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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 16, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	Stoke Therapeutics, Inc.
Entity Central Index Key	0001623526
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well Known Seasoned Issuer	No
Entity Public Float			$ 490
Entity Common Stock, Shares Outstanding		32,943,670
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-38938
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	47-1144582
Entity Address, Address Line One	45 Wiggins Ave
Entity Address City Or Town	Bedford
Entity Address State Or Province	MA
Entity Address Postal Zip Code	01730
City Area Code	781
Local Phone Number	430-8200
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	STOK
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Portions of the Proxy Statement for the registrant’s 2020 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K. Except with respect to information specifically incorporated by reference in this Annual Report, the Proxy Statement shall not be deemed to be filed as part hereof.

Consolidated balance sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 222,471	$ 105,399
Prepaid expenses and other current assets	3,281	548
Interest receivable	281	196
Total current assets	226,033	106,143
Restricted cash	205	204
Property and equipment, net	2,512	1,192
Total assets	228,750	107,539
Current liabilities:
Accounts payable	751	1,071
Accrued and other current liabilities	3,350	1,396
Total current liabilities	4,101	2,467
Long term liabilities	221	4
Total liabilities	4,322	2,471
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred Stock, value
Common stock, par value of $0.0001 per share; 300,000,000 and 278,527,249 shares authorized, 32,861,842 and 727,413 shares issued and outstanding as of December 31, 2019 and 2018, respectively	3
Additional paid-in capital	282,460	130,776
Accumulated deficit	(58,035)	(25,710)
Total stockholders’ equity	224,428	105,068
Total liabilities and stockholders’ equity	$ 228,750	107,539
Convertible Preferred Stock
Stockholders’ equity
Preferred Stock, value		2
Total stockholders’ equity		$ 2

Consolidated balance sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	278,527,249
Common stock, shares issued	32,861,842	727,413
Common stock, shares outstanding	32,861,842	727,413
Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	225,584,874
Preferred stock, shares issued	0	22,677,585
Preferred stock, shares outstanding	0	22,677,585
Preferred stock, aggregate liquidation preference		$ 130,850

Consolidated statements of operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 23,764	$ 8,371
General and administrative	11,914	4,410
Total operating expenses	35,678	12,781
Loss from operations	(35,678)	(12,781)
Other income (expense):
Interest income	3,351	270
Other income, net	2	(10)
Total other income (expense)	3,353	260
Net loss and comprehensive loss	$ (32,325)	$ (12,521)
Net loss per share attributable to common stockholders—basic and diluted	$ (1.80)	$ (17.65)
Weighted average common shares outstanding—basic and diluted	17,971,443	709,336

Consolidated statements of stockholders' equity (deficit) - USD ($) $ in Thousands	Total	Initial Public Offering	Convertible Preferred Stock	Common Stock	Common Stock Initial Public Offering	Additional Paid-in Capital	Additional Paid-in Capital Initial Public Offering	Accumulated Deficit
Balance at Dec. 31, 2017	$ (1,292)					$ 11,897		$ (13,189)
Balance, Shares at Dec. 31, 2017			4,980,168	670,090
Stock-based compensation	240					240
Issuance of common stock upon exercise of stock options	$ 19					19
Issuance of common stock upon exercise of stock options, Shares	57,324			57,323
Issuance of convertible Preferred Stock, net of issuance costs	$ 118,622		$ 2			118,620
Issuance of convertible Preferred Stock, net of issuance costs, Shares			17,697,417
Net loss	(12,521)							(12,521)
Balance at Dec. 31, 2018	105,068		$ 2			130,776		(25,710)
Balance, Shares at Dec. 31, 2018			22,677,585	727,413
Stock-based compensation	1,922					1,922
Issuance of common stock upon exercise of stock options	$ 314					314
Issuance of common stock upon exercise of stock options, Shares	382,068			382,068
Issuance of common stock		$ 149,449			$ 1		$ 149,448
Issuance of common stock, Shares					9,074,776
Conversion of preferred stock to common stock			$ (2)	$ 2
Conversion of preferred stock to common stock, Shares			(22,677,585)	22,677,585
Net loss	$ (32,325)							(32,325)
Balance at Dec. 31, 2019	$ 224,428			$ 3		$ 282,460		$ (58,035)
Balance, Shares at Dec. 31, 2019				32,861,842

Consolidated statements of stockholders' equity (deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Statement Of Stockholders Equity [Abstract]
Stock issuance cost	$ 378

Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (32,325)	$ (12,521)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	450	214
Stock-based compensation	1,922	240
Loss on disposal of property and equipment	3	10
Changes in assets and liabilities:
Prepaid expenses and other current assets	(2,024)	(632)
Accounts payable and accrued liabilities	891	1,735
Deferred rent	28	(10)
Net cash used in operating activities	(31,055)	(10,964)
Cash flows from investing activities:
Purchases of property and equipment	(1,635)	(935)
Proceeds from sale of property and equipment	1	10
Net cash used in investing activities	(1,634)	(925)
Cash flows from financing activities:
Proceeds from issuance of convertible Preferred Stock		116,000
Preferred Stock Issuance Cost		(378)
Proceeds from issuance of common stock upon initial public offering	151,912
Payments of initial public offering costs	(2,463)
Proceeds from exercise of stock options	315	19
Other	(2)	(2)
Net cash provided by financing activities	149,762	115,639
Net increase in cash, cash equivalents and restricted cash	117,073	103,750
Cash, cash equivalents and restricted cash—beginning of year	105,603	1,853
Cash, cash equivalents and restricted cash—end of year	222,676	105,603
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment included in accrued expenses and accounts payable	$ 140	19
Issuance of convertible Preferred Stock in exchange for simple agreement for future equity		$ 3,000

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Nature of the business and basis of presentation

1. Nature of the business and basis of presentation

Organization

Stoke Therapeutics, Inc. (the Company) was founded in June 2014 and was incorporated under the laws of the State of Delaware. The Company is an early-stage biopharmaceutical company pioneering a new way to treat the underlying causes of severe genetic diseases by precisely upregulating protein expression.

Initial public offering

On June 21, 2019, the Company completed an initial public offering (“IPO”) of its common stock and issued and sold 9,074,776 shares of common stock at a public offering price of $18.00 per share, which included 1,183,666 shares sold upon full exercise of the underwriters’ option to purchase additional shares, resulting in net proceeds of approximately $149.4 million after deducting underwriting discounts, commissions and offering costs of $13.9 million. Upon closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into shares of common stock (see Note 8). Upon conversion of the convertible preferred stock, the Company reclassified the carrying value of the convertible preferred stock to common stock and additional paid-in capital.

On June 6, 2019, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock. Upon the effectiveness of the reverse stock split, (i) all shares of outstanding common stock and convertible preferred stock were adjusted; (ii) the number of shares of common stock for which each outstanding option to purchase common stock is exercisable were adjusted; and (iii) the exercise price of each outstanding option to purchase common stock were adjusted. All of the outstanding common stock share numbers (including shares of common stock subject to the Company’s options and as converted for the outstanding convertible preferred stock shares), share prices, exercise prices and per share amounts contained in the consolidated financial statements have been retroactively adjusted in the consolidated financial statements to reflect this reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split.

On June 21, 2019, the Company filed an amended and restate certificate of incorporation with the Secretary of State of the State of Delaware to authorize the issuance of up to 300 million shares of common stock. $0.0001 par value, and 10 million shares of undesignated preferred stock, $0.0001 par value per share.

Uncertainties

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Liquidity

The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. As of the issuance date of its consolidated financial statements for the year ended December 31, 2019, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements through at least twelve months from the issuance date of its consolidated financial statements.

The Company plans to seek additional funding through public or private equity offerings, debt financings, other collaborations, strategic alliances and licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into strategic alliances or other arrangements on favorable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be required to delay, reduce or eliminate research and development programs, product portfolio expansion or future commercialization efforts, which could adversely affect its business prospects.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of significant accounting policies and recent accounting pronouncements

2. Summary of significant accounting policies and recent accounting pronouncements

Basis of presentation and consolidation

The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP), and include the accounts of Stoke Therapeutics, Inc. and its wholly-owned subsidiary. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).All intercompany transactions between and among the Company and its’ consolidated subsidiary have been eliminated.

Use of estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from those estimates.

Cash and cash equivalents

The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. The Company deposits its cash in checking, sweep and money market accounts.

Restricted cash

At December 31, 2019, restricted cash consisted of money market accounts collateralizing letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities.

The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows:

	As of December 31,
	2019		2018
Cash and cash equivalents	$	222,471	$	105,399
Restricted cash		205		204
	$	222,676	$	105,603

Concentration of credit risk

Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash and cash equivalents. The Company maintains its cash and cash equivalents at an accredited financial institution in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Fair value of financial instruments

ASC Topic 820, Fair Value Measurement (ASC 820), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are those that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier value hierarchy that distinguishes between the following:

Level 1—Quoted market prices in active markets for identical assets or liabilities.

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Deferred offering costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the consolidated statement of stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss.

Property and equipment

Property and equipment are initially recorded at cost less accumulated depreciation. Cost includes the acquisition costs and all costs necessary to bring the asset to the location and working condition necessary for its intended use. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the accompanying consolidated statements of operations and comprehensive loss. Expenditures for normal, recurring or periodic repairs and maintenance related to property and equipment are charged to expense as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if it will result in future economic benefits.

Estimated useful lives for property and equipment are as follows:


Property and equipment		Estimated useful life
Computer and office equipment		3-5 years
Laboratory equipment and Furniture and fixtures		5-7 years
Leasehold improvements		Lesser of estimated useful life or remaining lease term

Impairment of long-lived assets

The Company reviews the recoverability of its long-lived assets when events or changes in circumstances occur that indicate that the carrying value of the assets may not be recoverable. The assessment of possible impairment is based on the ability to recover the carrying value of the assets from the expected future cash flows (undiscounted and without interest expense) of the related operations. If these cash flows are less than the carrying value of such assets, an impairment loss for the difference between the estimated fair value and carrying value is recorded. There were no impairment losses recognized during the years ended December 31, 2019 and 2018.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, facilities costs, depreciation, third-party license fees, and costs related to third parties engaged to conduct preclinical research development activities.

The Company has entered into various research and development contracts with research institutions and other companies to conduct research on its behalf. These agreements are generally cancellable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Stock options

The Company measures its stock-based awards granted based on the estimated fair values of the awards and recognizes the compensation for employees and nonemployees over the requisite service period. The Company uses the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. The Company has elected the practical expedient to use the midpoint between vesting date and the contractual term as the expected term for certain awards with service or performance conditions. Stock-based compensation is recognized using the straight-line method. Forfeitures of unvested stock-based awards are accounted for when they occur.

Patent costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss.

Rent expense

The Company’s real estate operating leases provide for scheduled annual rent increases throughout the lease term. The Company recognizes the effects of the scheduled rent increases on a straight-line basis over the full term of the leases. Tenant improvement allowances, if any, provided by a landlord are recorded as deferred rent and amortized as reduction to rent expense over the lease term.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the estimated future tax consequences attributable to temporary differences between the consolidated financial statement carrying amounts of existing assets and liabilities and their respective tax base. Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the temporary differences are expected to be settled or recovered. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. At December 31, 2019 and 2018, the Company has recorded a full valuation allowance.

Reserves are provided for tax benefits for which realization is uncertain. Such benefits are only recognized when the underlying tax position is considered more-likely-than-not to be sustained on examination by a taxing authority, assuming they possess full knowledge of the position and facts. Interest and penalties related to uncertain tax positions are recognized in the provision of income taxes; however, the Company currently has no interest or penalties related to uncertain income tax benefits.

The Tax Cuts and Jobs Act (the TCJA) was enacted on December 22, 2017. The TCJA reduced the U.S. federal corporate tax rate from a top rate of 35% to a flat rate of 21%. The Company continues to monitor for legislative developments, issuance of regulations and technical memorandum to provide further clarification and/or interpretations of the TCJA and will adjust its consolidated financial statements as needed.

Net loss per share

The Company calculates basic and diluted net loss per share attributable to common stockholders in conformity with the two-class method required for participating securities. The Company considers its convertible preferred stock (Preferred Stock) to be participating securities as in the event a dividend is paid on common stock, the holders of Preferred Stock would be entitled to receive dividends on a basis consistent with the common stockholders. Under the two-class method, the net loss attributable to common stockholders is not allocated to the Preferred Stock as the holders of the Preferred Stock do not have a contractual obligation to share in losses.

Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock.

Segment and geographic information

Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company operates in one segment in the United States. The Company’s chief executive officer, as the chief operating decision-maker, manages and allocates resources to the operations of the Company on a total company basis using consolidated financial information.

Emerging growth company and smaller reporting company status

The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the 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 new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, the Company’s consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.

The Company will remain an emerging growth company until the earliest of (i) the last day of the Company’s first fiscal year (a) following the fifth anniversary of the completion of our IPO, (b) in which the Company has total annual gross revenues of at least $1.07 billion, or (c) when the Company is deemed to be a large accelerated filer, which means the market value of the Company’s common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30^th and (ii) the date on which the Company has issued more than $1.0 billion in non-convertible debt securities during the prior three-year period.

The Company is also a “smaller reporting company,” meaning that in the event of an initial public offering the market value of its stock held by non-affiliates plus the proposed aggregate amount of gross proceeds to the Company as a result of such offering is less than $700 million and its annual revenue is less than $100 million during the most recently completed fiscal year. The Company may continue to be a smaller reporting company as long as either (i) the market value of its stock held by non-affiliates is less than $250 million or (ii) its annual revenue is less than $100 million during the most recently completed fiscal year and the market value of its stock held by non-affiliates is less than $700 million. If the Company is a smaller reporting company at the time it ceases to be an emerging growth company, the Company may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, the Company may choose to present only the two most recent fiscal years of audited financial statements in its Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation.

Recently adopted Accounting Pronouncements

In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting, which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The amendments in this ASU should be applied prospectively to an award modified on or after the adoption date. The Company adopted ASU 2017-09 effective January 1, 2018, and the adoption of ASU 2017-09 did not impact the Company’s consolidated financial statements or financial statement disclosures.

Recently issued accounting pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and lease liabilities on their balance sheet that arise from leases as well as provide disclosures with respect to certain qualitative and quantitative information related to a company's leasing arrangements. For Income Statement purposes, a dual model was retained requiring leases to be classified as either operating or finance. Operating leases result in straight line expense while finance leases results in a front-loaded expense pattern. In July 2018, the FASB issues ASU 2018-11, which provided for an alternative transfer method by allowing entities to apply Topic 842 as of the adoption date. The Company adopted Topic 842 on January 1, 2020 using the modified retrospective approach and elected to apply the transition method that allows companies to continue applying guidance under the lease standard in effect at that time in the comparative period financial statements and recognize a cumulative-effect adjustment to the balance sheet on the date of adoption. The Company has also elected the package of practical expedients to not reassess our prior conclusions about lease identification, lease classification and indirect costs and to not separate lease and non-lease components.

Upon adoption of Topic 842 on January 1, 2020, the Company recorded right-of-use assets of $2.2 million and operating lease liabilities of $2.2 million and the elimination of deferred rent of $0.03 million. Adoption of the standard did not result in the Company recording a cumulative effect adjustment to retained earnings.

In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480) and Derivatives and Hedging (Topic 815): I. Accounting for Certain Financial Instruments with Down Round Features; II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception. Part I of this update addresses the complexity of accounting for certain financial instruments with down round features. Down round features are features of certain equity-linked instruments (or embedded features) that result in the strike price being reduced on the basis of the pricing of future equity offerings. Current accounting guidance creates cost and complexity for entities that issue financial instruments (such as warrants and convertible instruments) with down round features that require fair value measurement of the entire instrument or conversion option. Part II of this update addresses the difficulty of navigating Topic 480, Distinguishing Liabilities from Equity, because of the existence of extensive pending content in the FASB Accounting Standards Codification. This pending content is the result of the indefinite deferral of accounting requirements about mandatorily redeemable financial instruments of certain nonpublic entities and certain mandatorily redeemable noncontrolling interests. The amendments in Part II of this update do not have an accounting effect. For public business entities, the amendments in Part I of ASU-2017-11 are effective for fiscal years and interim periods within those years beginning after December 15, 2018. For all other entities, the amendments in Part I of this update are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. The Company intends to adopt Part I of this update on January 1, 2020. Early adoption is permitted for all entities, including adoption in an interim period. The Company is currently assessing the potential impact of adopting ASU 2017-11 on its consolidated financial statements and financial statement disclosures and does not expect that the adoption of this update will have a material impact on its consolidated financial statements.

In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”. This ASU removed the following disclosure requirements: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements. Additionally, this update added the following disclosure requirements: (1) the changes in unrealized gains and losses for the period included in other comprehensive income and loss for recurring Level 3 fair value measurements held at the end of the reporting period; (2) the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information (such as the median or arithmetic average) in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. ASU 2018-13 will be effective for all entities, for fiscal years beginning after December 15, 2019 with early adoption permitted. The Company intends to adopt this standard on January 1, 2020 and does not expect that the adoption of this update will have a material impact on its consolidated financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair value measurements

3. Fair value measurements

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:

	Fair value measurements as of December 31, 2019
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	222,471	$	—	$	—	$	222,471
Total	$	222,471	$	—	$	—	$	222,471

	Fair value measurements as of December 31, 2018
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	105,399	$	—	$	—	$	105,399
Total	$	105,399	$	—	$	—	$	105,399

The Company’s assets with fair value categorized as Level 1 within the fair value hierarchy include money market funds. Money market funds are publicly traded mutual funds and are presented as cash equivalents on the consolidated balance sheets as of December 31, 2019 and 2018.

The following table presents a roll-forward of the fair value of the Simple Agreement for Future Equity (SAFE) for which fair value is determined by Level 3 inputs:

Balance as of January 1, 2018	$	3,000
Fair value adjustment		—
Conversion into Preferred Stock, January 2018		(3,000	)
Balance as of December 31, 2018	$	—

Fair value of the SAFE on issuance was determined to be equal to the proceeds received. Fair value of the SAFE on conversion into Preferred Stock (see Notes 6 and 8) was determined to be equal to the fair value of the 788,042 Preferred Stock received ($3.0 million).

There were no transfers among Level 1, Level 2, or Level 3 categories in the periods presented.

The carrying value of cash, cash equivalents, accounts payable and accrued expenses that are reported on the consolidated balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

- Definition

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

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Property and equipment, net

4. Property and equipment, net

Property and equipment, net consisted of the following:

	As of December 31,
	2019			2018
Laboratory equipment	$	2,489		$	1,485
Furniture and fixtures		108			—
Leasehold improvements		40			—
Office equipment		79			70
Construction in progress		611			16
		3,327			1,571
Less accumulated depreciation		(815	)		(379	)
	$	2,512		$	1,192

Depreciation expense was $0.5 million and $0.2 million for the years ended December 31, 2019 and 2018, respectively.

Accrued and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Accrued and other current liabilities

5. Accrued and other current liabilities

Accrued and other current liabilities consisted of the following:

	As of December 31,
	2019		2018
Accrued employee compensation costs	$	2,053		901
Accrued professional		228		200
Accrued research and development costs		959		234
Accrued other		56		61
Other current liabilities		54		-
	$	3,350	$	1,396

Simple Agreement For Future Equity

12 Months Ended

Dec. 31, 2019

Stockholders Equity Note [Abstract]

Simple agreement for future equity

6. Simple agreement for future equity

In October 2017, the Company entered into the SAFE with an investor, receiving $3.0 million in exchange for the investor’s right to participate in a future equity financing. The SAFE contained a number of conversion and redemption provisions, including settlement upon liquidity or dissolution events. The Company elected the fair value option of accounting for the SAFE (see Note 3). In January 2018, the investor exercised its rights to convert the SAFE in connection with the Company’s equity financing (See Note 8) and exchanged the SAFE for 788,042 shares of Series A-2 convertible Preferred Stock (Series A-2 Preferred).

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and contingencies

7. Commitments and contingencies

Operating lease

In August 2018, the Company entered into an agreement to lease approximately 23,000 square feet of space for a term of three years. Lease terms are triple net lease commencing at $0.9 million per year, then with three percent annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was December 10, 2018.

In December 2018, the Company entered into an agreement to lease 2,485 square feet of space for a term of three years. The lease includes one renewal option for an additional two years. Lease terms commence at $0.2 million per annum, with 2.5 percent annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was May 1, 2019.

As of December 31, 2019, the future minimum payments for operating leases are as follows:

2020		1,149
2021		1,102
2022		81
2023		—
Thereafter		—
	$	2,332

Rent expense incurred under operating leases was approximately $1.1 million and $0.3 million for the years ended December 31, 2019 and 2018, respectively.

Consulting Agreement

In October 2014, we entered into a consulting agreement with a member of our board of directors, who is also an employee of Cold Spring Harbor Laboratory (CSHL), to provide consulting services related to scientific research related to the development of antisense-based drugs, therapies, diagnostic and research tools, products, services and intellectual property. We recognized expense of $0.1 million in each of the years ended December 31, 2019 and 2018, respectively, for such consulting services. The initial term of this agreement was five years and has been extended by the mutual consent of the Company and the board member.

License and research agreements

In July 2015, the Company entered into a worldwide license agreement, or the CSHL Agreement, with CSHL, with respect to Targeted Augmentation of Nuclear Gene Output (TANGO) patents. Under the CSHL Agreement, the Company receives an exclusive (except with respect to certain government rights and non-exclusive licenses), worldwide license under certain patents and applications relating to TANGO. As part of the CSHL Agreement, the Company granted CSHL 164,927 shares of common stock valued based on an independent appraisal at approximately $0.07 million. The CSHL Agreement obligates the Company to make additional payments that are contingent upon certain milestones being achieved. The Company is also required to pay royalties, tiered based on the scope of patent coverage for each licensed product, ranging from a low-single digit percentage to a mid-single digit percentage on annual net sales. These royalty obligations apply on a licensed product-by-licensed product and country-by-country basis until the latest of (i) the expiration of the last valid claim of a CSHL patent covering the applicable licensed product or (ii) the expiration of any regulatory exclusivity for the applicable licensed product. In addition, if the Company sublicenses the rights under the CSHL Agreement, the Company is required to pay a maximum of twenty percent of the sublicense revenue to CSHL, which may be reduced to a mid-teens or a mid-single digit percentage upon achievement of certain clinical milestones for the applicable licensed product. Finally, the Company is required to pay an annual license maintenance fee of $0.01 million, which amount is creditable against any owed royalty or milestone payments. The maximum aggregate potential milestone payments payable total approximately $0.9 million. Additionally, certain licenses under the CSHL Agreement require the Company to reimburse CSHL for certain past and ongoing patent related expenses, however there were no expenses related to these reimbursable patent costs during the years ended December 31, 2019 and 2018.

In April 2016, the Company entered into an exclusive, worldwide license agreement with the University of Southampton, or the Southampton Agreement, whereby the Company acquired rights to foundational technologies related to the Company’s TANGO technology. Under the Southampton Agreement, the Company receives an exclusive, worldwide license under certain licensed patents and applications relating to TANGO. As part of the Southampton Agreement, the Company paid 0.06 million pounds sterling (approximately $0.07 million as of the date thereof) as an up-front license fee. Under the Southampton Agreement, the Company may be obligated to make additional payments that are contingent upon certain milestones being achieved, as well as royalties on future product sales. These royalty obligations survive until the latest of (i) the expiration of the last valid claim of a licensed patent covering a subject product or (ii) the expiration of any regulatory exclusivity for the subject product in a country. In addition, if the Company sublicenses its rights under the Southampton Agreement, the Company is required to pay a mid-single digit percentage of the sublicense revenue to the University of Southampton. The maximum aggregate potential milestone payments payable by the Company total approximately 0.4 million pounds sterling (approximately $0.5 million as of December 31, 2019). As of December 31, 2019, and 2018, the Company has recorded no liabilities under the Southampton Agreement.

Litigation

The Company may periodically become subject to legal proceedings and claims arising in connection with ongoing business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which it is focused. As of December 31, 2019, the Company had no legal proceedings to which it was a party or to which its property was subject.

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2019

Stockholders Equity Note [Abstract]

Convertible preferred stock

8. Convertible preferred stock

As of December 31, 2018, the Company’s amended and restated certificate of incorporation authorized the Company to issue 22,677,585 shares of $0.0001 par value convertible preferred stock, 4,980,168 are designated Series A convertible preferred stock (Series A Preferred), 7,617,746 are designated Series A-2 Preferred and 10,079,671 are designated Series B convertible preferred stock (Series B Preferred) (collectively, the Preferred Stock). Upon closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into shares of common stock. Upon conversion of the convertible preferred stock, the Company reclassified their carrying value of the convertible preferred stock to common stock and additional paid-in capital.

The following table summarizes the Company’s issued and outstanding Preferred Stock:

	Series A Preferred						Series A-2 Preferred						Series B Preferred						Total convertible Preferred
	Shares			Amount			Shares			Amount			Shares			Amount			Shares			Amount
Balance, December 31, 2017		4,980,168			11,725			—			—			—			—			4,980,168			11,725
Issuance upon conversion of SAFE		—			—			788,042			3,000			—			—			788,042			3,000
Issuance, net of issuance costs of $120		—			—			6,829,704			25,880			—			—			6,829,704			25,880
Issuance, net of issuance costs of $258		—			—			—			—			10,079,671			89,742			10,079,671			89,742
Balance, December 31, 2018		4,980,168		$	11,725			7,617,746		$	28,880			10,079,671		$	89,742			22,677,585		$	130,347
Conversion to Common Stock upon initial public offering		(4,980,168	)		(11,725	)		(7,617,746	)		(28,880	)		(10,079,671	)		(89,742	)		(22,677,585	)		(130,347	)
Balance, December 31, 2019		—			—			—			—			—			—			—			—

The Company’s Preferred Stock has the following rights and preferences, privileges and restrictions:

Voting rights

On any matter presented to the stockholders of the Company for their action or consideration at any meeting of stockholders of the Company, each holder of outstanding shares of Preferred Stock shall be entitled to cast the number of votes equal to the number of whole shares of Common Stock into which the shares of Preferred Stock held by such holder are convertible as of the record date for determining stockholders entitled to vote on such matter. Except as provided by law or by the other provisions of the certificate of incorporation of the Company, holders of Preferred Stock shall vote together with the holders of Common Stock as a single class.

For so long as any shares of Preferred Stock remain outstanding, the holders of record of the shares of Preferred Stock, exclusively and as a separate class, shall be entitled to elect two directors of the Company.

Dividends

The holders of shares of Preferred Stock shall be entitled to receive non-cumulative dividends at the rate of eight percent of the original issue price (see below) of such series of such Preferred Stock per annum on such shares of Preferred Stock (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Preferred Stock) when, as, and if declared by the Board of Directors (the Preferred Dividend).

The Company shall not declare, pay or set aside any dividends on shares of any other class or series of capital stock of the Company (other than dividends on shares of Common Stock payable in shares of Common Stock) unless the holders of the Preferred Stock then outstanding shall first receive, or simultaneously receive, a dividend on each outstanding share of Preferred Stock in an amount at least equal to the sum of (i) the amount of the Preferred Dividend then accrued on such share of Preferred Stock for the calendar year in which such dividends are being paid hereunder and not previously paid and (ii) (A) in the case of a dividend on common stock or any class or series that is convertible into common stock, that dividend per share of Preferred Stock as would equal the product of (l) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common stock and (2) the number of shares of common stock issuable upon conversion of a share of such Preferred Stock, in each case calculated on the record date for determination of holders entitled to receive such dividend or (B) in the case of a dividend on any class or series that is not convertible into common stock, at a rate per share of Preferred Stock determined by (1) dividing the amount of the dividend payable on each share of such class or series of capital stock by the original issuance price of such class or series of capital stock (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to such class or series) and (2) multiplying such fraction by an amount equal to the original issue price (see below) of such Preferred Stock; provided that, if the Company declares, pays or sets aside, on the same date, a dividend on shares of more than one class or series of capital stock of the Company, the dividend payable to the holders of a series of Preferred Stock shall be calculated based upon the dividend on the class or series of capital stock that would result in the highest dividend to such series of Preferred Stock.

The original issue price shall mean $8.9289 per share of Series B Preferred, subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Series B Preferred, $2.3794 per share of Series A Preferred, subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Series A Preferred, and $3.8069 per share of Series A-2 Preferred, subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Series A-2 Preferred.

Optional conversion rights

Each share of Preferred Stock shall be convertible, at the option of the holder thereof, at any time and from time to time, and without the payment of additional consideration by the holder thereof, into such number of fully paid and non-assessable shares of common stock as is determined by dividing the original issue price of such share of Preferred Stock by the conversion price (as described below) of such share of Preferred Stock in effect at the time of conversion. The conversion price for each share of Preferred Stock shall initially be equal to the original issue price of such share of Preferred Stock. Such initial conversion price, and the rate at which shares of Preferred Stock may be converted into shares of common stock, is subject to adjustment.

Mandatory conversion rights

Upon either (a) an initial public offering valuing the company at least $275,000 and for total offering proceeds not less than $75,000 or (b) the date and time, or the occurrence of an event, specified by vote or written consent of (i) a majority of the then-outstanding shares of Series A Preferred and Series A-2 Preferred, voting as a single class and (b) a majority of the outstanding Series B Preferred Stock voting together as a single class, then all outstanding shares of Preferred Stock shall automatically be converted into shares of common stock, at the then effective conversion rate.

Liquidation

In the event of (i) any voluntary or involuntary liquidation, dissolution or winding up of the Company or (ii) the merger or consolidation of the Company or a subsidiary relinquishing a majority of the voting power of the capital stock, or the sale, lease, transfer, exclusive license or other disposition of all or substantially all assets of the Company (Deemed Liquidation Event), the holders of shares of Preferred Stock then outstanding shall be entitled to be paid out of the assets of the Company available for distribution to its stockholders before any payment shall be made to the holders of common stock by reason of their ownership thereof, an amount per share equal to the original issue price of such share of Preferred Stock, plus any dividends declared but unpaid thereon. If upon any such liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, the assets of the Company available for distribution to its stockholders shall be insufficient to pay the holders of shares of Preferred Stock the full amount to which they shall be entitled, the holders of shares of Preferred Stock shall share ratably and on a pari passu basis in any distribution of the assets available for distribution in proportion to the respective amounts which would otherwise be payable in respect of the shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full.

In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, after the payment of all preferential amounts required to be paid to the holders of shares of Preferred Stock the remaining assets of the Company available for distribution to its stockholders shall be distributed among the holders of the shares of Preferred Stock and common stock, pro rata based on the number of shares held by each such holder, treating for this purpose all such securities as if they had been converted to common stock pursuant to the terms of the certificate of incorporation of the Company immediately prior to such liquidation, dissolution or winding up of the Company.

Anti-Dilution

Holders of convertible Preferred Stock are afforded certain anti-dilution protection with respect to corporate events such as stock splits and recapitalizations.

Redemption

The Company’s convertible Preferred Stock is not redeemable except in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or a Deemed Liquidation Event, and only if elected by a majority of the Company’s Board of Directors.

Common Stock

12 Months Ended

Dec. 31, 2019

Stockholders Equity Note [Abstract]

Common stock

9. Common stock

In June 2014, the Company issued 502,638 shares of common stock to its two founders. The shares vest at a rate of 1/3 on the first anniversary date and in 36 equal monthly installments thereafter. These shares were fully vested as of December 31, 2018. In July 2015, the Company issued 164,927 shares of common stock to CSHL in exchange for an exclusive license to a patent (Note 7).

Share-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

10. Share-Based Compensation

In June 2014, the Company’s board of directors and stockholders approved the 2014 Equity Incentive Plan (the 2014 Plan) under which it may grant incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 679,222 shares of common stock to employees, officers, directors and consultants of the Company. In January 2018, the Company increased the number of shares of common stock reserved for issuance under the 2014 Plan to 4,652,098 shares.

In June 2019, the Company’s board of directors and stockholders approved the 2019 Equity Incentive Plan (the “2019 Plan”) which became effective on June 17, 2019 and replaced the Company’s 2014 Equity Incentive Plan (the “2014 Plan”). In addition to the shares of common stock reserved for future issuance under the 2014 Plan that were added to the 2019 Plan upon its effective date, the Company initially reserved 2,200,000 shares of common stock for issuance under the 2019 Plan. The number of shares reserved for issuance under the Company’s 2019 Plan will increase automatically on January 1 of each of 2020 through 2029 by the number of shares equal to 4% of the aggregate number of outstanding shares of the Company’s common stock as of the immediately preceding December 31, or a lesser number as may be determined by the Company’s board of directors.

As of December 31, 2019, there were no shares available for future issuance under the 2014 Plan and 2,180,010 shares were available under the 2019 Plan.

During the year ended December 31, 2019, the Company granted options to purchase 1,234,569 shares of common stock to certain of its employees, and directors, respectively. The options vest over four years except for certain options granted to members of our board of directors which vest over one or three years and are exercisable at a per share price equal to the fair value of the common stock on the grant date.

A summary of stock option activity for awards is presented below:

	Number of shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value⁽¹⁾
Outstanding as of January 1, 2018		585,441		$	0.40		8.0	$	—
Granted		2,969,181			1.34
Exercised		(57,324	)		0.44
Forfeited or expired		(12,670	)		0.40
Outstanding as of December 31, 2018		3,484,628			1.20		8.9		3,436
Granted		1,234,569			10.39
Exercised		(382,068	)		0.91
Forfeited or expired		(94,772	)		1.24
Outstanding as of December 31, 2019		4,242,357		$	3.91		8.8	$	106,138
Exercisable as of December 31, 2019		1,583,859		$	1.03		8.0	$	43,223

(1)	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2019 and 2018.

The weighted average grant date fair value per share of stock options granted during the years ended December 31, 2019 and 2018 was $6.06 and $0.79, respectively. The aggregate grant date fair value of stock options granted during the years ended December 31, 2019 and 2018 was approximately $7.5 million and $2.3 million, respectively. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2019 and 2018 was approximately $10.5 million and $0.1 million, respectively.

Stock-based compensation

The Company recorded stock-based compensation expense of $1.9 million and $0.2 million during the years ended December 31, 2019 and 2018, respectively. As of December 31, 2019, there was $7.5 million of unrecognized compensation cost related to unvested stock-based compensation arrangements granted under the 2014 and the 2019 Plans. The compensation is expected to be recognized over a weighted average period of 4 years as of December 31, 2019.

Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying consolidated statements of operations is as follows:

	Year ended December 31,
	2019		2018
Research and development	$	499	$	117
General and administrative		1,423		123
	$	1,922	$	240

The Company uses the Black-Scholes option pricing model to calculate the grant-date fair value of an award. The fair values of the options granted to employees and directors were calculated using the following assumptions for the years ended December 31, 2019 and 2018:

	Year ended December 31,
	2019			2018
Risk-free interest rate	1.42-2.81%			2.67%—2.84%
Expected dividend yield		0	%	0%
Expected life	5.5-6.375 years			6.25—6.375 years
Expected volatility	60-68%			57%—60%

2019 Employee stock purchase plan

In June 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective on June 18, 2019. The Company initially reserved 315,000 shares of common stock for sale under the ESPP. The number of shares reserved for issuance under the ESPP will increase automatically on January 1st of each of the first ten calendar years following the first offering date by the number of shares equal to the lesser of 1% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31 or a lower amount determined by the Company’s board of directors. The aggregate number of shares issued over the term of the ESPP will not exceed 3,150,000 shares of the Company’s common stock.

Net Loss Per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net loss per share attributable to common stockholders

11. Net loss per share attributable to common stockholders

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company:

	Year ended December 31,
	2019			2018
Numerator:
Net loss	$	(32,325	)	$	(12,521	)
Denominator:
Weighted-average number of common shares, basic and diluted		17,971,443			709,336
Net loss per common share attributable to common stockholders, basic and diluted	$	(1.80	)	$	(17.65	)

The Company’s potential dilutive securities, which include Preferred Stock and common stock options, have been excluded from the computation of diluted net loss per share as the effect would be anti-dilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same.

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

	December 31,
	2019		2018
Preferred Stock		—		22,677,585
Outstanding options to purchase common stock		4,242,357		3,484,628
		4,242,357		26,162,213

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income taxes

12. Income taxes

A reconciliation of the expected income tax expense (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year ended December 31,
	2019			2018
Expected income tax benefit at the federal statutory rate		21.0			21.0
State income taxes, net of federal benefit		6.7			6.2
Non-deductible items		(0.4	)		(0.3	)
Research and development credit, net		4.3			0.9
Other		0.3			0.1
Change in valuation allowance		(31.9	)		(27.9	)
Total	0.0%			0.0%

The principal components of the Company’s deferred tax assets and liabilities consist of the following:

	As of December 31,
	2019			2018
Deferred tax assets:
Federal and state net operating loss carryforwards	$	14,999		$	6,637
Research and development tax credits		2,171			778
Other	761				210
Gross deferred tax assets	$	17,931			7,625
Less: valuation allowance		(17,931	)		(7,625	)
Net deferred tax assets	$	—		$	—

As of December 31, 2019 and 2018, the Company had federal net operating loss carryforwards of $54.5 million and $24.4 million, respectively, which may be available to reduce future taxable income, and expire at various dates beginning in 2034, for those net operating loss carryforwards generated prior to 2018. Net operating losses generated in 2018 and beyond have no expiration. As of December 31, 2019 and 2018, the Company had state net operating loss carry forwards of $56.3 million and $24.0 million, respectively, which may be available to reduce future taxable income and expire at various dates beginning in 2034. In addition, at December 31, 2019 and 2018, the Company had federal research and development tax credit carryforwards of $1.5 million and $0.4 million, respectively, and state research and development tax credit carry forwards of $0.8 million and $0.4 million, respectively. Both federal and state research and development tax credit carry forwards may be available to reduce future tax liabilities and expire at various dates beginning in 2030. In accordance with Statement of ASC 740, Accounting for Income Taxes, management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards. Management has determined that it is more likely than not that the Company will not recognize the benefits of federal and state deferred tax assets and, as a result, a full valuation allowance of $17.9 million and $7.6 million was established at December 31, 2019 and 2018, respectively. The change in the valuation allowance was an increase of $10.3 million and $3.5 million in 2019 and 2018, respectively.

Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended (the Code) due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. The Company has not conducted a formal study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined for purposes of Section 382 and 383 of the Code, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards may be subject to an annual limitation under Section 382 and 383 of the Code, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization.

The Company applies ASC 740 related to accounting for uncertainty in income taxes. The Company’s reserves related to income taxes are based on a determination of whether, and how much of, a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. At December 31, 2019, and 2018 the Company had no unrecognized tax benefits. Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying consolidated statements of operations and comprehensive loss.

Employee Benefits

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

Employee benefits

13. Employee benefits

In 2016, the Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the 401(k) Plan). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. The Company is not required to make and has not made any contributions to the 401(k) Plan for the years ended December 31, 2019 and 2018.

Selected Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Information (Unaudited)

14. Selected Quarterly Financial Information (Unaudited)

Selected quarterly results from operations for the years ended December 31, 2019 and 2018 are as follows:

(in thousands, except for per share data)

	2019 Quarter End
	March 31			June 30			September 30			December 31
Revenue		-			-			-			-
Operating expenses	$	6,322		$	8,445		$	9,842		$	11,069
Loss from operations		(6,322	)		(8,445	)		(9,842	)		(11,069	)
Net loss		(5,742	)		(7,819	)		(8,604	)		(10,160	)
Net loss per share attributable to common stockholders, basic and diluted	$	(6.89	)	$	(1.54	)	$	(0.26	)	$	(0.31	)

	2018 Quarter End
	March 31			June 30			September 30			December 31
Revenue		-			-			-			-
Operating expenses	$	1,912		$	3,010		$	3,317		$	4,542
Loss from operations		(1,912	)		(3,010	)		(3,317	)		(4,542	)
Net loss		(1,912	)		(3,010	)		(3,317	)		(4,282	)
Net loss per share attributable to common stockholders, basic and diluted	$	(2.78	)	$	(4.36	)	$	(4.75	)	$	(6.05	)

Subsequent Events

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent events

15. Subsequent events

The Company has evaluated subsequent events through the issuance date of these consolidated financial statements. The Company has concluded that no events or transactions have occurred that require disclosure in the accompanying consolidated financial statements.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Basis of Presentation and Consolidation

Basis of presentation and consolidation

Use of Estimates

Use of estimates

Cash and Cash Equivalents

Cash and cash equivalents

Restricted Cash

Restricted cash

The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows:

	As of December 31,
	2019		2018
Cash and cash equivalents	$	222,471	$	105,399
Restricted cash		205		204
	$	222,676	$	105,603

Concentration of Credit Risk

Concentration of credit risk

Fair Value of Financial Instruments

Fair value of financial instruments

Level 1—Quoted market prices in active markets for identical assets or liabilities.

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

Deferred Offering Costs

Deferred offering costs

Property and Equipment

Property and equipment

Estimated useful lives for property and equipment are as follows:


Property and equipment		Estimated useful life
Computer and office equipment		3-5 years
Laboratory equipment and Furniture and fixtures		5-7 years
Leasehold improvements		Lesser of estimated useful life or remaining lease term

Impairment of Long-Lived Assets

Impairment of long-lived assets

Research and Development Costs

Research and development costs

Stock options

Patent costs

Rent expense

Income taxes

Net loss per share

Segment and Geographic Information

Segment and geographic information

Emerging Growth Company and Smaller Reporting Company Status

Emerging growth company and smaller reporting company status

Recently Adopted Accounting Pronouncements

Recently adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Recently issued accounting pronouncements

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of Cash and Cash Equivalents and Restricted Cash

The following table reconciles cash and cash equivalents and restricted cash per the consolidated balance sheet to the statement of cash flows:

	As of December 31,
	2019		2018
Cash and cash equivalents	$	222,471	$	105,399
Restricted cash		205		204
	$	222,676	$	105,603

Schedule of Estimated Useful Lives for Property and Equipment

Estimated useful lives for property and equipment are as follows:


Property and equipment		Estimated useful life
Computer and office equipment		3-5 years
Laboratory equipment and Furniture and fixtures		5-7 years
Leasehold improvements		Lesser of estimated useful life or remaining lease term

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized

	Fair value measurements as of December 31, 2019
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	222,471	$	—	$	—	$	222,471
Total	$	222,471	$	—	$	—	$	222,471

	Fair value measurements as of December 31, 2018
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	105,399	$	—	$	—	$	105,399
Total	$	105,399	$	—	$	—	$	105,399

Summary of Fair Value is Determined by Level 3 Inputs

The following table presents a roll-forward of the fair value of the Simple Agreement for Future Equity (SAFE) for which fair value is determined by Level 3 inputs:

Balance as of January 1, 2018	$	3,000
Fair value adjustment		—
Conversion into Preferred Stock, January 2018		(3,000	)
Balance as of December 31, 2018	$	—

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Summary of Property, and Equipment, Net

Property and equipment, net consisted of the following:

	As of December 31,
	2019			2018
Laboratory equipment	$	2,489		$	1,485
Furniture and fixtures		108			—
Leasehold improvements		40			—
Office equipment		79			70
Construction in progress		611			16
		3,327			1,571
Less accumulated depreciation		(815	)		(379	)
	$	2,512		$	1,192

Accrued and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Schedule of Accrued and Other Current Liabilities

Accrued and other current liabilities consisted of the following:

	As of December 31,
	2019		2018
Accrued employee compensation costs	$	2,053		901
Accrued professional		228		200
Accrued research and development costs		959		234
Accrued other		56		61
Other current liabilities		54		-
	$	3,350	$	1,396

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments for Operating Leases

As of December 31, 2019, the future minimum payments for operating leases are as follows:

2020		1,149
2021		1,102
2022		81
2023		—
Thereafter		—
	$	2,332

Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders Equity Note [Abstract]

Summary of Issued and Outstanding Preferred Stock

The following table summarizes the Company’s issued and outstanding Preferred Stock:

	Series A Preferred						Series A-2 Preferred						Series B Preferred						Total convertible Preferred
	Shares			Amount			Shares			Amount			Shares			Amount			Shares			Amount
Balance, December 31, 2017		4,980,168			11,725			—			—			—			—			4,980,168			11,725
Issuance upon conversion of SAFE		—			—			788,042			3,000			—			—			788,042			3,000
Issuance, net of issuance costs of $120		—			—			6,829,704			25,880			—			—			6,829,704			25,880
Issuance, net of issuance costs of $258		—			—			—			—			10,079,671			89,742			10,079,671			89,742
Balance, December 31, 2018		4,980,168		$	11,725			7,617,746		$	28,880			10,079,671		$	89,742			22,677,585		$	130,347
Conversion to Common Stock upon initial public offering		(4,980,168	)		(11,725	)		(7,617,746	)		(28,880	)		(10,079,671	)		(89,742	)		(22,677,585	)		(130,347	)
Balance, December 31, 2019		—			—			—			—			—			—			—			—

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity for Awards

A summary of stock option activity for awards is presented below:

	Number of shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value⁽¹⁾
Outstanding as of January 1, 2018		585,441		$	0.40		8.0	$	—
Granted		2,969,181			1.34
Exercised		(57,324	)		0.44
Forfeited or expired		(12,670	)		0.40
Outstanding as of December 31, 2018		3,484,628			1.20		8.9		3,436
Granted		1,234,569			10.39
Exercised		(382,068	)		0.91
Forfeited or expired		(94,772	)		1.24
Outstanding as of December 31, 2019		4,242,357		$	3.91		8.8	$	106,138
Exercisable as of December 31, 2019		1,583,859		$	1.03		8.0	$	43,223

Summary of Stock-based Compensation Expense

Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying consolidated statements of operations is as follows:

	Year ended December 31,
	2019		2018
Research and development	$	499	$	117
General and administrative		1,423		123
	$	1,922	$	240

Summary of Fair Values of Options Granted to Employees and Directors

	Year ended December 31,
	2019			2018
Risk-free interest rate	1.42-2.81%			2.67%—2.84%
Expected dividend yield		0	%	0%
Expected life	5.5-6.375 years			6.25—6.375 years
Expected volatility	60-68%			57%—60%

Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company:

	Year ended December 31,
	2019			2018
Numerator:
Net loss	$	(32,325	)	$	(12,521	)
Denominator:
Weighted-average number of common shares, basic and diluted		17,971,443			709,336
Net loss per common share attributable to common stockholders, basic and diluted	$	(1.80	)	$	(17.65	)

Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	December 31,
	2019		2018
Preferred Stock		—		22,677,585
Outstanding options to purchase common stock		4,242,357		3,484,628
		4,242,357		26,162,213

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Reconciliation of Expected Income Tax Expense (Benefit) using Federal Statutory Income Tax Rate to Effective Income Tax Rate

A reconciliation of the expected income tax expense (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year ended December 31,
	2019			2018
Expected income tax benefit at the federal statutory rate		21.0			21.0
State income taxes, net of federal benefit		6.7			6.2
Non-deductible items		(0.4	)		(0.3	)
Research and development credit, net		4.3			0.9
Other		0.3			0.1
Change in valuation allowance		(31.9	)		(27.9	)
Total	0.0%			0.0%

Schedule of Deferred Tax Assets and Liabilities

The principal components of the Company’s deferred tax assets and liabilities consist of the following:

	As of December 31,
	2019			2018
Deferred tax assets:
Federal and state net operating loss carryforwards	$	14,999		$	6,637
Research and development tax credits		2,171			778
Other	761				210
Gross deferred tax assets	$	17,931			7,625
Less: valuation allowance		(17,931	)		(7,625	)
Net deferred tax assets	$	—		$	—

Selected Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Results from Operations

Selected quarterly results from operations for the years ended December 31, 2019 and 2018 are as follows:

(in thousands, except for per share data)

	2019 Quarter End
	March 31			June 30			September 30			December 31
Revenue		-			-			-			-
Operating expenses	$	6,322		$	8,445		$	9,842		$	11,069
Loss from operations		(6,322	)		(8,445	)		(9,842	)		(11,069	)
Net loss		(5,742	)		(7,819	)		(8,604	)		(10,160	)
Net loss per share attributable to common stockholders, basic and diluted	$	(6.89	)	$	(1.54	)	$	(0.26	)	$	(0.31	)

	2018 Quarter End
	March 31			June 30			September 30			December 31
Revenue		-			-			-			-
Operating expenses	$	1,912		$	3,010		$	3,317		$	4,542
Loss from operations		(1,912	)		(3,010	)		(3,317	)		(4,542	)
Net loss		(1,912	)		(3,010	)		(3,317	)		(4,282	)
Net loss per share attributable to common stockholders, basic and diluted	$	(2.78	)	$	(4.36	)	$	(4.75	)	$	(6.05	)

Nature of the Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Millions			12 Months Ended
	Jun. 21, 2019 USD ($) $ / shares shares	Jun. 06, 2019	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation state name			DE
Reverse stock split, description			On June 6, 2019, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock.
Reverse stock split		0.1005
Common stock, shares authorized	300,000,000		300,000,000	278,527,249
Common stock, per share par value \| $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Undesignated preferred stock, shares authorized	10,000,000		10,000,000	0
Undesignated preferred stock, per share par value \| $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from initial public offering \| $	$ 149.4
Initial Public Offering \| Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares	9,074,776		9,074,776
Stock issued, price per share \| $ / shares	$ 18.00
Offering costs \| $	$ 13.9
Underwriters’ Option \| Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares	1,183,666

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 222,471	$ 105,399
Restricted cash	205	204
Total cash, cash equivalents and restricted cash	$ 222,676	$ 105,603	$ 1,853

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Estimated Useful Lives for Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Computer and Office Equipment \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	3 years
Computer and Office Equipment \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Laboratory Equipment and Furniture and Fixtures \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful life	5 years
Laboratory Equipment and Furniture and Fixtures \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful life	7 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful life	Lesser of estimated useful life or remaining lease term

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Jan. 01, 2020 USD ($)
Accounting Policies [Line Items]
Impairment losses recognized	$ 0	$ 0
Unrecognized income tax benefits, interest or penalties	$ 0
Federal corporate tax rate	21.00%	21.00%	35.00%
Number of operating segments \| Segment	1
Subsequent Event
Accounting Policies [Line Items]
Right-of-use assets				$ 2,200,000
Operating lease liabilities				2,200,000
Deferred rent				$ 30,000

Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 222,471	$ 105,399
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	222,471	105,399
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	222,471	105,399
Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 222,471	$ 105,399

Fair Value Measurements - Summary of Fair Value is Determined by Level 3 Inputs (Details) - Simple Agreement For Future Equity $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of January 1, 2018	$ 3,000
Conversion into Preferred Stock, January 2018	$ (3,000)

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value assets, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0
Fair value liabilities, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0
Simple Agreement For Future Equity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Conversion of preferred stock, shares	788,042
Conversion into preferred stock shares received	$ (3,000)

Property and Equipment, Net - Summary of Property, and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property, and equipment, gross	$ 3,327	$ 1,571
Less accumulated depreciation	(815)	(379)
Property, and equipment, net	2,512	1,192
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, and equipment, gross	2,489	1,485
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property, and equipment, gross	108
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, and equipment, gross	40
Office Equipment
Property Plant And Equipment [Line Items]
Property, and equipment, gross	79	70
Construction in Progress
Property Plant And Equipment [Line Items]
Property, and equipment, gross	$ 611	$ 16

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation	$ 450	$ 214

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued employee compensation costs	$ 2,053	$ 901
Accrued professional	228	200
Accrued research and development costs	959	234
Accrued other	56	61
Other current liabilities	54
Total accrued and other current liabilities	$ 3,350	$ 1,396

Simple Agreement For Future Equity - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2018	Oct. 31, 2017
Class Of Stock [Line Items]
Preferred stock, shares issued	0	0
Simple Agreement For Future Equity
Class Of Stock [Line Items]
Future equity financing				$ 3.0
Series A-2 Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		7,617,746
Series A-2 Preferred Stock \| Simple Agreement For Future Equity
Class Of Stock [Line Items]
Preferred stock, shares issued			788,042

Commitments and Contingencies - Additional Information (Details)	1 Months Ended					12 Months Ended
	Dec. 31, 2018 USD ($) ft² Option	Aug. 31, 2018 USD ($) ft²	Apr. 30, 2016 USD ($)	Apr. 30, 2016 GBP (£)	Jul. 31, 2015 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 GBP (£)
Commitments And Contingencies [Line Items]
Area of space subject to operating lease \| ft²	2,485	23,000
Operating lease term	3 years	3 years					3 years
Operating lease cost per year	$ 200,000	$ 900,000
Annual base rent increase percentage for operating lease	2.50%	3.00%
Operating lease commencement date	May 01, 2019	Dec. 10, 2018
Number of options to renew operating lease term \| Option	1
Operating lease, renewal term	2 years						2 years
Operating leases, rent expense						$ 1,100,000	$ 300,000
Liabilities recorded under agreement	$ 2,471,000					4,322,000	2,471,000
CSHL Agreement
Commitments And Contingencies [Line Items]
Stock issued during period, shares \| shares					164,927
Shares of common stock granted, value					$ 70,000
Percentage of maximum required payment of sublicense revenue					20.00%
Annual license maintenance fee						10,000
Maximum aggregate potential milestone payments payable						900,000
Expenses related to reimbursable patent costs						0	0
Southampton Agreement
Commitments And Contingencies [Line Items]
Maximum aggregate potential milestone payments payable						500,000		£ 400,000
Payment of up-front license fee			$ 70,000	£ 60,000
Liabilities recorded under agreement	$ 0					0	0
Member of Board of Directors
Commitments And Contingencies [Line Items]
Consulting services expenses						$ 100,000	$ 100,000
Consulting services agreement term						5 years

Commitments and Contingencies - Schedule of Future Minimum Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Future minimum payments for operating leases
2020	$ 1,149
2021	1,102
2022	81
Total	$ 2,332

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jun. 21, 2019
Class Of Stock [Line Items]
Preferred stock, shares issued	0	0
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Proceeds from issuance of convertible Preferred Stock		$ 116,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued	0	22,677,585
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, voting rights description	On any matter presented to the stockholders of the Company for their action or consideration at any meeting of stockholders of the Company, each holder of outstanding shares of Preferred Stock shall be entitled to cast the number of votes equal to the number of whole shares of Common Stock into which the shares of Preferred Stock held by such holder are convertible as of the record date for determining stockholders entitled to vote on such matter. Except as provided by law or by the other provisions of the certificate of incorporation of the Company, holders of Preferred Stock shall vote together with the holders of Common Stock as a single class.
Percentage of preferred stock dividend rate	8.00%
Preferred stock, mandatory terms of conversion	Upon either (a) an initial public offering valuing the company at least $275,000 and for total offering proceeds not less than $75,000 or (b) the date and time, or the occurrence of an event, specified by vote or written consent of (i) a majority of the then-outstanding shares of Series A Preferred and Series A-2 Preferred, voting as a single class and (b) a majority of the outstanding Series B Preferred Stock voting together as a single class, then all outstanding shares of Preferred Stock shall automatically be converted into shares of common stock, at the then effective conversion rate.
Preferred stock, redemption terms	The Company’s convertible Preferred Stock is not redeemable except in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or a Deemed Liquidation Event, and only if elected by a majority of the Company’s Board of Directors.
Convertible Preferred Stock \| Minimum
Class Of Stock [Line Items]
Proceeds from issuance of convertible Preferred Stock	$ 75,000
Convertible Preferred Stock \| Minimum \| Initial Public Offering
Class Of Stock [Line Items]
Proceeds from issuance of convertible Preferred Stock	$ 275,000
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		4,980,168
Original issue price subject to recapitalization adjustments	$ 2.3794
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		7,617,746
Original issue price subject to recapitalization adjustments	3.8069
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		10,079,671
Original issue price subject to recapitalization adjustments	$ 8.9289

Convertible Preferred Stock - Summary of Issued and Outstanding Preferred Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Issuance upon conversion of SAFE		$ 118,622
Balance, Shares	0	0
Balance, Shares	0
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Balance	$ 11,725	$ 11,725
Conversion to Common Stock upon initial public offering	$ (11,725)
Conversion to Common Stock upon initial public offering, Shares	(4,980,168)
Balance		$ 11,725
Balance, Shares		4,980,168
Balance, Shares	4,980,168	4,980,168
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Balance	$ 28,880
Issuance upon conversion of SAFE		$ 3,000
Issuance upon conversion of SAFE, Shares		788,042
Issuance, net of issuance costs		$ 25,880
Issuance, net of issuance costs, Shares		6,829,704
Conversion to Common Stock upon initial public offering	$ (28,880)
Conversion to Common Stock upon initial public offering, Shares	(7,617,746)
Balance		$ 28,880
Balance, Shares		7,617,746
Balance, Shares	7,617,746
Series A-2 Convertible Preferred Stock \| Simple Agreement For Future Equity
Class Of Stock [Line Items]
Issuance upon conversion of SAFE		$ 3,000
Issuance upon conversion of SAFE, Shares		788,042
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Balance	$ 89,742
Issuance, net of issuance costs		$ 89,742
Issuance, net of issuance costs, Shares		10,079,671
Conversion to Common Stock upon initial public offering	$ (89,742)
Conversion to Common Stock upon initial public offering, Shares	(10,079,671)
Balance		$ 89,742
Balance, Shares		10,079,671
Balance, Shares	10,079,671
Convertible Preferred Stock
Class Of Stock [Line Items]
Balance	$ 130,347
Issuance upon conversion of SAFE		$ 2
Issuance upon conversion of SAFE, Shares		17,697,417
Conversion to Common Stock upon initial public offering	$ (130,347)
Conversion to Common Stock upon initial public offering, Shares	(22,677,585)
Balance		$ 130,347
Balance, Shares	0	22,677,585
Balance, Shares	22,677,585	4,980,168

Convertible Preferred Stock - Summary of Issued and Outstanding Preferred Stock (Parenthetical) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Stock issuance cost		$ 378
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Stock issuance cost	$ 120
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Stock issuance cost	$ 258

Common Stock - Additional Information (Details)	1 Months Ended		12 Months Ended
Common Stock - Additional Information (Details)	Jul. 31, 2015 shares	Jun. 30, 2014 Founder shares	Dec. 31, 2019	Dec. 31, 2018 shares
Class Of Stock [Line Items]
Shares vesting period			4 years
Vested shares of common stock				502,638
CSHL Agreement
Class Of Stock [Line Items]
Issuance of common stock, Shares	164,927
Founder
Class Of Stock [Line Items]
Issuance of common stock, Shares		502,638
Shares vesting percentage		33.33%
Number of founders \| Founder		2
Shares vesting period		36 months

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2014	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted to purchase shares			1,234,569	2,969,181
Options vest over period			4 years
Weighted average grant date fair value per share of stock options granted			$ 6.06	$ 0.79
Aggregate grant date fair value of stock options granted			$ 7,500	$ 2,300
Aggregate intrinsic value of stock options exercised			10,500	100
Stock based compensation expense			1,922	$ 240
Unrecognized compensation cost			$ 7,500
Expected weighted average period			4 years
Maximum \| Member of Board of Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vest over period			3 years
Minimum \| Member of Board of Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vest over period			1 year
The 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance					4,652,098
Number of common shares available for future issuance			0
The 2014 Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted to purchase shares		679,222
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	2,200,000
Percentage of increase in reserved common shares	4.00%
Number of common shares available for future issuance			2,180,010
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	315,000
2019 ESPP \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	3,150,000
Percentage of increase in reserved common shares	1.00%

Share-Based Compensation - Summary of Stock Option Activity for Awards (Details) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Number of shares, Outstanding balance

3,484,628

585,441

Number of shares, Granted

1,234,569

2,969,181

Number of shares, Exercised

(382,068)

(57,324)

Number of shares, Forfeited or expired

(94,772)

(12,670)

Number of shares, Outstanding balance

4,242,357

3,484,628

585,441

Number of shares, Exercisable as of December 31, 2019

1,583,859

Weighted average exercise price, Outstanding balance

$ 1.20

$ 0.40

Weighted average exercise price, Granted

10.39

1.34

Weighted average exercise price, Exercised

0.91

0.44

Weighted average exercise price, Forfeited or expired

1.24

0.40

Weighted average exercise price, Outstanding balance

3.91

$ 1.20

$ 0.40

Weighted average exercise price, Exercisable as of December 31, 2019

$ 1.03

Weighted average remaining contractual life, Outstanding

8 years 9 months 18 days

8 years 10 months 24 days

8 years

Weighted average remaining contractual life, Exercisable

8 years

Aggregate intrinsic value, Outstanding value

^[1]

$ 106,138

$ 3,436

Aggregate intrinsic value, Exercisable as of December 31, 2019

^[1]

$ 43,223

[1]	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2019 and 2018.

Share-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,922	$ 240
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	499	117
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,423	$ 123

Share-Based Compensation - Summary of Fair Values of Options Granted to Employees and Directors (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.42%	2.67%
Risk-free interest rate, maximum	2.81%	2.84%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	60.00%	57.00%
Expected volatility, maximum	68.00%	60.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 6 months	6 years 3 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 4 months 15 days	6 years 4 months 15 days

Net Loss Per Share Attributable to Common Stockholders - Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (10,160)	$ (8,604)	$ (7,819)	$ (5,742)	$ (4,282)	$ (3,317)	$ (3,010)	$ (1,912)	$ (32,325)	$ (12,521)
Denominator:
Weighted-average number of common shares, basic and diluted									17,971,443	709,336
Net loss per common share attributable to common stockholders, basic and diluted	$ (0.31)	$ (0.26)	$ (1.54)	$ (6.89)	$ (6.05)	$ (4.75)	$ (4.36)	$ (2.78)	$ (1.80)	$ (17.65)

- Definition

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

+ References + Details

Net Loss Per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,242,357	26,162,213
Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount		22,677,585
Outstanding Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,242,357	3,484,628

Income Taxes - Reconciliation of Expected Income Tax Expense (Benefit) using Federal Statutory Income Tax Rate to Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Expected income tax benefit at the federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of federal benefit	6.70%	6.20%
Non-deductible items	(0.40%)	(0.30%)
Research and development credit, net	4.30%	0.90%
Other	0.30%	0.10%
Change in valuation allowance	(31.90%)	(27.90%)
Total	0.00%	0.00%

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 14,999	$ 6,637
Research and development tax credits	2,171	778
Other	761	210
Gross deferred tax assets	17,931	7,625
Less: valuation allowance	$ (17,931)	$ (7,625)

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Valuation allowance	$ 17,931,000	$ 7,625,000
Change in valuation allowance	10,300,000	3,500,000
Unrecognized tax benefits	0	0
Federal
Income Taxes [Line Items]
Operating loss carryforwards	$ 54,500,000	$ 24,400,000
Operating loss carryforwards, expiration beginning year	2034	2034
Federal \| Research and Development Tax Credit
Income Taxes [Line Items]
Tax credit carryforwards	$ 1,500,000	$ 400,000
Tax credit carryforwards, expiration beginning year	2030	2030
State
Income Taxes [Line Items]
Operating loss carryforwards	$ 56,300,000	$ 24,000,000
Operating loss carryforwards, expiration beginning year	2034	2034
State \| Research and Development Tax Credit
Income Taxes [Line Items]
Tax credit carryforwards	$ 800,000	$ 400,000
Tax credit carryforwards, expiration beginning year	2030	2030

Employee Benefits - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Contributions to 401(k) Plan	$ 0	$ 0

Selected Quarterly Financial Information (Unaudited) - Selected Quarterly Results from Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating expenses	$ 11,069	$ 9,842	$ 8,445	$ 6,322	$ 4,542	$ 3,317	$ 3,010	$ 1,912	$ 35,678	$ 12,781
Loss from operations	(11,069)	(9,842)	(8,445)	(6,322)	(4,542)	(3,317)	(3,010)	(1,912)	(35,678)	(12,781)
Net loss	$ (10,160)	$ (8,604)	$ (7,819)	$ (5,742)	$ (4,282)	$ (3,317)	$ (3,010)	$ (1,912)	$ (32,325)	$ (12,521)
Net loss per common share attributable to common stockholders, basic and diluted	$ (0.31)	$ (0.26)	$ (1.54)	$ (6.89)	$ (6.05)	$ (4.75)	$ (4.36)	$ (2.78)	$ (1.80)	$ (17.65)

- Definition

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

+ References + Details