheet. Most prominent among the changes in the standard is the recognition of ROU assets and lease liabilities by lessees for those leases classified as operating leases. Under the standard, disclosures are required to meet the objective of enabling users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. The Company elected to early adopt the standard effective January 1, 2018 and elected the available practical expedients on adoption.

In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows, Restricted Cash (ASU 2016-18). This ASU requires changes in restricted cash during the period to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. If cash, cash equivalents and restricted cash are presented in more than one line item on the balance sheet, the new guidance requires a reconciliation of the total in the statement of cash flows to the related captions in the balance sheet. The Company elected to adopt ASU 2016-18 on January 1, 2019 and has reflected the adoption in its financial statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows:


	December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	248,009	$	32,570
Restricted cash	2,027		—
Total cash, cash equivalents and restricted cash as shown on the statements of cash flows	$	250,036	$	32,570

In addition, the Company adopted ASU No 2016-15, Statement of Cash Flow (ASU 2016-15) in 2019. The guidance reduces diversity in how certain cash receipts and cash payments are presented and classified in the statements of cash flows. The adoption of ASU 2016-15 did not have a material impact on the Company’s financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. The standard became effective for the Company in the first quarter of 2020, with early adoption permitted beginning the first quarter of 2019. The modified retrospective approach should be applied upon adoption of this new guidance. The Company’s financial instruments that are in the scope of ASU 2016-13 include available-for-sale debt securities. The Company adopted this standard on January 1, 2020 and this amendment did not have a material impact on its financial statements.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. This guidance will be effective for the Company in the first quarter of 2021 on a prospective basis, and early adoption is permitted. The Company has adopted this standard as of January 1, 2020, which did not have a material impact on its financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

FAIR VALUE MEASUREMENTS

The Company follows authoritative accounting guidance, which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability.

The Company measures and reports its cash equivalents, investments, and convertible notes at fair value.

Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as Level 1. Investments measured at fair value based on inputs other than quoted prices that are derived from observable market data are classified as Level 2.

Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of December 31, 2020 and 2019 were as follows:


	December 31, 2020
	Level 1		Level 2		Level 3		Fair Value
			(in thousands)
Financial Assets:
Money market funds	$	114,184	$	—	$	—	$	114,184
Certificates of deposit	1,229		—		—		1,229
Corporate bonds	—		40,736		—		40,736
U.S. agency securities	—		10,001		—		10,001
U.S. treasury securities	284,721		—		—		284,721
Total financial assets	$	400,134	$	50,737	$	—	$	450,871


	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds	$	112	$	—	$	—	$	112
Certificates of deposit	1,715		—		—		1,715
Commercial paper	—		4,489		—		4,489
Corporate bonds	—		26,432		—		26,432
U.S. agency securities	—		1,499		—		1,499
U.S. treasury securities	36,880		—		—		36,880
Total financial assets	$	38,707	$	32,420	$	—	$	71,127

The carrying amounts of accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income- and market-based approaches, for which all significant inputs are observable, either directly or indirectly.

The Company did not have any financial assets or liabilities as of December 31, 2020 and 2019 that required Level 3 inputs. There were no transfers of assets between the fair value measurement levels during any of the periods presented in the accompanying financial statements.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Investments

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Investments

INVESTMENTS

The fair value and amortized cost of available-for-sale securities by major security type as of December 31, 2020 and 2019 were as follows:


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
			(in thousands)
Money market funds	$	114,184	$	—	$	—	$	114,184
Certificates of deposit	1,225		4		—		1,229
Corporate bonds	40,743		9		(16)		40,736
U.S. agency securities	9,999		2		—		10,001
U.S. treasury securities	284,739		3		(21)		284,721
Total cash equivalents and investments	$	450,890	$	18	$	(37)	$	450,871


	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	112	$	—	$	—	$	112
Certificates of deposit	1,715		—		—		1,715
Commercial paper	4,490		—		(1)		4,489
Corporate bonds	26,444		1		(13)		26,432
U.S. agency securities	1,500		—		(1)		1,499
U.S. treasury securities	36,884		1		(5)		36,880
Total cash equivalents and investments	$	71,145	$	2	$	(20)	$	71,127

These available-for-sale securities were classified on the Company’s balance sheets as of December 31, 2020 and 2019 as:


	Fair Value
	December 31,
	2020		2019
	(in thousands)
Cash equivalents	$	236,818	$	6,751
Short-term investments	165,052		59,614
Long-term investments	49,001		4,762
Total cash equivalents and investments	$	450,871	$	71,127

The fair values of available-for-sale securities by contractual maturity as of December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
	(in thousands)
Due in 1 year or less	$	287,686	$	66,253
Due in 1 to 2 years	49,001		4,762
Instruments not due at a single maturity date	114,184		112
Total cash equivalents and investments	$	450,871	$	71,127

As of December 31, 2020 and 2019, the remaining contractual maturities of available-for-sale securities were less than two years, respectively. There have been no significant realized losses on available-for-sale securities for any of the periods presented in the accompanying financial statements. Based on the Company’s review of its available-for-sale securities, the Company believes that it had no other-than-temporary impairments on these securities as of December 31, 2020 and 2019 because the Company does not intend to sell these securities nor does it believe that it will be required to sell these securities before the recovery of their amortized cost basis. Gross realized gains and gross realized losses were immaterial for any of the periods presented in the accompanying financial statements.

As of December 31, 2020 and 2019, unrealized losses on available-for-sale investments are not attributed to credit risk. The Company believes that an allowance for credit losses is unnecessary because the unrealized losses on certain of the Company’s marketable securities are due to market factors.

Prepaid Expenses And Other Current Assets

12 Months Ended

Dec. 31, 2020

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Prepaid Expenses and Other Current Assets

PREPAID EXPENSES AND OTHER CURRENT ASSETS

Prepaid expenses and other current assets consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Accrued interest on short-term available-for-sale securities	$	612	$	198
Prepaid equipment service contracts	383		191
Prepaid external research and development and outside services	1,889		113
Prepaid software	736		180
Prepaid insurance	2,881		23
Prepaid rent and other	240		414
Total prepaid expenses and other current assets	$	6,741	$	1,119

Property and Equipment, Net

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

PROPERTY AND EQUIPMENT, NET

Property and equipment, net consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Property and equipment:
Lab equipment	$	5,619	$	3,978
Leasehold improvements	8,957		—
Furniture and fixtures	216		—
Finance lease on R&D equipment	139		139
Construction in progress	—		50
Total property and equipment	14,931		4,167
Less: Accumulated depreciation and amortization	(1,285)		(446)
Total property and equipment, net	$	13,646	$	3,721

Depreciation and amortization expense was $0.8 million, $0.4 million, and $0.1 million for the years ended December 31, 2020, 2019, and 2018, respectively.

Accrued Expenses and Current Portion of Other Liabilities

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Accrued Expenses and Current Portion of Other Liabilities

ACCRUED EXPENSES AND CURRENT PORTION OF OTHER LIABILITIES

Accrued expenses consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Accrued compensation	$	2,274	$	528
Accrued taxes	558		43
External research and development	1,017		241
Accrued leasehold improvements	927		—
Other accrued expenses	198		6
Total accrued expenses	$	4,974	$	818

Current portion of other liabilities consist of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Current portion of finance lease liability	$	5	$	32
Current portion of unvested early exercised share liability	2,174		56
ESPP withholdings	216		—
Total current portion of other liabilities	$	2,395	$	88

Preferred Stock

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Preferred Stock

PREFERRED STOCK

Convertible Preferred Stock

On May 22, 2018, the Company completed a private placement (Series Seed Financing) in which it issued an aggregate of 7,806,977 shares of its Series Seed Convertible Preferred Stock (Series Seed Preferred Stock) at a purchase price of $2.30769 per share, for aggregate gross proceeds of $18.0 million.

On July 1, 2019, the Company completed a private placement (the Series A Financing) in which it issued 13,697,916 shares of its Series A Convertible Preferred Stock (Series A Preferred Stock) at a purchase price of $7.6654 per share, for aggregate gross proceeds of $105.0 million less issuance costs of $0.1 million.

Upon the completion of the IPO (See Note 1), all outstanding shares of convertible preferred stock were automatically converted into 22,687,625 shares of common stock.

The Preferred Stock consisted of the following as of December 31, 2019:


	December 31, 2019
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
	(in thousands, except share amounts)
Series Seed Preferred Stock	7,806,977	7,806,977	$	17,985	$	18,016	8,236,347
Series A Preferred Stock	13,700,000	13,697,916	104,922		105,000		14,451,278
Total	21,506,977	21,504,893	$	122,907	$	123,016	22,687,625

Preferred Stock

Pursuant to the Amended and Restated Certificate of Incorporation filed on October 14, 2020, as amended, the Company is authorized to issue a total of 10,000,000 shares of undesignated preferred stock, par value $0.001, of which no shares were issued or outstanding as of December 31, 2020.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2020
Equity [Abstract]
Common Stock	COMMON STOCKPursuant to the Company’s amended and restated certificate of incorporation filed on October 14, 2020, as amended, the Company is authorized to issue a total of 200,000,000 shares of its common stock, par value $0.001. As of December 31, 2020 and December 31, 2019, there were 54,073,901 and 5,660,391 shares issued and outstanding, respectively.Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company's stockholders. Subject to the rights of the Preferred Stock, holders of the Company’s common stock are entitled to receive dividends, as may be declared by the Board of Directors.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

STOCK-BASED COMPENSATION

2017 Equity Incentive Plan

The Company's 2017 Equity Incentive Plan, as amended (the Prior Plan), provided that the Company may sell or issue shares of common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of shares of common stock, to employees, members of the Board of Directors, and consultants of the Company. Under the Prior Plan, the total number of shares the Company may have issued was 3,692,500 as of December 31, 2019.

2020 Equity Incentive Plan

In October 2020, the Company adopted its 2020 Equity Incentive Plan (the 2020 Plan) which replaced the 2017 Equity Incentive Plan (Prior Plan) upon completion of the IPO. The 2020 Plan provides for the grant of incentive stock options or nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of awards to employees, directors, and consultants of the Company. Under the 2020 Plan, the maximum number of shares of common stock that may be issued increased to 11,938,152 shares. The number of shares of common stock reserved for issuance under the 2020 Plan will automatically increase each year for a period of ten years, beginning in 2021 and continuing through 2030, in an amount equal to (1) 5.0% of the total numbers of shares of the Company’s common stock outstanding on December 31st of the immediately preceding year, or (2) a lesser number of shares determined by the Board of Directors no later than December 31st of the immediately preceding year.

Under both the 2020 Plan and the Prior Plan, the exercise prices, vesting, and other restrictions are determined at the discretion of the Board of Directors, or a designated committee thereof, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the common stock on the date of grant and the term of stock option may not be greater than 10 years. The Company recognizes the impact of forfeitures on stock-based compensation expense as forfeitures occur. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions. Vesting periods are determined at the discretion of the Board of Directors. Stock options typically vest over four years. The maximum contractual term is 10 years.

As of December 31, 2020, there were 3,696,370 shares reserved by the Company under the 2020 Plan for the future issuance of equity awards.

Stock Option Valuation

The Company estimates the fair value of each stock option grant on the date of grant using the Black-Scholes option-pricing model. This model requires the use of highly subjective assumptions to determine the fair value of stock-based awards, including:

•Fair Value of Common Stock—For grants before the completion of the IPO in October 2020 when the Company was a privately held company with no public market for its common stock, the fair value of its common stock underlying share-based awards was estimated on each grant date by its Board of Directors. In order to determine the fair value of our common stock underlying option grants, the Company’s Board of Directors considered, among other things, valuations of its common stock prepared by an unrelated third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accounts Practice Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. For all grants subsequent to our IPO in October 2020, the fair value of common stock was determined by taking the closing price per share of common stock as reported on the Nasdaq Stock Market.

•Expected Term—The expected term represents the period that the stock-based awards are expected to be outstanding. The Company uses the simplified method to determine the expected term, which is based on the average of the time-to-vesting and the contractual life of the options.

•Expected Volatility—The expected volatility for the years ended December 31, 2020, 2019 and 2018 is estimated based on the average historical volatilities of common stock of comparable publicly traded entities over a period equal to the expected term of the stock option grants. The comparable companies are chosen based on their size, stage in the product development cycle or area of specialty. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

•Risk-Free Interest Rate—The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the awards.

•Expected Dividend—The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero.

The Black-Scholes option-pricing model assumptions that the Company used to determine the grant-date fair value of stock options for the years ended December 31, 2020, 2019, and 2018 were as follows, presented on a weighted-average basis:


	Year Ended December 31,
	2020		2019		2018
Fair value of common stock per share	$	10.52	$	2.27	$	0.24
Expected term (in years)	6.00		6.07		6.08
Expected volatility	78.36%		70.20%		67.93		%
Risk-free interest rate	0.71%		1.81%		2.85		%
Expected dividend	—%		—%		—		%

The weighted-average grant-date fair value per share of stock options granted, using the assumptions listed above, was $7.25, $1.42, and $0.16 during the years ended December 31, 2020, 2019, and 2018, respectively. The weighted-average grant-date fair value per share of stock options vested was $1.01, $0.14, and $0.03 during the years ended December 31, 2020, 2019, and 2018, respectively.

Stock Options

Stock option activity under the 2020 Plan as of December 31, 2020 is summarized as follows:


	Number of Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
				(in years)	(in thousands)
Balance at December 31, 2019	1,726,233	$	1.19
Granted	5,196,257	10.52
Forfeited	(121,086)	0.85
Exercised	(550,245)	1.17
Balance at December 31, 2020	6,251,159	$	8.95	9.27	$	132,089
Exercisable at December 31, 2020	297,609	$	2.37	8.76	$	8,185
Unvested and expected to vest at December 31, 2020	5,953,550	$	9.28	9.30	$	123,904

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on the Nasdaq Global Select Market on December 31, 2020. The intrinsic value of options exercised for the years ended December 31, 2020, 2019, and 2018 was $6.1 million, $0.7 million and $10,000, respectively, determined as of the applicable date of exercise. There was no future tax benefit related to options exercised, as the Company had accumulated net operating losses as of December 31, 2020 and December 31, 2019.

For the years ended December 31, 2020, 2019, and 2018, total stock-based compensation related to stock options was classified in the Company’s statements of operations and comprehensive loss as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development expenses	$	1,061	$	54	$	3
General and administrative expenses	1,451		54		22
Total stock-based compensation expense	$	2,512	$	108	$	25

As of December 31, 2020 and 2019, there was $36.3 million and $1.3 million of unrecognized stock-based compensation related to stock options, respectively, which is expected to be recognized over a weighted average period of 3.70 and 3.64 years, respectively.

2020 Employee Stock Purchase Plan

In October 2020, the Company adopted its 2020 Employee Stock Purchase Plan (ESPP), which initially reserved 688,000 shares of the Company’s common stock for employee purchase under terms and provisions established by the Board of Directors. The number of shares of our common stock reserved for issuance under the ESPP automatically increases in 2021 and continuing through 2030, by the lesser of (i) 1.0% of the total number of shares of common stock outstanding on December 31st of the immediately preceding year, and (ii) 1,376,000 shares, except before the date of any increase, the Board of Directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). The ESPP is intended to qualify as an ‘employee stock purchase plan’ under Section 423 of the Internal Revenue Code. Under the current offering adopted pursuant the ESPP, each offering period shall not exceed 27 months, with shorter duration purchase periods within each offering. Employees are eligible to participate if they are employed by the Company for at least 20 hours per week and more than five months of the year.

Under the ESPP, employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of common stock on the first trading day of each offering period or on the purchase date. The initial offering period commenced on October 8, 2020, the date of the underwriting agreement related to the Company’s IPO. A new offering (Subsequent Offering) will automatically begin in 2021, and every six months thereafter over the term of the ESPP. Each Subsequent Offering will be approximately 24 months long and will consist of four purchase periods (with the purchase dates occurring on June 30 and December 31 each year during the term of the Subsequent Offering). Contributions under the ESPP are limited to a maximum of 15% of an employee’s eligible compensation.

The fair values of the rights granted under the ESPP were calculated using the following assumptions:


						Year Ended December 31, 2020
Expected term (in years)						0.68-2.19
Expected volatility						89.25%-110.84%
Risk-free interest rate						0.12%-0.19%
Dividend yield						—%

For the year ended December 31, 2020, total stock-based compensation related to the ESPP was $0.3 million, with $0.1 million recorded in general and administrative expenses and $0.2 million recorded in research and development expenses in the statements of operations and comprehensive loss.

Restricted Stock

Restricted stock awards and units as of December 31, 2020 are summarized as follows:


	Number of Restricted Stock	Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Vesting Life	Aggregate Intrinsic Value
				(in years)	(in thousands)
Unvested at December 31, 2019	215,220	$	0.05
Granted - restricted stock awards and units	839,758	22.15
Vested and converted to shares	(244,781)	2.34
Unvested at December 31, 2020	810,197	$	22.26	2.79	$	24,201
Vested and expected to vest at December 31, 2020	810,197	$	22.26	2.79	$	24,201

For the year ended December 31, 2020, the Company granted 274,341 restricted stock awards (RSAs) to a certain executive officer pursuant to the 2020 Plan. The RSAs are subject to lapsing repurchase rights and in order to vest, are subject to the holder’s service to the Company.

The Company recorded stock-based compensation expense for the RSAs of $0.6 million in general and administrative expenses and $5,000 in research and development expenses in the statements of operations and comprehensive loss for the year ended December 31, 2020. For the years ended December 31, 2019 and 2018, the Company recorded $5,000 in each year, respectively, in research and development expenses in the statements of operations and comprehensive loss. As of December 31, 2020, there was $0.5 million of unrecognized stock-based compensation related to RSAs, which is expected to be recognized over a weighted average period of 3.58 years.

The total grant date fair value for RSAs vested during the years ended December 31, 2020, 2019, and 2018 was $0.6 million, $5,000, and $5,000, respectively.

In December 2020, the Company issued 565,417 restricted stock units (RSUs) to executive officers pursuant to the 2020 Plan. These RSUs have a three year vest period and in order to vest, the holder is required to provide service to the Company.

The Company recognized $0.3 million of stock-based compensation expense related to the RSUs for the year ended December 31, 2020, of which $0.1 million and $0.2 million are recorded in research and development and general and administrative expenses, respectively, in the current year statement of operations and comprehensive loss. As of December 31, 2020, there was $17.1 million of unrecognized stock-based compensation related to RSUs, which is expected to be recognized over a weighted average period of 2.94 years. No RSUs have vested as of December 31, 2020.

Stock-Based Compensation Summary

Total stock-based compensation expense was classified in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2020, 2019, and 2018 as follows for stock options, RSAs, RSUs, and ESPP:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development expenses	$	1,390	$	59	$	8
General and administrative expenses	2,363		54		22
Total stock-based compensation expense	$	3,753	$	113	$	30

Early Exercised Options

The terms of certain stock options granted under the Prior Plan allow the holder to exercise options prior to vesting. The shares related to early exercised stock options are subject to the Company’s lapsing repurchase right upon termination of employment or service on the Board of Directors at the lesser of the original purchase price or fair market value at the time of repurchase. In order to vest, the holders are required to provide continued service to the Company. The early exercise by an employee or consultant of a stock option is not considered to be a substantive exercise for accounting purposes, and therefore the payment received by the employer for the exercise price is recognized as a liability. For accounting purposes, unvested early exercised shares are not considered issued and outstanding and therefore are not reflected as issued and outstanding in the accompanying statements of convertible preferred stock and stockholders' equity (deficit) until the awards vest.

The deposits received are initially recorded in current portion of other liabilities and other noncurrent liabilities for the noncurrent portion. The liabilities are reclassified to common stock and paid-in capital as the repurchase right lapses. During the years ended December 31, 2020 and 2019, 1,551,361, and 60,924 shares of the Company’s common stock were early exercised, respectively. During the three months ended December 31, 2020, 117,921 shares of common stock that were previously early exercised were repurchased by the Company at a price of $0.76 per share. The repurchase was triggered by the departure of one employee whose early exercises had not fully vested at the date of departure. At December 31, 2020 and 2019, there was $2.2 million and $0.1 million recorded in current portion of other liabilities, and $2.5 million and $0.1 million recorded in other noncurrent liabilities, respectively, related to shares held by employees and nonemployees that were subject to repurchase.

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

INCOME TAXES

The Company did not record any income tax expense for the years ended December 31, 2020, 2019, and 2018. The Company has incurred net operating losses for all the periods presented and has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has recorded a full valuation allowance against all of its deferred tax assets as it is not more likely than not that such assets will be realized in the near future.

Reconciliation of the income tax expense calculated at the statutory rate to our zero expense for income taxes for the years ended December 31, 2020, 2019, and 2018 were as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Tax benefit at federal statutory rate	$	(18,573)	$	(3,384)	$	(1,367)
State taxes	(2,748)		(232)		(90)
Research tax credits	(475)		(427)		(165)
Change in valuation allowance	15,062		3,958		1,694
Change in fair value of convertible notes	5,756		—		—
Other	978		85		(72)
Expense/(Benefit) for income taxes	$	—	$	—	$	—

The Company’s deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets or liabilities for financial reporting purposes and the amounts used for income tax purposes as of December 31, 2020 and 2019. Significant components of the Company’s deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2020		2019
	(in thousands)
Deferred tax assets:
Lease liabilities	$	8,312	$	119
Stock-based compensation	—		4
Accrued compensation	495		127
Net operating loss carryforwards	19,710		5,276
Tax credit carryforwards	673		496
Other	1		1
Total deferred tax assets	29,191		6,023
Deferred tax liabilities:
Right-of-use assets	(7,085)		(114)
Fixed assets	(411)		(173)
Stock-based compensation	(898)		—
Total deferred tax liabilities	(8,394)		(287)
Net deferred tax assets	20,797		5,736
Valuation allowance	(20,797)		(5,736)
Net deferred tax assets	$	—	$	—

The Company records a valuation allowance for certain temporary differences for which it is more likely than not that it will not receive future tax benefits. The Company assesses its past earnings history, income tax planning and projections of future net income when determining whether it is more likely than not future tax benefits will be realized. Based on the Company’s history of losses, the Company has maintained a full valuation allowance of approximately $20.8 million and $5.7 million for the years ended December 31, 2020 and 2019, respectively. The change in valuation allowance is approximately $15.1 million.

The following table sets forth the Company’s federal and state net operating loss and research credit carryforwards as of December 31, 2020:


	Amount		Expiration
	(in thousands)
Net operating losses, federal	$	76,873	Indefinite
Net operating losses, federal	$	601	2037
Net operating losses, state	$	54,450	2037-2040
Tax credits, federal	$	673	2037-2040

Current federal and state tax laws include substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change as defined under Section 382 of the Internal Revenue Code of 1986, as amended. Accordingly, the Company’s ability to use these carryforward attributes may be limited as a result of such ownership change.

The Company applies the provisions of ASC Topic 740 to account for uncertain income tax positions. A reconciliation of the beginning and ending amount of unrecognized tax benefits were as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Balance at beginning of the year	$	109	$	32	$	—
Additions based on tax positions related to the current year	91		77		32
Additions to tax positions of prior years	—		—		—
Reductions of tax positions of prior years	(59)		—		—
Lapse of the applicable statute of limitations	—		—		—
Balance at the end of the year	$	141	$	109	$	32

It is the Company’s policy to record penalties and interest related to income taxes as a component of income tax expense. The Company has not recorded any interest or penalties related to income taxes during the three and years ended December 31, 2020, 2019, and 2018. Unrecognized tax benefits are not expected to change during the next 12 months. The reversal of the unrecognized tax benefits would not affect the effective tax rate. The Company is subject to examination by U.S. federal and state tax authorities for all years since its inception.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Net Loss Per Share

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

NET LOSS PER SHARE

The following table summarizes the computation of basic and diluted net loss per share of the Company for the years ended December 31, 2020, 2019, and 2018:


	Year Ended December 31,
	2020		2019		2018
	(in thousands, except share and per share amounts)
Net loss	$	(88,444)	$	(16,117)	$	(6,721)
Weighted-average common stock outstanding, basic and diluted	16,277,247		5,278,748		4,856,774
Net loss per share, basic and diluted	$	(5.43)	$	(3.05)	$	(1.38)

The Company’s potentially dilutive securities, which include the Preferred Stock and options to purchase shares of the Company's common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each stated period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	December 31,
	2020	2019
Convertible preferred stock	—	22,687,625
Stock options to purchase common stock	4,536,337	951,302
Early exercised stock options subject to future vesting	1,714,822	774,931
Restricted stock awards subject to future vesting	244,780	215,220
Restricted stock units subject to future vesting	565,417	—
Total	7,061,356	24,629,078

Commitment and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

COMMITMENTS AND CONTINGENCIES

Asset Purchase Agreement

In July 2020, the Company entered into an asset purchase agreement (Gilead Asset Purchase Agreement) with Gilead Sciences, Inc. (Gilead), pursuant to which the Company acquired certain assets from Gilead related to entospletinib (ENTO) and lanraplenib (LANRA), and patents and other intellectual property covering or related to the development, manufacture and commercialization of ENTO and LANRA.

In consideration for such assets, on the date of the Gilead Asset Purchase Agreement, the Company made a $3.0 million upfront cash payment and issued a $3.0 million principal amount convertible promissory note to Gilead (Gilead Note). The Company also made a $0.7 million payment to reimburse Gilead for certain liabilities assumed by the Company pursuant to the Gilead Asset Purchase Agreement. In addition, the Company is required to make milestone payments upon successful achievement of certain regulatory and sales milestones for ENTO, LANRA and other selective spleen tyrosine kinase inhibitor compounds covered by the patent rights acquired pursuant to the Gilead Asset Purchase Agreement and developed by the Company as a back-up to ENTO or LANRA (Other Compounds). Upon initiation of the Company’s planned registrational Phase 3 clinical trial of ENTO in combination with induction chemotherapy in acute myeloid leukemia patients with NPM1 mutations, the Company will be required to pay a milestone to Gilead of $29.0 million, and upon successful completion of certain other regulatory milestones in the United States, European Union and United Kingdom for ENTO, LANRA and any Other Compounds, across up to two distinct indications, the Company will be required to pay to Gilead an aggregate total of $51.3 million. Upon achieving certain thresholds for the aggregate annual net sales of ENTO, LANRA and any Other Compounds combined, the Company would owe to Gilead potential milestone payments totaling $115.0 million.

Gilead is also eligible to receive (i) tiered marginal royalties ranging from the very low-teens to high-teens on annual worldwide net sales of ENTO, (ii) tiered marginal royalties ranging from high-single digits to the mid-teens on annual worldwide net sales of LANRA and (iii) tiered marginal royalties ranging from low single digits to mid-single digits on annual worldwide net sales of any Other Compounds. The royalties in the foregoing clauses are subject to reduction, on a country-by-country basis, for products not covered by certain claims within the assigned patents, for generic entry and, in the case of ENTO and LANRA, for any royalties paid for future licenses of third party intellectual property required to develop or commercialize ENTO or LANRA. The Company’s royalty obligation with respect to a given product in a given country begins upon the first commercial sale of such product in such country and ends on the latest of (i) expiration of the last claim of a defined set of the assigned patent rights covering such product in such country; (ii) loss of exclusive data or marketing rights to such product in such country; or (iii) 10 years from the first commercial sale of such product in such country.

Under the Gilead Asset Purchase Agreement, the Company is required to use commercially reasonable efforts to develop, obtain regulatory approval for and commercialize either ENTO or LANRA.

The Gilead Note accrued interest at a rate of 6% per year, compounded annually, and had a maturity date of July 14, 2022. The Gilead Note, including unpaid accrued interest, was settled in exchange for 188,567 shares of common stock in connection with the closing of the Company’s IPO (See Note 1) at a settlement price of $16.15 per share, which is equal to 85% of the price per share to the public in the IPO.

On issuance, the Company had elected to account for the Gilead Note at fair value with any changes in fair value being recognized through the statements of operations and comprehensive loss until the Gilead Note settled. The fair value of the Gilead Note was determined to be $3.6 million on issuance.

The Company determined the fair value of the Gilead Note at inception by determining the present value of the Gilead Note if they were to settle either upon closing of an IPO, a deemed liquidation, or a qualified or non-qualified equity fundraise. Key valuation assumptions are as follows:


At inception
	Fundraise scenario		IPO cash payout scenario		IPO conversion scenario		Liquidation cash payout scenario		Liquidation conversion scenario
Expected term (years)	2.00		0.30		0.30		2.00		2.00
Discount rate	24.2	%	24.2		24.2	%	24.2		24.2	%
Weighting	18.6	%	12.9	%	—	%	50.0	%	18.6	%

The fair value upon settlement was determined by calculating the fair value of the 188,567 shares converted at the price per share to the public upon the closing of the IPO of $19.00, resulting in a fair value upon settlement of $3.6 million.

In the normal course of business, the Company enters into contracts with CROs for preclinical studies and other vendors for other services and products for operating purposes. These agreements generally provide for termination or cancellation, other than for costs already incurred.

Contingencies

In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown, because it involves claims that may be made against the Company in the future, but have not yet been made. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Indemnification

In accordance with the Company’s amended and restated certificate of incorporation and amended and restated bylaws, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving in such capacity. There have been no claims to date, and the Company has a directors and officers liability insurance policy that may enable it to recover a portion of any amounts paid for future claims.

Leases

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Leases

LEASESIn May 2020, the Company amended its month-to-month rental agreement for the 21 Erie Street, Cambridge, Massachusetts lab space, to extend its non-cancellable lease term through May 31, 2021. As the lease term was longer than 12 months, the Company determined that this amendment required assessment under ASC 842. In November 2020, the Company entered into a lease termination for this lab space to terminate the lease as of January 31, 2021, rather than May 31, 2021. The cost for early termination is a payment of $0.1 million. The Company accounted for this change in lease term as a modification of the originally amended lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured. As of December 31, 2020, the remaining operating lease right-of-use asset of $0.2 million was recognized on the balance sheet. There is no remaining lease liability as of December 31, 2020.

On February 28, 2020, the Company entered into an 11-year lease agreement to move its research and development operations from 21 Erie Street, Cambridge, Massachusetts, to a 40,514 square-feet facility at 301 Binney Street, Cambridge, Massachusetts (new Cambridge facility). The new lease commenced on February 28, 2020 with an initial annual base rent of $4.1 million. The initial rent payment was paid as of September 30, 2020, with rent payments escalating 3.0% annually after the initial 12 payments. As discussed in Note 2, the Company executed a letter of credit for $2.0 million in connection with the lease. The lease includes $3.7 million in certain tenant improvement allowances, which the Company included in its calculation of the right-of-use asset in the lease at commencement. As of December 31, 2020, $2.9 million in improvement costs incurred by the Company were reimbursed by the lessor are now included within the total lease liability. In connection with the lease, the Company recognized an operating lease right-of-use asset of $25.1 million and an aggregate lease liability of $30.1 million on the December 31, 2020 balance sheet. The remaining lease term is 10 years and 2 months, and the estimated incremental borrowing rate is 8.50%.

In July 2018, the Company entered into a lease agreement for a 4,661 square-foot office space to be used for general and administrative activities in San Mateo, California. The lease commenced on August 1, 2018 and has a 37-month initial term expiring on August 31, 2021. The lease also contains an option for the Company to extend the lease upon its initial expiration. In connection with the lease, the Company made a one-time cash security deposit in the amount of $28,000. In May 2020, the Company amended its agreement to extend the lease for its office in San Mateo, California through April 2025. The initial annual base rent is $0.3 million, and such amount will increase by 3% annually on each anniversary of the commencement date. In connection with the lease, the Company recognized an operating lease right-of-use asset of $1.1 million and $0.5 million and an aggregate lease liability of $1.1 million and $0.5 million on the December 31, 2020 and December 31, 2019 balance sheets, respectively. The Company expanded to an adjacent suite in July 2020, which is treated as a separate lease for accounting purposes. The additional space is approximately 3,414 square feet and will similarly be used for general and administrative activities. The lease commenced on July 1, 2020 and will expire on April 30, 2025. In connection with the additional space leased, the Company made a one-time additional cash security deposit in the amount of $25,000. The initial annual base rent for the expansion is $0.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. In connection with the lease, the Company recognized an operating lease right-of-use asset of $0.8 million and an aggregate lease liability of $0.8 million on the December 31, 2020 balance sheet. The remaining lease term is for both spaces is 4 years and 4 months, and the estimated incremental borrowing rate is 12.07%.

In March 2018, the Company entered into a finance lease for R&D equipment that has a bargain purchase option at the end of its three-year term. The finance lease is included in property and equipment, net, other current liabilities, and other noncurrent liabilities on the Company’s balance sheets.

The following table summarizes the presentation of the Company’s finance lease in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Property and equipment, net	$	83	$	103
Liabilities:
Current portion of other liabilities	5		32
Other noncurrent liabilities	—		5
Total finance lease liabilities	$	5	$	37

The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Operating lease assets	$	27,322	$	473
Liabilities:
Current portion of operating lease liabilities	$	937	$	285
Noncurrent operating lease liabilities	31,120		211
Total operating lease liabilities	$	32,057	$	496

The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	20	$	20	$	17
Interest expense	1		3		4
Total finance lease cost	$	21	$	23	$	21

The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	4,272	$	—	$	—
General and administrative	1,293		310		128
Total operating lease cost	$	5,565	$	310	$	128

The Company made cash payments of $2.8 million, $0.3 million, and $0.2 million under the lease agreements during the years ended December 31, 2020, 2019, and 2018, respectively.

The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2020 for the next five years and thereafter is expected to be as follows:


Period Ending December 31,	Amount
	(in thousands)
2021	$	4,764
2022	4,789
2023	4,933
2024	5,081
2025 and thereafter	30,834
Total undiscounted lease payments	50,401
Less: Present value adjustment	(17,568)
Less: Tenant improvement allowance	(776)
Present value of operating lease liabilities	$	32,057

Leases

The following table summarizes the presentation of the Company’s finance lease in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Property and equipment, net	$	83	$	103
Liabilities:
Current portion of other liabilities	5		32
Other noncurrent liabilities	—		5
Total finance lease liabilities	$	5	$	37

The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Operating lease assets	$	27,322	$	473
Liabilities:
Current portion of operating lease liabilities	$	937	$	285
Noncurrent operating lease liabilities	31,120		211
Total operating lease liabilities	$	32,057	$	496

The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	20	$	20	$	17
Interest expense	1		3		4
Total finance lease cost	$	21	$	23	$	21

The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	4,272	$	—	$	—
General and administrative	1,293		310		128
Total operating lease cost	$	5,565	$	310	$	128

The Company made cash payments of $2.8 million, $0.3 million, and $0.2 million under the lease agreements during the years ended December 31, 2020, 2019, and 2018, respectively.

The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2020 for the next five years and thereafter is expected to be as follows:


Period Ending December 31,	Amount
	(in thousands)
2021	$	4,764
2022	4,789
2023	4,933
2024	5,081
2025 and thereafter	30,834
Total undiscounted lease payments	50,401
Less: Present value adjustment	(17,568)
Less: Tenant improvement allowance	(776)
Present value of operating lease liabilities	$	32,057

2020 Notes	12 Months Ended
2020 Notes	Dec. 31, 2020
Debt Disclosure [Abstract]
2020 Notes	2020 NOTES In August 2020, the Company entered into a note purchase agreement pursuant to which it sold and issued an aggregate of $155.2 million in convertible promissory notes (2020 Notes) and received net cash proceeds of $151.3 million. The 2020 Notes did not accrue interest. The 2020 Notes were settled in exchange for 9,610,713 shares of common stock in connection with the closing of the Company’s IPO (See Note 1) at a settlement price of $16.15 per share, which is equal to 85% of the price per share to the public in the IPO. On issuance, the Company had elected to account for the 2020 Notes at fair value with any changes in fair value being recognized through the statements of operations until the 2020 Notes settled. On issuance, the fair value of the 2020 Notes was determined to be equal to $155.2 million, which is the principal amount of the 2020 Notes, and total debt issuance costs of $3.9 million were expensed and recognized as interest expense in the accompanying statements of operations and comprehensive loss. The fair value of the 2020 Notes was determined to be $182.6 million upon settlement. The fair value upon settlement was determined by using the IPO price per share $19.00 of the 9,610,713 shares converted. For the year ended December 31, 2020, the Company recognized a $27.4 million loss in the accompanying statements of operations and comprehensive loss for the change in fair value of the 2020 Notes.

Related Parties	12 Months Ended
Related Parties	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Parties	RELATED PARTIES On December 1, 2017, the Company entered into a three-year services agreement with Two River Consulting, LLC (Two River) to provide various clinical development, operational, managerial, accounting and financial, and administrative services to the Company. Arie Belldegrun, M.D., FACS, the Chairman of the Board of Directors, is the Chairman of Two River. Mr. Joshua Kazam and Mr. David Tanen, each a director of the Company, are each partners of Two River. Mr. Tanen additionally serves as our Corporate Secretary. Mr. Christopher Wilfong, a strategic advisor to the Company, is an Operating Partner of Two River and Mr. Sean Algeo, serving as the Company’s Financial Consultant, is the Chief Financial Officer of Two River. During the years ended December 31, 2020, 2019, and 2018, the Company incurred expense of $1.2 million, $0.9 million, and $0.6 million, respectively, for these services. Some of the Company’s expenses are periodically paid by Two River. The Company reimburses Two River for these expenses and no interest is charged on the outstanding balance. These reimbursable expenses totaled $27,000, $49,000, and $39,000 for the years ended December 31, 2020, 2019, and 2018, respectively. As of December 31, 2020 and 2019, the Company had payables to Two River of $182,000 and $75,000, respectively. In 2019, the Company entered into a consulting agreement with Bellco Capital, LLC (Bellco) to provide various executive services to the Company. Arie Belldegrun, M.D., FACS, the Chairman of the Board of Directors, is the Chairman of Bellco. Rebecka Belldegrun, M.D., who served as a director of the Company through January 25, 2021, is the President and Chief Executive Officer of Bellco. The Company incurred expenses of $25,000 each year for these services for the years ended December 31, 2020 and 2019.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS In preparing the financial statements as of the year ended December 31, 2020, the Company evaluated subsequent events for recognition and measurement purposes. The Company concluded that no events or transactions have occurred that require disclosure in the accompanying financial statements, other than the following: New lease agreement In February 2021, the Company entered into a new lease agreement for its office space in San Mateo, California to move from its current suites, totaling 8,075 square feet, to a larger suite of 17,340 square feet, with a target move date of July 1, 2021. As a result of the move, the initial annual base rent will increase to $1.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. In connection with the larger space leased, the Company will also make an additional one-time cash security deposit in the amount of $59,700. The new lease agreement also extends the termination date from April 30, 2025 to the last day of the 60th calendar month following the New Premises Commencement Date or August 31, 2026, if earlier.

Significant Accounting Policies, Estimates and Judgments (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

The accompanying financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and accounting principles generally accepted in the United States of America (GAAP).

Use of Estimates

Research and Development Expenses

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.

Restricted Cash

Concentration of Credit Risk and Other Risks and Uncertainties

Investments

Fair Value Measurement

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.

Level 3— Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Fair Value Option

Property and Equipment, Net

Estimated useful lives in years are generally as follows:


Description						Estimated Useful Life
Lab equipment						3 to 7 years
Leasehold improvements						Shorter of useful life or lease term
Furniture and fixtures						5 to 7 years

Deferred Offering Costs

Deferred Offering CostsOffering costs, including legal, accounting, and filing fees related to the IPO, were deferred and were offset against the offering proceeds upon the completion of the IPO. Prior to the IPO, all deferred offering costs were capitalized in other noncurrent assets.

Leases

Impairment of Long-Lived Assets

Stock-Based Compensation

Income Taxes

Comprehensive Loss

Net Loss Per Share

Recently Adopted Accounting Pronouncements


	December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	248,009	$	32,570
Restricted cash	2,027		—
Total cash, cash equivalents and restricted cash as shown on the statements of cash flows	$	250,036	$	32,570

Significant Accounting Policies, Estimates and Judgments (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Property, Plant and Equipment

Estimated useful lives in years are generally as follows:


Description						Estimated Useful Life
Lab equipment						3 to 7 years
Leasehold improvements						Shorter of useful life or lease term
Furniture and fixtures						5 to 7 years

Property and equipment, net consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Property and equipment:
Lab equipment	$	5,619	$	3,978
Leasehold improvements	8,957		—
Furniture and fixtures	216		—
Finance lease on R&D equipment	139		139
Construction in progress	—		50
Total property and equipment	14,931		4,167
Less: Accumulated depreciation and amortization	(1,285)		(446)
Total property and equipment, net	$	13,646	$	3,721

Schedule of Cash, Cash Equivalents, and Restricted Cash Equivalents

A reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows is as follows:


	December 31,
	2020		2019
	(in thousands)
Cash and cash equivalents	$	248,009	$	32,570
Restricted cash	2,027		—
Total cash, cash equivalents and restricted cash as shown on the statements of cash flows	$	250,036	$	32,570

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis


	December 31, 2020
	Level 1		Level 2		Level 3		Fair Value
			(in thousands)
Financial Assets:
Money market funds	$	114,184	$	—	$	—	$	114,184
Certificates of deposit	1,229		—		—		1,229
Corporate bonds	—		40,736		—		40,736
U.S. agency securities	—		10,001		—		10,001
U.S. treasury securities	284,721		—		—		284,721
Total financial assets	$	400,134	$	50,737	$	—	$	450,871


	December 31, 2019
	Level 1		Level 2		Level 3		Fair Value
	(in thousands)
Financial Assets:
Money market funds	$	112	$	—	$	—	$	112
Certificates of deposit	1,715		—		—		1,715
Commercial paper	—		4,489		—		4,489
Corporate bonds	—		26,432		—		26,432
U.S. agency securities	—		1,499		—		1,499
U.S. treasury securities	36,880		—		—		36,880
Total financial assets	$	38,707	$	32,420	$	—	$	71,127

Investments (Tables)

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Investments Classified by Contractual Maturity Date

The fair value and amortized cost of available-for-sale securities by major security type as of December 31, 2020 and 2019 were as follows:


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
			(in thousands)
Money market funds	$	114,184	$	—	$	—	$	114,184
Certificates of deposit	1,225		4		—		1,229
Corporate bonds	40,743		9		(16)		40,736
U.S. agency securities	9,999		2		—		10,001
U.S. treasury securities	284,739		3		(21)		284,721
Total cash equivalents and investments	$	450,890	$	18	$	(37)	$	450,871


	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(in thousands)
Money market funds	$	112	$	—	$	—	$	112
Certificates of deposit	1,715		—		—		1,715
Commercial paper	4,490		—		(1)		4,489
Corporate bonds	26,444		1		(13)		26,432
U.S. agency securities	1,500		—		(1)		1,499
U.S. treasury securities	36,884		1		(5)		36,880
Total cash equivalents and investments	$	71,145	$	2	$	(20)	$	71,127

These available-for-sale securities were classified on the Company’s balance sheets as of December 31, 2020 and 2019 as:


	Fair Value
	December 31,
	2020		2019
	(in thousands)
Cash equivalents	$	236,818	$	6,751
Short-term investments	165,052		59,614
Long-term investments	49,001		4,762
Total cash equivalents and investments	$	450,871	$	71,127

The fair values of available-for-sale securities by contractual maturity as of December 31, 2020 and 2019 were as follows:


	December 31,
	2020		2019
	(in thousands)
Due in 1 year or less	$	287,686	$	66,253
Due in 1 to 2 years	49,001		4,762
Instruments not due at a single maturity date	114,184		112
Total cash equivalents and investments	$	450,871	$	71,127

Prepaid Expenses And Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2020

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Schedule of Prepaid Expenses and Other Assets

Prepaid expenses and other current assets consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Accrued interest on short-term available-for-sale securities	$	612	$	198
Prepaid equipment service contracts	383		191
Prepaid external research and development and outside services	1,889		113
Prepaid software	736		180
Prepaid insurance	2,881		23
Prepaid rent and other	240		414
Total prepaid expenses and other current assets	$	6,741	$	1,119

Property, Plant, and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Estimated useful lives in years are generally as follows:


Description						Estimated Useful Life
Lab equipment						3 to 7 years
Leasehold improvements						Shorter of useful life or lease term
Furniture and fixtures						5 to 7 years

Property and equipment, net consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Property and equipment:
Lab equipment	$	5,619	$	3,978
Leasehold improvements	8,957		—
Furniture and fixtures	216		—
Finance lease on R&D equipment	139		139
Construction in progress	—		50
Total property and equipment	14,931		4,167
Less: Accumulated depreciation and amortization	(1,285)		(446)
Total property and equipment, net	$	13,646	$	3,721

Accrued Expenses And Current Portion Of Other Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities

Accrued expenses consisted of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Accrued compensation	$	2,274	$	528
Accrued taxes	558		43
External research and development	1,017		241
Accrued leasehold improvements	927		—
Other accrued expenses	198		6
Total accrued expenses	$	4,974	$	818

Other Current Liabilities

Current portion of other liabilities consist of the following as of December 31, 2020 and 2019:


	December 31,
	2020		2019
	(in thousands)
Current portion of finance lease liability	$	5	$	32
Current portion of unvested early exercised share liability	2,174		56
ESPP withholdings	216		—
Total current portion of other liabilities	$	2,395	$	88

Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Preferred Stock

The Preferred Stock consisted of the following as of December 31, 2019:


	December 31, 2019
	Preferred Stock Authorized	Preferred Stock Issued and Outstanding	Carrying Value		Liquidation Preference		Common Stock Issuable Upon Conversion
	(in thousands, except share amounts)
Series Seed Preferred Stock	7,806,977	7,806,977	$	17,985	$	18,016	8,236,347
Series A Preferred Stock	13,700,000	13,697,916	104,922		105,000		14,451,278
Total	21,506,977	21,504,893	$	122,907	$	123,016	22,687,625

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Option-pricing Model Assumptions


	Year Ended December 31,
	2020		2019		2018
Fair value of common stock per share	$	10.52	$	2.27	$	0.24
Expected term (in years)	6.00		6.07		6.08
Expected volatility	78.36%		70.20%		67.93		%
Risk-free interest rate	0.71%		1.81%		2.85		%
Expected dividend	—%		—%		—		%

Stock Option Activity

Stock option activity under the 2020 Plan as of December 31, 2020 is summarized as follows:


	Number of Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
				(in years)	(in thousands)
Balance at December 31, 2019	1,726,233	$	1.19
Granted	5,196,257	10.52
Forfeited	(121,086)	0.85
Exercised	(550,245)	1.17
Balance at December 31, 2020	6,251,159	$	8.95	9.27	$	132,089
Exercisable at December 31, 2020	297,609	$	2.37	8.76	$	8,185
Unvested and expected to vest at December 31, 2020	5,953,550	$	9.28	9.30	$	123,904

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The fair values of the rights granted under the ESPP were calculated using the following assumptions:


						Year Ended December 31, 2020
Expected term (in years)						0.68-2.19
Expected volatility						89.25%-110.84%
Risk-free interest rate						0.12%-0.19%
Dividend yield						—%

Schedule of Nonvested Share Activity

Restricted stock awards and units as of December 31, 2020 are summarized as follows:


	Number of Restricted Stock	Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Vesting Life	Aggregate Intrinsic Value
				(in years)	(in thousands)
Unvested at December 31, 2019	215,220	$	0.05
Granted - restricted stock awards and units	839,758	22.15
Vested and converted to shares	(244,781)	2.34
Unvested at December 31, 2020	810,197	$	22.26	2.79	$	24,201
Vested and expected to vest at December 31, 2020	810,197	$	22.26	2.79	$	24,201

Stock-based Compensation, Classified in Statements of Operations


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development expenses	$	1,061	$	54	$	3
General and administrative expenses	1,451		54		22
Total stock-based compensation expense	$	2,512	$	108	$	25


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development expenses	$	1,390	$	59	$	8
General and administrative expenses	2,363		54		22
Total stock-based compensation expense	$	3,753	$	113	$	30

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

Reconciliation of the income tax expense calculated at the statutory rate to our zero expense for income taxes for the years ended December 31, 2020, 2019, and 2018 were as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Tax benefit at federal statutory rate	$	(18,573)	$	(3,384)	$	(1,367)
State taxes	(2,748)		(232)		(90)
Research tax credits	(475)		(427)		(165)
Change in valuation allowance	15,062		3,958		1,694
Change in fair value of convertible notes	5,756		—		—
Other	978		85		(72)
Expense/(Benefit) for income taxes	$	—	$	—	$	—

Schedule of Deferred Taxes

Significant components of the Company’s deferred tax assets and liabilities are as follows:


	Year Ended December 31,
	2020		2019
	(in thousands)
Deferred tax assets:
Lease liabilities	$	8,312	$	119
Stock-based compensation	—		4
Accrued compensation	495		127
Net operating loss carryforwards	19,710		5,276
Tax credit carryforwards	673		496
Other	1		1
Total deferred tax assets	29,191		6,023
Deferred tax liabilities:
Right-of-use assets	(7,085)		(114)
Fixed assets	(411)		(173)
Stock-based compensation	(898)		—
Total deferred tax liabilities	(8,394)		(287)
Net deferred tax assets	20,797		5,736
Valuation allowance	(20,797)		(5,736)
Net deferred tax assets	$	—	$	—

Schedule of Net Operating Loss and Research Credit Carryforwards

The following table sets forth the Company’s federal and state net operating loss and research credit carryforwards as of December 31, 2020:


	Amount		Expiration
	(in thousands)
Net operating losses, federal	$	76,873	Indefinite
Net operating losses, federal	$	601	2037
Net operating losses, state	$	54,450	2037-2040
Tax credits, federal	$	673	2037-2040

Schedule of Unrecognized Tax Benefits Roll Forward

The Company applies the provisions of ASC Topic 740 to account for uncertain income tax positions. A reconciliation of the beginning and ending amount of unrecognized tax benefits were as follows:


	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Balance at beginning of the year	$	109	$	32	$	—
Additions based on tax positions related to the current year	91		77		32
Additions to tax positions of prior years	—		—		—
Reductions of tax positions of prior years	(59)		—		—
Lapse of the applicable statute of limitations	—		—		—
Balance at the end of the year	$	141	$	109	$	32

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table summarizes the computation of basic and diluted net loss per share of the Company for the years ended December 31, 2020, 2019, and 2018:


	Year Ended December 31,
	2020		2019		2018
	(in thousands, except share and per share amounts)
Net loss	$	(88,444)	$	(16,117)	$	(6,721)
Weighted-average common stock outstanding, basic and diluted	16,277,247		5,278,748		4,856,774
Net loss per share, basic and diluted	$	(5.43)	$	(3.05)	$	(1.38)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each stated period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	December 31,
	2020	2019
Convertible preferred stock	—	22,687,625
Stock options to purchase common stock	4,536,337	951,302
Early exercised stock options subject to future vesting	1,714,822	774,931
Restricted stock awards subject to future vesting	244,780	215,220
Restricted stock units subject to future vesting	565,417	—
Total	7,061,356	24,629,078

Commitment and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Key Valuation Assumptions

Key valuation assumptions are as follows:


At inception
	Fundraise scenario		IPO cash payout scenario		IPO conversion scenario		Liquidation cash payout scenario		Liquidation conversion scenario
Expected term (years)	2.00		0.30		0.30		2.00		2.00
Discount rate	24.2	%	24.2		24.2	%	24.2		24.2	%
Weighting	18.6	%	12.9	%	—	%	50.0	%	18.6	%

Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Assets and Liabilities, Finance Leases, Lessee

The following table summarizes the presentation of the Company’s finance lease in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Property and equipment, net	$	83	$	103
Liabilities:
Current portion of other liabilities	5		32
Other noncurrent liabilities	—		5
Total finance lease liabilities	$	5	$	37

Assets and Liabilities, Operating Leases, Lessee

The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of December 31, 2020 and 2019:


Balance Sheet Caption	December 31,
	2020		2019
	(in thousands)
Assets:
Operating lease assets	$	27,322	$	473
Liabilities:
Current portion of operating lease liabilities	$	937	$	285
Noncurrent operating lease liabilities	31,120		211
Total operating lease liabilities	$	32,057	$	496

Summary of Lease Costs

The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	20	$	20	$	17
Interest expense	1		3		4
Total finance lease cost	$	21	$	23	$	21

The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2020, 2019, and 2018:


Statement of Operations and Comprehensive Loss Caption	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Research and development	$	4,272	$	—	$	—
General and administrative	1,293		310		128
Total operating lease cost	$	5,565	$	310	$	128

Schedule of Maturities on Lease Liabilities

The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2020 for the next five years and thereafter is expected to be as follows:


Period Ending December 31,	Amount
	(in thousands)
2021	$	4,764
2022	4,789
2023	4,933
2024	5,081
2025 and thereafter	30,834
Total undiscounted lease payments	50,401
Less: Present value adjustment	(17,568)
Less: Tenant improvement allowance	(776)
Present value of operating lease liabilities	$	32,057

2020 Notes (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Key Valuation Assumptions

Key valuation assumptions are as follows:


At inception
	Fundraise scenario		IPO cash payout scenario		IPO conversion scenario		Liquidation cash payout scenario		Liquidation conversion scenario
Expected term (years)	2.00		0.30		0.30		2.00		2.00
Discount rate	24.2	%	24.2		24.2	%	24.2		24.2	%
Weighting	18.6	%	12.9	%	—	%	50.0	%	18.6	%

Nature of Operations and Basis of Presentation (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended			40 Months Ended
	Oct. 02, 2020	Oct. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2020 USD ($) segment $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2017 shares
Subsidiary, Sale of Stock [Line Items]
Number of operating segments \| segment					1
Convertible preferred stock, shares outstanding (in shares)			0	21,504,893	0	21,504,893	7,806,977		0
Cash, cash equivalents, and short-term investments \| $			$ 462,100		$ 462,100
Net loss \| $			$ 88,444	$ 16,117	$ 88,444	$ 16,117	$ 6,721	$ 111,900
Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)					9,799,280
Forward stock split ratio	1.055
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued in private placement (in shares)		15,131,579
Shares issued in private placement, price per share (in dollars per share) \| $ / shares		$ 19.00
Net proceeds from stock offering \| $		$ 263,700
Payments of underwriting discounts and commissions \| $		(20,100)
Payments of offering costs \| $		$ (3,700)
Conversion of stock, shares converted (in shares)		21,504,893
Convertible preferred stock, shares outstanding (in shares)		0
IPO \| Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)		22,687,625
IPO \| Common Stock \| 2020 Convertible Notes
Subsidiary, Sale of Stock [Line Items]
Shares issued in private placement, price per share (in dollars per share) \| $ / shares			$ 19.00		$ 19.00
Shares issued upon conversion of convertible preferred stock (in shares)		9,610,713
IPO \| Common Stock \| 2020 Gilead Notes
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)		188,567
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Shares issued in private placement (in shares)		1,973,684

Significant Accounting Policies, Estimates and Judgments - R&D Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Asset Acquisition [Line Items]
Research and development	$ 43,250	$ 13,446	$ 5,033
Gilead Asset Purchase
Schedule Of Asset Acquisition [Line Items]
Research and development	$ 6,600

Significant Accounting Policies, Estimates and Judgments - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Restricted cash	$ 2,027	$ 0

Significant Accounting Policies, Estimates and Judgments - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Lab equipment \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Lab equipment \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years
Furniture and fixtures \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years

Significant Accounting Policies, Estimates and Judgments - Deferred Offering Costs (Details) - USD ($)	1 Months Ended
	Oct. 31, 2020	Dec. 31, 2019
Subsidiary, Sale of Stock [Line Items]
Deferred offering costs		$ 0
IPO
Subsidiary, Sale of Stock [Line Items]
Payments of offering costs	$ 3,700,000

Significant Accounting Policies, Estimates and Judgments - Schedule of Cash, Cash Equivalents, and Restricted Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 248,009	$ 32,570
Restricted cash	2,027	0
Total cash, cash equivalents and restricted cash as shown on the statements of cash flows	$ 250,036	$ 32,570	$ 10,226	$ 1,524

Fair Value Measurements (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 450,871	$ 71,127
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	114,184	112
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,229	1,715
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		4,489
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	40,736	26,432
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	10,001	1,499
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	284,721	36,880
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	400,134	38,707
Level 1 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	114,184	112
Level 1 \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,229	1,715
Level 1 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		0
Level 1 \| Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 1 \| U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 1 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	284,721	36,880
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	50,737	32,420
Level 2 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0	0
Level 2 \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 2 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		4,489
Level 2 \| Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	40,736	26,432
Level 2 \| U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	10,001	1,499
Level 2 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0	0
Level 3 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0	0
Level 3 \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		0
Level 3 \| Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 \| U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	$ 0	$ 0

Investments - Fair Value and Amortized Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	$ 236,818	$ 6,751
Total cash equivalents and investments, amortized cost	450,890	71,145
Total cash equivalents and investments, unrealized gains	18	2
Total cash equivalents and investments, unrealized losses	(37)	(20)
Total cash equivalents and investments, fair value	450,871	71,127
Money market funds
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	114,184	112
Certificates of deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,225	1,715
Unrealized Gains	4	0
Unrealized Losses	0	0
Fair Value	1,229	1,715
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		4,490
Unrealized Gains		0
Unrealized Losses		(1)
Fair Value		4,489
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	40,743	26,444
Unrealized Gains	9	1
Unrealized Losses	(16)	(13)
Fair Value	40,736	26,432
U.S. agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,999	1,500
Unrealized Gains	2	0
Unrealized Losses	0	(1)
Fair Value	10,001	1,499
U.S. treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	284,739	36,884
Unrealized Gains	3	1
Unrealized Losses	(21)	(5)
Fair Value	$ 284,721	$ 36,880

Investments - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Cash equivalents	$ 236,818	$ 6,751
Short-term investments	165,052	59,614
Long-term investments	49,001	4,762
Total cash equivalents and investments	$ 450,871	$ 71,127

Investments - Contractual Maturity (Details) - USD ($)	12 Months Ended
Investments - Contractual Maturity (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less	$ 287,686,000	$ 66,253,000
Due in 1 to 2 years	49,001,000	4,762,000
Instruments not due at a single maturity date	114,184,000	112,000
Total cash equivalents and investments	450,871,000	71,127,000
Other-than-temporary impairments on available-for-sale securities	$ 0	$ 0

Prepaid Expenses And Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Accrued interest on short-term available-for-sale securities	$ 612	$ 198
Prepaid equipment service contracts	383	191
Prepaid external research and development and outside services	1,889	113
Prepaid software	736	180
Prepaid insurance	2,881	23
Prepaid rent and other	240	414
Prepaid expenses and other current assets	$ 6,741	$ 1,119

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Leasehold improvements	$ 139	$ 139	$ 139	$ 139
Total property and equipment	14,931	4,167	14,931	4,167
Less: Accumulated depreciation and amortization	(1,285)	(446)	(1,285)	(446)
Total property and equipment, net	13,646	3,721	13,646	3,721
Depreciation and amortization	800	400	839	356	$ 91
Lab equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,619	3,978	5,619	3,978
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,957	0	8,957	0
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	216	0	216	0
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 0	$ 50	$ 0	$ 50

Accrued Expenses And Current Portion Of Other Liabilities - Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued compensation	$ 2,274	$ 528
Accrued taxes	558	43
External research and development	1,017	241
Accrued leasehold improvements	927	0
Other accrued expenses	198	6
Total accrued expenses	$ 4,974	$ 818

Accrued Expenses And Current Portion Of Other Liabilities - Current Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Current portion of finance lease liability	$ 5	$ 32
Current portion of unvested early exercised share liability	2,174	56
ESPP withholdings	216	0
Total current portion of other liabilities	$ 2,395	$ 88

Preferred Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 01, 2019	May 22, 2018	Dec. 31, 2020	Oct. 14, 2020
Temporary Equity [Line Items]
Preferred stock, shares authorized (in shares)				10,000,000
Preferred stock, par value (in dollars per share)				$ 0.001
Preferred stock, shares issued (in shares)			0
Preferred stock, shares outstanding (in shares)			0
Common Stock
Temporary Equity [Line Items]
Issuance costs			$ 23,775
Shares issued upon conversion of convertible preferred stock (in shares)			9,799,280
Series Seed Preferred Stock \| Convertible Notes
Temporary Equity [Line Items]
Shares issued in private placement, price per share (in dollars per share)		$ 2.30769
Series Seed Preferred Stock \| Private Placement
Temporary Equity [Line Items]
Shares issued in private placement (in shares)		7,806,977
Gross proceeds received in private placement		$ 18,000
Series A Preferred Stock \| Private Placement
Temporary Equity [Line Items]
Shares issued in private placement (in shares)	13,697,916
Gross proceeds received in private placement	$ 105,000
Shares issued in private placement, price per share (in dollars per share)	$ 7.6654
Issuance costs	$ 100

Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Preferred Stock Authorized (in shares)	0	21,506,977
Preferred Stock Issued (in shares)	0	21,504,893
Preferred Stock Outstanding (in shares)	0	21,504,893	7,806,977	0
Carrying Value	$ 0	$ 122,907	$ 17,985	$ 0
Temporary Equity, Liquidation Preference	$ 0	$ 123,016
Common Stock Issuable Upon Conversion (in shares)		22,687,625
Series Seed Preferred Stock
Temporary Equity [Line Items]
Preferred Stock Authorized (in shares)		7,806,977
Preferred Stock Issued (in shares)		7,806,977
Preferred Stock Outstanding (in shares)		7,806,977
Carrying Value		$ 17,985
Temporary Equity, Liquidation Preference		$ 18,016
Common Stock Issuable Upon Conversion (in shares)		8,236,347
Series A Preferred Stock
Temporary Equity [Line Items]
Preferred Stock Authorized (in shares)		13,700,000
Preferred Stock Issued (in shares)		13,697,916
Preferred Stock Outstanding (in shares)		13,697,916
Carrying Value		$ 104,922
Temporary Equity, Liquidation Preference		$ 105,000
Common Stock Issuable Upon Conversion (in shares)		14,451,278

Common Stock (Details) - $ / shares	Dec. 31, 2020	Oct. 02, 2020	Dec. 31, 2019	Jul. 01, 2019
Equity [Abstract]
Common stock, shares authorized (in shares)	200,000,000	200,000,000	40,000,000
Common stock, par value (in dollars per share)	$ 0.001		$ 0.001	$ 0.001
Common stock, shares issued (in shares)	54,073,901		5,660,391
Common stock, shares outstanding (in shares)	54,073,901		5,660,391

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value, options granted (in dollars per share)	$ 7.25	$ 1.42	$ 0.16
Weighted-average grant-date fair value, options vested (in dollars per share)	$ 1.01	$ 0.14	$ 0.03
Stock options exercised, intrinsic value	$ 6,100	$ 700	$ 10
Stock options, unrecognized cost	$ 36,300	$ 1,300
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that may be issued (in shares)		3,692,500
2020 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that may be issued (in shares)				11,938,152
Shares that may be issued, percent increase as total of common stock outstanding				5.00%
Number of shares reserved for future issuance (in shares)	3,696,370
2020 And 2017 Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2020 And 2017 Equity Incentive Plans \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2020 And 2017 Equity Incentive Plans \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options recognized, weighted average period	3 years 8 months 12 days	3 years 7 months 20 days

Stock-Based Compensation - Option-pricing Model Assumptions (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock per share (dollars per share)	$ 10.52	$ 2.27	$ 0.24
Expected term (in years)	6 years	6 years 25 days	6 years 29 days
Expected volatility	78.36%	70.20%	67.93%
Risk-free interest rate	0.71%	1.81%	2.85%
Expected dividend	0.00%	0.00%	0.00%

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Stock Option Activity Under the 2017 Plan [Roll Forward]
Beginning Balance (in shares) \| shares	1,726,233
Granted (in shares) \| shares	5,196,257
Forfeited (in shares) \| shares	(121,086)
Exercised (in shares) \| shares	(550,245)
Ending Balance (in shares) \| shares	6,251,159
Exercisable (in shares) \| shares	297,609
Unvested and expected to vest (in shares) \| shares	5,953,550
Stock Options, Weighted Average Exercise Price [Roll Forward]
Beginning Balance (dollars per share) \| $ / shares	$ 1.19
Granted (dollars per share) \| $ / shares	10.52
Forfeited (dollars per share) \| $ / shares	0.85
Exercised (dollars per share) \| $ / shares	1.17
Ending Balance (dollars per share) \| $ / shares	8.95
Exercisable (in dollars per share) \| $ / shares	2.37
Unvested and expected to vest (in dollars per share) \| $ / shares	$ 9.28
Stock Option Activity, Additional Disclosures [Abstract]
Balance, Weighted-Average Remaining Contractual Term	9 years 3 months 7 days
Exercisable, Weighted-Average Remaining Contractual Term	8 years 9 months 3 days
Unvested and expected to vest, Weighted-Average Remaining Contractual Term	9 years 3 months 18 days
Balance, Aggregate Intrinsic Value \| $	$ 132,089
Exercisable, Aggregate Intrinsic Value \| $	8,185
Unvested and expected to vest, Aggregate Intrinsic Value \| $	$ 123,904

Stock-Based Compensation - Stock Based Compensation - Stock Options (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,753	$ 113	$ 30
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,512	108	25
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,390	59	8
Research and development expenses \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,061	54	3
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,363	54	22
General and administrative expenses \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,451	$ 54	$ 22

Stock-Based Compensation - Classified in Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 3,753	$ 113	$ 30
Research and development expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,390	59	8
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,363	$ 54	$ 22

Stock-Based Compensation - ESPP (Details) $ in Thousands	1 Months Ended	12 Months Ended
Stock-Based Compensation - ESPP (Details) $ in Thousands	Oct. 31, 2020 period shares	Dec. 31, 2020 USD ($) hour	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 3,753	$ 113	$ 30
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		2,363	54	22
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 1,390	$ 59	$ 8
The ESPP \| Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that may be issued (in shares) \| shares	688,000
Number of shares that may be issued, increase percentage	1.00%
Number of shares that may be issued, increase (in shares) \| shares	1,376,000
Employment eligibility, number of hours employed per week \| hour		20
Stock-based compensation expense		$ 300
The ESPP \| Employee stock purchase plan \| General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		100
The ESPP \| Employee stock purchase plan \| Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 200
The ESPP \| Employee stock purchase plan \| Initial Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Offering period		27 months
The ESPP \| Employee stock purchase plan \| Subsequent Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Offering period	24 months
Number of offering periods \| period	4
Minimum \| The ESPP \| Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		8 months 4 days
Expected volatility		89.25%
Risk-free interest rate		0.12%
Expected dividend		0.00%
Maximum \| The ESPP \| Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		2 years 2 months 8 days
Expected volatility		110.84%
Risk-free interest rate		0.19%

Stock-Based Compensation - Restricted Stock Awards Activity (Details) - Restricted stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020
Number of Restricted Stock
Unvested Beginning Balance (in shares)	215,220
Granted - restricted stock awards and units (in shares)	839,758
Vested and converted to shares (in shares)	(244,781)
Unvested Ending Balance (in shares)	810,197
Weighted-Average Grant Date Fair Value
Unvested Beginning Balance (in dollars per share)	$ 0.05
Granted - restricted stock awards and units (in dollars per share)	22.15
Vested and converted to shares (in dollars per share)	2.34
Unvested Ending Balance (in dollars per share)	$ 22.26
Unvested, Weighted Average Remaining Vesting Life	2 years 9 months 14 days
Unvested, Aggregate Intrinsic Value	$ 24,201
Vested and expected to vest, Outstanding (in shares)	810,197
Vested and expected to vest, Weighted Average Grant Date Fair Value	$ 22.26
Vested and expected to vest, Weighted Average Remaining Vesting Life	2 years 9 months 14 days
Vested and expected to vest, Aggregate Intrinsic Value	$ 24,201

Stock-Based Compensation - Restricted Stock Awards (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 3,753	$ 113	$ 30
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		1,390	59	8
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 2,363	54	22
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)		839,758
Unrecognized stock based compensation	$ 500	$ 500
Awards weighted average recognition period		3 years 6 months 29 days
Total grant date fair value for awards vested		$ 600	5	5
Vested (in shares)		244,781
Restricted stock \| Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5	$ 5	$ 5
Restricted stock \| General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 600
Restricted stock \| Executive Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)		274,341
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 300
Unrecognized stock based compensation	$ 17,100	$ 17,100
Awards weighted average recognition period		2 years 11 months 8 days
Vested (in shares)		0
Restricted Stock Units (RSUs) \| Executive Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)	565,417
Vesting period	3 years
Restricted Stock Units (RSUs) \| Executive Employee \| Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 100
Restricted Stock Units (RSUs) \| Executive Employee \| General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 200

Stock-Based Compensation - Early Exercised Options (Details) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) employee $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Early exercised stock options (in shares) \| shares		1,551,361	60,924
Current liabilities related to shares that were subject to repurchase	$ 2,174	$ 2,174	$ 56
Shares of common stock repurchased \| shares	117,921
Shares of common stock repurchased, price per share (in dollars per share) \| $ / shares	$ 0.76
Number employees departing resulting in stock repurchase \| employee	1
Current portion of other liabilities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Current liabilities related to shares that were subject to repurchase	$ 2,200	2,200	100
Other noncurrent liabilities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-current liabilities related to shares that were subject to repurchase	$ 2,500	$ 2,500	$ 100

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 0	$ 0
Valuation allowance	(20,797,000)	(5,736,000)
Valuation allowance increase	(15,100,000)
Accrued interest or penalties related to uncertain tax positions	$ 0	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	$ (18,573,000)	$ (3,384,000)	$ (1,367,000)
State taxes	(2,748,000)	(232,000)	(90,000)
Research tax credits	(475,000)	(427,000)	(165,000)
Change in valuation allowance	15,062,000	3,958,000	1,694,000
Change in fair value of convertible notes	5,756,000	0	0
Other	978,000	85,000	(72,000)
Expense/(Benefit) for income taxes	$ 0	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Components of Net Deferred Tax Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Lease liabilities	$ 8,312	$ 119
Stock-based compensation	0	4
Accrued compensation	495	127
Net operating loss carryforwards	19,710	5,276
Tax credit carryforwards	673	496
Other	1	1
Deferred tax assets, gross	29,191	6,023
Deferred tax liabilities:
Right-of-use assets	(7,085)	(114)
Fixed assets	(411)	(173)
Stock-based compensation	(898)	0
Total deferred tax liabilities	(8,394)	(287)
Net deferred tax asset before valuation allowance	20,797	5,736
Valuation allowance	(20,797)	(5,736)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Net Operating Loss and Research Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Federal \| Expiring Indefinitely
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 76,873
Federal \| Expiring In 2037
Operating Loss Carryforwards [Line Items]
Net operating losses	601
Federal \| Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credits	673
State
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 54,450

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$ 109	$ 32	$ 0
Additions based on tax positions related to the current year	91	77	32
Additions to tax positions of prior years	0	0	0
Reductions of tax positions of prior years	(59)	0	0
Lapse of the applicable statute of limitations	0	0	0
Balance at the end of the year	$ 141	$ 109	$ 32

Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended			40 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (88,444)	$ (16,117)	$ (88,444)	$ (16,117)	$ (6,721)	$ (111,900)
Weighted-average shares of common stock, basic and diluted (in shares)	16,277,247	5,278,748	16,277,247	5,278,748	4,856,774
Net loss per share, basic and diluted (in dollars per share)	$ (5.43)	$ (3.05)	$ (5.43)	$ (3.05)	$ (1.38)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Section 45
-Paragraph 1A
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Section 50
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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+ Details

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	24,629,078	7,061,356
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	22,687,625	0
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	951,302	4,536,337
Early exercised stock options subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	774,931	1,714,822
Restricted stock awards subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	215,220	244,780
Restricted stock units subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	565,417

Commitment and Contingencies - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Oct. 31, 2020	Aug. 31, 2020	Jul. 31, 2020	Dec. 31, 2020
Schedule Of Asset Acquisition [Line Items]
Royalty obligation, termination, period from first commercial sale				10 years
IPO
Schedule Of Asset Acquisition [Line Items]
Settlement price, percentage		85.00%
Common Stock
Schedule Of Asset Acquisition [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)				9,799,280
Common Stock \| IPO
Schedule Of Asset Acquisition [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)	22,687,625
2020 Gilead Notes \| Common Stock \| IPO
Schedule Of Asset Acquisition [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)	188,567
Settlement price per share (in dollars per share)	$ 16.15
2020 Gilead Notes \| Convertible Notes
Schedule Of Asset Acquisition [Line Items]
Interest rate				6.00%
2020 Notes			$ 3.6
Asset Purchase Agreement
Schedule Of Asset Acquisition [Line Items]
Sales milestone payment			29.0
Regulatory milestone payment			51.3
Aggregate sales milestone payment			115.0
Gilead Asset Purchase
Schedule Of Asset Acquisition [Line Items]
Upfront cash payment			3.0
Convertible promissory note issued			3.0
Payments for reimbursements			$ 0.7

Commitment and Contingencies - Key Valuation Assumptions (Details)	Jul. 31, 2020
Remaining term (years) \| Fundraise scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	2.00
Remaining term (years) \| IPO cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.30
Remaining term (years) \| IPO conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.30
Remaining term (years) \| Liquidation cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	2.00
Remaining term (years) \| Liquidation conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	2.00
Discount rate \| Fundraise scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.242
Discount rate \| IPO cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.242
Discount rate \| IPO conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.242
Discount rate \| Liquidation cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.242
Discount rate \| Liquidation conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.242
Weighting \| Fundraise scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.186
Weighting \| IPO cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.129
Weighting \| IPO conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0
Weighting \| Liquidation cash payout scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.500
Weighting \| Liquidation conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	0.186

Leases - Additional Information (Details)				12 Months Ended
Leases - Additional Information (Details)	Jul. 01, 2020 USD ($) ft²	Mar. 01, 2020 USD ($) ft²	Aug. 01, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Nov. 30, 2020 USD ($)	Jul. 31, 2018 ft²	Jun. 30, 2018
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				$ 27,322,000	$ 473,000
Lease liabilities				32,057,000	496,000
Lease payments				2,800,000	300,000	$ 200,000
R&D Equipment
Lessee, Lease, Description [Line Items]
Finance lease, term									3 years
21 Erie Street, Cambridge, Massachusetts \| Cambridge, Massachusetts
Lessee, Lease, Description [Line Items]
Cost for early lease termination							$ 100,000
Operating lease right-of-use assets				200,000
Lease liabilities				0
301 Binney Street, Cambridge, Massachusetts
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				25,100,000
Lease liabilities				30,100,000
Lease term		11 years
Facility size \| ft²		40,514
Annual base rent		$ 4,100,000
Escalating rent payments, percent		3.00%
Letter of credit				2,000,000.0
Improvement costs incurred, reimbursed by lessor				$ 2,900,000
Tenant improvement allowances		$ 3,700,000
Remaining lease term				10 years 2 months 12 days
Incremental borrowing rate				8.50%
San Mateo, California
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				$ 1,100,000	500,000
Lease liabilities				1,100,000	$ 500,000
Lease term			37 months
Facility size \| ft²								4,661
Escalating rent payments, percent			3.00%
Security deposit			$ 28,000
Initial annual base rent			$ 300,000
San Mateo, California, Adjacent Space
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				800,000
Lease liabilities				$ 800,000
Facility size \| ft²	3,414
Escalating rent payments, percent	3.00%
Remaining lease term				4 years 4 months 24 days
Incremental borrowing rate				12.07%
Security deposit	$ 25,000
Initial annual base rent	$ 200,000

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance lease cost	$ 21	$ 23	$ 21		$ 21
Interest expense	1	3	4		4
Operating lease cost			5,565	$ 310	128
Research and development
Lessee, Lease, Description [Line Items]
Finance lease cost	$ 20	$ 20	17		17
Operating lease cost			4,272	0	0
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease cost			$ 1,293	$ 310	$ 128

Leases - Supplemental Balance Sheet Information - Finance Lease (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Property and equipment, net	$ 83	$ 103
Liabilities:
Current portion of finance lease liability	5	32
Other noncurrent liabilities	0	5
Total finance lease liabilities	$ 5	$ 37

Leases - Supplemental Balance Sheet Information - Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Operating lease assets	$ 27,322	$ 473
Liabilities:
Current portion of operating lease liabilities	937	285
Noncurrent operating lease liabilities	31,120	211
Total operating lease liabilities	$ 32,057	$ 496

Leases - Schedule of Maturities on Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 4,764
2022	4,789
2023	4,933
2024	5,081
2025 and thereafter	30,834
Total undiscounted lease payments	50,401
Less: Present value adjustment	(17,568)
Tenant Improvements	(776)
Present value of operating lease liabilities	$ 32,057	$ 496

2020 Notes - Narrative (Details) - USD ($)	1 Months Ended		12 Months Ended
2020 Notes - Narrative (Details) - USD ($)	Oct. 31, 2020	Aug. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Net cash proceeds			$ 151,275,000	$ 0	$ 0
Total debt issuance costs expensed and recognized			3,889,000	0	0
Loss in fair value			$ (27,408,000)	$ 0	$ 0
Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)			9,799,280
IPO
Debt Instrument [Line Items]
Settlement price, percentage		85.00%
Shares issued in private placement, price per share (in dollars per share)	$ 19.00
IPO \| Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)	22,687,625
2020 Convertible Notes \| IPO \| Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)	9,610,713
Shares issued in private placement, price per share (in dollars per share)			$ 19.00
Convertible Notes \| Convertible Notes Payable (2020 Notes)
Debt Instrument [Line Items]
Debt instrument, face amount		$ 155,200,000
Net cash proceeds		151,300,000
2020 Notes		155,200,000	$ 182,600,000
Total debt issuance costs expensed and recognized		$ 3,900,000
Loss in fair value			$ (27,400,000)

Related Party Disclosures (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Two River Consulting, LLC
Related Party Transaction [Line Items]
Services agreement term			3 years
Expenses from transaction with related party	$ 1,200	$ 900	$ 600
Reimbursable expenses to related parties		49	27		$ 39
Payables to related parties	182	$ 75	$ 182	$ 75
Bellco Capital, LLC
Related Party Transaction [Line Items]
Expenses from transaction with related party	$ 25			$ 25

Subsequent Events (Details)	1 Months Ended
Subsequent Events (Details)	Feb. 28, 2021 USD ($) ft²	Jul. 01, 2020 ft²
San Mateo, California. Original Lease
Subsequent Event [Line Items]
Facility size \| ft²		8,075
Subsequent Event \| San Mateo, California. February 2021 Lease Agreement
Subsequent Event [Line Items]
Facility size \| ft²	17,340
Escalating rent payments, percent	3.00%
Initial annual base rent \| $	$ 1,200,000
Security deposit \| $	$ 59,700