ARS Pharmaceuticals (SPRY) 10-K 31 Mar 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 28, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Entity Registrant Name	Silverback Therapeutics, Inc.
Entity Central Index Key	0001671858
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Document Annual Report	true
Entity Well-known Seasoned Issuer	No
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Title of 12(b) Security	Common Stock
Trading Symbol	SBTX
Security Exchange Name	NASDAQ
Entity File Number	001-39756
Entity Tax Identification Number	81-1489190
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	500 Fairview Ave N
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	Seattle
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98109
City Area Code	206
Local Phone Number	456-2900
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
ICFR Auditor Attestation Flag	false
Entity Emerging Growth Company	true
Entity Public Float			$ 676.8
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		35,143,186
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for its 2022 Annual Meeting of Stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2021, are incorporated by reference into Part III of this Annual Report on Form 10-K.
Auditor Name	Ernst & Young LLP
Auditor Location	Seattle, Washington
Auditor Firm ID	42

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 254,045	$ 386,569
Prepaid expenses and other current assets	7,447	4,087
Total current assets	261,492	390,656
Investments	64,780	0
Restricted cash	250	350
Right-of-use assets	4,733	2,180
Property and equipment, net	2,212	1,618
Total assets	333,467	394,804
Current liabilities:
Accounts payable	2,078	2,583
Accrued expenses	11,727	5,278
Term loan payable, net	0	844
Current portion of lease liability	1,087	896
Total current liabilities	14,892	9,601
Lease liability, net of current portion	4,760	2,326
Total liabilities	19,652	11,927
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred Stock, $0.0001 par value per share; 10,000,000 shares authorized at December 31, 2021 and 2020; no shares issued and outstanding at December 31, 2021 and 2020	0	0
Common stock, $0.0001 par value per share; 200,000,000 shares authorized at December 31, 2021 and 2020, 35,133,934 and 34,801,537 shares issued and 35,107,651 and 34,701,274 shares outstanding at December 31, 2021 and 2020, respectively	4	3
Additional paid-in capital	500,349	479,608
Accumulated other comprehensive loss	(326)	0
Accumulated deficit	(186,212)	(96,734)
Total stockholders' equity	313,815	382,877
Total liabilities, and stockholders' equity	$ 333,467	$ 394,804

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock , shares authorized	10,000,000	10,000,000
Preferred stock, shares, issued	0	0
Preferred stock, shares, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	35,133,934	34,801,537
Common stock, shares, outstanding	35,107,651	34,701,274

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses:
Research and development	$ 61,501	$ 24,577
General and administrative	28,083	8,341
Total operating expenses	89,584	32,918
Loss from operations	(89,584)	(32,918)
Interest income (expense), net	106	(29)
Net loss	(89,478)	(32,947)
Unrealized loss on available-for-sale securities	(326)	0
Comprehensive loss attributable to common stockholders	$ (89,804)	$ (32,947)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.56)	$ (11.33)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted	34,926,403	2,907,542

Statements of Redeemable Conver

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]
Temporary equity, Beginning balance at Dec. 31, 2019						$ 53,174
Temporary equity, Beginning balance, shares at Dec. 31, 2019						15,714,283
Beginning balance at Dec. 31, 2019	$ (58,777)		$ 5,010		$ (63,787)
Beginning balance, shares at Dec. 31, 2019		664,431
Issuance of redeemable convertible preferred stock for cash (Note 8)							$ 68,401
Issuance of redeemable convertible preferred stock for cash (Note 8), shares							31,760,528
Issuance of redeemable convertible preferred stock upon conversion of convertible notes							$ 10,095	$ 84,897
Issuance of redeemable convertible preferred stock upon conversion of convertible notes, shares							4,673,388	24,926,685
Redeemable convertible preferred stock converted into shares of common stock ,values	216,567	$ 2	216,565			$ (216,567)
Initial public offering of common stock, net of $22,386 in issuance costs , values	255,339	$ 1	255,338
Initial public offering of common stock, net of $22,386 in issuance costs, shares		13,225,000
Exercise of common stock options and vesting of early exercised common stock options	55		55
Exercise of common stock options and vesting of early exercised common stock options, shares		53,745
Stock-based compensation	2,640		2,640
Net loss and comprehensive loss	(32,947)				(32,947)
Ending balance at Dec. 31, 2020	$ 382,877	$ 3	479,608		(96,734)
Ending balance, shares at Dec. 31, 2020	34,701,274	34,701,274
Redeemable convertible preferred stock converted into shares of common stock, shares		20,758,098				77,074,884
Exercise of common stock options and vesting of early exercised common stock options, shares	261,567
Exercise of common stock options, shares issued under the employee stock purchase plan, and vesting of early exercised common stock options	$ 1,555	$ 1	1,554
Exercise of common stock options, shares issued under the employee stock purchase plan, and vesting of early exercised common stock options, shares		406,377
Stock-based compensation	19,187		19,187
Net loss and comprehensive loss	(89,804)			$ (326)	(89,478)
Ending balance at Dec. 31, 2021	$ 313,815	$ 4	$ 500,349	$ (326)	$ (186,212)
Ending balance, shares at Dec. 31, 2021	35,107,651	35,107,651

Statements of Redeemable Conv_2

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
IPO [Member]
Stock issuance costs	$ 22,386
Series B Redeemable Convertible Preferred Stock [Member]
Stock issuance costs	$ 76

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (89,478)	$ (32,947)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	783	637
Stock-based compensation	19,187	2,640
Non-cash lease expense	1,146	1,073
Amortization of debt issuance costs	2	31
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,360)	(3,535)
Accounts payable and accrued expenses	6,034	1,790
Lease liability	(1,074)	(885)
Net cash used in operating activities	(66,760)	(31,196)
Cash flows from investing activities:
Purchases of available-for-sale securities	(65,106)	0
Purchase of property and equipment	(1,372)	(917)
Net cash used in investing activities	(66,478)	(917)
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	0	153,351
Proceeds from issuance of common stock upon initial public offering, net of underwriting discounts and commissions	0	258,284
Payment of deferred offering costs	0	(2,606)
Principal payments on term loan payable	(846)	(700)
Proceeds from exercise of common stock options and employee stock purchase plan	1,460	177
Net cash provided by financing activities	614	408,506
Change in cash, cash equivalents, and restricted cash	(132,624)	376,393
Cash, cash equivalents, and restricted cash at beginning of period	386,919	10,526
Cash, cash equivalents, and restricted cash at end of period	254,295	386,919
Supplemental disclosure of cash flow information:
Unpaid initial public offering costs included in accounts payable and accrued expenses	0	339
Right-of-use assets and lease liabilities recognized	3,699	0
Issuance of Series B redeemable convertible preferred stock upon conversion of convertible notes	0	10,095
Conversion of redeemable convertible preferred stock upon closing of initial public offering	$ 0	$ 216,567

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Nature of Business	1. Nature of Business Silverback Therapeutics, Inc. (“Silverback” or “the Company”) is a biopharmaceutical company focused on leveraging its proprietary ImmunoTAC technology platform to develop systemically delivered, tissue targeted therapeutics for the treatment of chronic viral infections, cancer, and other serious diseases. The Company’s ImmunoTAC platform is the result of a focused effort to discover ways to systemically deliver disease-modifying small molecules in a directed fashion to sites of disease. The Company’s platform enables it to strategically pair proprietary linker-payloads that modulate key disease-modifying pathways with monoclonal antibodies directed to specific disease sites. The Company was formed in Seattle, Washington and incorporated in the state of Delaware on January 4, 2016. Initial Public Offering In December 2020, the Company completed its initial public offering of common stock (“IPO”) of 13,225,000 shares of common stock at a public offering price of $ 21.00 per share, resulting in net proceeds of $ 255.3 million after deducting underwriting discounts and commissions and offering expenses paid by the Company. In connection with the IPO, all 77,074,884 shares of redeemable convertible preferred stock outstanding at the time of the IPO converted into 20,758,098 shares of the Company’s common stock. Additionally, in November 2020, the Company’s Board of Directors approved an amendment to the Company’s certificate of incorporation to effect a reverse split of shares of the Company’s common stock on a one-for-3.713 basis, which was effected on November 30, 2020 (the “Reverse Stock Split”) in anticipation of the IPO. All references to common stock and options to purchase common stock share data, per share data, and related information contained in the financial statements have been retroactively adjusted to reflect the effect of the Reverse Stock Split for all periods presented. Risks and Uncertainties The Company is subject to a number of inherent risks which include, but are not limited to, the need to obtain adequate additional funding, possible failure of clinical trials or other events demonstrating a lack of clinical safety or efficacy of its product candidates, dependence on key personnel, reliance on third-party service providers for manufacturing drug product and conducting clinical trials, the ability to successfully secure its proprietary technology, and risks related to the regulatory approval and commercialization of a product candidate. Additionally, the development and commercialization of new drug products is highly competitive. Products or technologies developed by competitors may diminish or render obsolete the Company’s existing products under development. Liquidity and Capital Resources The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. The Company has incurred net operating losses since its inception and had an accumulated deficit of $ 186.2 million as of December 31, 2021 . The Company had cash, cash equivalents, restricted cash, and investments of $ 319.1 million as of December 31, 2021 and has not generated positive cash flows from operations. To date, the Company has funded its operations primarily through the issuance of redeemable convertible preferred stock, convertible notes, and the sale of common stock in connection with the IPO. The Company’s currently available cash, cash equivalents, restricted cash, and investments as of December 31, 2021 are sufficient to meet its anticipated cash requirements for at least the 12 months following the date the financial statements are issued. Management considers that there are no conditions or events, in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern for a period of at least 12 months from the date the financial statements are issued. Management expects operating losses to continue for the foreseeable future. There can be no assurance that the Company will ever earn revenues or achieve profitability, or if achieved, that they will be sustained on a continuing basis. In addition, the manufacturing, clinical and preclinical development activities as well as the commercialization of the Company’s products, if approved, will require significant additional financing. The Company may be unable to secure such financing when needed, or if available, such financings may be under terms that are unfavorable to the Company or the current stockholders. If the Company is unable to raise additional funds when needed, it may be required to delay, reduce the scope of, or eliminate development programs, which may adversely affect its business and operations.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”), and Accounting Standards Update (“ASU”), of the Financial Accounting Standards Board (“FASB”). Use of Estimates The preparation of the Company’s financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to accruals for research and development expenses, valuation of equity awards, and valuation allowances for deferred tax assets. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates. The full extent to which the coronavirus (“COVID-19”) pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trial 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 Company has considered potential impacts arising from the COVID-19 pandemic and is not presently aware of any events or circumstances that would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities. Segments The Company has determined that it operates and manages one operating segment, which is the business of developing and commercializing tissue targeted therapeutics. The Company’s chief operating decision maker, its chief executive officer, reviews financial information on an aggregate basis for the purpose of allocating resources. Fair Value of Financial Instruments Cash and cash equivalents, restricted cash, and investments are carried at fair value. Accounts payable and accrued expenses are carried at cost, which approximates fair value given their short-term nature. The term loan payable is carried at cost, which approximates fair value as its effective interest rate approximates current market rates. Cash and Cash Equivalents Cash equivalents are comprised of short-term, highly-liquid investments with maturities of 90 days or less at the date of purchase. At December 31, 2021 and December 31, 2020 , the Company’s cash equivalents consisted of money market funds. Restricted Cash Restricted cash consists of a deposit securing a collateral letter of credit issued in connection with the operating lease for the Company’s headquarters. The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the balance sheets that sum to the amounts shown in the statements of cash flows (in thousands): December 31, December 31, Cash and cash equivalents $ 254,045 $ 386,569 Restricted cash 250 350 Total cash and cash equivalents and restricted cash $ 254,295 $ 386,919 Investments The Company invests excess cash in investment grade intermediate-term fixed income securities. These investments are included in long-term investments on the balance sheets, classified as available-for-sale, and reported at fair value with unrealized gains and losses included in accumulated other comprehensive loss. Realized gains and losses on the sale of these securities are recognized in net loss. The Company periodically evaluates whether declines in fair values of its investments 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 investment until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any investment before recovery of its amortized cost basis. Factors considered include quoted market prices, recent financial results and operating trends, implied values from any recent transactions or offers of investee securities, credit quality of debt instrument issuers, other publicly available information that may affect the value of the investments, duration and severity of the decline in value, and the Company's strategy and intentions for holding the investment. Concentrations of Credit Risk The Company is subject to credit risk from holding its cash and cash equivalents at a limited number of commercial banks. The Company limits its exposure to credit losses by investing in money market funds through a U.S. bank with high credit ratings and U.S. Treasury securities. Cash may consist of deposits held with banks that may at times exceed federally insured limits, however, exposure to credit risk in the event of default by the financial institution is limited to the extent of amounts recorded on the balance sheets. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Prepaid Expenses and Other Assets Prepaid expenses consist primarily of operating expenses paid in advance of when services are provided. Property and Equipment, Net Property and equipment, net consists of furniture and fixtures and laboratory equipment and is stated at cost, less accumulated depreciation. Furniture and fixtures and laboratory equipment are depreciated over the estimated useful lives of the assets (each three to five years) using the straight-line method. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. Repairs and maintenance costs are charged to expense as incurred. Leases Leases consist of the Company’s operating leases. In accordance with ASC 842, Leases, the Company determines if an arrangement is a lease at inception and evaluates each lease agreement to determine whether the lease is an operating or finance lease. For leases where the Company is the lessee, right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent an obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. Operating lease ROU assets also include any prepaid lease payments, lease incentives received, and costs which will be incurred in exiting a lease. The Company’s leases include options to extend or terminate the leases. Periods covered by an option to extend a lease are included in the lease term when it is reasonably certain that the Company will exercise that option. Periods covered by an option to terminate a lease are included in the lease term when it is reasonably certain that the Company will not exercise that option. Short-term leases with an initial term of 12 months or less are not recorded on the balance sheet. The Company does not have material short-term lease costs. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. For real estate leases, the Company does not separate lease and non-lease components. The Company’s lease agreements do not contain any material residual value guarantees or material restrictive covenants. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and ROU assets. These assets 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. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. The Company has not recognized any impairment losses through December 31, 2021. Research and Development Expenses All research and development costs are expensed in the period incurred. Research and development expenses consist primarily of direct and indirect costs incurred in connection with the development of the Company’s ImmunoTAC technology platform, discovery efforts, and preclinical study and clinical trial activities related to the Company’s program pipeline. Direct costs include expenses incurred under agreements with CROs and other vendors that conduct the Company’s preclinical and clinical activities, expenses associated with manufacturing the Company’s product candidates including under agreements with contract development and manufacturing organizations (“CDMOs”) and other vendors, and consulting fees. Indirect costs include personnel-related expenses, consisting of employee salaries, bonuses, benefits, and stock-based compensation expense and recruiting costs for personnel engaged in research and development activities, facility and equipment related expenses, consisting of indirect and allocated expenses for rent, depreciation, and equipment maintenance, and other unallocated research and development expenses incurred in connection with the Company’s research and development programs, including laboratory materials and supplies and license fees. Research and development expenses are charged to operating expenses as incurred when these expenditures relate to the Company’s research and development efforts and have no alternative future uses. The Company is obligated to make upfront payments upon execution of certain research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are capitalized until such goods are delivered or the related services are performed, or such time when the Company does not expect the goods to be delivered or services to be performed. The Company estimates the period over which such services will be performed and the level of effort to be expended in each period. If actual timing of performance or the level of effort varies from the estimate, the Company will adjust the amounts recorded accordingly. Since inception, the Company has not experienced any material differences between accrued or prepaid costs and actual costs. General and Administrative Expenses General and administrative expenses consist primarily of personnel-related expenses, including employee salaries, bonuses, benefits, and stock-based compensation, and recruiting costs for personnel in executive, finance, and other administrative functions. Other significant general and administrative expenses include legal fees relating to intellectual property and corporate matters, professional fees for accounting, tax and consulting services, insurance costs, travel expenses and facility related expenses. General and administrative costs are expensed as incurred. Stock-Based Compensation The cost of employee services received in exchange for an award of an equity instrument is measured at the grant date based on the award’s estimated fair value using the Black-Scholes option pricing model. The estimated fair value of the awards is recognized into expense on a straight-line basis over the requisite service period. Stock-based compensation expense for an award with a performance condition is recognized when the achievement of such performance condition is determined to be probable. If the outcome of such performance condition is not determined to be probable or is not met, no compensation expense is recognized, and any previously recognized compensation expense is reversed. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance condition at each reporting date. Forfeitures are recognized as a reduction of stock-based compensation expense as they occur. The option plan permits, but does not require, the inclusion of early exercise provisions in individual awards. Proceeds from early option exercises are recorded as a liability until the underlying restricted shares vest. While the restricted shares have voting rights, they are not considered outstanding for accounting purposes. Employee Stock Purchase Plan In December 2020, the Company’s Employee Stock Purchase Plan (“ESPP”) became effective, pursuant to which eligible employees can purchase shares of the Company’s common stock at a discount to the fair market value at semi-annual intervals. In determining the grant date fair value of shares expected to be purchased under the ESPP, the Company uses the Black-Scholes option pricing model. Black-Scholes inputs are determined in the same manner as for stock option awards. The estimated grant date fair value of shares expected to be purchased is recognized into expense on a straight-line basis over the requisite service period. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company is more likely than not able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes in the period in which the adjustment is made. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. The Company did not have any uncertain tax positions as of December 31, 2021 and 2020. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company presents one continuous Statement of Operations and Comprehensive Loss. The Company’s comprehensive loss includes unrealized gains and losses on investments. Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration of potentially dilutive securities. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company. For purposes of this calculation, redeemable convertible preferred stock, stock options, employee stock purchase rights, and unvested common stock subject to repurchase are considered to be common stock equivalents but are not included in the calculations of diluted net loss per share for the periods presented as their effect would be antidilutive. Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with certain new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (1) no longer an emerging growth company or (2) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than temporary impairments on investment securities are recorded. The guidance is effective for the Company beginning on January 1, 2023, with early adoption permitted. The Company is currently evaluating the impact the standard may have on its financial statements and related disclosures.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. 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 defined as the exchange price that would be received to sell an asset or paid to transfer a liability (at exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The three levels of inputs that may be used to measure fair value include: Level 1: Quoted prices in Active Markets for identical assets or liabilities. Level 2: Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities in active markets or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs that are supported by little or no market activity. The following table identifies the Company’s assets and liabilities that were measured at fair value on a recurring basis (in thousands): December 31, 2021 Level Amortized Cost Gross unrealized gains Gross unrealized losses Fair Value Money market funds 1 $ 253,945 $ — $ — $ 253,945 Long-term investments - U.S. Treasury securities 1 65,106 — ( 326 ) 64,780 Total 319,051 — ( 326 ) 318,725 December 31, 2020 Money market funds 1 $ 386,369 $ — $ — $ 386,369 There were no transfers between the Level 1 and Level 2 categories or into or out of the Level 3 category during the periods presented. The Company’s long-term investments portfolio contains investments in U.S. Treasury securities that have an effective maturity date that is more than one year, but less than two years, from the respective balance sheet date. The Company evaluated its investments for other-than-temporary impairment and considers the decline in market value for the securities to be primarily attributable to current economic and market conditions. For the investments, it is not more-likely-than-not that the Company will be required to sell the investments, and the Company does not intend to do so prior to the recovery of the amortized cost basis.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment are summarized as follows (in thousands): December 31, 2021 December 31, 2020 Furniture and fixtures $ 367 $ 269 Laboratory equipment 4,679 3,401 Property and equipment, gross 5,046 3,670 Less accumulated depreciation ( 2,834 ) ( 2,052 ) Total property and equipment, net $ 2,212 $ 1,618 Depreciation expense was $ 0.8 million and $ 0.6 million for the years ended December 31, 2021 and 2020, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2021 December 31, 2020 Research and development expenses $ 6,528 $ 2,063 Employee compensation and benefits 4,605 2,634 Professional services and other 594 581 Total accrued expenses $ 11,727 $ 5,278

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	6. Leases The Company leases office and laboratory space in Seattle, Washington. The components of lease expense and related cash flows were as follows (in thousands): Years Ended December 31, 2021 2020 Lease expense Operating lease expense $ 1,452 $ 1,388 Variable lease expense 459 386 Total lease expense 1,911 1,774 Operating cash outflows from operating leases $ 1,841 $ 1,591 On July 1, 2021, the Company entered into a sublease agreement for additional office space in Seattle, Washington. The commencement date of the sublease was August 1, 2021. The contractual term of the sublease is two years with an option to extend for one additional year and an option to terminate after one year subject to a termination fee . The annual minimum rent payable by the Company under the sublease is $ 0.3 million annually. The ROU asset obtained in exchange for the new operating lease liability was $ 0.6 million as of the lease commencement date. The weighted-average remaining term on the Company's leases was 4.7 years and 1.8 years as of December 31, 2021 and 2020, respectively. To compute the present value of the lease liabilities, the Company used weighted average discount rates of 7.5 % and 8.5 % as of December 31, 2021 and 2020, respectively. During the year ended December 31, 2021, there was a change in the expected lease term of the Company’s Seattle, Washington headquarters, whereby the Company became reasonably certain that it will not exercise its option to terminate the lease. As a result, the ROU asset and lease liability were remeasured using the present value of the remaining lease payments. The re-measurement resulted in an addition to the ROU asset and lease liability of $ 3.1 million. The change in the expected lease term has no effect on the classification of the lease. Future minimum commitments due under the operating lease agreements as of December 31, 2021 are as follows (in thousands): Years Ended December 31, Amount 2022 1,481 2023 1,513 2024 1,348 2025 1,389 Thereafter 1,186 Total undiscounted lease payments 6,917 Present value adjustment ( 1,070 ) Total present value of lease payments $ 5,847

Term Loan Payable

Term Loan Payable	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Term Loan Payable	7. Term Loan Payable In November 2016, the Company entered into a loan and security agreement with Silicon Valley Bank (“SVB”) and borrowed $ 3.5 million as a term loan. The outstanding principal amount of the term loan accrued interest at an annual rate of 1.75 % per annum. At closing, the Company incurred de minimis debt issuance costs and owed a final payment fee of $ 0.3 million, both of which are amortized to interest expense over the remaining term of the debt under the effective interest method. The effective interest rate of the Company’s term loan was 5.14 %. The term loan’s original maturity date was November 1, 2020 . However, in April 2020, the Company amended the loan and security agreement to defer principal payments for six months and extend the maturity date to May 1, 2021 . There were no costs or additional warrant issuances in connection with this amendment. The Company accounted for the amendment as a debt modification and amortized the remaining debt discount over the remaining term. On May 1, 2021, the Company made its final scheduled payment to SVB under the loan and security agreement including the final payment fee.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Stockholders' Equity (Deficit)	8. Stockholders’ Equity (Deficit) Authorized Shares The Company’s current Amended and Restated Certificate of Incorporation authorizes 200,000,000 shares of common stock, par value $ 0.0001 per share, and 10,000,000 shares of preferred stock, par value $ 0.0001 per share. Redeemable Convertible Preferred Stock Prior to its conversion to common stock in December 2020, the Company’s redeemable convertible preferred stock was classified as mezzanine equity on the Company’s balance sheets as the shares are contingently redeemable upon a deemed liquidation such as a change in control and in that event, there is no guarantee that all stockholders would be entitled to receive the same form of consideration. No accretion to redemption value was recorded during the year ended December 31, 2020 as a deemed liquidation event was not considered probable. During the year ended December 31, 2020, the Company issued convertible preferred stock as follows: In March 2020, the Company issued 14,701,054 shares of its Series B redeemable convertible preferred stock, including 4,673,388 shares issued upon conversion of then outstanding convertible notes and accrued interest, and 10,027,666 shares issued for cash at a purchase price of $ 2.16 per share, resulting in gross proceeds of $ 21.5 million. The Series B purchase agreement provided that the Company would issue, and the Series B holders would purchase, an additional 21,732,862 shares of the Company’s Series B redeemable convertible preferred stock across two tranches for aggregate proceeds of $ 46.9 million in the event that certain agreed upon milestones were achieved or the preferred majority approved their closing. The Series B tranches did not meet the definition of freestanding instruments or the definition of derivatives, therefore, they were not accounted for separately or bifurcated. On July 1, 2020, the Company issued 10,669,834 shares of its Series B redeemable convertible preferred stock for cash at a purchase price of $ 2.16 per share, resulting in gross proceeds of $ 23.0 million. In September 2020, the Company issued 11,063,028 additional shares of its Series B redeemable convertible preferred stock for cash at a purchase price of $ 2.16 per share, resulting in gross proceeds of $ 23.9 million, and 24,926,685 shares of its Series C redeemable convertible preferred stock for cash at a purchase price of $ 3.41 per share, resulting in gross proceeds of $ 84.9 million. The Series C purchase agreement did not contain any embedded features that meet the definition of freestanding instruments or the definition of derivatives, therefore, they were not accounted for separately or bifurcated. Common Stock The Company has reserved shares of common stock for the following potential future issuances: December 31, December 31, Shares underlying outstanding equity awards 6,370,873 6,316,569 Shares available for future equity award grants 2,931,012 1,506,806 Shares underlying early exercised equity awards 26,283 100,263 Shares underlying ESPP withholdings — 4,393 Total 9,328,168 7,928,031

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	9. Stock-Based Compensation Stock-based compensation expense recognized for all equity awards has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years Ended December 31, 2021 2020 Research and development expense $ 8,331 $ 1,180 General and administrative expense 10,856 1,460 Total stock-based compensation expense $ 19,187 $ 2,640 As of December 31, 2021 , the total unrecognized stock-based compensation expense was $ 50.5 million, which is expected to be recognized over a remaining weighted-average period of approximately 2.49 years. Stock Option Awards As of December 31, 2021 , the Company’s equity incentive plans authorized a total of 9,564,798 shares, of which 2,931,012 shares are available for future grant, and 6,370,873 shares are outstanding. Not included in the outstanding option balance are 26,283 shares pursuant to stock options that were early exercised and subject to repurchase that remain unvested as of December 31, 2021. Stock options granted under the Company’s equity incentive plans expire no later than 10 years from the date of grant and generally vest over a four year period, with vesting either occurring at a rate of 25 % at the end of the first and thereafter in 36 equal monthly installments or on a monthly basis. In the case of awards granted to our non-employee board members, vesting generally occurs on a monthly basis over three years or in full on an annual basis. The Company issues new shares of common stock upon the exercise of stock options. A summary of the Company’s stock option activity for the year ended December 31, 2021 is as follows (in thousands, except share and per share data and years): Stock Options Outstanding Shares Weighted- Weighted- Aggregate Balance at December 31, 2020 6,316,569 $ 10.93 Granted 511,773 Exercised ( 261,567 ) Cancelled ( 195,902 ) Balance at December 31, 2021 6,370,873 12.82 8.58 11,385,117 Vested at December 31, 2021 1,974,776 $ 9.60 8.14 $ 4,887,808 The aggregate intrinsic value in the table above is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the Company’s common stock for all options that were in-the-money at December 31, 2021. The aggregate intrinsic value of options exercised during the years ended December 31, 2021 and 2020 was $ 7.7 million and $ 0.1 million, respectively. The weighted-average grant date fair value per share of option grants for the years ended December 31, 2021 and 2020 was $ 22.15 and $ 10.50 , respectively. The total fair value of shares vested during the years ended December 31, 2021 and 2020 was $ 17.0 million and $ 1.1 million, respectively. The grant date fair value of stock options was estimated using a Black-Scholes option pricing model with the following weighted-average assumptions: Years Ended December 31, 2021 2020 Expected term (in years) 6.0 6.0 Expected volatility 79 % 80 % Risk-free interest rate 0.98 % 0.51 % Expected dividend yield — — The fair value of stock options was determined using the Black-Scholes option-pricing model and the assumptions below. Each of these inputs is subjective and generally requires significant judgement. Fair Value of Common Stock . Prior to the Company's initial public offering in 2020, the grant date fair market value of the shares of common stock underlying stock options was determined by the Company’s board of directors. Following the closing of the Company’s IPO, the fair market value of the Company's common stock is based on its closing price as reported on the date of grant on the primary stock exchange on which the Company’s common stock is traded. Prior to the Company’s IPO, because there was no public market for the Company’s common stock, the board of directors exercised reasonable judgment and considered a number of objective and subjective factors to determine the best estimate of the fair market value, which included contemporaneous valuations performed by an independent third-party, the Company’s results of operations and financial position, including its levels of available capital resources, its stage of development and material risks related to the Company’s business, progress of the Company’s research and development activities, the Company’s business conditions and projections, the lack of marketability of the Company’s common stock and preferred stock as a private company, the prices at which the Company sold shares of its redeemable convertible preferred stock to outside investors in arms-length transactions, the rights, preferences and privileges of the Company’s redeemable convertible preferred stock relative to those of its common stock, the analysis of IPOs and the market performance of similar companies in the biopharmaceutical industry, the likelihood of achieving a liquidity event for the Company’s securityholders, such as an IPO or a sale of the company, given prevailing market conditions, the hiring of key personnel and the experience of management, trends and developments in the Company’s industry and external market conditions affecting the life sciences and biotechnology industry sectors. Expected Term . The expected term represents the period that the options granted are expected to be outstanding. The expected term of stock options issued is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term) as the Company has concluded that its stock option exercise history does not provide a reasonable basis upon which to estimate expected term. Expected Volatility . Given the Company’s limited historical stock price volatility data, the Company derived the expected volatility from the average historical volatilities over a period approximately equal to the expected term of comparable publicly traded companies within its peer group that were deemed to be representative of future stock price trends as the Company has limited trading history for its common stock. 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 rate, with maturities similar to the expected term of the stock options. Expected Dividend Yield . The Company has never paid dividends on its common stock and does not anticipate paying any dividends in the foreseeable future. Therefore, the Company uses an expected dividend yield of zero. Employee Stock Purchase Plan In November 2020, the Company’s board of directors and stockholders approved and adopted the 2020 ESPP. The ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to 15 % of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the ESPP. The price of common stock purchased under the ESPP is equal to 85% of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant date of purchase. As of December 31, 2021, a total of 698,015 shares were reserved under the ESPP, of which 627,185 shares are available for future issuance and 70,830 shares have been issued. The weighted average per share fair value rights granted during the year ended December 31, 2021 was $ 15.95 . In determining the grant date fair value of shares to be issued under the ESPP, the Company uses the Black-Scholes option pricing model. The Black-Scholes inputs are determined in the same manner as for stock option awards. The weighted average inputs used for the ESPP for the year ended December 31, 2021, were as follows: Years Ended December 31, 2021 2020 Expected term (in years) 1.2 1.2 Expected volatility 81 % 82 % Risk-free interest rate 0.14 % 0.11 % Expected dividend yield — —

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The Company’s effective tax rates for the years ended December 31, 2021 and 2020 differ from the U.S. federal statutory rate as follows (in thousands): Years Ended December 31, 2021 2020 Tax at the federal statutory rate $ ( 18,790 ) $ ( 6,919 ) Benefit from R&D tax credits ( 1,244 ) ( 586 ) Stock-based compensation 1,102 331 Non-deductible executive compensation 817 — Other temporary and permanent differences 33 21 Change in valuation allowance 18,082 7,153 Total provision for income taxes $ — $ — The significant components of the Company’s deferred tax assets and liabilities were as follows (in thousands): Years Ended December 31, 2021 2020 Deferred tax assets: Net operating loss carryforward 33,671 18,832 Lease liability 1,228 677 R&D tax credit carryforward 2,746 1,502 Share-based compensation 2,151 227 Other deferred tax assets 237 109 Total deferred tax assets 40,033 21,347 Deferred tax liabilities - Right of use asset ( 994 ) ( 458 ) Valuation allowance ( 39,039 ) ( 20,889 ) Net deferred tax assets $ — $ — At December 31, 2021, the Company had net operating loss carryforwards for income tax purposes of approximately $ 160.3 million. If not used, $ 18.2 million of this carryforward will begin to expire in 2036 and $ 142.1 million has no expiration. At December 31, 2021, the Company also had research and development tax credits of approximately $ 2.7 million which will begin to expire in 2037 if left unused. The Company did not have any foreign tax provision and did not generate material net operating losses in any states with an income tax. FASB ASC 740 requires that the tax benefit of net operating losses, temporary differences, and credit carryforwards be recorded as an asset to the extent that management assesses the realization is “more likely than not.” Realization of the future tax benefits from the net operating losses or credit carryforwards, if any, is dependent on the Company’s ability to generate sufficient taxable income within the applicable carryforward period. Because of the Company’s recent history of operating losses, the Company maintains a full valuation allowance in the amount of $ 39.0 million and $ 20.9 million for the years ended December 31, 2021 and 2020, respectively. The Company may have already experienced one or more ownership changes. Depending on the timing of any future utilization of its carryforwards, the Company may be limited as to the amount that can be utilized each year as a result of such previous ownership changes. However, the Company does not believe such limitations will cause its carryforwards to expire unutilized. Future changes in the Company’s stock ownership as well as other changes that may be outside the Company’s control could potentially result in further limitations on the Company’s ability to utilize its net operating loss and tax credit carryforwards. As of December 31, 2021 and 2020, the Company did no t have any liabilities for unrecognized income tax benefits associated with uncertain tax positions, including any interest and penalties.

Licensing Agreement

Licensing Agreement	12 Months Ended
	Dec. 31, 2021
Licensing Agreement [Abstract]
Licensing Agreement	11. Licensing Agreement Cell Line License Agreement with WuXi Biologics (Hong Kong) Limited In October 2019, the Company entered into a cell line license agreement with WuXi Biologics (Hong Kong) Limited (“WuXi Bio”). Under the license agreement, WuXi Bio granted the Company a non-exclusive, worldwide, sublicensable, under certain of WuXi Bio’s intellectual property rights, know-how and biological materials (“WuXi Bio Licensed Technology”), to make, use, sell, offer for sale and import a product developed through the use of the WuXi Bio Licensed Technology (“WuXi Bio Licensed Product”). The WuXi Bio Licensed Technology is currently used to manufacture a component of the Company’s ImmunoTAC platform. The Company has paid an aggregate of $ 150,000 in license fees that were recorded in research and development expense when incurred. In the event the Company manufactures its commercial supplies of a product produced by the Licensed Cell Line using a manufacturer other than WuXi Bio or its affiliates, the Company will become obligated to pay WuXi Bio aggregate milestone payments, upon achievement of certain sales milestones, of up to $ 10.8 million. The Company has the right to terminate the license by giving at least six months prior written notice to WuXi Bio and paying all amounts due to them through the termination date. In the event the Company fails to pay all amounts due to WuXi Bio under the license agreement, and fails to pay the amounts within 30 days after receiving written notice of such failure, WuXi Bio may terminate the license with 45 days written notice to the Company. In the event either party commits a material breach under the license and fails to cure the breach within 30 days after receiving written notice from the other party of such breach, either party may terminate the license immediately upon written notice to the other party.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Legal Proceedings From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of its business activities. The Company accrues a liability for such matters when it is probable that future expenditures will be made and can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount. On November 5, 2021, a securities class action complaint was filed against the Company and certain of the Company's officers and directors in the U.S. District for the Western District of Washington, captioned Dresner v. Silverback Therapeutics, Inc., et al., Case No. 2:21-cv-01499. The complaint alleges that between December 3, 2020 and September 10, 2021, the Company and certain of the Company's officers and directors violated (1) Sections 11 and 15 of the Securities Act of 1933, as amended; and (2) Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and Securities and Exchange Commission (“SEC”) Rule 10b-5 promulgated thereunder, by making allegedly false and misleading statements in various SEC filings and press releases regarding the clinical and commercial prospects of the Company’s product candidate, SBT6050, which is now discontinued. The complaint seeks unspecified damages and interest, as well as attorneys’ fees and other costs. The court recently appointed lead plaintiff and lead plaintiff's counsel. The Company and the other defendants have not yet filed a response to the complaint, and do not anticipate doing so until after the filing of an amended complaint. The Company cannot predict the outcome of this suit, and failure by the Company to obtain a favorable resolution could have a material adverse effect on its business, results of operations and financial condition. The Company’s chances of success on the merits are still uncertain and any possible loss or range of loss cannot be reasonably estimated and as such the Company has not recorded a liability as of December 31, 2021. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless, and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions or related to any indemnification agreements. The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ insurance coverage that reduces its exposure and enables the Company to recover a portion of any future amounts paid. The Company believes the estimated fair value of these indemnification agreements in excess of applicable insurance coverage is minimal. COVID-19 The global COVID-19 pandemic continues to rapidly evolve, and management continue to monitor the situation closely. The extent of the impact of COVID-19 on the Company’s business, operations, planned preclinical studies and clinical trials, and manufacturing timelines and plans remains uncertain, and will depend on certain developments, including the duration and spread of the outbreak and its impact on the Company’s CROs, third-party manufacturers, supply chains necessary for research and development and manufacturing, and other third parties with whom the Company does business, as well as its impact on regulatory authorities and the Company’s key scientific and management personnel. For example, the COVID-19 pandemic has caused the cost of obtaining animals for our preclinical studies to increase dramatically and, if the shortage continues, could also result in delays to our development timelines. To the extent possible, management is conducting business as usual, with necessary or advisable modifications to employee travel and some of the Company’s non-lab based employees working remotely. Management will continue to actively monitor the rapidly evolving situation related to COVID-19 and may take further actions that alter Company operations, including those that may be required by federal, state or local authorities, or that management determines are in the best interests of the Company’s employees and other third parties with whom the Company does business. At this point, the extent to which the COVID-19 pandemic may further affect the Company’s business, operations and clinical development timelines and plans, including the resulting impact on Company expenditures and capital needs, remains uncertain and is subject to change.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	13. Employee Benefit Plans The Company maintains a retirement plan, which is qualified under section 401(k) of the Internal Revenue Code of 1986, as amended, for the Company’s U.S. employees. The plan allows eligible employees to defer, at the employee’s discretion, pretax compensation up to the IRS annual limits. The Company did not match contributions made by employees through December 31, 2021. The Company began matching 4 % of employee contributions in 2022.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	14. Net Loss Per Share Attributable to Common Stockholders The following outstanding shares of potentially dilutive securities were excluded from the computation of the diluted net loss per share attributable to common stockholders for the periods presented because their effect would have been anti-dilutive: As of December 31, 2021 2020 Common stock options 6,370,873 6,316,569 Unvested common stock 26,283 100,263 ESPP withholdings — 4,393 Total potentially dilutive shares 6,397,156 6,421,225

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events Subsequent to December 31, 2021 through March 31, 2022, the Company’s board of directors approved the grant of options to purchase an aggregate of 1,815,926 shares of common stock at an exercise price of $ 4.85 per share. The unrecognized stock-based compensation expense for these grants is approximately $ 5.9 million. Additionally, the Company’s board of directors approved the grant of 266,744 restricted stock units. The unrecognized stock-based compensation expense for these awards is approximately $ 1.3 million. On March 28, 2022, the Company’s board of directors approved a corporate restructuring plan to discontinue the Company’s clinical development programs for SBT6050 and SBT6290 and to prioritize resources on the development of SBT8230 and early-stage discovery programs (the “Restructuring Plan”). In connection with the Restructuring Plan, the Company’s workforce will be reduced by 27 %, with substantially all of the reduction in personnel expected to be completed by July 15, 2022 . The Company initiated the reduction in force on March 31, 2022 and expects to provide severance payments, continuation of group health insurance coverage, and other benefits for a specified period to the affected employees. The Company currently estimates that it will incur costs of approximately $ 2.0 million for termination benefits related to the Restructuring Plan, all of which will be cash expenditures paid in 2022.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Polices)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”), and Accounting Standards Update (“ASU”), of the Financial Accounting Standards Board (“FASB”).
Use of Estimates	Use of Estimates The preparation of the Company’s financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to accruals for research and development expenses, valuation of equity awards, and valuation allowances for deferred tax assets. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates. The full extent to which the coronavirus (“COVID-19”) pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trial 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 Company has considered potential impacts arising from the COVID-19 pandemic and is not presently aware of any events or circumstances that would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities.
Segments	Segments The Company has determined that it operates and manages one operating segment, which is the business of developing and commercializing tissue targeted therapeutics. The Company’s chief operating decision maker, its chief executive officer, reviews financial information on an aggregate basis for the purpose of allocating resources.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Cash and cash equivalents, restricted cash, and investments are carried at fair value. Accounts payable and accrued expenses are carried at cost, which approximates fair value given their short-term nature. The term loan payable is carried at cost, which approximates fair value as its effective interest rate approximates current market rates.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents are comprised of short-term, highly-liquid investments with maturities of 90 days or less at the date of purchase. At December 31, 2021 and December 31, 2020 , the Company’s cash equivalents consisted of money market funds.
Restricted Cash	Restricted Cash Restricted cash consists of a deposit securing a collateral letter of credit issued in connection with the operating lease for the Company’s headquarters. The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the balance sheets that sum to the amounts shown in the statements of cash flows (in thousands): December 31, December 31, Cash and cash equivalents $ 254,045 $ 386,569 Restricted cash 250 350 Total cash and cash equivalents and restricted cash $ 254,295 $ 386,919
Investments	Investments The Company invests excess cash in investment grade intermediate-term fixed income securities. These investments are included in long-term investments on the balance sheets, classified as available-for-sale, and reported at fair value with unrealized gains and losses included in accumulated other comprehensive loss. Realized gains and losses on the sale of these securities are recognized in net loss. The Company periodically evaluates whether declines in fair values of its investments 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 investment until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any investment before recovery of its amortized cost basis. Factors considered include quoted market prices, recent financial results and operating trends, implied values from any recent transactions or offers of investee securities, credit quality of debt instrument issuers, other publicly available information that may affect the value of the investments, duration and severity of the decline in value, and the Company's strategy and intentions for holding the investment.
Concentrations of Credit Risk	Concentrations of Credit Risk The Company is subject to credit risk from holding its cash and cash equivalents at a limited number of commercial banks. The Company limits its exposure to credit losses by investing in money market funds through a U.S. bank with high credit ratings and U.S. Treasury securities. Cash may consist of deposits held with banks that may at times exceed federally insured limits, however, exposure to credit risk in the event of default by the financial institution is limited to the extent of amounts recorded on the balance sheets. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Prepaid Expenses and Other Assets	Prepaid Expenses and Other Assets Prepaid expenses consist primarily of operating expenses paid in advance of when services are provided.
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consists of furniture and fixtures and laboratory equipment and is stated at cost, less accumulated depreciation. Furniture and fixtures and laboratory equipment are depreciated over the estimated useful lives of the assets (each three to five years) using the straight-line method. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected in operations in the period realized. Repairs and maintenance costs are charged to expense as incurred.
Leases	Leases Leases consist of the Company’s operating leases. In accordance with ASC 842, Leases, the Company determines if an arrangement is a lease at inception and evaluates each lease agreement to determine whether the lease is an operating or finance lease. For leases where the Company is the lessee, right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent an obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. Operating lease ROU assets also include any prepaid lease payments, lease incentives received, and costs which will be incurred in exiting a lease. The Company’s leases include options to extend or terminate the leases. Periods covered by an option to extend a lease are included in the lease term when it is reasonably certain that the Company will exercise that option. Periods covered by an option to terminate a lease are included in the lease term when it is reasonably certain that the Company will not exercise that option. Short-term leases with an initial term of 12 months or less are not recorded on the balance sheet. The Company does not have material short-term lease costs. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. For real estate leases, the Company does not separate lease and non-lease components. The Company’s lease agreements do not contain any material residual value guarantees or material restrictive covenants.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment and ROU assets. These assets 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. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. The Company has not recognized any impairment losses through December 31, 2021.
Research and Development Expenses	Research and Development Expenses All research and development costs are expensed in the period incurred. Research and development expenses consist primarily of direct and indirect costs incurred in connection with the development of the Company’s ImmunoTAC technology platform, discovery efforts, and preclinical study and clinical trial activities related to the Company’s program pipeline. Direct costs include expenses incurred under agreements with CROs and other vendors that conduct the Company’s preclinical and clinical activities, expenses associated with manufacturing the Company’s product candidates including under agreements with contract development and manufacturing organizations (“CDMOs”) and other vendors, and consulting fees. Indirect costs include personnel-related expenses, consisting of employee salaries, bonuses, benefits, and stock-based compensation expense and recruiting costs for personnel engaged in research and development activities, facility and equipment related expenses, consisting of indirect and allocated expenses for rent, depreciation, and equipment maintenance, and other unallocated research and development expenses incurred in connection with the Company’s research and development programs, including laboratory materials and supplies and license fees. Research and development expenses are charged to operating expenses as incurred when these expenditures relate to the Company’s research and development efforts and have no alternative future uses. The Company is obligated to make upfront payments upon execution of certain research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are capitalized until such goods are delivered or the related services are performed, or such time when the Company does not expect the goods to be delivered or services to be performed. The Company estimates the period over which such services will be performed and the level of effort to be expended in each period. If actual timing of performance or the level of effort varies from the estimate, the Company will adjust the amounts recorded accordingly. Since inception, the Company has not experienced any material differences between accrued or prepaid costs and actual costs.
General and Administrative Expenses	General and Administrative Expenses General and administrative expenses consist primarily of personnel-related expenses, including employee salaries, bonuses, benefits, and stock-based compensation, and recruiting costs for personnel in executive, finance, and other administrative functions. Other significant general and administrative expenses include legal fees relating to intellectual property and corporate matters, professional fees for accounting, tax and consulting services, insurance costs, travel expenses and facility related expenses. General and administrative costs are expensed as incurred.
Stock-Based Compensation	Stock-Based Compensation The cost of employee services received in exchange for an award of an equity instrument is measured at the grant date based on the award’s estimated fair value using the Black-Scholes option pricing model. The estimated fair value of the awards is recognized into expense on a straight-line basis over the requisite service period. Stock-based compensation expense for an award with a performance condition is recognized when the achievement of such performance condition is determined to be probable. If the outcome of such performance condition is not determined to be probable or is not met, no compensation expense is recognized, and any previously recognized compensation expense is reversed. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance condition at each reporting date. Forfeitures are recognized as a reduction of stock-based compensation expense as they occur. The option plan permits, but does not require, the inclusion of early exercise provisions in individual awards. Proceeds from early option exercises are recorded as a liability until the underlying restricted shares vest. While the restricted shares have voting rights, they are not considered outstanding for accounting purposes.
Employee Stock Purchase Plan	Employee Stock Purchase Plan In December 2020, the Company’s Employee Stock Purchase Plan (“ESPP”) became effective, pursuant to which eligible employees can purchase shares of the Company’s common stock at a discount to the fair market value at semi-annual intervals. In determining the grant date fair value of shares expected to be purchased under the ESPP, the Company uses the Black-Scholes option pricing model. Black-Scholes inputs are determined in the same manner as for stock option awards. The estimated grant date fair value of shares expected to be purchased is recognized into expense on a straight-line basis over the requisite service period.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company is more likely than not able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes in the period in which the adjustment is made. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. The Company did not have any uncertain tax positions as of December 31, 2021 and 2020.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company presents one continuous Statement of Operations and Comprehensive Loss. The Company’s comprehensive loss includes unrealized gains and losses on investments.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period, without consideration of potentially dilutive securities. Diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders since the effect of potentially dilutive securities is anti-dilutive given the net loss of the Company. For purposes of this calculation, redeemable convertible preferred stock, stock options, employee stock purchase rights, and unvested common stock subject to repurchase are considered to be common stock equivalents but are not included in the calculations of diluted net loss per share for the periods presented as their effect would be antidilutive.
Emerging Growth Company Status	Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with certain new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (1) no longer an emerging growth company or (2) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than temporary impairments on investment securities are recorded. The guidance is effective for the Company beginning on January 1, 2023, with early adoption permitted. The Company is currently evaluating the impact the standard may have on its financial statements and related disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash and cash equivalents and restricted cash reported within the balance sheets that sum to the amounts shown in the statements of cash flows (in thousands): December 31, December 31, Cash and cash equivalents $ 254,045 $ 386,569 Restricted cash 250 350 Total cash and cash equivalents and restricted cash $ 254,295 $ 386,919

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table identifies the Company’s assets and liabilities that were measured at fair value on a recurring basis (in thousands): December 31, 2021 Level Amortized Cost Gross unrealized gains Gross unrealized losses Fair Value Money market funds 1 $ 253,945 $ — $ — $ 253,945 Long-term investments - U.S. Treasury securities 1 65,106 — ( 326 ) 64,780 Total 319,051 — ( 326 ) 318,725 December 31, 2020 Money market funds 1 $ 386,369 $ — $ — $ 386,369

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property and equipment	Property and equipment are summarized as follows (in thousands): December 31, 2021 December 31, 2020 Furniture and fixtures $ 367 $ 269 Laboratory equipment 4,679 3,401 Property and equipment, gross 5,046 3,670 Less accumulated depreciation ( 2,834 ) ( 2,052 ) Total property and equipment, net $ 2,212 $ 1,618

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
Summary of Accrued Expenses	Accrued expenses consisted of the following (in thousands): December 31, 2021 December 31, 2020 Research and development expenses $ 6,528 $ 2,063 Employee compensation and benefits 4,605 2,634 Professional services and other 594 581 Total accrued expenses $ 11,727 $ 5,278

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Summary of Operating Lease Cost	The Company leases office and laboratory space in Seattle, Washington. The components of lease expense and related cash flows were as follows (in thousands): Years Ended December 31, 2021 2020 Lease expense Operating lease expense $ 1,452 $ 1,388 Variable lease expense 459 386 Total lease expense 1,911 1,774 Operating cash outflows from operating leases $ 1,841 $ 1,591
Summary of Future Minimum Commitments Due Under the Operating Lease Agreement	Future minimum commitments due under the operating lease agreements as of December 31, 2021 are as follows (in thousands): Years Ended December 31, Amount 2022 1,481 2023 1,513 2024 1,348 2025 1,389 Thereafter 1,186 Total undiscounted lease payments 6,917 Present value adjustment ( 1,070 ) Total present value of lease payments $ 5,847

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Summary of Common Shares Reserved for Future Issuance	The Company has reserved shares of common stock for the following potential future issuances: December 31, December 31, Shares underlying outstanding equity awards 6,370,873 6,316,569 Shares available for future equity award grants 2,931,012 1,506,806 Shares underlying early exercised equity awards 26,283 100,263 Shares underlying ESPP withholdings — 4,393 Total 9,328,168 7,928,031

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of Share-based Compensation Expense	Stock-based compensation expense recognized for all equity awards has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years Ended December 31, 2021 2020 Research and development expense $ 8,331 $ 1,180 General and administrative expense 10,856 1,460 Total stock-based compensation expense $ 19,187 $ 2,640
Summary of Activity Related to Stock Option Grants	A summary of the Company’s stock option activity for the year ended December 31, 2021 is as follows (in thousands, except share and per share data and years): Stock Options Outstanding Shares Weighted- Weighted- Aggregate Balance at December 31, 2020 6,316,569 $ 10.93 Granted 511,773 Exercised ( 261,567 ) Cancelled ( 195,902 ) Balance at December 31, 2021 6,370,873 12.82 8.58 11,385,117 Vested at December 31, 2021 1,974,776 $ 9.60 8.14 $ 4,887,808
Summary of Fair Value of Each Option Grant Estimated Throughout Year Using Black-Scholes Option-pricing Model	The grant date fair value of stock options was estimated using a Black-Scholes option pricing model with the following weighted-average assumptions: Years Ended December 31, 2021 2020 Expected term (in years) 6.0 6.0 Expected volatility 79 % 80 % Risk-free interest rate 0.98 % 0.51 % Expected dividend yield — —
Summary of Weighted Average Inputs used under for the ESPP	The weighted average inputs used for the ESPP for the year ended December 31, 2021, were as follows: Years Ended December 31, 2021 2020 Expected term (in years) 1.2 1.2 Expected volatility 81 % 82 % Risk-free interest rate 0.14 % 0.11 % Expected dividend yield — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule Of Effective Income Tax Rate Reconciliation	The Company’s effective tax rates for the years ended December 31, 2021 and 2020 differ from the U.S. federal statutory rate as follows (in thousands): Years Ended December 31, 2021 2020 Tax at the federal statutory rate $ ( 18,790 ) $ ( 6,919 ) Benefit from R&D tax credits ( 1,244 ) ( 586 ) Stock-based compensation 1,102 331 Non-deductible executive compensation 817 — Other temporary and permanent differences 33 21 Change in valuation allowance 18,082 7,153 Total provision for income taxes $ — $ —
Schedule Of Deferred Tax Assets And Liabilities	The significant components of the Company’s deferred tax assets and liabilities were as follows (in thousands): Years Ended December 31, 2021 2020 Deferred tax assets: Net operating loss carryforward 33,671 18,832 Lease liability 1,228 677 R&D tax credit carryforward 2,746 1,502 Share-based compensation 2,151 227 Other deferred tax assets 237 109 Total deferred tax assets 40,033 21,347 Deferred tax liabilities - Right of use asset ( 994 ) ( 458 ) Valuation allowance ( 39,039 ) ( 20,889 ) Net deferred tax assets $ — $ —

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Summary of Antidilutive Securities Excluded from Computation of Earnings Per Share Amount	The following outstanding shares of potentially dilutive securities were excluded from the computation of the diluted net loss per share attributable to common stockholders for the periods presented because their effect would have been anti-dilutive: As of December 31, 2021 2020 Common stock options 6,370,873 6,316,569 Unvested common stock 26,283 100,263 ESPP withholdings — 4,393 Total potentially dilutive shares 6,397,156 6,421,225

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 03, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated deficit		$ (186,212)	$ (96,734)
Money market funds, amortized cost		254,045	$ 386,569
Cash, cash equivalents, and long term investments.		$ 319,100
Common stock, shares, issued		35,133,934	34,801,537
Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock outstanding				15,714,283
IPO [Member]
Offering price per share	$ 21
Net proceeds after deducting underwriting discounts and commissions and offering expenses	$ 255,300
Common stock, shares, issued	13,225,000
IPO [Member] | Common Stock [Member]
Conversion of preferred stock, common shares issued	20,758,098
IPO [Member] | Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock outstanding	77,074,884

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Reconciliation of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash and cash equivalents	$ 254,045	$ 386,569
Restricted cash	250	350
Total cash and cash equivalents and restricted cash	254,295	386,919	$ 10,526
Restricted Cash [Member]
Cash and cash equivalents	254,045	386,569
Restricted cash	250	350
Total cash and cash equivalents and restricted cash	$ 254,295	$ 386,919

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, amortized cost	$ 254,045	$ 386,569
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross unrealized gains	0
Gross unrealized losses	(326)
Total Amortized Cost	319,051
Total Fair Value	318,725
Level 1 [Member] | Fair Value, Recurring [Member] | Long-Term Investments - U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	65,106
Gross unrealized gains	0
Gross unrealized losses	(326)
Fair Value	64,780
Level 1 [Member] | Fair Value, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, amortized cost	253,945	386,369
Money market funds, fair value	$ 253,945	$ 386,369

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - Fair Value, Recurring [Member] $ in Thousands	Dec. 31, 2021USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value,assets transfers from Level 1 to Level 2	$ 0
Fair value,assets transfers from Level 2 to Level 1	0
Fair value, liabilities transfers from Level 1 to Level 2	0
Fair value, liabilities transfers from Level 2 to Level 1	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,046	$ 3,670
Less accumulated depreciation	(2,834)	(2,052)
Total property and equipment, net	2,212	1,618
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	367	269
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,679	$ 3,401

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 783	$ 637

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Research and development expenses	$ 6,528	$ 2,063
Employee compensation and benefits	4,605	2,634
Professional services and other	594	581
Total accrued expenses	$ 11,727	$ 5,278

Leases - Summary of Operating

Leases - Summary of Operating Lease Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Lease, Cost [Abstract]
Operating lease expense	$ 1,452	$ 1,388
Variable lease expense	459	386
Total lease expense	1,911	1,774
Operating cash outflows from operating leases	$ 1,841	$ 1,591

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Commitments Due Under Operating Lease Agreement (Detail) $ in Thousands	Dec. 31, 2021USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2022	$ 1,481
2023	1,513
2024	1,348
2025	1,389
Thereafter	1,186
Total undiscounted lease payments	6,917
Present value adjustment	(1,070)
Total present value of lease payments	$ 5,847

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	Jul. 01, 2021	Dec. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Sublease agreement description		On July 1, 2021, the Company entered into a sublease agreement for additional office space in Seattle, Washington. The commencement date of the sublease was August 1, 2021. The contractual term of the sublease is two years with an option to extend for one additional year and an option to terminate after one year subject to a termination fee.
Contractual term of sublease	2 years
Option to Extend	option to extend for one additional year
Option to Terminate	option to terminate after one year subject to a termination fee
Annual minimum rent payable	$ 0.3
Right-of-use asset obtained in exchange for operating lease liability	$ 0.6	$ 3.1
Operating Lease Weighted Average Remaining Lease Term		4 years 8 months 12 days	1 year 9 months 18 days
Operating Lease Weighted Average Discount Rate		7.50%	8.50%

Term Loan Payable - Additional

Term Loan Payable - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Apr. 30, 2020	Nov. 30, 2016	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Debt issuance costs			$ 2	$ 31
Term Loan [Member] | Silicon Valley Bank [Member] | Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Term loan		$ 3,500
Annual Interest rate		1.75%
Debt issuance costs		$ 300
Effective interest rate			5.14%
Maturity date		Nov. 1, 2020
Term Loan [Member] | Silicon Valley Bank [Member] | Amended Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Maturity date	May 1, 2021

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Summary of Common Shares Reserved for Future Issuance (Detail) - shares	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Total	9,328,168	7,928,031
Shares Underlying Outstanding Equity Awards [Member]
Class of Stock [Line Items]
Total	6,370,873	6,316,569
Shares Available For Future Equity Award Grants [Member]
Class of Stock [Line Items]
Total	2,931,012	1,506,806
Shares Underlying Early Exercised Equity Awards [Member]
Class of Stock [Line Items]
Total	26,283	100,263
Shares Underlying ESPP Withholdings [Member]
Class of Stock [Line Items]
Total	0	4,393

Stockholders' Equity (Deficit_3

Stockholders' Equity (Deficit) - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 01, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2021
Class of Stock [Line Items]
Common stock, par value				$ 0.0001	$ 0.0001
Common stock, shares authorized				200,000,000	200,000,000
Preferred stock , shares authorized				10,000,000	10,000,000
Preferred stock, par value				$ 0.0001	$ 0.0001
Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Accretion to Redemption value				$ 0
Redeemable Stock Excersible On Agreed Upon Milestones [Member] | Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Issuance of Series B redeemable convertible preferred stock			21,732,862
Proceeds from Issuance of Convertible Preferred Stock			$ 46,900
Series B [Member] | Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Issuance of Series B redeemable convertible preferred stock			14,701,054
Issuance of Series B redeemable convertible preferred stock for cash	10,669,834	11,063,028	4,673,388
Issuance of Series B redeemable convertible preferred stock upon conversion of convertible notes			10,027,666
Preferred stock, Par or Stated Value Per Share	$ 2.16	$ 2.16	$ 2.16
Proceeds from Issuance of Convertible Preferred Stock	$ 23,000	$ 23,900
Series B [Member] | Redeemable Stock Excersible On Agreed Upon Milestones [Member]
Class of Stock [Line Items]
Proceeds from Issuance of Convertible Preferred Stock			$ 21,500
Series C [Member] | Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Par or Stated Value Per Share		$ 3.41
Proceeds from Issuance of Convertible Preferred Stock		$ 84,900
Issuance of series C redeemable convertible preferred stock for cash		24,926,685

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 19,187	$ 2,640
Research and development expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	8,331	1,180
General and administrative expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 10,856	$ 1,460

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Activity Related to Stock Option Grants (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Subject to Options Outstanding, Beginning balance	6,316,569
Shares Subject to Options Outstanding, Granted	511,773
Shares Subject to Options Outstanding, Exercised	(261,567)
Shares Subject to Options Outstanding, Cancelled	(195,902)
Shares Subject to Options Outstanding, Ending balance	6,370,873
Shares Subject to Options Outstanding Vested, Ending balance	1,974,776
Weighted- Average Exercise Price, Beginning balance | $ / shares	$ 10.93
Weighted- Average Exercise Price, Ending balance | $ / shares	12.82
Weighted- Average Exercise Price Vested, Ending balance | $ / shares	$ 9.60
Weighted- Average Remaining Contractual Life (Years)	8 years 6 months 29 days
Weighted- Average Remaining Contractual Life (Years), Vested	8 years 1 month 20 days
Aggregate Intrinsic Value, Ending balance | $	$ 11,385,117
Aggregate Intrinsic Value, Vested Ending balance | $	$ 4,887,808

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Fair Value of Each Option Grant Estimated Throughout Year Using Black-Scholes Option-pricing Model (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Expected term (in years)	6 years	6 years
Expected volatility	79.00%	80.00%
Risk-free interest rate	0.98%	0.51%
Expected dividend yield	0.00%	0.00%

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Weighted Average Inputs used for the ESPP (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years	6 years
Expected volatility	79.00%	80.00%
Risk-free interest rate	0.98%	0.51%
Expected dividend yield	0.00%	0.00%
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year 2 months 12 days	1 year 2 months 12 days
Expected volatility	81.00%	82.00%
Risk-free interest rate	0.14%	0.11%
Expected dividend yield	0.00%	0.00%

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Nov. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 50.5
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		2 years 5 months 26 days
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		9,564,798
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		6,370,873	6,316,569
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		6,397,156	6,421,225
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		25.00%
Fair Value of Shares Vested		$ 17	$ 1.1
Share Based Compensation Number of Options Granted		511,773
Shares Available for Future Equity Award Grants		9,328,168	7,928,031
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 22.15	$ 10.50
Aggregate Intrinsic Value, Exercised		$ 7.7	$ 0.1
Common stock, shares, issued		35,133,934	34,801,537
Stock Option Awards [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Shares Available for Future Equity Award Grants		2,931,012
Employee Stock Purchase Plan [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Description	In November 2020, the Company’s board of directors and stockholders approved and adopted the 2020 ESPP. The ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to 15% of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the ESPP. The price of common stock purchased under the ESPP is equal to 85% of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant date of purchase.
Eligible Earnings	15.00%
Shares were Reserved Under the ESPP		698,015
Shares Available for Future Equity Award Grants		627,185
Weighted average per share fair value rights granted		$ 15.95
Common stock, shares, issued		70,830
Unvested Common Stock [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		26,283	100,263

Income Taxes - Schedule Of Effe

Income Taxes - Schedule Of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Tax at the federal statutory rate	$ (18,790)	$ (6,919)
Benefit from R&D tax credits	(1,244)	(586)
Stock-based compensation	1,102	331
Non-deductible executive compensation	817	0
Other temporary and permanent differences	33	21
Change in valuation allowance	18,082	7,153
Total provision for income taxes	$ 0	$ 0

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets And Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforward	$ 33,671	$ 18,832
Lease liability	1,228	677
R&D tax credit carryforward	2,746	1,502
Share-based compensation	2,151	227
Other deferred tax assets	237	109
Total deferred tax assets	40,033	21,347
Deferred tax liabilities - Right of use asset	(994)	(458)
Valuation allowance	(39,039)	(20,889)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 160,300
Operating loss carryforwards amount to expire if not used	$ 18,200
Operating loss carryforwards expiration year	2036
Operating loss carryforwards amount not subject to expiration	$ 142,100
Valuation allowance	39,039	$ 20,889
Unrecognized Tax Benefits	0	$ 0
Research Member
Operating Loss Carryforwards [Line Items]
Tax credit carry forward	$ 2,700
Tax credit carryforward expiration year	2037

Licensing Agreement - Additiona

Licensing Agreement - Additional Information (Detail) - WuXi Bio [Member] - USD ($)	Oct. 31, 2019	Dec. 31, 2021
Aggregate milestone payments upon achievement of certain sales milestones		$ 10,800,000
Agreement payment and license Term desciption		In the event the Company fails to pay all amounts due to WuXi Bio under the license agreement, and fails to pay the amounts within 30 days after receiving written notice of such failure, WuXi Bio may terminate the license with 45 days written notice to the Company.
Research and Development Expense [Member]
License fees paid	$ 150,000

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Equalization of employee contribution	4.00%

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Summary of Antidilutive Securities Excluded from Computation of Earnings Per Share Amount (Detail) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares	6,397,156	6,421,225
Common stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares	6,370,873	6,316,569
Unvested Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares	26,283	100,263
ESPP withholdings [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive shares	0	4,393

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Detail) - USD ($) $ / shares in Units, $ in Thousands	Mar. 28, 2022	Mar. 31, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount			$ 50,500
Subsequent Event [Member]
Subsequent Event [Line Items]
Shares common stock		1,815,926
Shares Issued, Price Per Share		$ 4.85
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 5,900
Unrecognized stock-based compensation expense		1,300
Subsequent Event [Member] | Restructuring Plan [Member]
Subsequent Event [Line Items]
Percentage of workforce reduced	27.00%
Expectation of workforce reduced period	Jul. 15, 2022
Restructuring charges		2,000
Subsequent Event [Member] | Restricted Stock Units (RSUs) [Member]
Subsequent Event [Line Items]
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 266,744