Kronos Bio (KRON) 10-K 24 Feb 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Feb. 18, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
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 400
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	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1.3
Entity Common Stock, Shares Outstanding		56,601,965
Entity Central Index Key	0001741830
Document Fiscal Year Focus	2021
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 2022 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 May 2, 2022.

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	Redwood City, California
Auditor Firm ID	42

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 198,270	$ 248,009
Short-term investments	141,239	165,052
Prepaid expenses and other current assets	8,045	6,741
Total current assets	347,554	419,802
Long-term investments	0	49,001
Total property and equipment, net	14,880	13,646
Operating lease right-of-use assets	26,904	27,322
Restricted cash	2,026	2,027
Other noncurrent assets	112	166
Total assets	391,476	511,964
Current liabilities:
Accounts payable	998	4,550
Accrued expenses	9,063	4,974
Current portion of operating lease liabilities	2,109	937
Current portion of other liabilities	1,456	2,395
Total current liabilities	13,626	12,856
Noncurrent operating lease liabilities	31,653	31,120
Other noncurrent liabilities	1,100	2,469
Total liabilities	46,379	46,445
Commitments and contingencies (Note 13)
Stockholder's equity:
Common stock, $0.001 par value, 200,000,000 and 200,000,000 shares authorized as of December 31, 2021 and 2020 respectively; 55,703,327 and 54,073,901 shares issued and outstanding as of December 31, 2021 and 2020, respectively.	56	54
Preferred stock, $0.001 par value; 10,000,000 authorized; no shares issued and outstanding
Additional paid-in capital	608,064	577,390
Accumulated deficit	(262,984)	(111,906)
Accumulated other comprehensive income (loss)	(39)	(19)
Total stockholders' equity	345,097	465,519
Total liabilities and stockholders’ equity	$ 391,476	$ 511,964

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020	Oct. 14, 2020
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000	200,000,000
Common stock, shares issued (in shares)	55,703,327	54,073,901
Common stock, shares outstanding (in shares)	55,703,327	54,073,901
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000	10,000,000
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 112,903	$ 43,250	$ 13,446
General and administrative	38,495	14,794	3,370
Total operating expenses	151,398	58,044	16,816
Loss from operations	(151,398)	(58,044)	(16,816)
Other Income and Expenses [Abstract]
Change in fair value of convertible notes payable	0	(27,408)	0
Interest expense	0	(3,890)	(3)
Interest and other income, net	320	898	702
Total other income (expense), net	320	(30,400)	699
Net loss	(151,078)	(88,444)	(16,117)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale securities	(20)	(1)	(18)
Net comprehensive loss	$ (151,098)	$ (88,445)	$ (16,135)
Net loss per share, basic and diluted (in dollars per share)	$ (2.76)	$ (5.43)	$ (3.05)
Weighted-average shares of common stock, basic and diluted (in shares)	54,753,599	16,277,247	5,278,748

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders' Equity (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, 2018	7,806,977
Convertible preferred stock, beginning balance at Dec. 31, 2018	$ 17,985
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
Common stock, beginning 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 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 gain (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 gain (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		9,799,280
Issuance of common stock upon conversion of convertible notes (in shares)	186,137	$ 10	186,127
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)
Convertible preferred stock, ending balance (in shares) at Dec. 31, 2021	0
Convertible preferred stock, ending balance at Dec. 31, 2021	$ 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)		1,533,703
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	3,127	$ 2	3,125
Stock-based compensation expense	26,211		26,211
Employee stock purchase plan (in shares)		95,723
Employee stock purchase plan	1,338		1,338
Net unrealized gain (loss) on available-for-sale securities	(20)			(20)
Net loss	(151,078)				(151,078)
Common stock, ending balance (in shares) at Dec. 31, 2021		55,703,327
Beginning balance at Dec. 31, 2021	$ 345,097	$ 56	$ 608,064	$ (39)	$ (262,984)

Statements of Convertible Pre_2

Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parentheticals) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / shares
Statement of Stockholders' Equity [Abstract]
Convertible preferred stock, par value (in dollars per share) | $ / shares	$ 7.67
Payments of stock issuance costs | $	$ 78

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended			54 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (151,078)	$ (88,444)	$ (16,117)	$ (263,000)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,977	839	356
Net amortization/accretion on marketable securities	3,997	326	(4)
Change in accrued interest on marketable securities	485	265	45
Change in fair value of convertible notes payable	0	27,408	0
Debt issuance costs on convertible notes payable	0	3,889	0
Acquired in-process research and development	0	3,565	0
Stock-based compensation expense	26,211	3,753	113
Noncash lease expense	2,104	4,027	249
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(975)	(5,226)	(607)
Other long-term assets	54	261	(153)
Accounts payable	(3,195)	2,807	716
Accrued expenses	4,786	3,229	620
Other liabilities	(2,309)	4,704	(48)
Right-of-use operating assets and liabilities, net	19	685	(252)
Net cash used in operating activities	(117,924)	(37,912)	(15,082)
Cash flows from investing activities:
Purchase of property and equipment	(4,260)	(9,568)	(2,948)
Purchase of marketable securities	(177,734)	(229,328)	(64,633)
Maturities of marketable securities	226,245	78,661	0
Sale of marketable securities	19,473	0	0
Net cash provided by (used in) investing activities	63,724	(160,235)	(67,581)
Cash flows from financing activities:
Proceeds from initial public offering, net of commission and issuance costs	0	263,725	0
Proceeds from issuance of convertible notes, net of issuance costs	0	151,275	0
Principal payments on finance lease	(5)	(32)	(30)
Proceeds from issuance of common stock upon exercise or vesting of stock options	3,127	645	115
Proceeds from issuance of common stock under the employee stock purchase plan	1,338	0	0
Proceeds from issuance of preferred stock, net of financing fees	0	0	104,922
Net cash provided by financing activities	4,460	415,613	105,007
Net increase (decrease) in cash and cash equivalents	(49,740)	217,466	22,344
Cash, cash equivalents and restricted cash at beginning of period	250,036	32,570	10,226
Cash, cash equivalents and restricted cash at end of period	200,296	250,036	32,570	200,296
Supplemental disclosures of non-cash activities:
Common stock issued on conversion of convertible preferred stock	0	122,907	0
Common stock issued on conversion of convertible notes payable	0	186,137	0
Property and equipment additions included in accounts payable and accrued expenses	226	1,280	116
Reduction of right-of-use asset due to modification	(1,741)	0	0
Right-of-use asset obtained in exchange for operating lease liability	3,764	28,839	4
Cash and cash equivalents	198,270	248,009	32,570	198,270
Restricted cash	2,026	2,027	0	2,026
Cash, cash equivalents and restricted cash at end of period	$ 200,296	$ 250,036	$ 32,570	$ 200,296

Nature of Operations and Basis

Nature of Operations and Basis of Presentation	12 Months Ended
	Dec. 31, 2021
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 an integrated discovery through late-stage clinical development biopharmaceutical company, with a focus on developing therapeutics that target the dysregulated transcription that causes cancer and other serious diseases. 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, all then outstanding shares of convertible preferred stock were automatically converted into 22,687,625 shares of common stock, and the then outstanding 2020 Notes (see Note 15) were automatically converted into 9,610,713 shares of common stock. At the closing of the IPO, the then outstanding 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 incurred 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 $339.5 million as of December 31, 2021. Since inception through December 31, 2021, the Company has incurred a cumulative net operating loss of $263.0 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 full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. 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

Significant Accounting Policies, Estimates and Judgments	12 Months Ended
	Dec. 31, 2021
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), investigator grants, 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, 2021 included a $29.0 million milestone payment to Gilead which became payable upon initiation of the Company’s registrational Phase 3 clinical trial of entospletinib in combination with induction chemotherapy in acute myeloid leukemia patients with NPM1 mutations. 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, 2021 and 2019. 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 at the date of purchase to be cash equivalents. Restricted Cash The Company has deposited cash of $2.0 million as of December 31, 2021 and 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, 2021 and 2020, 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, 2021 and 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, 2021 and 2020. 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 Computer equipment 3 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, 2021 and 2020. 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, 2021, 2020 and 2019, other comprehensive loss consisted of unrealized gains and losses from available-for-sale securities. 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. In May 2021, the FASB issued ASU No. 2021-04, Earnings Per Share (Topic 260), Debt—Modifications and Extinguishments (Subtopic 470-50), Compensation—Stock Compensation (Topic 718), and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options (a consensus of the FASB Emerging Issues Task Force)

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 were as follows: December 31, 2021 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 188,923 $ — $ — $ 188,923 Corporate bonds — 63,620 — 63,620 U.S. treasury securities 79,394 — — 79,394 Total financial assets $ 268,317 $ 63,620 $ — $ 331,937 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 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.

Investments

Investments	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 were as follows: December 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 188,923 $ — $ — $ 188,923 Corporate bonds 63,647 2 (29) 63,620 U.S. agency securities — — — — U.S. treasury securities 79,406 — (12) 79,394 Total cash equivalents and investments $ 331,976 $ 2 $ (41) $ 331,937 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 These available-for-sale securities were classified on the Company’s balance sheets as of December 31, 2021 and 2020 as: Fair Value December 31, 2021 2020 (in thousands) Cash equivalents $ 190,698 $ 236,818 Short-term investments 141,239 165,052 Long-term investments — 49,001 Total cash equivalents and investments $ 331,937 $ 450,871 The fair values of available-for-sale securities by contractual maturity as of December 31, 2021 and 2020 were as follows: December 31, 2021 2020 (in thousands) Due in 1 year or less $ 143,014 $ 287,686 Due in 1 to 2 years — 49,001 Instruments not due at a single maturity date 188,923 114,184 Total cash equivalents and investments $ 331,937 $ 450,871 As of December 31, 2021 and 2020, 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, 2021 and 2020 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, 2021 and 2020, 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 Curr

Prepaid Expenses And Other Current Assets	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020: December 31, 2021 2020 (in thousands) Accrued interest on short-term available-for-sale securities $ 816 $ 612 Prepaid equipment service contracts 360 383 Prepaid external research and development and outside services 3,074 1,889 Prepaid software 624 736 Prepaid insurance 2,644 2,881 Prepaid rent and other 527 240 Total prepaid expenses and other current assets $ 8,045 $ 6,741

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020: December 31, 2021 2020 (in thousands) Property and equipment: Lab equipment $ 8,164 $ 5,619 Leasehold improvements 9,335 8,957 Furniture and fixtures 596 216 Finance lease on R&D equipment — 139 Computer equipment 44 — Total property and equipment 18,139 14,931 Less: Accumulated depreciation and amortization (3,259) (1,285) Total property and equipment, net $ 14,880 $ 13,646

Accrued Expenses and Current Po

Accrued Expenses and Current Portion of Other Liabilities	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020: December 31, 2021 2020 (in thousands) Accrued compensation $ 4,570 $ 2,274 External research and development 2,655 1,017 Accrued outside services 1,598 — Accrued taxes — 558 Accrued leasehold improvements — 927 Other accrued expenses 240 198 Total accrued expenses $ 9,063 $ 4,974 December 31, 2021 2020 (in thousands) Current portion of finance lease liability $ — $ 5 Current portion of unvested early exercised share liability 1,364 2,174 ESPP withholdings 92 216 Total current portion of other liabilities $ 1,456 $ 2,395

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2021
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 Convertible Preferred Stock consisted of the following as of December 31, 2019: December 31, 2019 Preferred Stock Authorized Preferred Carrying Liquidation Common (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, 2021 and 2020.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
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, 2021 and December 31, 2020, there were 55,703,327 and 54,073,901 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

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION 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. As a result of the automatic annual increases, the maximum number of shares of common stock that may be issued under the 2020 Plan as of December 31, 2021 was 14,739,827 shares. Under the 2020 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, 2021 and 2020, there were 4,647,580 and 3,696,370 shares, respectively, 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, 2021, 2020 and 2019 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, 2021, 2020, and 2019 were as follows, presented on a weighted-average basis: Year Ended December 31, 2021 2020 2019 Fair value of common stock per share $ 25.99 $ 10.52 $ 2.27 Expected term (in years) 6.01 6.00 6.07 Expected volatility 85.26% 78.36% 70.20 % Risk-free interest rate 0.90% 0.71% 1.81 % Expected dividend —% —% — % The weighted-average grant-date fair value per share of stock options granted, using the assumptions listed above, was $18.52, $7.25, and $1.42 during the years ended December 31, 2021, 2020, and 2019, respectively. Stock Options Stock option activity under the 2020 Plan as of December 31, 2021 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, 2020 6,251,159 $ 8.95 Granted 1,678,306 25.99 Forfeited (1) (150,023) 13.57 Exercised (1,189,042) 2.60 Balance at December 31, 2021 6,590,400 $ 14.33 8.63 $ 35,325 Exercisable at December 31, 2021 1,626,371 $ 10.51 8.36 $ 11,721 Unvested and expected to vest at December 31, 2021 4,964,029 $ 15.58 8.72 $ 23,604 (1) Included in forfeited are 12,748 options that were early exercised, but not yet vested at the time of termination of the grantee, and repurchased by the Company. The weighted-average exercise price of the repurchased options was $0.61 per share. 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, 2021. The intrinsic value of options exercised for the years ended December 31, 2021, 2020, and 2019 was $23.8 million, $6.1 million and $0.7 million, res pectively, 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, 2021 and December 31, 2020. For the years ended December 31, 2021, 2020, and 2019, 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, 2021 2020 2019 (in thousands) Research and development expenses $ 7,753 $ 1,061 $ 54 General and administrative expenses 8,406 1,451 54 Total stock-based compensation expense $ 16,159 $ 2,512 $ 108 As of December 31, 2021 and 2020, there was $49.9 million and $36.3 million of unrecognized stock-based compensation related to stock options, respectively, which is expected to be recognized over a weighted average period of 2.93 and 3.70 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 to tal number of shares of common stock outstanding on December 31st of the immediately preceding year, and (ii) 1,376,000 shares, e xcept 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). Effective January 1, 2021, the number of shares authorized under the ESPP for employee purchases increased by 560,335 shares. 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. The Company issued and sold 95,723 shares of common stock under the ESPP during the year ended December 31, 2021 and no shares of common stock under the ESPP during the years ended December 31, 2020 and 2019. The Company has 1,152,612 shares reserved for future issuance under the ESPP as of December 31, 2021. 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) automatically began in 2021, and a new offering will begin 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, 2021 2020 Expected term (in years) 0.50 - 2.00 0.68 - 2.19 Expected volatility 71.67% - 94.85% 89.25% - 110.84% Risk-free interest rate 0.05% - 0.25% 0.12% - 0.19% Dividend yield —% —% For the years ended December 31, 2021 and 2020, total stock-based compensation related to the ESPP was $1.4 million and $0.3 million, respectively, with $0.3 million and $0.1 million, respectively, recorded in general and administrative expenses and $1.1 million and $0.2 million, respectively, 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, 2021 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, 2020 810,197 $ 22.26 Granted - restricted stock awards and units 347,267 29.14 Vested and converted to shares (344,661) 17.49 Forfeited (25,084) 29.83 Unvested at December 31, 2021 787,719 $ 26.88 2.07 $ 10,705 Vested and expected to vest at December 31, 2021 787,719 $ 26.88 2.07 $ 10,705 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 $0.1 million, $0.6 million, and zero in general and administrative expenses and $5,000, $5,000, and $5,000 in research and development expenses in the statements of operations and comprehensive loss for the years ended December 31, 2021, 2020 and 2019, respectively. As of December 31, 2021, there was $0.3 million of unrecognized stock-based compensation related to RSAs, which is expected to be recognized over a weighted average period of 2.58 years. The total grant date fair value for RSAs vested during the years ended December 31, 2021, 2020, and 2019 was $0.2 million, $0.6 million, and $5,000, respectively. For the years ended December 31, 2021 and 2020, the Company issued 347,267 and 565,417, restricted stock units (RSUs), respectively, to executive officers and non-executive employees 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 $8.5 million of stock-based compensation expense related to the RSUs for the year ended December 31, 2021, of which $4.1 million and $4.4 million are recorded in research and development and general and administrative expenses, respectively, in the current year statement of operations and comprehensive loss. 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, 2021, there was $17.9 million of unrecognized stock-based compensation related to RSUs, which is expected to be recognized over a weighted average period of 2.01 years. As of December 31, 2021 and 2020, 188,470 and zero RSUs have vested, respectively. 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, 2021, 2020, and 2019 as follows for stock options, RSAs, RSUs, and ESPP: Year Ended December 31, 2021 2020 2019 (in thousands) Research and development expenses $ 12,961 $ 1,390 $ 59 General and administrative expenses 13,250 2,363 54 Total stock-based compensation expense $ 26,211 $ 3,753 $ 113 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, 2021 and 2020, zero and 1,551,361 options were early exercised, respectively. At December 31, 2021 and 2020, there was $1.4 million and $2.2 million recorded in current portion of other liabilities, and $1.1 million and $2.5 million recorded in other noncurrent liabilities, respectively, related to shares held by employees and nonemployees that were subject to repurchase.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The Company recorded a small amount of income tax expense related to state minimum taxes for the year ended December 31, 2021 and did not record any income tax expense for the years ended December 31, 2020 and 2019. 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, 2021, 2020, and 2019 were as follows: Year Ended December 31, 2021 2020 2019 (in thousands) Tax benefit at federal statutory rate $ (31,726) $ (18,573) $ (3,384) State taxes (7,138) (2,748) (232) Research tax credits (597) (475) (427) Change in valuation allowance 38,846 15,062 3,958 Change in fair value of convertible notes — 5,756 — Other 615 978 85 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, 2021 and 2020. Significant components of the Company’s deferred tax assets and liabilities are as follows: Year Ended December 31, 2021 2020 (in thousands) Deferred tax assets: Lease liabilities $ 8,750 $ 8,312 Stock-based compensation 2,777 — Accrued compensation 1,320 495 Net operating loss carryforwards 52,052 19,710 Tax credit carryforwards 1,296 673 Other — 1 Total deferred tax assets 66,195 29,191 Valuation allowance (58,713) (20,797) Net deferred tax assets 7,482 8,394 Deferred tax liabilities: Right-of-use assets (6,973) (7,085) Fixed assets and intangibles (509) (411) Stock-based compensation — (898) Total deferred tax liabilities (7,482) (8,394) 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 $58.7 million and $20.8 million for the years ended December 31, 2021 and 2020, respectively. The change in valuation allowance of $37.9 million is due to increases in net operating losses and other deferred tax assets due to current year activity. The following table sets forth the Company’s federal and state net operating loss and research credit carryforwards as of December 31, 2021: Amount Expiration (in thousands) Net operating losses, federal $ 201,842 Indefinite Net operating losses, federal $ 601 2037 Net operating losses, state $ 150,932 2037-2041 Tax credits, federal $ 1,542 2037-2041 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, 2021 2020 2019 (in thousands) Balance at beginning of the year $ 141 $ 109 $ 32 Additions based on tax positions related to the current year 105 91 77 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 $ 246 $ 141 $ 109 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, 2021, 2020, and 2019. 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.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
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, 2021, 2020, and 2019: Year Ended December 31, 2021 2020 2019 (in thousands, except share and per share amounts) Net loss $ (151,078) $ (88,444) $ (16,117) Weighted-average common stock outstanding, basic and diluted 54,753,599 16,277,247 5,278,748 Net loss per share, basic and diluted $ (2.76) $ (5.43) $ (3.05) 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: Year Ended December 31, 2021 2020 2019 Stock options to purchase common stock 5,802,435 4,536,337 951,302 Early exercised stock options subject to future vesting 787,965 1,714,822 774,931 Restricted stock awards subject to future vesting 88,589 244,780 215,220 Restricted stock units subject to future vesting 699,129 565,417 — Convertible preferred stock — — 22,687,625 Total 7,378,118 7,061,356 24,629,078

Commitment and Contingencies

Commitment and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES R&D Services Agreement In October 2021, the Company entered into an agreement for research and development services (Tempus Agreement) with Tempus Labs, Inc. (Tempus), pursuant to which Tempus agreed to provide the Company with research and development services for a period of three years. The three primary services are analytical services, data licensing, and organoid services. The Company intends to utilize the services contemplated under the Tempus Agreement to advance the development of KB-0742 and lanraplenib. In consideration for the access to the services throughout the term of the Tempus Agreement, the Company has agreed to pay an annual minimum commitment of $1.5 million in year one, $2.0 million in year two, and $2.5 million in year three. Payments are made in quarterly installments. As of December 31, 2021, the Company has not made any payments under the Tempus Agreement. In addition, the Company is required to make milestone payments upon successful achievement of certain regulatory milestones for KB-0742, lanraplenib, and other discovery pipeline compounds up to a combined maximum of $22.4 million. For each milestone payment that becomes due, the Company has the right to pay up to 50% of such milestone payment amount in shares of its common stock as long as certain regulatory requirements are met. 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 and lanraplenib, and patents and other intellectual property covering or related to the development, manufacture and commercialization of entospletinib and lanraplenib. 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 entospletinib, lanraplenib 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 entospletinib or lanraplenib (Other Compounds). Upon initiation of the Company’s registrational Phase 3 clinical trial of entospletinib in combination with induction chemotherapy in acute myeloid leukemia patients with NPM1 mutations in December 2021, the Company paid a milestone payment to Gilead of $29.0 million. Upon successful completion of certain other regulatory milestones in the United States, European Union and United Kingdom for entospletinib, lanraplenib 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 entospletinib, lanraplenib 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 entospletinib, (ii) tiered marginal royalties ranging from high-single digits to the mid-teens on annual worldwide net sales of lanraplenib 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 entospletinib and lanraplenib, for any royalties paid for future licenses of third party intellectual property required to develop or commercialize entospletinib or lanraplenib. 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 entospletinib or lanraplenib. 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

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	LEASESIn November 2020, the Company entered into a lease termination for its lab space in Cambridge, Massachusetts to terminate the lease as of January 31, 2021, rather than May 31, 2021. The cost for early termination was 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 the modification date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease. In March 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 (Cambridge facility). The 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, 2021, $3.7 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 $23.6 million and an aggregate lease liability of $29.7 million on the December 31, 2021 balance sheet. The remaining lease term is 9 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 had a 37-month initial term expiring on August 31, 2021. The lease also contained 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 was $0.3 million, and such amount was to increase by 3% annually on each anniversary of the commencement date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease, which ended with the modification discussed below. The operating lease right-of-use asset and an aggregate lease liability were $1.1 million and $1.1 million, respectively as of December 31, 2020. In July 2020, the Company expanded to an adjacent suite in the San Mateo, California office space, which was treated as a separate lease for accounting purposes. The additional space was approximately 3,414 square feet and was used for general and administrative activities. The lease commenced on July 1, 2020 and had an initial expiration date of 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 was $0.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease, which ended with the modification discussed below. The operating lease right-of-use asset and aggregate lease liability for this suite were $0.8 million and $0.8 million, respectively, as of December 31, 2020. 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 totaling 17,340 square-feet, and a lease commencement date in the second quarter of 2021. The Company accounted for this change in lease term of the original suites 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 the modification date. The new 17,340 square foot suite will be treated as a separate lease for accounting purposes. The initial annual base rent for the new space will be $1.2 million, and such amount will increase by 3% annually on each anniversary of the new premises commencement date. In connection with the larger space leased, the Company has also made an additional one-time cash security deposit in the amount of $59,000. The new lease commenced in April 2021 and the new lease agreement extends the termination date from April 30, 2025 to June 1, 2026. In connection with the lease, the Company recognized an operating lease right-of-use asset of $3.3 million and an aggregate lease liability of $4.1 million as of December 31, 2021. The Company did not recognize any right-of-use asset or aggregate lease liability as of December 31, 2020. The remaining lease term is 4.5 years, and the estimated incremental borrowing rate is 11.18%. The following table summarizes the presentation of the Company’s finance lease in its balance sheets as of December 31, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Property and equipment, net $ — $ 83 Liabilities: Current portion of other liabilities — 5 Total finance lease liabilities $ — $ 5 The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of December 31, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Operating lease assets $ 26,904 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 2,109 $ 937 Noncurrent operating lease liabilities 31,653 31,120 Total operating lease liabilities $ 33,762 $ 32,057 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, 2021, 2020, and 2019: Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3 $ 20 $ 20 Interest expense — 1 3 Total finance lease cost $ 3 $ 21 $ 23 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, 2021, 2020, and 2019 : Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3,308 $ 4,272 $ — General and administrative 2,015 1,293 310 Total operating lease cost $ 5,323 $ 5,565 $ 310 The Company made cash payments of $4.4 million, $2.8 million, and $0.3 million under the lease agreements during the years ended December 31, 2021, 2020, and 2019, respectively. The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) 2022 $ 5,020 2023 5,581 2024 5,749 2025 5,921 2026 and thereafter 26,705 Total undiscounted lease payments 48,976 Less: Present value adjustment (15,214) Present value of operating lease liabilities $ 33,762
Leases	LEASESIn November 2020, the Company entered into a lease termination for its lab space in Cambridge, Massachusetts to terminate the lease as of January 31, 2021, rather than May 31, 2021. The cost for early termination was 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 the modification date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease. In March 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 (Cambridge facility). The 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, 2021, $3.7 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 $23.6 million and an aggregate lease liability of $29.7 million on the December 31, 2021 balance sheet. The remaining lease term is 9 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 had a 37-month initial term expiring on August 31, 2021. The lease also contained 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 was $0.3 million, and such amount was to increase by 3% annually on each anniversary of the commencement date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease, which ended with the modification discussed below. The operating lease right-of-use asset and an aggregate lease liability were $1.1 million and $1.1 million, respectively as of December 31, 2020. In July 2020, the Company expanded to an adjacent suite in the San Mateo, California office space, which was treated as a separate lease for accounting purposes. The additional space was approximately 3,414 square feet and was used for general and administrative activities. The lease commenced on July 1, 2020 and had an initial expiration date of 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 was $0.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. As of December 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease, which ended with the modification discussed below. The operating lease right-of-use asset and aggregate lease liability for this suite were $0.8 million and $0.8 million, respectively, as of December 31, 2020. 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 totaling 17,340 square-feet, and a lease commencement date in the second quarter of 2021. The Company accounted for this change in lease term of the original suites 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 the modification date. The new 17,340 square foot suite will be treated as a separate lease for accounting purposes. The initial annual base rent for the new space will be $1.2 million, and such amount will increase by 3% annually on each anniversary of the new premises commencement date. In connection with the larger space leased, the Company has also made an additional one-time cash security deposit in the amount of $59,000. The new lease commenced in April 2021 and the new lease agreement extends the termination date from April 30, 2025 to June 1, 2026. In connection with the lease, the Company recognized an operating lease right-of-use asset of $3.3 million and an aggregate lease liability of $4.1 million as of December 31, 2021. The Company did not recognize any right-of-use asset or aggregate lease liability as of December 31, 2020. The remaining lease term is 4.5 years, and the estimated incremental borrowing rate is 11.18%. The following table summarizes the presentation of the Company’s finance lease in its balance sheets as of December 31, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Property and equipment, net $ — $ 83 Liabilities: Current portion of other liabilities — 5 Total finance lease liabilities $ — $ 5 The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of December 31, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Operating lease assets $ 26,904 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 2,109 $ 937 Noncurrent operating lease liabilities 31,653 31,120 Total operating lease liabilities $ 33,762 $ 32,057 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, 2021, 2020, and 2019: Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3 $ 20 $ 20 Interest expense — 1 3 Total finance lease cost $ 3 $ 21 $ 23 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, 2021, 2020, and 2019 : Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3,308 $ 4,272 $ — General and administrative 2,015 1,293 310 Total operating lease cost $ 5,323 $ 5,565 $ 310 The Company made cash payments of $4.4 million, $2.8 million, and $0.3 million under the lease agreements during the years ended December 31, 2021, 2020, and 2019, respectively. The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) 2022 $ 5,020 2023 5,581 2024 5,749 2025 5,921 2026 and thereafter 26,705 Total undiscounted lease payments 48,976 Less: Present value adjustment (15,214) Present value of operating lease liabilities $ 33,762

2020 Notes

2020 Notes	12 Months Ended
	Dec. 31, 2021
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. For the years ended December 31, 2021 and 2019, the Company recognized no gain or loss in the accompanying statements of operations and comprehensive loss for the change in fair value of the 2020 Notes. There were no other similar transactions during the year ended December 31, 2021.

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Parties	RELATED PARTIES On December 1, 2017, the Company entered into a 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. On December 31, 2021, the Company amended the agreement to limit the scope to accounting and managerial accounting services. Arie Belldegrun, M.D., FACS, the Chair of the Board of Directors, is the Chair 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, 2021, 2020, and 2019, the Company incurred expenses of $0.3 million, $1.2 million, and $0.9 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 zero , $27,000, and $49,000 for the years ended December 31, 2021, 2020, and 2019, respectively. As of December 31, 2021 and 2020, the Company had payables to Two River of zero and $0.2 million, respectively.

Significant Accounting Polici_2

Significant Accounting Policies, Estimates and Judgments (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	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	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 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), investigator grants, 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, 2021 included a $29.0 million milestone payment to Gilead which became payable upon initiation of the Company’s registrational Phase 3 clinical trial of entospletinib in combination with induction chemotherapy in acute myeloid leukemia patients with NPM1 mutations. 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, 2021 and 2019. 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	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Restricted Cash The Company has deposited cash of $2.0 million as of December 31, 2021 and 2020 to secure a letter of credit in connection with the lease of the new Cambridge facility (see Note 14).
Concentration of Credit Risk and Other Risks and Uncertainties	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, 2021 and 2020, 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 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.
Fair Value Measurement	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, 2021 and 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, 2021 and 2020. 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, 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 Computer equipment 3 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	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	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	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	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 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, 2021, 2020 and 2019, other comprehensive loss consisted of unrealized gains and losses from available-for-sale securities.
Net Loss Per Share	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	Recent Accounting Pronouncements Not Yet Adopted In May 2021, the FASB issued ASU No. 2021-04, Earnings Per Share (Topic 260), Debt—Modifications and Extinguishments (Subtopic 470-50), Compensation—Stock Compensation (Topic 718), and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options (a consensus of the FASB Emerging Issues Task Force)

Significant Accounting Polici_3

Significant Accounting Policies, Estimates and Judgments (Tables)	12 Months Ended
	Dec. 31, 2021
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 Computer equipment 3 years Property and equipment, net consisted of the following as of December 31, 2021 and 2020: December 31, 2021 2020 (in thousands) Property and equipment: Lab equipment $ 8,164 $ 5,619 Leasehold improvements 9,335 8,957 Furniture and fixtures 596 216 Finance lease on R&D equipment — 139 Computer equipment 44 — Total property and equipment 18,139 14,931 Less: Accumulated depreciation and amortization (3,259) (1,285) Total property and equipment, net $ 14,880 $ 13,646

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	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, 2021 and 2020 were as follows: December 31, 2021 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 188,923 $ — $ — $ 188,923 Corporate bonds — 63,620 — 63,620 U.S. treasury securities 79,394 — — 79,394 Total financial assets $ 268,317 $ 63,620 $ — $ 331,937 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

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 were as follows: December 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 188,923 $ — $ — $ 188,923 Corporate bonds 63,647 2 (29) 63,620 U.S. agency securities — — — — U.S. treasury securities 79,406 — (12) 79,394 Total cash equivalents and investments $ 331,976 $ 2 $ (41) $ 331,937 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 These available-for-sale securities were classified on the Company’s balance sheets as of December 31, 2021 and 2020 as: Fair Value December 31, 2021 2020 (in thousands) Cash equivalents $ 190,698 $ 236,818 Short-term investments 141,239 165,052 Long-term investments — 49,001 Total cash equivalents and investments $ 331,937 $ 450,871 The fair values of available-for-sale securities by contractual maturity as of December 31, 2021 and 2020 were as follows: December 31, 2021 2020 (in thousands) Due in 1 year or less $ 143,014 $ 287,686 Due in 1 to 2 years — 49,001 Instruments not due at a single maturity date 188,923 114,184 Total cash equivalents and investments $ 331,937 $ 450,871

Prepaid Expenses And Other Cu_2

Prepaid Expenses And Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020: December 31, 2021 2020 (in thousands) Accrued interest on short-term available-for-sale securities $ 816 $ 612 Prepaid equipment service contracts 360 383 Prepaid external research and development and outside services 3,074 1,889 Prepaid software 624 736 Prepaid insurance 2,644 2,881 Prepaid rent and other 527 240 Total prepaid expenses and other current assets $ 8,045 $ 6,741

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
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 Computer equipment 3 years Property and equipment, net consisted of the following as of December 31, 2021 and 2020: December 31, 2021 2020 (in thousands) Property and equipment: Lab equipment $ 8,164 $ 5,619 Leasehold improvements 9,335 8,957 Furniture and fixtures 596 216 Finance lease on R&D equipment — 139 Computer equipment 44 — Total property and equipment 18,139 14,931 Less: Accumulated depreciation and amortization (3,259) (1,285) Total property and equipment, net $ 14,880 $ 13,646

Accrued Expenses And Current _2

Accrued Expenses And Current Portion Of Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses consisted of the following as of December 31, 2021 and 2020: December 31, 2021 2020 (in thousands) Accrued compensation $ 4,570 $ 2,274 External research and development 2,655 1,017 Accrued outside services 1,598 — Accrued taxes — 558 Accrued leasehold improvements — 927 Other accrued expenses 240 198 Total accrued expenses $ 9,063 $ 4,974
Other Current Liabilities	Current portion of other liabilities consist of the following as of December 31, 2021 and 2020: December 31, 2021 2020 (in thousands) Current portion of finance lease liability $ — $ 5 Current portion of unvested early exercised share liability 1,364 2,174 ESPP withholdings 92 216 Total current portion of other liabilities $ 1,456 $ 2,395

Preferred Stock (Tables)

Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2021
Temporary Equity Disclosure [Abstract]
Preferred Stock	The Convertible Preferred Stock consisted of the following as of December 31, 2019: December 31, 2019 Preferred Stock Authorized Preferred Carrying Liquidation Common (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 (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Option-pricing Model Assumptions	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, 2021, 2020, and 2019 were as follows, presented on a weighted-average basis: Year Ended December 31, 2021 2020 2019 Fair value of common stock per share $ 25.99 $ 10.52 $ 2.27 Expected term (in years) 6.01 6.00 6.07 Expected volatility 85.26% 78.36% 70.20 % Risk-free interest rate 0.90% 0.71% 1.81 % Expected dividend —% —% — %
Stock Option Activity	Stock option activity under the 2020 Plan as of December 31, 2021 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, 2020 6,251,159 $ 8.95 Granted 1,678,306 25.99 Forfeited (1) (150,023) 13.57 Exercised (1,189,042) 2.60 Balance at December 31, 2021 6,590,400 $ 14.33 8.63 $ 35,325 Exercisable at December 31, 2021 1,626,371 $ 10.51 8.36 $ 11,721 Unvested and expected to vest at December 31, 2021 4,964,029 $ 15.58 8.72 $ 23,604 (1) Included in forfeited are 12,748 options that were early exercised, but not yet vested at the time of termination of the grantee, and repurchased by the Company. The weighted-average exercise price of the repurchased options was $0.61 per share.
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, 2021 2020 Expected term (in years) 0.50 - 2.00 0.68 - 2.19 Expected volatility 71.67% - 94.85% 89.25% - 110.84% Risk-free interest rate 0.05% - 0.25% 0.12% - 0.19% Dividend yield —% —%
Schedule of Nonvested Share Activity	Restricted stock awards and units as of December 31, 2021 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, 2020 810,197 $ 22.26 Granted - restricted stock awards and units 347,267 29.14 Vested and converted to shares (344,661) 17.49 Forfeited (25,084) 29.83 Unvested at December 31, 2021 787,719 $ 26.88 2.07 $ 10,705 Vested and expected to vest at December 31, 2021 787,719 $ 26.88 2.07 $ 10,705
Stock-based Compensation, Classified in Statements of Operations	For the years ended December 31, 2021, 2020, and 2019, 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, 2021 2020 2019 (in thousands) Research and development expenses $ 7,753 $ 1,061 $ 54 General and administrative expenses 8,406 1,451 54 Total stock-based compensation expense $ 16,159 $ 2,512 $ 108 Total stock-based compensation expense was classified in the Company’s statements of operations and comprehensive loss for the years ended December 31, 2021, 2020, and 2019 as follows for stock options, RSAs, RSUs, and ESPP: Year Ended December 31, 2021 2020 2019 (in thousands) Research and development expenses $ 12,961 $ 1,390 $ 59 General and administrative expenses 13,250 2,363 54 Total stock-based compensation expense $ 26,211 $ 3,753 $ 113

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021, 2020, and 2019 were as follows: Year Ended December 31, 2021 2020 2019 (in thousands) Tax benefit at federal statutory rate $ (31,726) $ (18,573) $ (3,384) State taxes (7,138) (2,748) (232) Research tax credits (597) (475) (427) Change in valuation allowance 38,846 15,062 3,958 Change in fair value of convertible notes — 5,756 — Other 615 978 85 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, 2021 2020 (in thousands) Deferred tax assets: Lease liabilities $ 8,750 $ 8,312 Stock-based compensation 2,777 — Accrued compensation 1,320 495 Net operating loss carryforwards 52,052 19,710 Tax credit carryforwards 1,296 673 Other — 1 Total deferred tax assets 66,195 29,191 Valuation allowance (58,713) (20,797) Net deferred tax assets 7,482 8,394 Deferred tax liabilities: Right-of-use assets (6,973) (7,085) Fixed assets and intangibles (509) (411) Stock-based compensation — (898) Total deferred tax liabilities (7,482) (8,394) 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, 2021: Amount Expiration (in thousands) Net operating losses, federal $ 201,842 Indefinite Net operating losses, federal $ 601 2037 Net operating losses, state $ 150,932 2037-2041 Tax credits, federal $ 1,542 2037-2041
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, 2021 2020 2019 (in thousands) Balance at beginning of the year $ 141 $ 109 $ 32 Additions based on tax positions related to the current year 105 91 77 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 $ 246 $ 141 $ 109

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021, 2020, and 2019: Year Ended December 31, 2021 2020 2019 (in thousands, except share and per share amounts) Net loss $ (151,078) $ (88,444) $ (16,117) Weighted-average common stock outstanding, basic and diluted 54,753,599 16,277,247 5,278,748 Net loss per share, basic and diluted $ (2.76) $ (5.43) $ (3.05)
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: Year Ended December 31, 2021 2020 2019 Stock options to purchase common stock 5,802,435 4,536,337 951,302 Early exercised stock options subject to future vesting 787,965 1,714,822 774,931 Restricted stock awards subject to future vesting 88,589 244,780 215,220 Restricted stock units subject to future vesting 699,129 565,417 — Convertible preferred stock — — 22,687,625 Total 7,378,118 7,061,356 24,629,078

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
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)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Property and equipment, net $ — $ 83 Liabilities: Current portion of other liabilities — 5 Total finance lease liabilities $ — $ 5
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, 2021 and 2020: Balance Sheet Caption December 31, 2021 2020 (in thousands) Assets: Operating lease assets $ 26,904 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 2,109 $ 937 Noncurrent operating lease liabilities 31,653 31,120 Total operating lease liabilities $ 33,762 $ 32,057
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, 2021, 2020, and 2019: Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3 $ 20 $ 20 Interest expense — 1 3 Total finance lease cost $ 3 $ 21 $ 23 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, 2021, 2020, and 2019 : Statement of Operations and Comprehensive Loss Caption Year Ended December 31, 2021 2020 2019 (in thousands) Research and development $ 3,308 $ 4,272 $ — General and administrative 2,015 1,293 310 Total operating lease cost $ 5,323 $ 5,565 $ 310
Schedule of Maturities on Lease Liabilities	The undiscounted future non-cancellable lease payments under the Company's operating leases as of December 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) 2022 $ 5,020 2023 5,581 2024 5,749 2025 5,921 2026 and thereafter 26,705 Total undiscounted lease payments 48,976 Less: Present value adjustment (15,214) Present value of operating lease liabilities $ 33,762

2020 Notes (Tables)

2020 Notes (Tables)	12 Months Ended
	Dec. 31, 2021
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 Basi_2

Nature of Operations and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	Oct. 02, 2020	Oct. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2021USD ($)segment$ / sharesshares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Dec. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2018shares
Subsidiary, Sale of Stock [Line Items]
Number of operating segments | segment			1
Convertible preferred stock, shares outstanding (in shares)			0	0	21,504,893	0	7,806,977
Cash, cash equivalents, and short-term investments | $			$ 339,500			$ 339,500
Net loss | $			$ (151,078)	$ (88,444)	$ (16,117)	$ (263,000)
Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible notes (in shares)				9,799,280
Forward stock split ratio	1.055
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)		15,131,579
Shares issued, price per share (in dollars per share) | $ / shares		$ 19
Net proceeds from stock offering | $		$ 263,700
Payments of underwriting discounts and commissions | $		(20,100)
Payments of offering costs | $		$ (3,700)
Convertible preferred stock, shares outstanding (in shares)		0
IPO | Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible notes (in shares)		22,687,625
IPO | Common Stock | 2020 Notes
Subsidiary, Sale of Stock [Line Items]
Shares issued, price per share (in dollars per share) | $ / shares			$ 19			$ 19
Shares issued upon conversion of convertible notes (in shares)		9,610,713
IPO | Common Stock | Gilead Note
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible notes (in shares)		188,567
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)		1,973,684

Significant Accounting Polici_4

Significant Accounting Policies, Estimates and Judgments - R&D Expense (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Asset Acquisition [Line Items]
Research and development		$ 112,903	$ 43,250	$ 13,446
Asset Purchase Agreement
Schedule Of Asset Acquisition [Line Items]
Sales milestone payment	$ 29,000
Gilead Asset Purchase
Schedule Of Asset Acquisition [Line Items]
Research and development		$ 6,600

Significant Accounting Polici_5

Significant Accounting Policies, Estimates and Judgments - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Restricted cash	$ 2,026	$ 2,027	$ 0

Significant Accounting Polici_6

Significant Accounting Policies, Estimates and Judgments - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
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
Computer equipment
Property, Plant and Equipment [Line Items]
Useful life	3 years

Significant Accounting Polici_7

Significant Accounting Policies, Estimates and Judgments - Deferred Offering Costs (Details) - USD ($)	1 Months Ended
	Oct. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Subsidiary, Sale of Stock [Line Items]
Deferred offering costs		$ 0	$ 0
IPO
Subsidiary, Sale of Stock [Line Items]
Payments of offering costs	$ 3,700,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 331,937	$ 450,871
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	188,923	114,184
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		1,229
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	63,620	40,736
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		10,001
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	79,394	284,721
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	268,317	400,134
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	188,923	114,184
Level 1 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		1,229
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
Level 1 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	79,394	284,721
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	63,620	50,737
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
Level 2 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	63,620	40,736
Level 2 | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value		10,001
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
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
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 Am

Investments - Fair Value and Amortized Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	$ 190,698	$ 236,818
Total cash equivalents and investments, amortized cost	331,976	450,890
Total cash equivalents and investments, unrealized gains	2	18
Total cash equivalents and investments, unrealized losses	(41)	(37)
Total cash equivalents and investments, fair value	331,937	450,871
Money market funds
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	188,923	114,184
Certificates of deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		1,225
Unrealized Gains		4
Unrealized Losses		0
Fair Value		1,229
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	63,647	40,743
Unrealized Gains	2	9
Unrealized Losses	(29)	(16)
Fair Value	63,620	40,736
U.S. agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	9,999
Unrealized Gains	0	2
Unrealized Losses	0	0
Fair Value	0	10,001
U.S. treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	79,406	284,739
Unrealized Gains	0	3
Unrealized Losses	(12)	(21)
Fair Value	$ 79,394	$ 284,721

Investments - Balance Sheet (De

Investments - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Cash equivalents	$ 190,698	$ 236,818
Short-term investments	141,239	165,052
Long-term investments	0	49,001
Total cash equivalents and investments	$ 331,937	$ 450,871

Investments - Contractual Matur

Investments - Contractual Maturity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less	$ 143,014,000	$ 287,686,000
Due in 1 to 2 years	0	49,001,000
Instruments not due at a single maturity date	188,923,000	114,184,000
Total cash equivalents and investments	331,937,000	450,871,000
Other-than-temporary impairments on available-for-sale securities	$ 0	$ 0

Prepaid Expenses And Other Cu_3

Prepaid Expenses And Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Accrued interest on short-term available-for-sale securities	$ 816	$ 612
Prepaid equipment service contracts	360	383
Prepaid external research and development and outside services	3,074	1,889
Prepaid software	624	736
Prepaid insurance	2,644	2,881
Prepaid rent and other	527	240
Prepaid expenses and other current assets	$ 8,045	$ 6,741

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Leasehold improvements	$ 0	$ 139
Total property and equipment	18,139	14,931
Less: Accumulated depreciation and amortization	(3,259)	(1,285)
Total property and equipment, net	14,880	13,646
Depreciation and amortization	1,977	839	$ 356
Lab equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,164	5,619
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,335	8,957
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	596	216
Computer equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 44	$ 0

Accrued Expenses And Current _3

Accrued Expenses And Current Portion Of Other Liabilities - Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued compensation	$ 4,570	$ 2,274
External research and development	2,655	1,017
Accrued outside services	1,598	0
Accrued taxes	0	558
Accrued leasehold improvements	0	927
Other accrued expenses	240	198
Total accrued expenses	$ 9,063	$ 4,974

Accrued Expenses And Current _4

Accrued Expenses And Current Portion Of Other Liabilities - Current Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Current portion of finance lease liability	$ 0	$ 5
Current portion of unvested early exercised share liability	1,364	2,174
ESPP withholdings	92	216
Total current portion of other liabilities	$ 1,456	$ 2,395

Preferred Stock - Narrative (De

Preferred Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 01, 2019	May 22, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021	Oct. 14, 2020
Temporary Equity [Line Items]
Issuance costs			$ 23,775	$ 78
Preferred stock, shares authorized (in shares)			10,000,000		10,000,000	10,000,000
Preferred stock, par value (in dollars per share)			$ 0.001		$ 0.001	$ 0.001
Preferred stock, shares issued (in shares)			0		0
Preferred stock, shares outstanding (in shares)			0		0
Common Stock
Temporary Equity [Line Items]
Shares issued upon conversion of convertible notes (in shares)			9,799,280
Series Seed Preferred Stock | Convertible Notes
Temporary Equity [Line Items]
Shares issued, price per share (in dollars per share)		$ 2.30769
Series Seed Preferred Stock | Private Placement
Temporary Equity [Line Items]
Shares issued (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 shares)	13,697,916
Gross proceeds received in private placement	$ 105,000
Shares issued, price per share (in dollars per share)	$ 7.6654
Issuance costs	$ 100

Preferred Stock (Details)

Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Preferred Stock Authorized (in shares)			21,506,977
Preferred Stock Issued (in shares)			21,504,893
Preferred Stock Outstanding (in shares)	0	0	21,504,893	7,806,977
Carrying Value	$ 0	$ 0	$ 122,907	$ 17,985
Temporary Equity, Liquidation Preference			$ 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)

Common Stock (Details) - $ / shares	Dec. 31, 2021	Dec. 31, 2020	Oct. 14, 2020
Equity [Abstract]
Common stock, shares authorized (in shares)	200,000,000	200,000,000	200,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, shares issued (in shares)	55,703,327	54,073,901
Common stock, shares outstanding (in shares)	55,703,327	54,073,901

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value, options granted (in dollars per share)		$ 18.52	$ 7.25	$ 1.42
Stock options exercised, intrinsic value		$ 23,800,000	$ 6,100,000	$ 700,000
Stock options, unrecognized cost		$ 49,900,000	$ 36,300,000
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	14,739,827
Expiration period	10 years	10 years
Shares that may be issued, percent increase as total of common stock outstanding	5.00%
Exercise price per share of stock options as percent of fair market value of common stock	100.00%
Number of shares reserved for future issuance (in shares)		4,647,580	3,696,370
2020 Equity Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2020 Equity Incentive Plan | 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		2 years 11 months 4 days	3 years 8 months 12 days

Stock-Based Compensation - Opti

Stock-Based Compensation - Option-pricing Model Assumptions (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock per share (dollars per share)	$ 25.99	$ 10.52	$ 2.27
Expected term (in years)	6 years 3 days	6 years	6 years 25 days
Expected volatility	85.26%	78.36%	70.20%
Risk-free interest rate	0.90%	0.71%	1.81%
Expected dividend	0.00%	0.00%	0.00%

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Stock Option Activity Under the 2017 Plan [Roll Forward]
Beginning Balance (in shares) | shares	6,251,159
Granted (in shares) | shares	1,678,306
Forfeited (in shares) | shares	(150,023)
Exercised (in shares) | shares	(1,189,042)
Ending Balance (in shares) | shares	6,590,400
Exercisable (in shares) | shares	1,626,371
Unvested and expected to vest (in shares) | shares	4,964,029
Stock Options, Weighted Average Exercise Price [Roll Forward]
Beginning Balance (dollars per share) | $ / shares	$ 8.95
Granted (dollars per share) | $ / shares	25.99
Forfeited (dollars per share) | $ / shares	13.57
Exercised (dollars per share) | $ / shares	2.60
Ending Balance (dollars per share) | $ / shares	14.33
Exercisable (in dollars per share) | $ / shares	10.51
Unvested and expected to vest (in dollars per share) | $ / shares	$ 15.58
Stock Option Activity, Additional Disclosures [Abstract]
Balance, Weighted-Average Remaining Contractual Term	8 years 7 months 17 days
Exercisable, Weighted-Average Remaining Contractual Term	8 years 4 months 9 days
Unvested and expected to vest, Weighted-Average Remaining Contractual Term	8 years 8 months 19 days
Balance, Aggregate Intrinsic Value | $	$ 35,325
Exercisable, Aggregate Intrinsic Value | $	11,721
Unvested and expected to vest, Aggregate Intrinsic Value | $	$ 23,604
Forfeited options, early exercised but not vested and repurchased by company (in shares) | shares	12,748
Forfeited options, early exercised but not vested and repurchased by company, weighted-average exercise price (in dollars per share) | $ / shares	$ 0.61

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Based Compensation - Stock Options (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 26,211	$ 3,753	$ 113
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	16,159	2,512	108
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	12,961	1,390	59
Research and development expenses | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7,753	1,061	54
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	13,250	2,363	54
General and administrative expenses | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 8,406	$ 1,451	$ 54

Stock-Based Compensation - Clas

Stock-Based Compensation - Classified in Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 26,211	$ 3,753	$ 113
Research and development expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	12,961	1,390	59
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 13,250	$ 2,363	$ 54

Stock-Based Compensation - ESPP

Stock-Based Compensation - ESPP (Details) $ in Thousands	Jan. 01, 2021shares	Oct. 31, 2020periodshares	Dec. 31, 2021USD ($)hourshares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 26,211	$ 3,753	$ 113
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			13,250	2,363	54
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 12,961	$ 1,390	$ 59
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	560,335	1,376,000
Employment eligibility, number of hours employed per week | hour			20
Employee stock purchase plan (in shares) | shares			95,723	0	0
Number of shares reserved for future issuance (in shares) | shares			1,152,612
Expected dividend			0.00%
Stock-based compensation expense			$ 300	$ 1,400
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	300
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	$ 1,100
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)			6 months	8 months 4 days
Expected volatility			71.67%	89.25%
Risk-free interest rate			0.05%	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 years 2 months 8 days
Expected volatility			94.85%	110.84%
Risk-free interest rate			0.25%	0.19%

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Awards Activity (Details) - Restricted stock $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Number of Restricted Stock
Unvested Beginning Balance (in shares) | shares	810,197
Granted - restricted stock awards and units (in shares) | shares	347,267
Vested and converted to shares (in shares) | shares	(344,661)
Forfeited (in shares) | shares	(25,084)
Unvested Ending Balance (in shares) | shares	787,719
Weighted-Average Grant Date Fair Value
Unvested Beginning Balance (in dollars per share) | $ / shares	$ 22.26
Granted - restricted stock awards and units (in dollars per share) | $ / shares	29.14
Vested and converted to shares (in dollars per share) | $ / shares	17.49
Forfeited (in dollars per share) | $ / shares	29.83
Unvested Ending Balance (in dollars per share) | $ / shares	$ 26.88
Unvested, Weighted Average Remaining Vesting Life	2 years 25 days
Unvested, Aggregate Intrinsic Value | $	$ 10,705
Vested and expected to vest, Outstanding (in shares) | shares	787,719
Vested and expected to vest, Weighted Average Grant Date Fair Value | $ / shares	$ 26.88
Vested and expected to vest, Weighted Average Remaining Vesting Life	2 years 25 days
Vested and expected to vest, Aggregate Intrinsic Value | $	$ 10,705

Stock-Based Compensation - Re_2

Stock-Based Compensation - Restricted Stock Awards (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 26,211,000	$ 3,753,000	$ 113,000
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	12,961,000	1,390,000	59,000
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 13,250,000	2,363,000	54,000
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)	347,267
Unrecognized stock based compensation	$ 300,000
Awards weighted average recognition period	2 years 6 months 29 days
Total grant date fair value for awards vested	$ 200,000	$ 600,000	5,000
Vested (in shares)	344,661
Restricted stock | Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)		274,341
Restricted stock | Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,000	$ 5,000	5,000
Restricted stock | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	100,000	600,000	$ 0
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8,500,000	$ 300,000
Unrecognized stock based compensation	$ 17,900,000
Awards weighted average recognition period	2 years 3 days
Vested (in shares)	188,470	0
Restricted Stock Units (RSUs) | Executive Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)	347,267	565,417
Vesting period	3 years
Restricted Stock Units (RSUs) | Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,100,000	$ 100,000
Restricted Stock Units (RSUs) | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,400,000	$ 200,000

Stock-Based Compensation - Earl

Stock-Based Compensation - Early Exercised Options (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Early exercised stock options (in shares)	0	1,551,361
Current liabilities related to shares that were subject to repurchase	$ 1,364	$ 2,174
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	1,400	2,200
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	$ 1,100	$ 2,500

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 0	$ 0
Valuation allowance	(58,713,000)	(20,797,000)
Valuation allowance increase	(37,900,000)
Accrued interest or penalties related to uncertain tax positions	$ 0	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Tax benefit at federal statutory rate	$ (31,726,000)	$ (18,573,000)	$ (3,384,000)
State taxes	(7,138,000)	(2,748,000)	(232,000)
Research tax credits	(597,000)	(475,000)	(427,000)
Change in valuation allowance	38,846,000	15,062,000	3,958,000
Change in fair value of convertible notes	0	5,756,000	0
Other	615,000	978,000	85,000
Expense/(Benefit) for income taxes	$ 0	$ 0	$ 0

Income Taxes - Components of Ne

Income Taxes - Components of Net Deferred Tax Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Lease liabilities	$ 8,750	$ 8,312
Stock-based compensation	2,777	0
Accrued compensation	1,320	495
Net operating loss carryforwards	52,052	19,710
Tax credit carryforwards	1,296	673
Other	0	1
Total deferred tax assets	66,195	29,191
Valuation allowance	(58,713)	(20,797)
Net deferred tax assets	7,482	8,394
Deferred tax liabilities:
Right-of-use assets	(6,973)	(7,085)
Fixed assets and intangibles	(509)	(411)
Stock-based compensation	0	(898)
Total deferred tax liabilities	(7,482)	(8,394)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Loss and Research Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2021USD ($)
Federal | Expiring Indefinitely
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 201,842
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	1,542
State
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 150,932

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$ 141	$ 109	$ 32
Additions based on tax positions related to the current year	105	91	77
Additions to tax positions of prior years	0	0	0
Reductions of tax positions of prior years	0	(59)	0
Lapse of the applicable statute of limitations	0	0	0
Balance at the end of the year	$ 246	$ 141	$ 109

Net Loss Per Share (Details)

Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended			54 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (151,078)	$ (88,444)	$ (16,117)	$ (263,000)
Weighted-average shares of common stock, basic and diluted (in shares)	54,753,599	16,277,247	5,278,748
Net loss per share, basic and diluted (in dollars per share)	$ (2.76)	$ (5.43)	$ (3.05)

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	7,378,118	7,061,356	24,629,078
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)	5,802,435	4,536,337	951,302
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)	787,965	1,714,822	774,931
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)	88,589	244,780	215,220
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)	699,129	565,417	0
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)	0	0	22,687,625

Commitment and Contingencies -

Commitment and Contingencies - R&D Services Agreement (Details) - Tempus Labs, Inc. - Research And Development Services - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2021	Dec. 31, 2021
Long-term Purchase Commitment [Line Items]
Services contract term	3 years
Annual minimum commitment payment in year one	$ 1,500,000
Annual minimum commitment payment in year two	2,000,000
Annual minimum commitment payment in year three	2,500,000
Sales milestone payment	$ 22,400,000
Sales milestone payment in shares of common stock, percent threshold	50.00%
Payments under the agrement		$ 0

Commitment and Contingencies _2

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, 2021	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 notes (in shares)					9,799,280
Common Stock | IPO
Schedule Of Asset Acquisition [Line Items]
Shares issued upon conversion of convertible notes (in shares)	22,687,625
Gilead Note | Common Stock | IPO
Schedule Of Asset Acquisition [Line Items]
Shares issued upon conversion of convertible notes (in shares)	188,567
Settlement price per share (in dollars per share)	$ 16.15
Gilead Note | 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
Regulatory milestone payment			51.3
Aggregate sales milestone payment			115
Gilead Asset Purchase
Schedule Of Asset Acquisition [Line Items]
Upfront cash payment			3
Convertible promissory note issued			3
Payments for reimbursements			$ 0.7

Commitment and Contingencies _3

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
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
Remaining term (years) | Liquidation conversion scenario
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Key valuation assumptions	2
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

Leases - Additional Information (Details)	Jul. 01, 2020USD ($)ft²	Aug. 01, 2018USD ($)	Feb. 28, 2021USD ($)ft²	Mar. 31, 2020USD ($)ft²	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Nov. 30, 2020USD ($)	Jul. 31, 2018ft²
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					$ 26,904,000	$ 27,322,000
Lease liabilities					33,762,000	32,057,000
Lease payments					4,400,000	2,800,000	$ 300,000
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					0
Lease liabilities					0
301 Binney Street, Cambridge, Massachusetts
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					23,600,000
Lease liabilities					29,700,000
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
Improvement costs incurred, reimbursed by lessor					$ 3,700,000
Tenant improvement allowances				$ 3,700,000
Remaining lease term					9 years 2 months 12 days
Incremental borrowing rate					8.50%
San Mateo, California
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					$ 0	1,100,000
Lease liabilities					0	1,100,000
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					0	800,000
Lease liabilities					0	800,000
Facility size | ft²	3,414
Escalating rent payments, percent	3.00%
Security deposit	$ 25,000
Initial annual base rent	$ 200,000
San Mateo, California. Original Lease
Lessee, Lease, Description [Line Items]
Facility size | ft²	8,075
San Mateo, California. February 2021 Lease Agreement
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					3,300,000	0
Lease liabilities					$ 4,100,000	$ 0
Facility size | ft²			17,340
Escalating rent payments, percent			3.00%
Remaining lease term					4 years 6 months
Incremental borrowing rate					11.18%
Security deposit			$ 59,000
Initial annual base rent			$ 1,200,000

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Finance lease cost	$ 3	$ 21	$ 23
Interest expense	0	1	3
Operating lease cost	5,323	5,565	310
Research and development
Lessee, Lease, Description [Line Items]
Finance lease cost	3	20	20
Operating lease cost	3,308	4,272	0
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 2,015	$ 1,293	$ 310

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet Information - Finance Lease (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Property and equipment, net	$ 0	$ 83
Liabilities:
Current portion of finance lease liability	0	5
Total finance lease liabilities	$ 0	$ 5
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Current portion of other liabilities	Current portion of other liabilities
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other noncurrent liabilities	Other noncurrent liabilities
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities

Leases - Supplemental Balance_2

Leases - Supplemental Balance Sheet Information - Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Operating lease assets	$ 26,904	$ 27,322
Liabilities:
Current portion of operating lease liabilities	2,109	937
Noncurrent operating lease liabilities	31,653	31,120
Total operating lease liabilities	$ 33,762	$ 32,057

Leases - Schedule of Maturities

Leases - Schedule of Maturities on Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
2022	$ 5,020
2023	5,581
2024	5,749
2025	5,921
2026 and thereafter	26,705
Total undiscounted lease payments	48,976
Less: Present value adjustment	(15,214)
Present value of operating lease liabilities	$ 33,762	$ 32,057

2020 Notes - Narrative (Details

2020 Notes - Narrative (Details) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2020	Aug. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Net cash proceeds			$ 0	$ 151,275,000	$ 0
Total debt issuance costs expensed and recognized			0	3,889,000	0
Loss in fair value			$ 0	$ (27,408,000)	$ 0
Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible notes (in shares)				9,799,280
IPO
Debt Instrument [Line Items]
Settlement price, percentage		85.00%
Shares issued, price per share (in dollars per share)	$ 19
IPO | Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible notes (in shares)	22,687,625
2020 Notes | IPO | Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of convertible notes (in shares)	9,610,713
Shares issued, price per share (in dollars per share)			$ 19
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 (Deta

Related Party Disclosures (Details) - Affiliated Entity - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Two River Consulting, LLC
Related Party Transaction [Line Items]
Expenses from transaction with related party	$ 300,000	$ 1,200,000	$ 900,000
Reimbursable expenses to related parties	0	27,000	49,000
Payables to related parties	0	200,000
Bellco Capital, LLC
Related Party Transaction [Line Items]
Expenses from transaction with related party	$ 129,000	$ 25,000	$ 25,000