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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Aug. 12, 2019
Document and Entity Information
Entity Registrant Name	Akero Therapeutics, Inc.
Entity Central Index Key	0001744659
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		28,555,379
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 162,654	$ 75,975
Prepaid expenses and other current assets	454	1,156
Total current assets	163,108	77,131
Restricted cash	60	20
Total assets	163,168	77,151
Current liabilities:
Accounts payable	3,248	1,373
Accrued expenses and other current liabilities	1,492	969
Total current liabilities	4,740	2,342
Other liabilities	39
Total liabilities	4,779	2,342
Commitments and contingencies (Note 10)
Stockholders' equity (deficit):
Redeemable convertible preferred stock (Series A and B), $0.0001 par value; no shares authorized, issued and outstanding as of June 30, 2019; 64,730,410 shares authorized, issued and outstanding as of December 31, 2018; aggregate liquidation preference of $0 and $96,358 as of June 30, 2019 and December 31, 2018, respectively		124,728
Common stock, $0.0001 par value, 150,000,000 shares authorized as of June 30, 2019 and 75,000,000 shares authorized as of December 31, 2018; 28,555,379 and 238,986 shares issued and outstanding as of June 30, 2019 and December 31, 2019, respectively	3
Additional paid-in capital	257,541	36,646
Accumulated deficit	(99,155)	(86,565)
Total stockholders' equity (deficit)	158,389	(49,919)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 163,168	$ 77,151

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Condensed Consolidated Balance Sheets
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	64,730,410
Redeemable convertible preferred stock, shares issued	0	64,730,410
Redeemable convertible preferred stock, shares outstanding	0	64,730,410
Aggregate liquidation preference stock, Value	$ 0	$ 96,358
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	75,000,000
Common stock, shares issued	28,555,379	238,986
Common stock, shares outstanding	28,555,379	238,986

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 5,960	$ 8,420	$ 10,023	$ 8,646
General and administrative	1,649	242	3,098	437
Total operating expenses	7,609	8,662	13,121	9,083
Loss from operations	(7,609)	(8,662)	(13,121)	(9,083)
Other income (expense), net:
Change in fair value of anti-dilution right liability		(11)		(11)
Other income, net	381		531
Total other income (expense), net	381	(11)	531	(11)
Net loss and comprehensive loss	(7,228)	(8,673)	(12,590)	(9,094)
Accretion of redeemable convertible preferred stock to redemption value		(70)		(70)
Net loss attributable to common stockholders	$ (7,228)	$ (8,743)	$ (12,590)	$ (9,164)
Net loss per share attributable to common stockholders - basic and diluted	$ (2.21)	$ (94.86)	$ (7.29)	$ (137.97)
Weighted-average number of shares used in computing net loss per share attributable to common stockholders, basic and diluted	3,268,390	92,171	1,726,795	66,422

Condensed Consolidated Statements of Redeemable Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Redeemable convertible preferred stock (as converted to common stock)	Series A Preferred Stock	Common Stock	Treasury Stock	Additional Paid-In-Capital	Accumulated Deficit	Total
Balance at beginning at Dec. 31, 2017	$ 5,000					$ (4,564)	$ (4,564)
Balance at beginning (in shares) at Dec. 31, 2017	5,000,000		226,400
Issuance of treasury stock as founders' stock (in shares)			75,467	(75,467)
Issuance of stock		$ 8,787
Issuance of stock (in shares)		17,653,333
Accretion of redeemable convertible preferred stock to redemption value	$ 70					70	70
Net loss and comprehensive loss						(9,094)	(9,094)
Balance at ending at Jun. 30, 2018	$ 13,857					(13,728)	(13,728)
Balance at ending (in shares) at Jun. 30, 2018	22,653,333		226,400
Repurchase of founders' stock (in shares)			(75,467)	75,467
Balance at beginning at Dec. 31, 2018	$ 124,728		$ 0		$ 36,646	(86,565)	(49,919)
Balance at beginning (in shares) at Dec. 31, 2018	64,730,410		238,986
Conversion of convertible preferred stock into common stock upon closing of initial public offering	$ (124,728)		$ 2		124,726		124,728
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)	(64,730,410)		21,056,136
Issuance of stock			$ 1		95,452		95,453
Issuance of stock (in shares)			6,612,500
Issuance of restricted common stock upon early exercise of stock options (in shares)			487,933
Exercise of stock options					100		$ 100
Exercise of stock options (in shares)			159,824				647,757
Stock-based compensation expense					617		$ 617
Net loss and comprehensive loss						(12,590)	(12,590)
Balance at ending at Jun. 30, 2019			$ 3		$ 257,541	$ (99,155)	$ 158,389
Balance at ending (in shares) at Jun. 30, 2019			28,555,379

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss		$ (12,590)	$ (9,094)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense		617
Shares issued in connection with Amgen Agreement			1,353
Acquisition of technology in connection with Amgen Agreement			5,000
Issuance date fair-value of anti-dilution liability			1,639
Change in fair value of anti-dilution right liability	$ 11		11
Changes in operating assets and liabilities:
Prepaid expenses and other assets		697	15
Accounts payable		317	455
Accrued expenses and other current liabilities		193	32
Net cash used in operating activities		(10,766)	(589)
CASH FLOWS FROM INVESTING ACTIVITIES
Acquisition of technology in connection with Amgen Agreement			(5,000)
Net cash used in investing activities			(5,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs			14,784
Proceeds from issuance of common stock in initial public offering, net of issuance costs and underwriting fees		97,080
Proceeds from the early exercise of stock options in exchange for restricted common stock		300
Proceeds from exercise of stock options		100
Net cash provided by financing activities		97,480	14,784
Net increase in cash, cash equivalents and restricted cash		86,714	9,195
Cash and restricted cash at beginning of period		76,000	618
Cash, cash equivalents and restricted cash at end of period	9,813	162,714	9,813
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Conversion of convertible preferred stock into common stock upon closing of initial public offering		124,728
Accretion of redeemable convertible preferred stock to redemption value	$ 70		70
Issuance date fair value of preferred stock tranche obligation			7,350
Deferred offering costs included in accounts payable and accrued expenses and other current liabilities		$ 1,628
Common stock issued in connection with Amgen Agreement			$ 1,353

Nature of the business and basis of presentation	6 Months Ended
Nature of the business and basis of presentation	Jun. 30, 2019
Nature of the business and basis of presentation
Nature of the business and basis of presentation	1. Nature of the business and basis of presentation Akero Therapeutics, Inc., together with its wholly-owned subsidiary Akero Securities Corporation, (“Akero” or the “Company”) is a clinical-stage biotechnology company focused on developing and commercializing transformative treatments for patients with serious metabolic diseases. Akero’s initial focus is on nonalcoholic steatohepatitis (“NASH”), a disease without any approved therapies. NASH is a severe form of nonalcoholic fatty liver disease (“NAFLD”), characterized by inflammation and fibrosis in the liver that can progress to cirrhosis, liver failure, liver cancer and death. We are developing AKR‑001, an analog of fibroblast growth factor 21 (“FGF21”), for NASH and began dosing patients for a Phase 2a clinical trial (BALANCED) of AKR‑001 in July 2019. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, ability to secure additional capital to fund operations, completion and success of clinical testing, compliance with governmental regulations, development by competitors of new technological innovations, dependence on key personnel and protection of proprietary technology. AKR‑001 will require extensive clinical testing prior to regulatory approval and commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Basis of presentation The accompanying condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company after elimination of all intercompany accounts and transactions. All adjustments necessary for the fair presentation of the Company’s condensed consolidated financial statements for the periods have been presented. The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2018, included in the Company’s registration statement on Form S‑1 relating to our initial public offering (“IPO”), (File No. 333‑231747) dated and filed on May 24, 2019 with the U.S. Securities and Exchange Commission ( the “SEC”) as amended (the “Registration Statement”). Since the date of those financial statements, there have been no changes to the Company’s significant accounting policies. Initial public offering On June 19, 2019, the Registration Statement became effective. The IPO closed on June 24, 2019 at which time the Company issued 6,612,500 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 862,500 additional shares of common stock, at a public offering price of $16.00 per share. The Company received $98,394, net of underwriting discounts and commissions, but before deducting offering costs payable by the Company, which were $2,942. Upon the closing of the IPO, all outstanding shares of redeemable convertible preferred stock converted into 21,056,136 shares of common stock (see Note 4). In connection with the completion of its IPO in June 2019, the Company amended its certificate of incorporation to authorize the issuance of up to 150,000,000 shares of $0.0001 par value common stock and 10,000,000 shares of $0.0001 par value preferred stock designated as undesignated preferred stock. Reverse stock split On June 6, 2019, the Company effected a one-for-3.07418 reverse stock split of the Company’s common stock. All common stock, stock options and per share information presented in the unaudited condensed consolidated financial statements have been adjusted to reflect the reverse stock split on a retroactive basis for all periods presented. There was no change in the par value of the Company’s common stock. The ratio by which shares of preferred stock are convertible into shares of common stock was adjusted to reflect the effects of the reverse stock split. Going concern In accordance with Accounting Standards Update (“ASU”) No. 2014‑15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205‑40), the Company has evaluated whether there are certain conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the condensed consolidated financial statements are issued. Since its inception, the Company has funded its operations primarily with proceeds from sales of redeemable convertible preferred stock and most recently with proceeds from the IPO. The Company has incurred recurring losses since its inception, including a net loss of $7,228 and $8,673 for the three months ended June 30, 2019 and 2018, respectively and net losses of $12,590 and $9,094 for the six months ended June 30, 2019 and 2018, respectively. In addition, as of June 30, 2019, the Company had an accumulated deficit of $99,155. The Company expects to continue to generate operating losses for the foreseeable future. As of August 12, 2019, the issuance date of these condensed consolidated financial statements, the Company expects that its existing cash and cash equivalents of $162,654 as of June 30, 2019, will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of these condensed consolidated financial statements. The Company expects that it will require additional funding beyond this time to complete the clinical development of AKR‑001, commercialize AKR‑001, if it receives regulatory approval, and pursue in-licenses or acquisitions of other product candidates. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Summary of significant accounting policies

6 Months Ended

Jun. 30, 2019

Summary of significant accounting policies

Summary of significant accounting policies

2. Summary of significant accounting policies

Unaudited interim financial statements

The accompanying unaudited condensed consolidated financial statements have been prepared by the Company in accordance with GAAP for interim financial reporting and as required by Regulation S-X, Rule 10‑01. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair statement of the Company’s financial position as of June 30, 2019 and the results of its operations and its cash flows for the three and six months ended June 30, 2019 and 2018 and the condensed consolidated statement of stockholders’ equity (deficit) as of June 30, 2019. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2019 and 2018 are unaudited. The results for the three and six months ended June 30, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year or period.

Use of estimates

The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuations of common stock, preferred stock tranche obligation, anti-dilution right liability and the valuation allowance for deferred tax assets.

Cash and cash equivalents

The Company classifies as cash and cash equivalents amounts on deposit in banks and cash invested temporarily in various instruments, primarily money market accounts, with original maturities of three months or less at the time of purchase. The carrying amounts reported in the condensed consolidated balance sheet represents the fair values of cash and cash equivalents.

Restricted cash

As of December 31, 2018 and June 30, 2019, the Company was required to maintain a separate cash balance of $20 and $40, respectively, to collateralize corporate credit cards with a bank, which was classified as restricted cash (non-current) on its condensed consolidated balance sheets.

As of December 31, 2018, the Company was required to maintain a separate cash balance of $5 for the benefit of the landlord in connection with the Company’s office space lease in California (the “Lease”), which is classified as other current assets on its condensed consolidated balance sheets. As of June 30, 2019, in connection with the First Amendment to the Lease, the Company was required to maintain a separate cash balance of $20 for the benefit of the landlord in connection with the Lease, which was classified as restricted cash (non-current) on its condensed consolidated balance sheets (see Note 10).

Deferred offering costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process preferred stock or common stock equity financings as deferred offering costs until such financings are consummated. As of December 31, 2018, the Company recorded deferred offering costs of $361 in the accompanying condensed consolidated balance sheets. As of June 30, 2019, the Company did not have any deferred offering costs recorded.

Fair value measurements

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

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

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Stock-based compensation

The Company measures all stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company accounts for forfeitures as they occur. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model. Prior to our initial public offering, the exercise price for all stock options granted was at the estimated fair value of the underlying common stock as determined on the date of grant by the Company’s Board of Directors

Anti-dilution right liability

The Company classified the anti-dilution right under its license agreement with Amgen Inc. (“Amgen”) (see Note 7) as a derivative liability on its condensed consolidated balance sheets as the anti-dilution right represented a freestanding financial instrument that required the Company to transfer equity instruments upon future equity closings. The anti-dilution right liability was initially recorded at fair value upon the date of issuance and was subsequently remeasured to fair value at each reporting date.

In November 2018, in connection with the Company’s issuance and sale of Series A Preferred Stock, the Company satisfied its anti-dilution right under the Amgen Agreement (as discussed in Note 7 below).

Classification and accretion of redeemable convertible preferred stock

The Company classified its redeemable convertible preferred stock outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company. Costs incurred in connection with the issuance of redeemable convertible preferred stock, as well as the recognition of the preferred stock tranche obligation, were recorded as a reduction of gross proceeds from issuance. The net carrying value of redeemable convertible preferred stock were accreted to their redemption values through a charge to additional paid-in capital or accumulated deficit over the period from date of issuance to the earliest date on which the holders could, at their option, elect to redeem their shares. In December 2018, in connection with the Company’s issuance and sale of Series B Preferred Stock, the Company terminated the redemption rights associated with the Series A Preferred Stock that allowed the holders, at their option, to elect to redeem their shares at a specified date. Accordingly, the Company ceased accreting the net carrying value of the Series A redeemable convertible preferred stock to the redemption value.

Emerging growth company

The Company is an emerging growth company as defined in the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”). Under the JOBS Act, companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected this exemption to delay adopting new or revised accounting standards until such time as those standards apply to private companies. Where allowable, the Company has early adopted certain standards as described below.

Recently issued accounting pronouncements not yet adopted

In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842) (“ASU 2016‑02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases today. ASU 2016‑02 is effective for the Company for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years, and early adoption is permitted. The Company is in the process of completing its review of its existing lease agreements under ASC 842 and does not expect the adoption of ASU 2016‑02 to have a material impact on its financial position, results of operations or cash flows.

In July 2017, the FASB issued ASU No. 2017‑11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) (Part I) Accounting for Certain Financial Instruments with Down Round Features (Part 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 (“ASU 2017‑11”). Part I applies to entities that issue financial instruments such as warrants, convertible debt or convertible preferred stock that contain down-round features. Part II replaces the indefinite deferral for certain mandatorily redeemable noncontrolling interests and mandatorily redeemable financial instruments of non-public entities contained within Accounting Standards Codification (“ASC”) Topic 480 with a scope exception and does not impact the accounting for these mandatorily redeemable instruments. ASU 2017‑11 is effective for the Company for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years. The Company is currently evaluating the impact that the adoption of ASU 2017‑11 will have on its consolidated financial statements.

In August 2018, the FASB issued No. ASU 2018‑13, Fair Value Measurement (Topic 820)—Disclosure Framework (“ASU 2018‑13”), which improves the disclosure requirements for fair value measurements. For non-public entities, ASU 2018‑13 is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for any removed or modified disclosures. The Company is currently evaluating the impact that the adoption of ASU 2018‑13 will have on its consolidated financial statements.

Redeemable convertible preferred stock

6 Months Ended

Jun. 30, 2019

Redeemable convertible preferred stock

Redeemable convertible preferred stock

4. Redeemable convertible preferred stock

Upon completion of our IPO on June 24, 2019, all outstanding shares of our redeemable convertible preferred stock were converted into 21,056,136 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. Accordingly, there were no shares of redeemable convertible preferred stock outstanding as of June 30, 2019.

As of December 31, 2018, redeemable convertible preferred stock consisted of the following:


		Preferred
	Preferred	stock					Common stock
	stock	issued and	Carrying		Liquidation		issuable upon
	authorized	outstanding	value		preference		conversion
Series A Preferred Stock	50,858,462	50,858,462	$	79,457	$	50,858	50,858,462
Series B Preferred Stock	13,871,948	13,871,948	$	45,271	$	45,500	13,871,948
	64,730,410	64,730,410	$	124,728	$	96,358	64,730,410

Stockholder's equity (deficit)

6 Months Ended

Jun. 30, 2019

Stockholder's equity (deficit)

Stockholder's equity (deficit)

5. Stockholder’s equity (deficit)

Common stock

As of June 30, 2019 and December 31, 2018, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 shares and 75,000,000 shares of $0.0001 par value common stock, respectively. The voting, dividend and liquidation rights of the holders of the Company’s common stock were subject to and qualified by the rights, powers and preferences of the holders of the redeemable convertible preferred stock set forth in the Company’s audited annual consolidated financial statements and related notes included in the Registration Statement.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. The holders of common stock, voting exclusively and as a separate class, are entitled to elect one director of the Company. Common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any, subject to the preferential dividend rights of redeemable convertible preferred stock. Through June 30, 2019, no cash dividends had been declared or paid.

On June 24, 2019, the Company completed its IPO at which time the Company issued 6,612,500 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 862,500 additional shares of common stock, at a public offering price of $16.00 per share. The Company received $98,394, net of underwriting discounts and commissions, but before deducting offering costs payable by the Company, which were $2,942. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 21,056,136 shares of common stock (see Note 4). As of June 30, 2019 and December 31, 2018, there were 28,555,379 and 238,986 shares of common stock issued and outstanding, respectively.

The following shares of common stock were reserved for issuance as follows:


	June 30, 2019	December 31, 2018
Conversion of outstanding shares of preferred stock	—	21,056,136
Options outstanding under the 2018 Stock Option and Grant Plan	2,303,982	1,839,913
Options outstanding under the 2019 Stock Option and Incentive Plan	116,526	—
Options available for future grant	2,455,931	1,219,461
2019 Employee Stock Purchase Plan	273,869	—
	5,150,308	24,115,510

Undesignated preferred stock

As of June 30, 2019, the Company’s fourth amended and restated certificate of incorporation authorized the Company to issue up to 10,000,000 shares of undesignated preferred stock, par value $0.0001 per share. There were no undesignated preferred shares issued or outstanding as of June 30, 2019.

Restricted common stock

In March 2017, the Company issued an aggregate of 226,400 shares of restricted common stock under restricted stock agreements with the founders. Pursuant to the terms of the agreements, the restricted common stock was initially subject to a vesting schedule over a four-year period commencing in January 2017 and culminating in January 2021. During the vesting period, the Company has the right to repurchase up to all unvested shares at the amount paid if the relationship between the recipient and the Company ceases. Subject to the continued employment or other business relationship with the Company, all of the restricted common stock becomes fully vested within four years of the date of issuance.

In October 2017, 75,467 shares of restricted common stock were subject to repurchase by the Company when one of the founders terminated his relationship with the Company. The Company repurchased the shares in March 2018 for an immaterial amount and immediately reissued the shares to the remaining founders. In connection with the repurchase and reissuance of the shares, the Company amended the restricted stock agreements with the remaining founders such that the restricted common stock is now subject to a vesting schedule over a two-year period commencing in May 2018 and culminating in June 2020.

The Company accounted for the acceleration of vesting under the amended restricted stock agreement as a modification of the original awards and recognized the remaining unvested shares prospectively over the revised vesting period. The total fair value of restricted stock vested during the three and six months ended June 30, 2019 was insignificant.

In April and June 2019, the Company amended certain option grant agreements granted under the Company’s 2018 Stock Option and Grant Plan to allow the holders the right to early exercise unvested options, subject to a repurchase right held by the Company equal to the lesser of the original exercise price per share or the fair value of the shares on the repurchase date. The unvested shares issued as a result of the early exercise are deemed restricted stock pursuant to a restricted stock agreement and a vesting schedule identical to the vesting schedule of the original grant agreement. The proceeds related to unvested restricted common stock are recorded as liabilities until the stock vests, at which point they are reclassified to additional paid-in capital. Common shares issued for the early exercise of options are included in issued and outstanding shares. As of June 30, 2019, there were 487,933 shares of unvested restricted common stock that had been early exercised and were subject to repurchase.

The following table summarizes restricted stock activity since December 31, 2018:


		Grant-Date Fair
	Number of Shares	Value
Unvested restricted common stock as of December 31, 2018	80,190	$	—
Early exercise of unvested stock options	487,933		435
Vested	(28,296)		—
Unvested restricted common stock as of June 30, 2019	539,827	$	435

As of June 30, 2019, there were 539,827 shares of unvested restricted common stock consisting of 51,894 shares from unvested restricted common stock awards under restricted stock agreements with the founders and 487,933 shares from the early exercise of stock options.

Stock-based awards

6 Months Ended

Jun. 30, 2019

Stock-based awards

Stock-based awards

6. Stock-based awards

2018 Stock option and grant plan

The Company’s 2018 Stock Option and Grant Plan (the “2018 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards and other stock-based awards to employees, directors and consultants of the Company. The 2018 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

The total number of shares of common stock that could have been issued under the 2018 Plan was 3,071,960 shares, of which 107,635 shares remained available for grant on June 18, 2019, the date that the Company’s 2019 Stock Option and Incentive Plan (the “2019 Plan”) became effective. Upon the effectiveness of the 2019 Plan, the 107,635 remaining shares available under the 2018 Plan were transferred and became available for issuance under the 2019 Plan. Shares of common stock underlying outstanding awards under the 2018 Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) will be added to the shares of common stock available for issuance under the 2019 Plan.

2019 Stock option and incentive plan

The 2019 Plan was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 Plan became effective on June 18, 2019 and replaced the Company’s 2018 Plan on that date. The 2019 Plan allows the board of directors or the compensation committee of the board of directors to make equity-based incentive awards to the Company’s officers, employees, directors or other key persons (including consultants). The number of shares initially reserved for issuance under the 2019 Plan is 2,572,457, which includes the 107,635 shares transferred from the 2018 Plan, and shall be cumulatively increased on January 1, 2020 and each January 1 thereafter by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors.

The 2019 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. All incentive options granted to any person possessing more than 10% of the total combined voting power of all classes of shares may not have an exercise price of less than 110% of the fair market value of the common stock on the grant date. Stock options granted to employees, officers, members of the board of directors and consultants will typically vest over a four-year period.

Shares that are expired, terminated, surrendered or canceled under the 2019 Plan without having been fully exercised will be available for future awards.

2019 Employee stock purchase plan

The 2019 Employee Stock Purchase Plan (the “2019 ESPP”) was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 ESPP became effective on June 18, 2019, at which time 273,869 shares were reserved for issuance. The 2019 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2020 and each January 1 thereafter through January 1, 2029, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 410,803 shares or (iii) such number of shares as determined by the compensation committee.

Stock option valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees, directors and consultants were as follows, presented on a weighted average basis:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019			2018	2019			2018
Expected term (in years)		6.07		n/a		6.04		n/a
Volatility		71.20	%	n/a		69.80	%	n/a
Risk-free interest rate		2.28	%	n/a		2.39	%	n/a
Dividend yield		0.00	%	n/a		0.00	%	n/a
Weighted average fair value of common stock	$	9.72		n/a	$	8.26		n/a

Stock options

The following table summarizes the Company’s stock option activity since December 31, 2018:


		Weighted-		Weighted-
		Average		Average
		Exercise		remaining	Aggregate
	Number	Price per		contractual	Intrinsic
	of Options	Share		term (years)	Value
Balance Outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,228,352	$	7.61
Options exercised	(647,757)	$	0.62
Balance Outstanding, June 30, 2019	2,420,508	$	4.17	9.48	$	36,271
Exercisable, June 30, 2019	23,691	$	4.17	9.42	$	352
Vested and expected to vest, June 30, 2019	2,420,508	$	4.29	9.48	$	36,271

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

The weighted average grant-date fair value per share of stock options granted during the three and six months ended June 30, 2019 was $5.41 and $4.85.

Stock-based compensation

The Company did not grant any options as of June 30, 2018 and accordingly did not record any stock-based compensation expense for the three and six months ended June 30, 2018. The Company recorded total stock-based compensation for options granted for the three and six months ended June 30, 2019 of $402 and $617, with $94 and $176 classified as research and development expense and $308 and $441 classified as general and administrative expense, respectively, in the condensed consolidated statements of operations and comprehensive loss.

As of June 30, 2019, total unrecognized compensation cost related to the unvested stock-based awards was $6,702, which is expected to be recognized over a weighted average period of 3.35 years.

In April and June 2019, certain option holders early exercised options to purchase 487,933 shares of common stock, at an exercise price of $0.61 per share, for cash proceeds of $300 (See Note 5). Stock-based compensation expense related to these options will continue to be recognized over the requisite service period of the awards based on the grant-date fair value which was determined using the Black-Scholes option-pricing model.

Net loss per share

6 Months Ended

Jun. 30, 2019

Net loss per share

Net loss per share

9. Net loss per share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Numerator:
Net loss	$	(7,228)	$	(8,673)	$	(12,590)	$	(9,094)
Accretion of redeemable convertible preferred stock to redemption value		—		(70)		—		(70)
Net loss attributable to common stockholders, basic and diluted	$	(7,228)	$	(8,743)	$	(12,590)	$	(9,164)
Denominator:
Weighted average common shares outstanding, basic and diluted		3,268,390		92,171		1,726,795		66,422
Net loss per share attributable to common stockholders, basic and diluted	$	(2.21)	$	(94.86)	$	(7.29)	$	(137.97)

The Company excluded 56,765 shares and 134,229 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share attributable to common stockholders for the three months ended June 30, 2019 and 2018, respectively, because those shares had not vested. The Company excluded 63,801 shares and 159,878 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share attributable to common stockholders for the six months ended June 30, 2019 and 2018, respectively, because those shares had not vested.

The Company’s potentially dilutive securities, which include stock options, unvested restricted common stock and redeemable convertible preferred stock, have been excluded from the computation of diluted net loss per share attributable to common stockholders as the effect would be to reduce the net loss per share. 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 each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	Three and six months ended
	June 30,
	2019	2018
Options to purchase common stock	2,420,508	—
Unvested restricted stock	539,827	108,486
Redeemable convertible preferred stock (as converted to common stock)	—	7,368,894
Total	2,960,335	7,477,380

Summary of significant accounting policies (Policies)

6 Months Ended

Jun. 30, 2019

Summary of significant accounting policies

Unaudited interim financial statements

Use of estimates

Cash and cash equivalents

Restricted cash

Deferred offering costs

Fair value measurements

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

Stock-based compensation

Anti-dilution right liability

Classification and accretion of redeemable convertible preferred stock

Emerging growth company

Recently issued accounting pronouncements not yet adopted

Redeemable convertible preferred stock (Tables)

6 Months Ended

Jun. 30, 2019

Redeemable convertible preferred stock

Schedule of redeemable convertible preferred stock


		Preferred
	Preferred	stock					Common stock
	stock	issued and	Carrying		Liquidation		issuable upon
	authorized	outstanding	value		preference		conversion
Series A Preferred Stock	50,858,462	50,858,462	$	79,457	$	50,858	50,858,462
Series B Preferred Stock	13,871,948	13,871,948	$	45,271	$	45,500	13,871,948
	64,730,410	64,730,410	$	124,728	$	96,358	64,730,410

Stockholder's equity (deficit) (Tables)

6 Months Ended

Jun. 30, 2019

Stockholder's equity (deficit)

Schedule of common stock reserved for issuance


	June 30, 2019	December 31, 2018
Conversion of outstanding shares of preferred stock	—	21,056,136
Options outstanding under the 2018 Stock Option and Grant Plan	2,303,982	1,839,913
Options outstanding under the 2019 Stock Option and Incentive Plan	116,526	—
Options available for future grant	2,455,931	1,219,461
2019 Employee Stock Purchase Plan	273,869	—
	5,150,308	24,115,510

Summary of restricted stock activity

The following table summarizes restricted stock activity since December 31, 2018:


		Grant-Date Fair
	Number of Shares	Value
Unvested restricted common stock as of December 31, 2018	80,190	$	—
Early exercise of unvested stock options	487,933		435
Vested	(28,296)		—
Unvested restricted common stock as of June 30, 2019	539,827	$	435

Stock-based awards (Tables)

6 Months Ended

Jun. 30, 2019

Stock-based awards

Schedule of assumptions used to determine grant-date fair value of stock options granted


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019			2018	2019			2018
Expected term (in years)		6.07		n/a		6.04		n/a
Volatility		71.20	%	n/a		69.80	%	n/a
Risk-free interest rate		2.28	%	n/a		2.39	%	n/a
Dividend yield		0.00	%	n/a		0.00	%	n/a
Weighted average fair value of common stock	$	9.72		n/a	$	8.26		n/a

Summary of stock option activity


		Weighted-		Weighted-
		Average		Average
		Exercise		remaining	Aggregate
	Number	Price per		contractual	Intrinsic
	of Options	Share		term (years)	Value
Balance Outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,228,352	$	7.61
Options exercised	(647,757)	$	0.62
Balance Outstanding, June 30, 2019	2,420,508	$	4.17	9.48	$	36,271
Exercisable, June 30, 2019	23,691	$	4.17	9.42	$	352
Vested and expected to vest, June 30, 2019	2,420,508	$	4.29	9.48	$	36,271

Net loss per share (Tables)

6 Months Ended

Jun. 30, 2019

Net loss per share

Schedule of basic and diluted net loss per share attributable to common stockholders


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Numerator:
Net loss	$	(7,228)	$	(8,673)	$	(12,590)	$	(9,094)
Accretion of redeemable convertible preferred stock to redemption value		—		(70)		—		(70)
Net loss attributable to common stockholders, basic and diluted	$	(7,228)	$	(8,743)	$	(12,590)	$	(9,164)
Denominator:
Weighted average common shares outstanding, basic and diluted		3,268,390		92,171		1,726,795		66,422
Net loss per share attributable to common stockholders, basic and diluted	$	(2.21)	$	(94.86)	$	(7.29)	$	(137.97)

Schedule of computation of diluted net loss per share attributable to common stockholders


	Three and six months ended
	June 30,
	2019	2018
Options to purchase common stock	2,420,508	—
Unvested restricted stock	539,827	108,486
Redeemable convertible preferred stock (as converted to common stock)	—	7,368,894
Total	2,960,335	7,477,380

Nature of the business and basis of presentation (Details) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 06, 2019	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares
Subsidiary, Sale of Stock
Common stock issued (in shares)			28,555,379		28,555,379		238,986
Authorized common stock (in shares)			150,000,000		150,000,000		75,000,000
Par value common stock (in dollars per share) \| $ / shares			$ 0.0001		$ 0.0001		$ 0.0001
Reverse stock split of the common stock		3.07418
Net loss \| $			$ 7,228	$ 8,673	$ 12,590	$ 9,094
Accumulated deficit \| $			99,155		99,155		$ 86,565
Cash and cash equivalents \| $			$ 162,654		$ 162,654		$ 75,975
IPO
Subsidiary, Sale of Stock
Common stock issued (in shares)	6,612,500
Public offering price (in dollars per share) \| $ / shares	$ 16.00
Proceeds from issuing shares \| $	$ 98,394
Offering costs \| $	$ 2,942
Conversion of convertible preferred stock into common stock	21,056,136
Authorized common stock (in shares)	150,000,000
Par value common stock (in dollars per share) \| $ / shares	$ 0.0001
Authorized Preferred stock (in shares)	10,000,000
Par value preferred stock (in dollars per share) \| $ / shares	$ 0.0001
Over allotment
Subsidiary, Sale of Stock
Proceeds from issuing shares \| $	$ 98,394
Over allotment \| Maximum
Subsidiary, Sale of Stock
Common stock issued (in shares)	862,500

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued expenses and other current liabilities
Accrued employee compensation and benefits	$ 563	$ 304
Accrued external research and development expenses	580	430
Accrued legal and professional fees	66	106
Liability for early exercise of stock options and restricted stock	261
Other	22	129
Total	$ 1,492	$ 969

Redeemable convertible preferred stock (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 24, 2019	Dec. 31, 2018	Jun. 30, 2019
Temporary Equity
Redeemable convertible preferred stock outstanding		64,730,410	0
Preferred stock authorized		64,730,410	0
Preferred stock issued and outstanding		64,730,410
Carrying value		$ 124,728
Liquidation preference		$ 96,358
Common stock issuable upon conversion		64,730,410
IPO
Temporary Equity
Number of shares converted	21,056,136
Redeemable convertible preferred stock outstanding			0
Series A Preferred Stock
Temporary Equity
Preferred stock authorized		50,858,462
Preferred stock issued and outstanding		50,858,462
Carrying value		$ 79,457
Liquidation preference		$ 50,858
Common stock issuable upon conversion		50,858,462
Series B Preferred Stock
Temporary Equity
Preferred stock authorized		13,871,948
Preferred stock issued and outstanding		13,871,948
Carrying value		$ 45,271
Liquidation preference		$ 45,500
Common stock issuable upon conversion		13,871,948

Stockholder's equity (deficit) - Common stock (Details) $ / shares in Units, $ in Thousands			6 Months Ended
	Jun. 30, 2019 $ / shares shares	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 30, 2019 Vote $ / shares shares	Jun. 18, 2019 shares	Dec. 31, 2018 $ / shares shares
Class of Stock
Common stock, shares authorized	150,000,000		150,000,000		75,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001		$ 0.0001		$ 0.0001
Number of votes per share \| Vote			1
Cash dividend declared \| $ / shares	0
Cash dividend paid \| $ / shares	$ 0
Common stock, shares issued	28,555,379		28,555,379		238,986
Offering costs \| $		$ 2,942
Common stock, shares outstanding	28,555,379		28,555,379		238,986
Common stock were reserved for issuance
Options available for future grant	5,150,308		5,150,308		24,115,510
Options
Common stock were reserved for issuance
Options available for future grant	2,455,931		2,455,931		1,219,461
2018 Stock option and grant plan
Common stock were reserved for issuance
Options available for future grant	2,303,982		2,303,982	107,635	1,839,913
2019 Stock Option and Incentive plan [Member]
Common stock were reserved for issuance
Options available for future grant	116,526		116,526
2019 Employee Stock Purchase Plan
Common stock were reserved for issuance
Options available for future grant	273,869		273,869
Redeemable convertible preferred stock (as converted to common stock)
Class of Stock
Number of shares converted		21,056,136	(64,730,410)
Common stock were reserved for issuance
Options available for future grant					21,056,136
IPO
Class of Stock
Common stock, shares authorized		150,000,000
Common stock, par value (in dollars per share) \| $ / shares		$ 0.0001
Common stock, shares issued		6,612,500
Proceeds received, net of underwriting discounts and commissions \| $		$ 98,394
Number of shares converted		21,056,136
Over allotment
Class of Stock
Public offering price \| $ / shares		$ 16.00
Proceeds received, net of underwriting discounts and commissions \| $		$ 98,394
Over allotment \| Maximum
Class of Stock
Common stock, shares issued		862,500

Stockholder's equity (deficit) - Undesignated preferred stock and Restricted common stock (Details) - $ / shares	1 Months Ended				6 Months Ended
	Jun. 30, 2019	Apr. 30, 2019	Oct. 31, 2017	Mar. 31, 2017	Jun. 30, 2019
Common Stock
Class of Stock
Issuance of restricted common stock upon early exercise of stock options (in shares)	487,933	487,933			487,933
Restricted stock
Class of Stock
Shares issued (in shares)				226,400
Stock options vesting period			2 years	4 years
Number of shares subject to be repurchased			75,467
Undesignated Preferred Stock
Class of Stock
Preferred stock, par value (in dollars per share)	$ 0.0001				$ 0.0001
Preferred stock, Shares Issued	0				0
Preferred stock, Shares Outstanding	0				0
Undesignated Preferred Stock \| Maximum
Class of Stock
Preferred stock, shares authorized	10,000,000				10,000,000

Stock-based awards (Details) - shares		1 Months Ended
Stock-based awards (Details) - shares	Jun. 18, 2019	Jun. 30, 2019	Dec. 31, 2018
Share-based awards
Number of shares remained available for grant		5,150,308	24,115,510
2018 Stock option and grant plan
Share-based awards
Number of shares of common stock issued	3,071,960
Number of shares remained available for grant	107,635	2,303,982	1,839,913
Stock Options And Grant Plan 2019 [Member]
Share-based awards
Number of shares remained available for grant	107,635
Number of shares initially reserved for issuance		2,572,457
Percent of shares reserved and available for issuance automatically increase annually on January 1		4.00%
Stock options vesting period		4 years
2019 Employee stock purchase plan
Share-based awards
Number of shares initially reserved for issuance	273,869
Percent of shares reserved and available for issuance automatically increase annually on January 1		1.00%
Number of shares reserved and available for issuance automatically increase annually on January 1 (in shares)		410,803
Maximum \| Stock Options And Grant Plan 2019 [Member]
Share-based awards
Term of stock option		10 years

Stock based awards - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
	Dec. 31, 2018	Jun. 30, 2019	Jun. 30, 2019
Number of options
Balance Outstanding, Beginning of the period (in shares)			1,839,913
Options granted ( in shares)			1,228,352
Options exercised ( in shares)			(647,757)
Balance Outstanding, End of the period (in shares)	1,839,913	2,420,508	2,420,508
Exercisable ( in shares)		23,691	23,691
Vested and expected to vest ( in shares)		2,420,508	2,420,508
Weighted-Average Exercise Price per Share
Weighted-average exercise price, Beginning of the period (in dollars per share)			$ 0.61
Weighted-average exercise price, Granted (in dollars per share)			7.61
Weighted-average exercise price, Exercised (in dollars per share)			0.62
Weighted-average exercise price, End of the period (in dollars per share)	$ 0.61	$ 4.17	4.17
Weighted-average exercise price, Exercisable ( in dollars per share )		4.17	4.17
Weighted-average exercise price, Vested and expected to vest at end of the period (in dollars per share)		$ 4.29	$ 4.29
Weighted-Average remaining contractual term (years) and Aggregate Intrinsic Value
Weighted-average remaining contractual term outstanding (in years)	9 years 8 months 27 days		9 years 5 months 23 days
Weighted-average remaining contractual term , Options Exercisable(in years)			9 years 5 months 1 day
Weighted-average remaining contractual term vested and expected to vest (in years)			9 years 5 months 23 days
Aggregate Intrinsic Value Balance outstanding	$ 10,577	$ 36,271	$ 36,271
Aggregate Intrinsic Value Exercisable		352	352
Aggregate Intrinsic Value Vested and Expected to vest		$ 36,271	$ 36,271
Weighted average grant-date fair value per share of stock options granted		$ 5.41	$ 4.85

Stock based awards - Stock-based compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2019	Apr. 30, 2019	Jun. 30, 2019	Jun. 30, 2019
Stock-based compensation
Total stock based compensation for options granted			$ 402	$ 617
Total unrecognized compensation cost related to unvested stock-based awards	$ 6,702		6,702	$ 6,702
Weighted average period of recognition for unrecognized compensation cost				3 years 4 months 6 days
Proceeds from the early exercise of stock options in exchange for restricted common stock				$ 300
Common Stock
Stock-based compensation
Issuance of restricted common stock upon early exercise of stock options (in shares)	487,933	487,933		487,933
Exercise price of common stock purchase	$ 0.61	$ 0.61
Proceeds from the early exercise of stock options in exchange for restricted common stock	$ 300	$ 300
Research and Development Expense
Stock-based compensation
Total stock based compensation for options granted			94	$ 176
General and Administrative Expense
Stock-based compensation
Total stock based compensation for options granted			$ 308	$ 441

Amgen license agreement (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
Amgen license agreement (Details) - USD ($)	Nov. 30, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued value under agreement					$ 95,453,000
Loss recognized related to change in fair value of the anti-dilution right liability prior to extinguishment				$ (11,000)		$ (11,000)
Research and development expense			$ 5,960,000	$ 8,420,000	10,023,000	8,646,000
Upfront cash payment						5,000,000
Fair value of issuance of the anti-dilution right liability						$ 1,639,000
Amgen Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Initial fair value of the anti-dilution right liability	$ 7,404,000
Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Ownership interest of the outstanding shares (as a percent)		10.00%		10.00%		10.00%
Amgen Agreement \| Research and Development Expense
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Initial fair value of the anti-dilution right liability		$ 1,639,000
Research and development expense				$ 7,992,000		$ 7,992,000
Upfront cash payment			5,000,000		5,000,000
Fair value of shares of Series A Preferred Stock issued to Amgen			1,353,000		1,353,000
Fair value of issuance of the anti-dilution right liability			$ 1,639,000		$ 1,639,000
Amgen Agreement \| Other expense
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Loss recognized related to change in fair value of the anti-dilution right liability prior to extinguishment		11,000
Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront payment		5,000,000
Total consideration transferred to Amgen		$ 6,353,000
Amgen Agreement \| Series A Preferred Stock
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued value under agreement	$ 3,205,128
Amgen Agreement \| Series A Preferred Stock \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued under agreement		2,653,333
Share Issued value under agreement		$ 1,353,000

Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss	$ (7,228)	$ (8,673)	$ (12,590)	$ (9,094)
Accretion of redeemable convertible preferred stock to redemption value		(70)		(70)
Net loss attributable to common stockholders, basic and diluted	$ (7,228)	$ (8,743)	$ (12,590)	$ (9,164)
Denominator:
Weighted average common shares outstanding, basic and diluted	3,268,390	92,171	1,726,795	66,422
Net loss per share attributable to common stockholders, basic and diluted	$ (2.21)	$ (94.86)	$ (7.29)	$ (137.97)
Number of weighted average restricted common stock	56,765,000	134,229,000	63,801,000	159,878,000

- Definition

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

+ References + Details

Condensed Consolidated Statements of Redeemable Preferred Stock and Stockholders' Equity (Deficit) - Parenthetical - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidated Statements of Redeemable Preferred Stock and Stockholders' Equity (Deficit)
Net issuance costs and underwriting fees	$ 10,348
Net Issuance cost		$ 216

Amgen license agreement	6 Months Ended
Amgen license agreement	Jun. 30, 2019
Amgen license agreement
Amgen license agreement	7. Amgen license agreement In June 2018, the Company entered into a license agreement (the “Amgen Agreement”) with Amgen pursuant to which the Company was granted an exclusive license to certain patents and intellectual property related to a long-acting FGF21 analog in order to commercially develop, manufacture, use and distribute FGF21 as a treatment for NASH and other serious metabolic diseases. The Amgen Agreement provides the Company with exclusive global rights to the licensed products and the right to grant sublicenses that cover AKR‑001 to third parties. In exchange for these rights, the Company made an upfront payment of $5,000 and issued 2,653,333 shares of Series A Preferred Stock with a fair value of $1,353 to Amgen. The total consideration transferred to Amgen under the agreement of $6,353 is included within research and development expense in the condensed consolidated statements of operations and comprehensive loss. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the total consideration transferred to Amgen as research and development expense in the condensed consolidated statements of operations and comprehensive loss because the acquired technology represented in-process research and development and had no alternative future use. In addition, under the Amgen Agreement, Amgen was entitled to maintain a 10% ownership interest of the outstanding shares of the Company’s common stock, on a fully diluted and converted basis, through the second closing of the Company’s Series A Preferred Stock financing. The Company assessed the Amgen anti-dilution right and determined that the right (i) met the definition of a freestanding financial instrument that was not indexed to the Company’s own stock and (ii) met the definition of a derivative and did not qualify for equity classification. The anti-dilution right liability was initially valued at $1,639 which the Company recorded as research and development expense in June 2018. Changes in the fair value of the anti-dilution right liability continued to be recognized until the Company satisfied the obligation which occurred in November 2018. The Company recognized a loss of $11 within other expense in the condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2018, related to the change in fair value of the anti-dilution right liability prior to its extinguishment in November 2018. In November 2018, in connection with the second closing of the Company’s Series A Preferred Stock financing, the Company issued 3,205,128 shares of Series A Preferred Stock to Amgen for a total value of $7,404 satisfying its anti-dilution obligation under the Amgen Agreement. The Company reclassified the carrying value of the anti-dilution right liability, equal to the then current fair value of $7,404, to the carrying value of the Series A Preferred Stock. During the three and six months ended June 30, 2018, the Company recorded research and development expense of $7,992 in connection with the Amgen Agreement, including the upfront cash payment of $5,000, the fair value of $1,353 of shares of Series A Preferred Stock issued to Amgen, the fair value of $1,639 for the issuance of the anti-dilution right liability. During the three and six months ended June 30, 2019, the Company did not record any research and development expense in connection with the Amgen Agreement.

Income taxes	6 Months Ended
Income taxes	Jun. 30, 2019
Income taxes
Income taxes	8. Income taxes During the three and six months ended June 30, 2019 and 2018, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each period due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States..

Commitments and contingencies	6 Months Ended
Commitments and contingencies	Jun. 30, 2019
Commitments and contingencies
Commitments and contingencies	10. Commitments and contingencies Lease agreements The Company entered into a use and occupancy agreement for office space in Cambridge, Massachusetts on August 15, 2018, with Atlas Venture Life Science Advisors, LLC, a related party (See Note 11). The agreement commenced on August 15, 2018 and continues for an initial 9‑month period after which the agreement becomes cancelable by either party upon 60 days written notice. Monthly lease payments include base rent for the office space of approximately $12 annually and non-rent shared tenant occupancy costs. In October 2018, the Company entered into a lease agreement for office space in South San Francisco, California. In March 2019, the Company amended this lease agreement (the “First Amendment”) to extend the term of the lease and expand the square footage of the existing leased office space. The First Amendment lease expires in March 2021. Monthly lease payments to be paid under the amended agreement total $19 which are subject to a 3% annual increase beginning in October 2019 and continuing for each successive year until the lease has expired or been terminated. The Company provided a security deposit of approximately $20, which is included as a component of restricted cash on the Company’s condensed consolidated balance sheet as of June 30, 2019. The Company recognizes rent expense on a straight-line basis over the respective lease periods and has recorded rent expense of $89 and $138 for the three and six months ended June 30, 2019, respectively. Research and manufacturing commitments The Company has entered into agreements with contract research organizations and contract manufacturing organizations to provide services in connection with its nonclinical studies and clinical trials and to manufacture clinical development materials. As of June 30, 2019, the Company had non-cancelable purchase commitments under these agreements totaling $5,172. Indemnification agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not currently aware of any indemnification claims and has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of June 30, 2019. Legal proceedings The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

Related party transactions	6 Months Ended
Related party transactions	Jun. 30, 2019
Related party transactions
Related party transactions	11. Related party transactions Atlas Venture Life Science Advisors, LLC A partner of Atlas Venture Life Science Advisors, LLC (“Atlas”), a significant investor in the Company, has served on the Company’s board of directors since 2018. In August 2018, the Company entered into a use and occupancy agreement for office space with Atlas in Cambridge, Massachusetts. The agreement commenced on August 15, 2018 and continues for an initial 9‑month period after which the agreement becomes cancelable by either party upon 60 days written notice. Base rent for the office space is approximately $12 annually (See Note 10). As of June 30, 2019, in association with the use and occupancy agreement, the Company owed $8 to Atlas, which was recorded in accrued expenses in the condensed consolidated balance sheets.

Subsequent events	6 Months Ended
Subsequent events	Jun. 30, 2019
Subsequent events
Subsequent events	12. Subsequent events The Company evaluated subsequent events through August 12, 2019, the date on which these financial statements were issued. On July 2, 2019 the Company announced the dosing of the first patient in its Phase 2a clinical trial of AKR‑001, which resulted in a $2,500 milestone obligation under the Amgen Agreement. The Company will recognize this obligation as research and development expense in its financial statements for the three months ended September 30, 2019.

Summary of significant accounting policies - Restricted cash (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Summary of significant accounting policies
Separate cash balance	$ 60	$ 20
Separate cash balance to collateralize corporate credit cards with a bank	40	20
Separate cash balance for the landlord	$ 20	$ 5

Summary of significant accounting policies - Deferred offering costs (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Summary of significant accounting policies
Deferred offering costs	$ 0	$ 361

Stockholder's equity (deficit) - Restricted stock activity (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) shares
Number of Shares
Beginning balance of unvested restricted common stock	80,190
Early exercise of unvested stock options	487,933
Vested	(28,296)
Ending balance of unvested restricted common stock	539,827
Grant-Date Fair Value
Early exercise of unvested stock options \| $	$ 435
Ending balance of unvested restricted common stock \| $	$ 435

Stock-based awards - Stock option valuation (Details) - $ / shares	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Assumptions to determine grant-date fair value of stock options granted
Expected term (in years)	6 years 26 days	6 years 15 days
Volatility	71.20%	69.80%
Risk-free interest rate	2.28%	2.39%
Dividend yield	0.00%	0.00%
Weighted average fair value of common stock	$ 9.7200	$ 8.2600

Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Income taxes (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income taxes
Income tax benefits	$ 0	$ 0	$ 0	$ 0

Net loss per share (Details) - shares	6 Months Ended
Net loss per share (Details) - shares	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	2,960,335	7,477,380
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	2,420,508
Unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	539,827	108,486
Redeemable convertible preferred stock (as converted to common stock)
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total		7,368,894

Commitments and contingencies (Details) - USD ($) $ in Thousands			3 Months Ended	6 Months Ended
	Oct. 01, 2019	Aug. 15, 2018	Jun. 30, 2019	Jun. 30, 2019
Commitments and contingencies
Non cancellation period for use and occupancy agreement		9 months
Written notice for cancellation of agreement		60 days
Base rental expense for the office space		$ 12
Monthly lease payments payable under the amended agreement	$ 19
Increase in rental expense (as a percentage)	3.00%
Security deposit			$ 20	$ 20
Rent expense			89	138
Non-cancelable purchase commitments with contract research organizations and contract manufacturing organizations			$ 5,172	$ 5,172

Related party transactions (Details) - USD ($) $ in Thousands		6 Months Ended
	Aug. 15, 2018	Jun. 30, 2019
Related Party Transaction
Non cancellation period for use and occupancy agreement	9 months
Written notice for cancellation of agreement	60 days
Base rental expense for the office space	$ 12
Atlas Venture Life Science Advisors, LLC
Related Party Transaction
Non cancellation period for use and occupancy agreement	9 months
Written notice for cancellation of agreement	60 days
Base rental expense for the office space	$ 12
Amount owed to related party		$ 8

Subsequent events (Details) $ in Thousands	Jul. 02, 2019 USD ($)
Subsequent events \| Amgen Agreement
Subsequent events
Milestone obligation	$ 2,500