Viela Bio (VIE) 10-Q 14 Nov 19 2019 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 14, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	VIELA BIO, INC.
Entity Central Index Key	0001734517
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		50,962,060
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	VIE
Security Exchange Name	NASDAQ
Entity File Number	001-39067
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-4187338
Entity Address, Address Line One	One MedImmune Way
Entity Address, Address Line Two	First Floor, Area Two
Entity Address, City or Town	Gaithersburg
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20878
City Area Code	240
Local Phone Number	558-0038
Document Quarterly Report	true
Document Transition Report	false

BALANCE SHEETS (Unaudited)

BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 155,747	$ 126,898
Marketable securities	42,495
Receivable from stockholders		12,000
Accounts receivable	5,128
Prepaid and other current assets	4,577	456
Total current assets	207,947	139,354
Marketable securities, non-current	24,915
Property and equipment, net	905	473
Other assets	73
Total assets	233,840	139,827
Current liabilities:
Accounts payable	5,660	1,142
Accrued expenses	7,487	2,769
Related party liability	13,100	12,054
Total current liabilities	26,247	15,965
Commitments and contingencies (Note 11)
Redeemable convertible preferred stock	467,253	312,253
Stockholders’ deficit:
Common stock, $.001 par value; 46,159,941 and 41,254,509 shares authorized as of September 30, 2019 and December 31, 2018; 872,324 and 10 shares issued and outstanding as of September 30, 2019 and December 31, 2018	1
Additional paid-in capital	5,498	1,879
Accumulated other comprehensive loss	(30)
Accumulated deficit	(265,129)	(190,270)
Total stockholders’ deficit	(259,660)	(188,391)
Total liabilities, redeemable convertible preferred stock and stockholders’ deficit	233,840	139,827
Series A-1 Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	142,253	142,253
Series A-2 Preferred Stock
Current assets:
Receivable from stockholders		12,000
Current liabilities:
Redeemable convertible preferred stock	170,000	$ 170,000
Series A-3 Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	80,000
Series B Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	$ 75,000

BALANCE SHEETS (Unaudited) (Par

BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Feb. 23, 2018
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001
Redeemable convertible preferred stock, shares authorized	40,618,706		37,695,912
Common stock, par value (in dollars per share)	$ 0.001		$ 0.001
Common stock, shares authorized	46,159,941		41,254,509
Common stock, shares issued	872,324		10
Common stock, shares outstanding	872,324		10
Series A-1 Preferred Stock
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001			$ 0.001
Redeemable convertible preferred stock, shares authorized	14,225,324		14,225,324
Redeemable convertible preferred stock, shares issued	14,225,324		14,225,324			14,225,324
Redeemable convertible preferred stock, shares outstanding	14,225,324	14,225,324	14,225,324	14,225,324	14,225,324
Series A-2 Preferred Stock
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001			$ 0.001
Redeemable convertible preferred stock, shares authorized	17,000,000		17,000,000
Redeemable convertible preferred stock, shares issued	17,000,000		17,000,000			14,000,000
Redeemable convertible preferred stock, shares outstanding	17,000,000	17,000,000	17,000,000	14,000,000	14,000,000
Series A-3 Preferred Stock
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001
Redeemable convertible preferred stock, shares authorized	4,705,882		6,470,588
Redeemable convertible preferred stock, shares issued	4,705,882		0
Redeemable convertible preferred stock, shares outstanding	4,705,882		0
Series B Preferred Stock
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	4,687,500		0
Redeemable convertible preferred stock, shares issued	4,687,500	4,687,500	0
Redeemable convertible preferred stock, shares outstanding	4,687,500	4,687,500	0

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Total revenue			$ 20,000
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 38,700	$ 13,928	$ 72,113	$ 28,892
General and administrative	10,230	2,401	24,575	4,399
Acquisition of in-process research and development				143,333
Total operating expenses	48,930	16,329	96,688	176,624
Loss from operations	(48,930)	(16,329)	(76,688)	(176,624)
Other income:
Interest income	520	647	1,829	1,408
Total other income	520	647	1,829	1,408
Net loss	$ (48,410)	$ (15,682)	$ (74,859)	$ (175,216)
Net loss per share attributable to common stockholders— basic and diluted	$ (65)	$ (1,568,200)	$ (150)	$ (17,521,600)
Weighted average common shares outstanding— basic and diluted	749,539	10	497,924	10
Other comprehensive loss
Change in unrealized gains losses on marketable securities, net	$ (30)		$ (30)
Total other comprehensive loss	(30)		(30)
Total comprehensive loss	$ (48,440)	$ (15,682)	$ (74,889)	$ (175,216)

STATEMENTS OF REDEEMABLE CONVER

STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT (Unaudited) - USD ($) $ in Thousands	Total	Series A-1 Preferred Stock	Series A-2 Preferred Stock	Series A-3 Preferred Stock	Series B Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balances, Shares at Dec. 31, 2017						10
Stock-based compensation expense	$ 1,268						$ 1,268
Issuance of preferred stock		$ 142,253	$ 140,000
Issuance of preferred stock, Shares		14,225,324	14,000,000
Net loss	(175,216)								$ (175,216)
Redeemable convertible preferred stock, Ending Balance, Shares at Sep. 30, 2018		14,225,324	14,000,000
Redeemable convertible preferred stock, Ending Balance at Sep. 30, 2018		$ 142,253	$ 140,000
Ending Balances, Shares at Sep. 30, 2018						10
Ending Balances at Sep. 30, 2018	(173,948)						1,268		(175,216)
Redeemable convertible preferred stock, Beginning Balance, Shares at Jun. 30, 2018		14,225,324	14,000,000
Redeemable convertible preferred stock, Beginning Balance at Jun. 30, 2018		$ 142,253	$ 140,000
Beginning Balances, Shares at Jun. 30, 2018						10
Beginning Balances at Jun. 30, 2018	(158,846)						688		(159,534)
Stock-based compensation expense	580						580
Net loss	(15,682)								(15,682)
Redeemable convertible preferred stock, Ending Balance, Shares at Sep. 30, 2018		14,225,324	14,000,000
Redeemable convertible preferred stock, Ending Balance at Sep. 30, 2018		$ 142,253	$ 140,000
Ending Balances, Shares at Sep. 30, 2018						10
Ending Balances at Sep. 30, 2018	(173,948)						1,268		(175,216)
Redeemable convertible preferred stock, Beginning Balance, Shares at Dec. 31, 2018		14,225,324	17,000,000	0	0
Redeemable convertible preferred stock, Beginning Balance at Dec. 31, 2018	312,253	$ 142,253	$ 170,000
Beginning Balances, Shares at Dec. 31, 2018						10
Beginning Balances at Dec. 31, 2018	(188,391)						1,879		(190,270)
Stock-based compensation expense	2,218						2,218
Issuance of common stock for stock options exercised	$ 1,402					$ 1	1,401
Issuance of common stock for stock options exercised shares	493,525					493,525
Issuance of common stock upon vesting of RSAs						$ 378,789
Issuance of preferred stock				$ 80,000	$ 75,000
Issuance of preferred stock, Shares				4,705,882	4,687,500
Net loss	$ (74,859)								(74,859)
Other comprehensive loss	(30)							$ (30)
Redeemable convertible preferred stock, Ending Balance, Shares at Sep. 30, 2019		14,225,324	17,000,000	4,705,882	4,687,500
Redeemable convertible preferred stock, Ending Balance at Sep. 30, 2019	467,253	$ 142,253	$ 170,000	$ 80,000	$ 75,000
Ending Balances, Shares at Sep. 30, 2019						872,324
Ending Balances at Sep. 30, 2019	(259,660)					$ 1	5,498	(30)	(265,129)
Redeemable convertible preferred stock, Beginning Balance, Shares at Jun. 30, 2019		14,225,324	17,000,000		4,687,500
Redeemable convertible preferred stock, Beginning Balance at Jun. 30, 2019		$ 142,253	$ 170,000		$ 75,000
Beginning Balances, Shares at Jun. 30, 2019						724,795
Beginning Balances at Jun. 30, 2019	(212,528)					$ 1	4,190		(216,719)
Stock-based compensation expense	931						931
Issuance of common stock for stock options exercised	377						377
Issuance of common stock for stock options exercised shares						132,529
Issuance of common stock upon vesting of RSAs						$ 15,000
Issuance of preferred stock				$ 80,000
Issuance of preferred stock, Shares				4,705,882
Net loss	(48,410)								(48,410)
Other comprehensive loss	(30)							(30)
Redeemable convertible preferred stock, Ending Balance, Shares at Sep. 30, 2019		14,225,324	17,000,000	4,705,882	4,687,500
Redeemable convertible preferred stock, Ending Balance at Sep. 30, 2019	467,253	$ 142,253	$ 170,000	$ 80,000	$ 75,000
Ending Balances, Shares at Sep. 30, 2019						872,324
Ending Balances at Sep. 30, 2019	$ (259,660)					$ 1	$ 5,498	$ (30)	$ (265,129)

STATEMENTS OF CASH FLOWS (Unaud

STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (74,859)	$ (175,216)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	44	36
Stock-based compensation expense	2,218	1,268
Acquisition of in-process research and development		143,333
Amortization of premium and discount on marketable securities, net	(3)
Changes in operating assets and liabilities:
Accounts receivable	(5,000)
Prepaid and other current assets	(867)	(280)
Accounts payable, accrued expenses and related party liability	9,265	15,261
Net cash used in operating activities	(69,202)	(15,598)
Cash flows from investing activities:
Purchase of marketable securities	(67,436)
Purchase of property and equipment	(476)	(467)
Acquisition of in-process research and development		(143,333)
Net cash used in investing activities	(67,912)	(143,800)
Cash flows from financing activities:
Proceeds from exercise of common stock options	1,273
Proceeds from issuance of redeemable convertible preferred stock	167,000	282,253
Payment of deferred offering costs	(2,310)
Net cash provided by financing activities	165,963	282,253
Net increase in cash and cash equivalents	28,849	122,855
Cash and cash equivalents at beginning of period	126,898
Cash and cash equivalents at end of year	155,747	$ 122,855
Supplemental disclosure of non-cash financing and investing activities:
Cash due from stock option exercises	128
Deferred offering costs	$ 1,017

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the business and basis of presentation Viela Bio, Inc. (“Viela” or the “Company”) is a clinical-stage biotechnology research and development company pioneering and advancing treatments for severe inflammation and autoimmune diseases by selectively targeting shared critical pathways that are the root cause of disease. The Company was incorporated on December 11, 2017 under the laws of the State of Delaware. From December 11, 2017 to December 31, 2017 the Company had no substantive operations. In February 2018, pursuant to an Asset Purchase Agreement (the “Asset Purchase Agreement”) with MedImmune, LLC, MedImmune Limited (collectively, “MedImmune”), and AstraZeneca Collaboration Ventures, LLC (“AZ”, and, together with MedImmune, the “AZ Parties”), the Company acquired intellectual property and the biological, regulatory and other materials associated with a portfolio of clinical and pre-clinical molecules, for a purchase price of approximately $142,253 financed by AZ’s purchase of the Company’s Series A preferred stock. Following the asset purchase, the Company entered into several agreements with AZ and MedImmune, including a license agreement, sublicense agreements, a transition services agreement, a clinical supply agreement and a commercial supply agreement. 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 applicable governmental regulations, development by competitors of new technological innovations, dependence on key personnel and protection of proprietary technology. Drug candidates currently under development 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. I n October, 2019, the Company completed an initial public offering (the “IPO”) of its common stock and issued and sold 7,900,000 shares of common stock at a public offering price of $19.00 per share, resulting in gross proceeds of $150,100 and net proceeds of $136,266 after deducting underwriting discounts and commissions and offering expenses of approximately $13,834. In addition, and contemporaneously with the closing of the issuance and sale of the aforementioned shares, the Company issued and sold an additional 1,185,000 shares of common stock, pursuant to the full exercise of the underwriter’s option to purchase additional shares, for gross proceeds of $22,515 and net proceeds of $20,939 after deducting underwriting discounts and commissions of $1,576. Thus, the aggregate gross proceeds to the Company from the IPO were $172,615 and net proceeds after deducting underwriting discounts and commissions and other offering costs, were $157,205. Upon the closing of the IPO, the outstanding shares of series A redeemable convertible preferred stock (the “Series A Preferred Stock”), and series B redeemable convertible preferred stock (the “Series B Preferred Stock” and together with the Series A Preferred Stock, the “Preferred Stock”) converted into an aggregate of 40,618,706 shares of common stock. Basis of Presentation The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). All adjustments necessary for the fair presentation of the Company’s financial statements have been presented. The accompanying balance sheet as of September 30, 2019, the related statements of operations and comprehensive loss and redeemable convertible preferred stock and stockholders’ deficit for the three and nine months ended September 30, 2019 and 2018, and the statements of cash flows for the nine months ended September 30, 2019 and 2018 and related footnote disclosures are unaudited. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying interim balance sheet, statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ deficit and cash flows have been made. The results for the nine months ended September 30, 2019 and 2018, 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of significant accounting policies Use of estimates The preparation of the Company’s 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 financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the recognition of research and development expenses based on when services are performed, the valuations of share based compensation arrangements, and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Cash and cash equivalents The Company considers all highly liquid instruments with an original maturity of 90 days or less at acquisition to be cash equivalents. Marketable Securities The Company’s marketable securities are classified as available-for-sale and are carried at fair value, with the unrealized gains and losses reported as a component of accumulated other comprehensive loss in stockholder’s deficit. Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the statements of operations and comprehensive loss. Marketable securities that mature within one year from the balance sheet date are classified as short-term. The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustments to fair value reflects a decline in the value of the investment that the Company considers to be “other-than-temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Concentrations of credit risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and the Company’s money market fund investment. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. 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 amount of the Company’s financial instruments, including cash and cash equivalents and accounts payable approximate their fair values. No transfer of assets between Level 1 and Level 2 of the fair value hierarchy occurred during the three and nine months ended September 30, 2019 and 2018. Deferred Offering Costs The Company has deferred offering costs, consisting of legal, accounting, printer and filing fees related to the IPO, that were deferred and were offset against the offering proceeds upon the completion of the IPO in October, 2019. As of September 30, 2019, $3,327 of deferred offering costs were recorded within prepaids and other current assets on the balance sheet. As of December 31, 2018, no amounts were deferred. Segment information The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is developing and commercializing transformative treatments for severe inflammation and autoimmune diseases. Research and development expenses Research and development expenses are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, allocated facility-related and depreciation expenses, third-party license fees and external costs including fees paid to consultants and clinical research organizations (“CROs”), in connection with nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Costs incurred in purchasing technology or technology licenses are charged immediately to research and development expense if the technology has not reached technological feasibility and has no alternative future uses. Clinical trial costs are a significant component of research and development expenses and include costs associated with third-party contractors. A majority of these payments are pass-through payments that are made to AZ Parties due to the existing contracts in place associated with the in-process research and development (“IPR&D”) assets acquired (see Note 7, “Asset acquisition”). The Company, through the AZ Parties outsources a substantial portion of its clinical trial activities, utilizing external entities such as CROs, independent clinical investigators, and other third-party service providers to assist it with the execution of its clinical studies. For each clinical trial that the Company conducts, certain clinical trial costs are expensed immediately, while others are expensed over time based on the expected total number of patients in the trial, the rate at which patients enter the trial, and/or the period over which clinical investigators or CROs are expected to provide services. Clinical activities which relate principally to clinical sites and other administrative functions to manage the Company’s clinical trials are performed primarily by CROs. CROs typically perform most of the start-up activities for the Company’s trials, including document preparation, site identification, screening and preparation, pre-study visits, training, and program management. These start-up costs usually occur within a few months after the contract has been executed and are event-driven in nature. The remaining activities and related costs, such as patient monitoring and administration, generally occur ratably throughout the life of the individual contract or study. In the event of early termination of a clinical trial, the Company accrues and recognizes expenses in an amount based on its estimate of the remaining non-cancelable obligations associated with the winding down of the clinical trial and/or penalties. For clinical study sites, where payments are made periodically on a per-patient basis to the institutions performing the clinical study, the Company accrues expenses on an estimated cost-per-patient basis, based on subject enrollment and activity in each period. The amount of clinical study expense recognized in a period may vary from period to period based on the duration and progress of the study, the activities to be performed by the sites each quarter, the required level of patient enrollment, the rate at which patients actually enroll in and drop out of the clinical study, and the number of sites involved in the study. Clinical trials that bear the greatest risk of change in estimates are typically those that have a significant number of sites, require a large number of patients, have complex patient screening requirements, and span multiple years. During the course of a trial, the Company adjusts its rate of clinical expense recognition if actual results differ from the Company’s estimates. The Company’s estimates and assumptions for clinical expense recognition could differ significantly from the Company’s actual results, which could cause material increases or decreases in research and development expenses in future periods when the actual results become known. 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. Property and equipment Property and equipment, which consists mainly of laboratory equipment, are carried at cost less accumulated depreciation. Depreciation is computed over the estimated useful lives of the respective assets, generally ten years, using the straight-line method. Leasehold improvements are amortized over the shorter of the estimated useful lives of the assets or the lease term. Expenditures for maintenance and repairs which do not materially extend the useful lives of the assets are charged to expense as incurred. The cost and accumulated depreciation or amortization of assets that meet the guidance within Accounting Standards Codification (“ASC”) Topic 360 as either retired or sold are removed from the respective accounts, and any gain or loss is recognized in operations upon closing of the transaction. The Company periodically assesses the recoverability of long-lived assets, such as property and equipment, and evaluates such assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Revenue Recognition for Contracts with Customers To date, the Company has recognized revenues through commercialization and collaboration agreements. Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue (ASC 606): Revenue from Contracts with Customers (“ASC 606”), using the modified retrospective transition method. Under this method, results for reporting periods beginning on January 1, 2019 are presented under ASC 606, while prior periods were prepared and reported in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The adoption of ASC 606 resulted in no cumulative adjustment as the Company had substantially no assets until executing the Asset Acquisition in February 2018 (as described in Note 7, “Asset acquisition”) and did not enter into a revenue contract with a customer until May 2019 (as described in Note 13, “Collaboration agreements”). ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. We assess if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right is accounted for as a contract modification for accounting purposes. The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. Amounts recognized as revenue for which the Company has the contractual right to bill, but has not yet received, are classified as accounts receivable in the accompanying balance sheets. Amounts recognized as revenue for which the Company does not have the contractual right to bill are generally recognized as contract assets in the accompanying balance sheets. Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current liabilities in the accompanying balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as long-term liabilities. Licenses of Intellectual Property – The terms of the Company’s contracts with customers may include the license of functional intellectual property, given the functionality of the intellectual property is not expected to change substantially as a result of the Company’s ongoing activities. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from the portion of the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises (that is, for licenses that are not distinct from other promised goods and services in an arrangement), the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments – If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. Royalties – For arrangements that include sales-based royalties, including milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue or milestone payments resulting from any of its licensing arrangements. Significant Financing Component – In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed each of its revenue arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements. Collaborative Arrangements – The Company enters into collaboration agreements, which are within the scope of ASC 606, to discover, develop, manufacture or commercialize product candidates. The terms of these agreements typically contain multiple promises or obligations, which may include: (1) licenses, or options to obtain licenses, to use the Company’s technology, (2) research and development activities to be performed on behalf of the collaboration partner, and (3) in certain cases, services in connection with the manufacturing of preclinical and clinical material. Payments the Company receives under these arrangements typically include one or more of the following: non-refundable, upfront license fees; clinical and development, regulatory, and sales milestone payments; and royalties on future product sales. The Company also analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, the Company applies the five-step model described above. Stock-based compensation The Company measures all stock-based awards granted to employees based on the fair value on the date of the grant and recognizes compensation expense into either general and administrative expense or research and development expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for forfeitures as they occur. For stock-based awards with service-based vesting conditions, the Company recognizes compensation expense using the straight-line method. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option The Company classifies stock-based compensation expense in its statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Income taxes The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes The Company recognizes the impact of an uncertain tax position if the position will more likely than not be sustained upon examination by a taxing authority, based on the technical merits of the position. The Company’s policy is to recognize interest related to unrecognized tax benefits as interest expense and penalties as operating expenses. As of September 30, 2019, the Company had no unrecognized tax benefits and as such, no liability, interest or penalties were required to be recorded. The Company does not expect this to change significantly in the next twelve months. Net loss per share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing net loss by the weighted average number of common shares adjusted for the dilutive effect of common equivalent shares outstanding during the period. As of September 30, 2019, and December 31, 2018, common stock equivalents consisted of the Preferred Stock and stock options that were vested and exercisable as of September 30, 2019 and December 31, 2018. Net loss per share attributable to common stockholders is calculated using the two-class method, which is an earnings allocation formula that determines net loss per share for the holders of the Company’s common shares and participating securities. The Company’s Preferred Stock contains participating rights in any dividend paid by the Company and are deemed to be participating securities. Net loss attributable to common stockholders and participating preferred shares is allocated to each share on an as-converted basis as if all of the earnings for the period had been distributed. The participating securities do not include a contractual obligation to share in the losses of the Company and are not included in the calculation of net loss per share in the periods that have a net loss. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect on net loss per share. Diluted net loss per share is computed using the more dilutive of (a) the two-class method or (b) the if-converted method. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Diluted net loss per share is equivalent to basic net loss per share for the periods presented herein because common stock equivalent shares from the Series A and Series B Preferred Stock were anti-dilutive. Due to their dilutive effect, the calculation of diluted net loss per share for the nine months ended September 30, 2019, and 2018 does not include the following common stock equivalent shares: September 30, 2019 2018 Series A Preferred Stock 35,931,206 28,225,324 Series B Preferred Stock 4,687,500 — Stock Options 391,720 — Total 41,010,426 28,225,324 For the three and nine months ended September 30, 2019 and 2018, there were no reconciling items between basic and diluted net loss per share. 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 adopted accounting pronouncements In January 2017, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and ASC 606 (“ASU 2018-18”). The amendments in ASU 2018-18 make targeted improvements to GAAP for collaborative arrangements by clarifying that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation, and disclosure requirements. In addition, unit-of-account guidance in ASU 2018-18 was aligned with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted, including adoption in any interim period. The amendments should be applied retrospectively to the date of initial application of ASC 606. The Company adopted this guidance effective January 1, 2019 with its initial application of ASC 606. The adoption of the standard did not have an impact on the Company’s financial statements. Recently issued accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 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 In August 2018, the FASB issued No. ASU 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Marketable securities	3. Marketable securities The following is a summary of the Company’s available-for-sale marketable securities and cash equivalents as of September 30, 2019: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Cash equivalents Certificates of deposit and time deposits $ 400 $ — $ — $ 400 Commercial paper 11,532 — (1 ) 11,531 Total cash equivalents $ 11,932 $ — $ (1 ) $ 11,931 Current marketable securities: Certificates of deposit and time deposits $ 3,802 $ — $ (1 ) $ 3,801 Commercial paper 17,922 — (2 ) 17,920 Corporate debt securities 20,783 3 (12 ) 20,774 Total marketable securities, current $ 42,507 $ 3 $ (15 ) $ 42,495 Non-current marketable securities: U.S. Treasury securities $ 8,037 $ — $ (8 ) $ 8,029 Corporate debt securities 16,895 3 (12 ) 16,886 Total marketable securities, non-current $ 24,932 $ 3 $ (20 ) $ 24,915 Total marketable securities $ 67,439 $ 6 $ (35 ) $ 67,410 The maturities of the Company’s long-term marketable securities ranges from one to two years. The Company did not hold any available-for-sale marketable securities as of December 31, 2018.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurement	4. Fair value measurement As of September 30, 2019, the Company held certain assets that required to be measured at fair value on a recurring basis, as follows: September 30, 2019 Cash and Cash equivalents Short-Term Marketable Securities Long-Term Marketable Securities Cash $ 123,863 $ — $ — Level 1 Money market funds 19,953 — — Level 2 U.S. Treasury securities — — 8,029 Certificates of deposits and time deposits 400 3,801 — Corporate debt securities — 20,774 16,886 Commercial paper 11,531 17,920 — Subtotal 11,931 42,495 24,915 Total $ 155,747 $ 42,495 $ 24,915 As of December 31, 2018, the Company held certain assets that required to be measured at fair value on a recurring basis, as follows: December 31, 2018 Cash and Cash equivalents Short-Term Marketable Securities Long-Term Marketable Securities Cash $ 21,681 $ — $ — Level 1 Money market funds 105,217 — — Total $ 126,898 $ — $ —

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Common Stock	5. Common stock As of September 30, 2019 and December 31, 2018, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 46,159,941 and 41,254,509 shares, respectively, of $0.001 par value common stock. As of September 30, 2019 and December 31, 2018, there were 872,324 shares and 10 shares of common stock issued and outstanding, respectively. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders, provided, however, that except as otherwise required by law, holders of common stock shall not be entitled to vote on any amendment to the Company’s certificate of incorporation that relates solely to the terms of one or more outstanding series of preferred stock, if the holders of the affected series are entitled to vote thereon. 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 preferred stock. Through September 30, 2019, no cash dividends had been declared or paid. During the year ended December 31, 2018, the Company granted 757,577 shares of restricted common stock to employees under the 2018 Equity Incentive Plan. The Company did not grant any shares of restricted common stock to employees under the 2018 Equity Incentive Plan during the nine months ended September 30, 2019. As of September 30, 2019, 378,789 shares granted under the 2018 Equity Incentive Plan have vested. No shares had vested as of December 31, 2018.

Convertible Redeemable Preferre

Convertible Redeemable Preferred Stock	9 Months Ended
	Sep. 30, 2019
Temporary Equity [Abstract]
Convertible Redeemable Preferred Stock	6. Convertible redeemable preferred stock At September 30, 2019 and December 31, 2018, the Company had 40,618,706 and 37,695,912 shares of preferred stock, par value $0.001 per share, in authorized capital, respectively. At September 30, 2019, the Company’s redeemable convertible preferred stock consisted of the following: Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Series A-1 Preferred Stock 14,225,324 14,225,324 $ 142,253 Series A-2 Preferred Stock 17,000,000 17,000,000 170,000 Series A-3 Preferred Stock 4,705,882 4,705,882 80,000 Series B Preferred Stock 4,687,500 4,687,500 75,000 Total 40,618,706 40,618,706 $ 467,253 At December 31, 2018, the Company’s redeemable convertible preferred stock also consisted of the following: Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Series A-1 Preferred Stock 14,225,324 14,225,324 $ 142,253 Series A-2 Preferred Stock 17,000,000 17,000,000 170,000 Series A-3 Preferred Stock 6,470,588 — — Series B Preferred Stock — — — Total 37,695,912 31,225,324 $ 312,253 Series A Preferred Stock On February 23, 2018 (the “Transaction Date”), pursuant to the Series A Preferred Stock Purchase Agreement, by and among the Company and certain purchasers, and as part of an initial tranche closing, the Company issued 14,225,324 shares of Series A-1 preferred stock and 14,000,000 shares of Series A-2 preferred stock, par value $0.001 per share, at a purchase price of $10.00 per share, resulting in gross proceeds of approximately $282,253 to the Company (the “Initial Tranche Closing”). In addition to the Initial Tranche Closing, the Series A Preferred Stock Purchase Agreement provided for the issuance of up to 6,470,588 shares of Series A-3 at a purchase price of $17.00 per share upon acceptance for review by the U.S. FDA of the Company’s first biologics license application for lead product candidate, inebilizumab, for the indication neuromyelitis optica spectrum disorder (the “Milestone Closing”). However, at any time prior to the Milestone Closing, the board of directors could determine that the Company required additional capital to fund its operations, upon which the board of directors may cause the Company to sell and the holders of the Series A-2 to purchase up to 3,000,000 additional shares of Series A-2 preferred stock at a purchase price of $10.00 per share (the “Additional Closing”). In December 2018, the Additional Closing occurred, and the Company received $30,000 in exchange for 3,000,000 shares of Series A-2. As of December 31, 2018, $12,000 of the $30,000 was recorded as a receivable as funds were not received until January 2019 and the Company provided supplemental non-cash financing disclosure on its statement of cash flows for the year ended December 31, 2018. The proceeds received upon the Additional Closing would reduce the proceeds from the Milestone Closing. Both the Additional Closing and Milestone Closing were evaluated and determined to be embedded features within the Series A Preferred Stock that did not require bifurcation. In addition, if any holder of Series A-2 preferred stock failed to purchase the committed amount under either the Additional Closing or Milestone Closing (“Purchaser Default”), then all shares of Series A-2 preferred stock held by such holder would automatically be converted into shares of Common Stock as is determined by dividing (i) the aggregate number of shares of Series A-2 preferred stock held by such individual by (ii) 10 and (b) if such individual had previously converted their Series A-2 shares to Common Stock, 90% of such shares would automatically be redeemed by the Company for no consideration (the “Special Mandatory Redemption”). The Special Mandatory Redemption was evaluated and determined to be accounted for as an embedded derivative. However, the Company determined an insignificant value should be ascribed to the Special Mandatory Redemption as the likelihood of a Purchaser Default occurring was deemed to be remote both at the Transaction Date and December 31, 2018. In September 2019, the Company issued an aggregate of 4,705,882 shares of preferred stock at a purchase price of $17.00 per share for an aggregate gross consideration of $80,000. Series B Preferred Stock During June 2019, pursuant to the Series B Preferred Stock Purchase Agreement, by and among the Company and certain purchasers, the Company issued 4,687,500 shares of Series B preferred stock, par value $0.001 per share, at a purchase price of $16.00 per share, resulting in gross proceeds of approximately $75,000 to the Company. Prior to the closing of the IPO, the holders of the Preferred Stock had the following rights and preferences: Voting Each holder of the Preferred Stock was entitled to the number of votes equal to the number of shares of Common Stock into which the number of shares of Preferred Stock held by such holder were convertible and should vote together with the holders of Common Stock as a single class. The holders of the preferred stock were entitled to elect seven of the eight directors on the Board of Directors. Two of the seven directors were elected by the Series A-1 preferred stockholders, four of the directors were elected by the Series A-2 preferred stockholders, one of the directors was elected by the Series B preferred stockholders, and the remaining director is the Company’s chief executive officer. Dividends The Series B preferred stock accrued cumulative dividends on a daily basis at a fixed dividend rate of $1.28 per share per annum payable only when, as and if declared by the Board of Directors of the Company, prior and in preference to any declaration or payment of any dividend on shares of any other class or series of capital stock of the Company (“Accruing Dividends”) unless the holders of the Series B preferred stock first (and Series A preferred stock thereafter) received, or simultaneously received, a dividend in an amount at least equal to the formula included in the Company’s charter which varied based on whether the dividend was on the Common Stock or on any other class or series not convertible into Common Stock. Through September 30, 2019, no dividends had been declared or paid by the Company. Liquidation In the event of any liquidation, dissolution or winding-up of the Company or a Deemed Liquidation Event (as defined below), the holders of the Series B preferred stock then outstanding would be entitled to be paid out of the assets of the Company available for distribution to stockholders, and before any payment would be made to holders of Series A preferred stock and Common Stock, in an amount per share equal to the original issue price per share, plus all Accruing Dividends accrued but unpaid thereon, whether or not declared, together with all other declared but unpaid dividends thereon. If upon such event, the assets of the Company available for distribution were insufficient to permit payment in full to the holders of Series B preferred stock, the proceeds would be ratably distributed among the holders of Series B preferred stock. After satisfaction of the Series B preferred stock liquidation preference, the holders of the Series A preferred stock were entitled to be paid before any payment shall be made to the holders of Common Stock in an amount equal to the original issue price per share, plus any declared but unpaid dividends thereon. Due to this redemption option, the Preferred Stock was recorded in mezzanine equity and subject to subsequent measurement under the guidance provided under ASC 480-10-S99. In accordance with that guidance, the Company has elected to not recognize any subsequent changes in the redemption value as the Company has determined it is not probable that the Preferred Stock will become redeemable. After payments have been made in full to the holders of the Preferred Stock, the remaining assets of the Company available for distribution would be distributed among the holders of Preferred Stock and the holders of Common Stock on a pro-rata basis as if the shares of Preferred Stock were converted into Common Stock immediately prior to the liquidation event. A merger or consolidation involving the Company in which the stockholders of the Company do not own a majority of the outstanding shares of the surviving company shall be considered a Deemed Liquidation Event. A sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company shall also be considered a Deemed Liquidation Event. As of September 30, 2019 and December 31, 2018, the liquidation preference of the outstanding shares of the Preferred Stock was approximately $468,995 and $312,253, respectively. Conversion Each share of Preferred Stock was convertible into Common Stock at the option of the holder at any time after the date of issuance. In addition, each share of Preferred Stock would be automatically converted into shares of Common Stock, at the applicable conversion ratio then in effect, upon the earlier of (i) a qualified public offering with net proceeds of at least $75,000 and a price of not less than $17.60 per share, subject to appropriate adjustment for any stock dividend, stock split, combination or other similar recapitalization, (ii) by the affirmative vote of the holders of at least 75% of the then-outstanding Series A preferred stock and a majority of the holders of the outstanding shares of the Series B preferred stock, if such vote was obtained prior to the Milestone Closing or (iii) by the affirmative vote of the holders of at least 75% of the then-outstanding shares of Series A-2 preferred stock and Series A-3 preferred stock (voting together as a single class on an as-converted to Common Stock basis) and a majority of the outstanding shares of Series B preferred stock (voting together as a single class on an as-converted to Common Stock basis) if such vote was obtained after the Milestone Closing. Upon conversion, the shares of Preferred Stock would be converted into Common Stock, at par value, with the remainder recorded to additional paid-in capital. The conversion ratio of the Preferred Stock was determined by dividing the original issue price per share by the conversion price in effect at the time of conversion. The initial conversion price was equal to the original issuance price of the Preferred Stock and was subject to appropriate adjustment in the event of any stock dividend, stock split, combination or recapitalization affecting the Preferred Stock. Upon the closing of the IPO, the Company’s outstanding Preferred Stock converted into an aggregate of 40,618,706 shares of common stock. Upon conversion of the Preferred Stock, the Company reclassified the carrying value of the Preferred Stock to common stock and additional paid-in capital.

Asset Acquisition

Asset Acquisition	9 Months Ended
	Sep. 30, 2019
Asset Acquisition [Abstract]
Asset Acquisition	7. Asset acquisition Contemporaneously on the Transaction Date, the Company entered into the Asset Purchase Agreement with the AZ Parties to acquire the intellectual property and the biological, regulatory and other materials associated with a portfolio of clinical molecules (“Clinical Molecules”) and pre-clinical molecules for potential therapies for autoimmune diseases and inflammation (collectively, the “Acquired Molecules”), for a purchase price of approximately $142,253 (“Asset Acquisition”), which includes direct and incremental transaction expenses of approximately $1,000. The Acquired Molecules consist of multiple in-process research and development projects related to biological therapies which are intended to treat an interrelated subset of auto-immune disorders, represented in part by common biological characteristics. As of the acquisition date, the Acquired Molecules were either in the pre-clinical stage, Phase 1a trial, Phase 1b trial or Phase 2 trial. Further, the Acquired Molecules are related to various potential indications, all of which were identified by the Company as preliminary on the Transaction Date. Until a lead indication is identified, it is not uncommon for the preliminary indications of a drug compound to change during the early clinical development stages. In addition to the Acquired Molecules, in connection with the Asset Acquisition certain former employees of the AZ Parties were either hired by the Company simultaneously or shortly following the Transaction Date. Further, the Company assumed certain ongoing CRO contracts from the AZ Parties related to the research and development of the Acquired Molecules. The services provided by the CRO contracts are readily available in the marketplace and are not considered to be unique or scarce. The estimated fair value associated with the employees and CRO contracts was deemed to be insignificant. The Asset Acquisition was accounted for as acquisition of assets that did not meet the definition of a business. The Asset Acquisition did not constitute a business as substantially all of the fair value of the gross assets acquired was concentrated in the Clinical Molecules, which represent a group of similar identifiable assets as of the acquisition date. As of the acquisition date, the Clinical Molecules were deemed to share similar risk characteristics as (1) each of the Clinical Molecules were in the early development stages of a drug compound and shared a similar financial, technical and regulatory risk profile, (2) only preliminary indications had been identified for any of the Clinical Molecules and (3) the underlying biologic therapies of the Clinical Molecules were similar in that each was intended to treat an interrelated subset of autoimmune disorders by interrupting biologic mechanisms that otherwise result in inflammation and tissue damage. Because the Acquired Molecules were accounted for as an asset acquisition that did not meet the definition of a business, the Acquired Molecules were recorded at their fair values, which equaled the fair value of the consideration paid of approximately $142,253. However, because the Acquired Molecules represent in-process research and development with no alternative future use, the Company immediately expensed the fair value of the Acquired Molecules in the Statement of Operations and Comprehensive Loss.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	8. Stock-based compensation The Company’s Amended and Restated 2018 Equity Incentive Plan (the “Equity Incentive Plan”) provides for the grant of stock options (both incentive and non-statutory), restricted stock awards, restricted stock unit awards, stock appreciation rights, and other forms of stock-based awards to employees, consultants and directors. During the nine months ended September 30, 2019 and 2018, the Company granted stock options that vest over four years and have a maximum contractual term of ten years. The Company also granted restricted stock awards that vest over two years during the nine months ended September 30, 2018. Vesting is subject to the holder’s continuous service with the Company. The Company reserved 5,541,224 shares of common stock for issuance under the Equity Incentive Plan. Stock options The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2019: Number of options Weighted- average exercise price Weighted- average remaining contractual term (years) Outstanding at December 31, 2018 2,485,650 $ 2.84 9.25 Granted 1,242,700 $ 11.92 Exercised (493,525 ) $ 2.84 Cancelled (92,000 ) $ 2.84 Outstanding at September 30, 2019 3,142,825 $ 6.43 9.0 Exercisable at September 30, 2019 391,720 $ 2.84 8.4 Vested and expected to vest at September 30, 2019 3,142,825 $ 6.43 9.0 No options were vested or exercisable as of December 31, 2018. The weighted average grant date fair value per share of options granted during the nine months ended September 30, 2019 and 2018 was $8.51 and $1.99, respectively. The aggregate intrinsic value of options vested and expected to vest as of September 30, 2019 was approximately $39,505. The aggregate intrinsic value of options vested and exercisable as of September 30, 2019 was approximately $6,330. As of September 30, 2019, there was approximately $13,071 total unrecognized compensation expense, related to the unvested stock options, which is expected to be recognized over a weighted average period of 2.99 years. Restricted common stock The following table summarizes the information about restricted stock awards (“RSA”) outstanding at September 30, 2019: Number of shares Grant-date fair value Unvested as of December 31, 2018 757,577 $ 2.84 Granted — $ — Vested/Released (378,789 ) $ 2.84 Cancelled (6,258 ) $ 2.84 Unvested as of September 30, 2019 372,530 $ 2.84 There were no shares of restricted common stock granted to employees during the nine months ended September 30, 2019. The restricted stock vests 50% on each anniversary date of the grant, over a two-year period. Vesting is subject to the holder’s continuous service with the Company. As of September 30, 2019, there was approximately $463 of total unrecognized compensation expense, related to the restricted stock grants, which is expected to be recognized over a weighted average period of 0.44 years. Stock-based compensation Stock-based compensation expense for the three and nine months ended September 30, 2019 and 2018 was comprised of the following: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development $ 460 $ 297 $ 1,100 $ 621 Selling, general and administrative 471 283 1,118 647 Total stock-based compensation expense $ 931 $ 580 $ 2,218 $ 1,268

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	9. Income taxes During the nine months ended September 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. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of September 30, 2019 and December 31, 2018. Management reevaluates the positive and negative evidence at each reporting period. As of September 30, 2019 and December 31, 2018, no facts or circumstances arose that affected the Company’s determination as to the full valuation established against the net deferred tax assets. As of September 30, 2019 and December 31, 2018, the Company had not recorded any amounts for unrecognized tax benefits. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of September 30, 2019 and December 31, 2018, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts had been recognized in the Company’s statements of operations and comprehensive loss. The Company files income tax returns in the U.S. and Maryland, as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company is open to future tax examination under statute from 2018 to the present.

Benefit Plan

Benefit Plan	9 Months Ended
	Sep. 30, 2019
Compensation And Retirement Disclosure [Abstract]
Benefit Plan	10. Benefit plan The Company maintains a defined contribution 401(k) plan, under which employee contributions are voluntary and are determined on an individual basis, limited by the maximum amounts allowable under federal tax regulations. The Company provides an automatic matching contribution of $1.00 per $1.00 of employee contribution into the plan up to a maximum of 4% of employee deferral. The Company’s matching contributions to employees totaled approximately $110 and $59, during the three months ended September 30, 2019 and 2018, respectively, and $353 and $111, during the nine months ended September 30, 2019 and 2018, respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and contingencies Contingencies In the ordinary course of business, the Company may become a party to lawsuits involving various matters. The Company is not currently a party, and its properties are not currently subject, to any legal proceedings that, in the opinion of management, are expected to have a material adverse effect on the Company’s business, financial condition or results of operations. Milestone and Royalty Payments At the inception of each license and collaboration agreement with third parties, which may require the Company to make milestone payments, the Company evaluates whether each milestone and royalty payments are substantive and at risk to both parties on the basis of the contingent nature of the milestone and royalty. The Company aggregates milestones into three categories (i) research milestones, (ii) development milestones and (iii) commercial milestones and royalties. Research milestones are typically achieved upon reaching certain criteria as defined in each agreement related to developing a molecule against the specified target. Development milestones are typically reached when a molecule reaches a defined phase of clinical research or passes such phase, or upon gaining regulatory approvals. Commercial milestones and royalties are typically achieved when an approved pharmaceutical product reaches the status for commercial sale or certain defined levels of net sales by the licensee, such as when a product first achieves global sales or annual sales of a specified amount. The Company made a regulatory milestone payment of approximately $19,800 in September 2019, in connection with acceptance for review by the FDA of the Company’s Biologics License Application (“BLA”) for inebilizumab in patients with neuromyelitis optica spectrum disorder (“NMOSD”) in August 2019. For the three and nine months ended September 30, 2019, the $19,800 of regulatory milestone payments were recorded within research and development expenses on the statement of operations. In addition, the Company expects to pay approximately $20,000 if the BLA is approved by the FDA for NMOSD. Employment Agreements The Company has entered into employment agreements with certain of its executive officers. Generally, the terms of these agreements provide that, if the Company terminates the officer other than for cause, death or disability, or if the officer terminates his or her employment with the Company for good cause, the officer shall be entitled to receive certain severance compensation and benefits as described in each such agreement. Office Lease The Company entered into an operating lease agreement with a related party for its headquarters in Gaithersburg, Maryland. The lease is effective July 1, 2018 and expires in June 2021 with the option to extend it by one year. Total lease payments under the lease are: $300 for 2018; $365 for the year ended December 31, 2019; $376 for the year ended December 31, 2020; and $191 for the remainder of the lease. Rent expense was $64 and $51 for the three months ended September 30, 2019 and 2018, respectively, and $167 and $119 for the nine months ended September 30, 2019 and 2018, respectively.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	12. Related party transactions In connection with the Asset Acquisition, the Company also entered into certain other agreements with the AZ Parties, including transition services agreement, a clinical supply agreement, a commercial supply agreement, a master supply and development services agreement, and a long-term lease agreement. During the nine months ended September 30, 2019, the Company incurred $28,805 of costs under these agreements, of which $13,100 is recorded as a related party liability on the Company’s balance sheet as of September 30, 2019. During the nine months ended September 30, 2018, the Company incurred $23,254 of costs under these agreements.

Collaboration Agreements

Collaboration Agreements	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborative Agreements	13. Collaboration agreements Commercial license and collaboration agreement with Hansoh On May 24, 2019 (the “Effective Date”), the Company entered into an exclusive commercial license and collaboration agreement with Hansoh Pharmaceutical Group Company Limited (“Hansoh”). By entering into this agreement, the Company promised to Hansoh the following goods or services: (i) deliver an exclusive, sub-licensable, license to commercialize any pharmaceutical product that includes inebilizumab, the Company’s lead product candidate, in the mainland of the People’s Republic of China, Hong Kong and Macau (the “Territory”) (the “Commercial License”); (ii) to use commercially reasonable efforts to obtain regulatory approval from the FDA for a monotherapy use of inebilizumab in connection with the NMOSD indication (“FDA Approval”); (iii) to use commercially reasonable efforts to obtain regulatory approval from the National Medical Products Administration (“NMPA”) for monotherapy use of inebilizumab in connection with the NMOSD indication, as well as any other licensed product containing inebilizumab (including both monotherapy use and in combination with other agents), as approved by the joint coordination committee (“JCC”) in the Territory (“NMPA Approval”); (iv) provide Hansoh the ability to select two or more of the following indications: Non-Hodgkin lymphoma (“NHL”), Chronic lymphocytic leukemia (“CLL”), Multiple Sclerosis (“MS”), Rheumatoid Arthritis (“RA”), Multiple Myeloma (“MM”), and for any other indication that is presented by Hansoh to the Company and approved by the Company to replace one of the predetermined indications for further development in the territory, each of which Hansoh will be responsible for the development and commercialization while the Company will be responsible for performing the regulatory approval activities in the Territory (collectively, the “Selected Indications”); (v) at the Company’s discretion, provide Hansoh with certain participation rights related to the Company’s development and commercialization of other uses of inebilizumab in the Territory, including both monotherapy and in combination with other agents, but excluding the following indications: NMOSD, NHL, CLL, MS, RA and MM (the “Opt-In”). In the event that Hansoh does not elect to participate in these development activities or meet its payment terms with respect to costs incurred in the Territory that are reimbursable to the Company, all commercial rights with respect to the developed indication revert to the Company; and (vi) deliver a co-exclusive license, which provides Hansoh with the exclusive rights to (i) develop inebilizumab, including any clinical trials and other activities directed toward obtaining regulatory approval in the Territory, for all indications within the Selected Indications and (ii) co-develop inebilizumab with the Company for those indications within the Opt-In (the “Co-Development License”). In addition, the Company and Hansoh formed a JCC to provide oversight to the activities performed under the agreement; however, the substance of the Company’s participation in the JCC does not represent an additional promised service, but rather, a right of the Company to protect its own interests in the arrangement. Further, the Company and Hansoh entered into a supply agreement through which the Company shall supply to Hansoh, and Hansoh agrees to purchase from the Company, any and all requirements of any licensed product including inebilizumab for development and commercialization in the Territory during the term. The terms of the supply agreement do not provide for either (i) an option to Hansoh to purchase product from the Company at a discount from the standalone selling price or (ii) minimum purchase quantities. Finally, Hansoh will bear (i) all costs and expenses for any development of inebilizumab for all indications in the Territory subject to the exclusive license and (ii) all costs and fees associated with applying for regulatory approval of any product candidates in the Territory. The Company received a non-refundable upfront payment of $15,000 in June 2019 and an additional $5,000 is payable within six months after the Effective Date. In addition, the Company has the ability to receive additional payments under the agreement of up to approximately $203,000, including up to $180,000 in commercial milestone payments and development milestone payments ranging from $2,000 to $5,000 on an indication-by-indication basis. The Company is also entitled to receive tiered royalties ranging from the low double-digit percentages to the upper-teen percentages on aggregate net sales of any products developed and commercialized in the Territory, subject to customary potential reductions. The Company assessed this arrangement in accordance with ASC 606 and concluded that the promises summarized above represent transactions with a customer within the scope of ASC 606. The Company determined that the following promises represent distinct promised services, and therefore, separate performance obligations: (i) the Commercialization License, (ii) FDA Approval, (iii) NMPA Approval, (iv) the Selected Indications (inclusive of the Co-Development License) and (y) the Opt-In (inclusive of the Co-Development License). Specifically, in making these determinations, the Company considered the following factors: • Shortly after the Effective Date, the Company received Breakthrough Therapy Designation for the treatment of NMOSD with Inebilizumab from the FDA and the Company submitted a BLA in June 2019. Accordingly, the Company is not promising, nor expecting, to perform additional research and development activities pursuant to the agreement that would either significantly modify or customize or be considered highly interdependent or interrelated with Inebilizumab. • The Commercialization License represents functional intellectual property given the functionality of the Commercialization License is not expected to change substantially as a result of the Company’s ongoing activities. • The Company previously incurred a significant portion of the total estimated costs necessary for FDA Approval prior to the Effective Date. That is, as of the Effective Date, the remaining costs to achieve FDA Approval are expected to be immaterial. • The services necessary to seek NMPA Approval are a readily available resource that are sold separately by third-party vendors. • Hansoh can benefit from both the Selected Indications and the Opt-In together with readily available resources. Further, the Company is not providing a significant service of integration, nor are they significantly modifying or customizing Inebilizumab through these promises. • The Co-Development License does not grant any development rights to Hansoh outside of those indications included within the Selected Indications and the Opt-In. • The Co-Development License is highly interdependent or interrelated with the Selected Indications and the Opt-In. Specifically, (1) the Co-Development License significantly affects the Selected Indications and the Opt-In because in the absence of the Co-Development License, Hansoh would be limited to just selecting certain indications that it would like to develop, but would have no legal right to develop such indication; and (2) the Selected Indications and the Opt-In significantly affect the Co-Development License because the scope of the Co-Development License is limited to the development of Inebilizumab for those indications included within the Selected Indications and the Opt-In. Under the agreement with Hansoh, in order to evaluate the appropriate transaction price, the Company determined that the upfront payment amount of approximately $20,000, $5,000 of which has yet to be received, constituted the entire consideration to be included in the transaction price as of the outset of the arrangement. While the Company identified multiple performance obligations, this amount was allocated entirely to the Commercialization License performance obligation as the standalone selling price of the remaining performance obligations was deemed to be immaterial at contract inception. In making this determination, the Company observed that the estimated costs associated with both the FDA Approval and NMPA Approval performance obligations are immaterial in the context of the arrangement with Hansoh. In addition, the Company also observed that significant uncertainty existed at the contract inception date related to whether (i) the Company would pursue any indications that would, in-turn, provide Hansoh with an opportunity to utilize the Opt-In (inclusive of the Co-Development License), (ii) Hansoh would pursue the development of any of the Selected Indications (inclusive of the Co-Development License), and (iii) the likelihood that any development activities would ultimately be successful. The potential commercial and development milestone payments that the Company is eligible to receive were excluded from the transaction price, as all milestone amounts were fully constrained based on the probability of achievement, since the milestones relate to successful achievement of certain commercialization, developmental and regulatory approval goals, which might not be achieved. None of the future royalty payments were included in the transaction price, as the potential payments were determined to be subject to the sales-based royalty exception. The Company will reevaluate the transaction price, including all constrained amounts, at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust its estimate of the transaction price. Because the entire transaction price was allocated to the Commercialization License performance obligation, which represents functional intellectual property, the Company recognized the associated revenue of $20,000 at the Effective Date. As noted previously, approximately $15,000 of the total upfront payment was received within 30 days after the Effective Date. The remaining $5,000 is payable to the Company within six months after the Effective Date, and therefore, was recorded within accounts receivable as of September 30, 2019 as the Company currently has the contractual right to bill for this amount.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent events On October 8, 2019, the Company, entered into a license agreement (the “License Agreement”), with Mitsubishi Tanabe Pharma Corporation (“MTPC”), for co-development and commercialization of inebilizumab in Japan, Thailand, South Korea, Indonesia, Vietnam, Malaysia, Philippines, Singapore, and Taiwan (the “MTPC Territory”) for NMOSD as well as other indications that the Company and MTPC mutually agree to add to the License Agreement. Under the terms of the License Agreement, the Company is eligible to receive up-front licensing fees of an aggregate of $30,000 as well as development and commercialization milestones and payments based, in part, on sales revenue. Pursuant to the License Agreement, the Company granted MTPC an (i) exclusive license under its intellectual property to develop, commercialize, and conduct final manufacturing of inebilizumab in the MTPC Territory, and (ii) a non-exclusive license under any patent it controls solely to the extent useful or necessary to enable MTPC to develop, commercialize and finally manufacture products in the MTPC Territory, but excluding rights to any active pharmaceutical ingredient or compound other than inebilizumab. MTPC will be responsible for leading development, commercialization, and final manufacturing of inebilizumab in the MTPC Territory. The Company will be responsible for supplying inebilizumab to MTPC pursuant to a supply agreement that it expects to enter into. On a country-by-country and product-by-product basis, the licenses will become perpetual, non-exclusive and fully paid-up upon the later of (a) the expiration of the last valid claim of a Company patent covering the product; (b) the expiration of any regulatory exclusivity with respect to the product; or (c) 10 years after the first commercial sale of the product in such country. The License Agreement continues for so long as MTPC is developing or commercializing inebilizumab in the MTPC Territory, unless terminated by MTPC or by the Company. MTPC may terminate the License Agreement at any time upon 180 days’ notice to the Company. The Company may terminate the License Agreement upon the occurrence of certain adverse events that are not cured by MTPC within the specified cure periods. Either party may terminate the License Agreement under specified circumstances relating to the other party’s insolvency.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). All adjustments necessary for the fair presentation of the Company’s financial statements have been presented. The accompanying balance sheet as of September 30, 2019, the related statements of operations and comprehensive loss and redeemable convertible preferred stock and stockholders’ deficit for the three and nine months ended September 30, 2019 and 2018, and the statements of cash flows for the nine months ended September 30, 2019 and 2018 and related footnote disclosures are unaudited. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying interim balance sheet, statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ deficit and cash flows have been made. The results for the nine months ended September 30, 2019 and 2018, 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	Use of estimates The preparation of the Company’s 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 financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the recognition of research and development expenses based on when services are performed, the valuations of share based compensation arrangements, and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and cash equivalents The Company considers all highly liquid instruments with an original maturity of 90 days or less at acquisition to be cash equivalents.
Marketable Securities	Marketable Securities The Company’s marketable securities are classified as available-for-sale and are carried at fair value, with the unrealized gains and losses reported as a component of accumulated other comprehensive loss in stockholder’s deficit. Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the statements of operations and comprehensive loss. Marketable securities that mature within one year from the balance sheet date are classified as short-term. The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustments to fair value reflects a decline in the value of the investment that the Company considers to be “other-than-temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Concentrations of Credit Risk	Concentrations of credit risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash and the Company’s money market fund investment. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Fair Value Measurements	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 amount of the Company’s financial instruments, including cash and cash equivalents and accounts payable approximate their fair values. No transfer of assets between Level 1 and Level 2 of the fair value hierarchy occurred during the three and nine months ended September 30, 2019 and 2018.
Deferred Offering Costs	Deferred Offering Costs The Company has deferred offering costs, consisting of legal, accounting, printer and filing fees related to the IPO, that were deferred and were offset against the offering proceeds upon the completion of the IPO in October, 2019. As of September 30, 2019, $3,327 of deferred offering costs were recorded within prepaids and other current assets on the balance sheet. As of December 31, 2018, no amounts were deferred.
Segment Information	Segment information The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is developing and commercializing transformative treatments for severe inflammation and autoimmune diseases.
Research and Development Expenses	Research and development expenses Research and development expenses are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, allocated facility-related and depreciation expenses, third-party license fees and external costs including fees paid to consultants and clinical research organizations (“CROs”), in connection with nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Costs incurred in purchasing technology or technology licenses are charged immediately to research and development expense if the technology has not reached technological feasibility and has no alternative future uses. Clinical trial costs are a significant component of research and development expenses and include costs associated with third-party contractors. A majority of these payments are pass-through payments that are made to AZ Parties due to the existing contracts in place associated with the in-process research and development (“IPR&D”) assets acquired (see Note 7, “Asset acquisition”). The Company, through the AZ Parties outsources a substantial portion of its clinical trial activities, utilizing external entities such as CROs, independent clinical investigators, and other third-party service providers to assist it with the execution of its clinical studies. For each clinical trial that the Company conducts, certain clinical trial costs are expensed immediately, while others are expensed over time based on the expected total number of patients in the trial, the rate at which patients enter the trial, and/or the period over which clinical investigators or CROs are expected to provide services. Clinical activities which relate principally to clinical sites and other administrative functions to manage the Company’s clinical trials are performed primarily by CROs. CROs typically perform most of the start-up activities for the Company’s trials, including document preparation, site identification, screening and preparation, pre-study visits, training, and program management. These start-up costs usually occur within a few months after the contract has been executed and are event-driven in nature. The remaining activities and related costs, such as patient monitoring and administration, generally occur ratably throughout the life of the individual contract or study. In the event of early termination of a clinical trial, the Company accrues and recognizes expenses in an amount based on its estimate of the remaining non-cancelable obligations associated with the winding down of the clinical trial and/or penalties. For clinical study sites, where payments are made periodically on a per-patient basis to the institutions performing the clinical study, the Company accrues expenses on an estimated cost-per-patient basis, based on subject enrollment and activity in each period. The amount of clinical study expense recognized in a period may vary from period to period based on the duration and progress of the study, the activities to be performed by the sites each quarter, the required level of patient enrollment, the rate at which patients actually enroll in and drop out of the clinical study, and the number of sites involved in the study. Clinical trials that bear the greatest risk of change in estimates are typically those that have a significant number of sites, require a large number of patients, have complex patient screening requirements, and span multiple years. During the course of a trial, the Company adjusts its rate of clinical expense recognition if actual results differ from the Company’s estimates. The Company’s estimates and assumptions for clinical expense recognition could differ significantly from the Company’s actual results, which could cause material increases or decreases in research and development expenses in future periods when the actual results become known.
Patent Costs	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.
Property and Equipment	Property and equipment Property and equipment, which consists mainly of laboratory equipment, are carried at cost less accumulated depreciation. Depreciation is computed over the estimated useful lives of the respective assets, generally ten years, using the straight-line method. Leasehold improvements are amortized over the shorter of the estimated useful lives of the assets or the lease term. Expenditures for maintenance and repairs which do not materially extend the useful lives of the assets are charged to expense as incurred. The cost and accumulated depreciation or amortization of assets that meet the guidance within Accounting Standards Codification (“ASC”) Topic 360 as either retired or sold are removed from the respective accounts, and any gain or loss is recognized in operations upon closing of the transaction. The Company periodically assesses the recoverability of long-lived assets, such as property and equipment, and evaluates such assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable.
Revenue Recognition for Contracts with Customers	Revenue Recognition for Contracts with Customers To date, the Company has recognized revenues through commercialization and collaboration agreements. Effective January 1, 2019, the Company adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue (ASC 606): Revenue from Contracts with Customers (“ASC 606”), using the modified retrospective transition method. Under this method, results for reporting periods beginning on January 1, 2019 are presented under ASC 606, while prior periods were prepared and reported in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The adoption of ASC 606 resulted in no cumulative adjustment as the Company had substantially no assets until executing the Asset Acquisition in February 2018 (as described in Note 7, “Asset acquisition”) and did not enter into a revenue contract with a customer until May 2019 (as described in Note 13, “Collaboration agreements”). ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. We assess if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right is accounted for as a contract modification for accounting purposes. The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. Amounts recognized as revenue for which the Company has the contractual right to bill, but has not yet received, are classified as accounts receivable in the accompanying balance sheets. Amounts recognized as revenue for which the Company does not have the contractual right to bill are generally recognized as contract assets in the accompanying balance sheets. Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current liabilities in the accompanying balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as long-term liabilities. Licenses of Intellectual Property – The terms of the Company’s contracts with customers may include the license of functional intellectual property, given the functionality of the intellectual property is not expected to change substantially as a result of the Company’s ongoing activities. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from the portion of the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises (that is, for licenses that are not distinct from other promised goods and services in an arrangement), the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments – If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. Royalties – For arrangements that include sales-based royalties, including milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue or milestone payments resulting from any of its licensing arrangements. Significant Financing Component – In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed each of its revenue arrangements in order to determine whether a significant financing component exists and concluded that a significant financing component does not exist in any of its arrangements. Collaborative Arrangements – The Company enters into collaboration agreements, which are within the scope of ASC 606, to discover, develop, manufacture or commercialize product candidates. The terms of these agreements typically contain multiple promises or obligations, which may include: (1) licenses, or options to obtain licenses, to use the Company’s technology, (2) research and development activities to be performed on behalf of the collaboration partner, and (3) in certain cases, services in connection with the manufacturing of preclinical and clinical material. Payments the Company receives under these arrangements typically include one or more of the following: non-refundable, upfront license fees; clinical and development, regulatory, and sales milestone payments; and royalties on future product sales. The Company also analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, the Company applies the five-step model described above.
Stock-based Compensation	Stock-based compensation The Company measures all stock-based awards granted to employees based on the fair value on the date of the grant and recognizes compensation expense into either general and administrative expense or research and development expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for forfeitures as they occur. For stock-based awards with service-based vesting conditions, the Company recognizes compensation expense using the straight-line method. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option The Company classifies stock-based compensation expense in its statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Income Taxes	Income taxes The Company accounts for income taxes in accordance with ASC Topic 740, Income Taxes The Company recognizes the impact of an uncertain tax position if the position will more likely than not be sustained upon examination by a taxing authority, based on the technical merits of the position. The Company’s policy is to recognize interest related to unrecognized tax benefits as interest expense and penalties as operating expenses. As of September 30, 2019, the Company had no unrecognized tax benefits and as such, no liability, interest or penalties were required to be recorded. The Company does not expect this to change significantly in the next twelve months.
Net Loss Per Share	Net loss per share Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing net loss by the weighted average number of common shares adjusted for the dilutive effect of common equivalent shares outstanding during the period. As of September 30, 2019, and December 31, 2018, common stock equivalents consisted of the Preferred Stock and stock options that were vested and exercisable as of September 30, 2019 and December 31, 2018. Net loss per share attributable to common stockholders is calculated using the two-class method, which is an earnings allocation formula that determines net loss per share for the holders of the Company’s common shares and participating securities. The Company’s Preferred Stock contains participating rights in any dividend paid by the Company and are deemed to be participating securities. Net loss attributable to common stockholders and participating preferred shares is allocated to each share on an as-converted basis as if all of the earnings for the period had been distributed. The participating securities do not include a contractual obligation to share in the losses of the Company and are not included in the calculation of net loss per share in the periods that have a net loss. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect on net loss per share. Diluted net loss per share is computed using the more dilutive of (a) the two-class method or (b) the if-converted method. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Diluted net loss per share is equivalent to basic net loss per share for the periods presented herein because common stock equivalent shares from the Series A and Series B Preferred Stock were anti-dilutive. Due to their dilutive effect, the calculation of diluted net loss per share for the nine months ended September 30, 2019, and 2018 does not include the following common stock equivalent shares: September 30, 2019 2018 Series A Preferred Stock 35,931,206 28,225,324 Series B Preferred Stock 4,687,500 — Stock Options 391,720 — Total 41,010,426 28,225,324 For the three and nine months ended September 30, 2019 and 2018, there were no reconciling items between basic and diluted net loss per share.
Emerging Growth Company	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 Adopted and Issued Accounting Pronouncements	Recently adopted accounting pronouncements In January 2017, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and ASC 606 (“ASU 2018-18”). The amendments in ASU 2018-18 make targeted improvements to GAAP for collaborative arrangements by clarifying that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement, presentation, and disclosure requirements. In addition, unit-of-account guidance in ASU 2018-18 was aligned with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted, including adoption in any interim period. The amendments should be applied retrospectively to the date of initial application of ASC 606. The Company adopted this guidance effective January 1, 2019 with its initial application of ASC 606. The adoption of the standard did not have an impact on the Company’s financial statements. Recently issued accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 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 In August 2018, the FASB issued No. ASU 2018-13, Fair Value Measurement (Topic 820)—Disclosure Framework

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	Due to their dilutive effect, the calculation of diluted net loss per share for the nine months ended September 30, 2019, and 2018 does not include the following common stock equivalent shares: September 30, 2019 2018 Series A Preferred Stock 35,931,206 28,225,324 Series B Preferred Stock 4,687,500 — Stock Options 391,720 — Total 41,010,426 28,225,324

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Available-For-Sale Marketable Securities and Cash Equivalents	The following is a summary of the Company’s available-for-sale marketable securities and cash equivalents as of September 30, 2019: Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Cash equivalents Certificates of deposit and time deposits $ 400 $ — $ — $ 400 Commercial paper 11,532 — (1 ) 11,531 Total cash equivalents $ 11,932 $ — $ (1 ) $ 11,931 Current marketable securities: Certificates of deposit and time deposits $ 3,802 $ — $ (1 ) $ 3,801 Commercial paper 17,922 — (2 ) 17,920 Corporate debt securities 20,783 3 (12 ) 20,774 Total marketable securities, current $ 42,507 $ 3 $ (15 ) $ 42,495 Non-current marketable securities: U.S. Treasury securities $ 8,037 $ — $ (8 ) $ 8,029 Corporate debt securities 16,895 3 (12 ) 16,886 Total marketable securities, non-current $ 24,932 $ 3 $ (20 ) $ 24,915 Total marketable securities $ 67,439 $ 6 $ (35 ) $ 67,410

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Financial Assets Measured at Fair Value on Recurring Basis	As of September 30, 2019, the Company held certain assets that required to be measured at fair value on a recurring basis, as follows: September 30, 2019 Cash and Cash equivalents Short-Term Marketable Securities Long-Term Marketable Securities Cash $ 123,863 $ — $ — Level 1 Money market funds 19,953 — — Level 2 U.S. Treasury securities — — 8,029 Certificates of deposits and time deposits 400 3,801 — Corporate debt securities — 20,774 16,886 Commercial paper 11,531 17,920 — Subtotal 11,931 42,495 24,915 Total $ 155,747 $ 42,495 $ 24,915 As of December 31, 2018, the Company held certain assets that required to be measured at fair value on a recurring basis, as follows: December 31, 2018 Cash and Cash equivalents Short-Term Marketable Securities Long-Term Marketable Securities Cash $ 21,681 $ — $ — Level 1 Money market funds 105,217 — — Total $ 126,898 $ — $ —

Convertible Redeemable Prefer_2

Convertible Redeemable Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2019
Temporary Equity [Abstract]
Summary of Redeemable Convertible Preferred Stock	At September 30, 2019, the Company’s redeemable convertible preferred stock consisted of the following: Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Series A-1 Preferred Stock 14,225,324 14,225,324 $ 142,253 Series A-2 Preferred Stock 17,000,000 17,000,000 170,000 Series A-3 Preferred Stock 4,705,882 4,705,882 80,000 Series B Preferred Stock 4,687,500 4,687,500 75,000 Total 40,618,706 40,618,706 $ 467,253 At December 31, 2018, the Company’s redeemable convertible preferred stock also consisted of the following: Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Series A-1 Preferred Stock 14,225,324 14,225,324 $ 142,253 Series A-2 Preferred Stock 17,000,000 17,000,000 170,000 Series A-3 Preferred Stock 6,470,588 — — Series B Preferred Stock — — — Total 37,695,912 31,225,324 $ 312,253

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Company's Stock Option Activity	The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2019: Number of options Weighted- average exercise price Weighted- average remaining contractual term (years) Outstanding at December 31, 2018 2,485,650 $ 2.84 9.25 Granted 1,242,700 $ 11.92 Exercised (493,525 ) $ 2.84 Cancelled (92,000 ) $ 2.84 Outstanding at September 30, 2019 3,142,825 $ 6.43 9.0 Exercisable at September 30, 2019 391,720 $ 2.84 8.4 Vested and expected to vest at September 30, 2019 3,142,825 $ 6.43 9.0
Summary of Restricted Stock Awards (RSA) Outstanding	The following table summarizes the information about restricted stock awards (“RSA”) outstanding at September 30, 2019: Number of shares Grant-date fair value Unvested as of December 31, 2018 757,577 $ 2.84 Granted — $ — Vested/Released (378,789 ) $ 2.84 Cancelled (6,258 ) $ 2.84 Unvested as of September 30, 2019 372,530 $ 2.84
Schedule of Stock-based Compensation Expense	Stock-based compensation expense for the three and nine months ended September 30, 2019 and 2018 was comprised of the following: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development $ 460 $ 297 $ 1,100 $ 621 Selling, general and administrative 471 283 1,118 647 Total stock-based compensation expense $ 931 $ 580 $ 2,218 $ 1,268

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Oct. 31, 2019	Feb. 28, 2018
Subsequent Event | Common Stock
Subsidiary Sale Of Stock [Line Items]
Number of outstanding preferred stock converted into aggregate shares of common stock	40,618,706
IPO | Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock	7,900,000
Common stock price per share	$ 19
Gross proceeds	$ 150,100
Net proceeds	136,266
Underwriting discounts and commissions and other offering expenses	$ 13,834
Underwriter's Option to Purchase Additional Shares | Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock	1,185,000
Gross proceeds	$ 22,515
Net proceeds	20,939
Underwriting discounts and commissions and other offering expenses	1,576
Aggregate Gross Proceeds from IPO | Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Gross proceeds	172,615
Net proceeds	$ 157,205
Asset Purchase Agreement
Subsidiary Sale Of Stock [Line Items]
Assets purchase price		$ 142,253

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Schedule Of Significant Accounting Policies [Line Items]
Fair value hierarchy, transfer of assets from level 1 to level 2	$ 0		$ 0
Fair value hierarchy, transfer of assets from level 2 to level 1	0		0
Fair value hierarchy, transfer of liabilities from level 1 to level 2	0		0
Fair value hierarchy, transfer of liabilities from level 2 to level 1	$ 0		$ 0
Deferred offering costs		$ 0
Property and equipment, estimated useful lives	10 years
Unrecognized tax benefits	$ 0	$ 0
Prepaid Expenses and Other Current Assets
Schedule Of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 3,327,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Schedule Of Significant Accounting Policies [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	41,010,426	28,225,324
Series A Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	35,931,206	28,225,324
Series B Preferred Stock
Schedule Of Significant Accounting Policies [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	4,687,500
Stock Options
Schedule Of Significant Accounting Policies [Line Items]
Anti-dilutive shares excluded from calculation of diluted net loss per share	391,720

Marketable Securities - Summary

Marketable Securities - Summary of Available-For-Sale Marketable Securities and Cash Equivalents (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Total cash equivalents, Amortized Cost	$ 11,932,000
Total cash equivalents, Gross Unrealized Losses	(1,000)
Total cash equivalents, Fair Market Value	11,931,000
Total marketable securities, current, Amortized Cost	42,507,000
Total marketable securities, current, Gross Unrealized gains	3,000
Total marketable securities, current, Gross Unrealized Losses	(15,000)
Total marketable securities, current, Fair Market Value	42,495,000
Total marketable securities, non-current, Amortized Cost	24,932,000
Total marketable securities, non-current, Gross Unrealized gains	3,000
Total marketable securities, non-current, Gross Unrealized Losses	(20,000)
Total marketable securities, non-current, Fair Market Value	24,915,000
Total marketable securities, Amortized Cost	67,439,000
Total marketable securities, Gross Unrealized gains	6,000
Total marketable securities, Gross Unrealized Losses	(35,000)
Total marketable securities, Fair Market Value	67,410,000	$ 0
Certificates of Deposit and Time Deposits
Marketable Securities [Line Items]
Total cash equivalents, Amortized Cost	400,000
Total cash equivalents, Fair Market Value	400,000
Total marketable securities, current, Amortized Cost	3,802,000
Total marketable securities, current, Gross Unrealized Losses	(1,000)
Total marketable securities, current, Fair Market Value	3,801,000
Commercial Paper
Marketable Securities [Line Items]
Total cash equivalents, Amortized Cost	11,532,000
Total cash equivalents, Gross Unrealized Losses	(1,000)
Total cash equivalents, Fair Market Value	11,531,000
Total marketable securities, current, Amortized Cost	17,922,000
Total marketable securities, current, Gross Unrealized Losses	(2,000)
Total marketable securities, current, Fair Market Value	17,920,000
U.S. Treasury Securities
Marketable Securities [Line Items]
Total marketable securities, non-current, Amortized Cost	8,037,000
Total marketable securities, non-current, Gross Unrealized Losses	(8,000)
Total marketable securities, non-current, Fair Market Value	8,029,000
Corporate Debt Securities
Marketable Securities [Line Items]
Total marketable securities, current, Amortized Cost	20,783,000
Total marketable securities, current, Gross Unrealized gains	3,000
Total marketable securities, current, Gross Unrealized Losses	(12,000)
Total marketable securities, current, Fair Market Value	20,774,000
Total marketable securities, non-current, Amortized Cost	16,895,000
Total marketable securities, non-current, Gross Unrealized gains	3,000
Total marketable securities, non-current, Gross Unrealized Losses	(12,000)
Total marketable securities, non-current, Fair Market Value	$ 16,886,000

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Available for sale marketable securities	$ 67,410,000	$ 0
Minimum [Member]
Marketable Securities [Line Items]
Long-term marketable securities, maturity	1 year
Maximum
Marketable Securities [Line Items]
Long-term marketable securities, maturity	2 years

Fair Value Measurement - Financ

Fair Value Measurement - Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	$ 155,747	$ 126,898
Short-Term Marketable Securities	42,495
Long-Term Marketable Securities	24,915
Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	123,863	21,681
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	19,953	$ 105,217
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	11,931
Short-Term Marketable Securities	42,495
Long-Term Marketable Securities	24,915
Level 2 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-Term Marketable Securities	8,029
Level 2 | Certificates of Deposit and Time Deposits
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	400
Short-Term Marketable Securities	3,801
Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-Term Marketable Securities	20,774
Long-Term Marketable Securities	16,886
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and Cash equivalents	11,531
Short-Term Marketable Securities	$ 17,920

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares authorized	46,159,941	41,254,509
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares issued	872,324	10
Common stock, shares outstanding	872,324	10
Dividends	$ 0
Restricted Common Stock
Class Of Stock [Line Items]
Shares granted	0
Shares vested	378,789
Restricted Common Stock | 2018 Equity Incentive Plan
Class Of Stock [Line Items]
Shares granted	0	757,577
Shares vested	378,789	0

Convertible Redeemable Prefer_3

Convertible Redeemable Preferred Stock - Additional Information (Details)	Oct. 03, 2019shares	Feb. 23, 2018USD ($)$ / sharesshares	Oct. 31, 2019USD ($)	Sep. 30, 2019USD ($)$ / sharesshares	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2019USD ($)Director$ / sharesshares	Sep. 30, 2018USD ($)
Redeemable Convertible Preferred Stock [Line Items]
Redeemable convertible preferred stock				40,618,706		37,695,912	40,618,706
Redeemable convertible preferred stock,Per share | $ / shares				$ 0.001		$ 0.001	$ 0.001
Proceeds from issuance of redeemable convertible preferred stock | $		$ 282,253,000					$ 167,000,000	$ 282,253,000
Receivables from redeemable convertible preferred stock | $						$ 12,000,000
Number of directors | Director							8
Dividends declared or paid | $							$ 0
IPO | Subsequent Event
Redeemable Convertible Preferred Stock [Line Items]
Proceeds from public offering | $			$ 136,266,000
Common Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock, liquidation preference | $				$ 468,995,000		$ 312,253,000	$ 468,995,000
Common Stock | IPO | Subsequent Event
Redeemable Convertible Preferred Stock [Line Items]
Number of outstanding preferred stock converted into aggregate shares of common stock	40,618,706
Maximum
Redeemable Convertible Preferred Stock [Line Items]
Shares issued, price per share | $ / shares				$ 17.60			$ 17.60
Minimum [Member]
Redeemable Convertible Preferred Stock [Line Items]
Proceeds from public offering | $							$ 75,000,000
Series A-1 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Redeemable convertible preferred stock				14,225,324		14,225,324	14,225,324
Redeemable convertible preferred stock,Per share | $ / shares		$ 0.001		$ 0.001		$ 0.001	$ 0.001
Convertible redeemable preferred stock, shares issued		14,225,324		14,225,324		14,225,324	14,225,324
Convertible redeemable preferred stock purchase price per share | $ / shares		$ 10
Preferred stock holder entitled to elect number of directors | Director							2
Series A-2 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Redeemable convertible preferred stock				17,000,000		17,000,000	17,000,000
Redeemable convertible preferred stock,Per share | $ / shares		$ 0.001		$ 0.001		$ 0.001	$ 0.001
Convertible redeemable preferred stock, shares issued		14,000,000		17,000,000		17,000,000	17,000,000
Convertible redeemable preferred stock purchase price per share | $ / shares		$ 10
Proceeds from issuance of redeemable convertible preferred stock | $						$ 30,000,000
Convertible redeemable preferred stock issuance of additional shares						3,000,000
Convertible redeemable preferred stock additional price per shares | $ / shares		$ 10
Receivables from redeemable convertible preferred stock | $						$ 12,000,000
Percentage of redeemable convertible preferred stock converted to common stock redeemed							90.00%
Preferred stock holder entitled to elect number of directors | Director							4
Series A-2 Preferred Stock | Maximum
Redeemable Convertible Preferred Stock [Line Items]
Convertible redeemable preferred stock issuance of additional shares		3,000,000
Series A-3 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Redeemable convertible preferred stock				4,705,882		6,470,588	4,705,882
Redeemable convertible preferred stock,Per share | $ / shares				$ 0.001		$ 0.001	$ 0.001
Convertible redeemable preferred stock, shares issued				4,705,882		0	4,705,882
Convertible redeemable preferred stock purchase price per share | $ / shares		$ 17		$ 17
Proceeds from issuance of redeemable convertible preferred stock | $				$ 80,000,000
Series A-3 Preferred Stock | Maximum
Redeemable Convertible Preferred Stock [Line Items]
Convertible redeemable preferred stock, shares issued		6,470,588
Series B Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Redeemable convertible preferred stock				4,687,500		0	4,687,500
Redeemable convertible preferred stock,Per share | $ / shares				$ 0.001	$ 0.001	$ 0.001	$ 0.001
Convertible redeemable preferred stock, shares issued				4,687,500	4,687,500	0	4,687,500
Convertible redeemable preferred stock purchase price per share | $ / shares					$ 16
Proceeds from issuance of redeemable convertible preferred stock | $					$ 75,000,000
Preferred stock holder entitled to elect number of directors | Director							1
Preferred stock, dividend per share | $ / shares							$ 1.28
Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock holder entitled to elect number of directors | Director							7
Series A Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Affirmative vote of outstanding shares percentage							75.00%
Series A-2 and A-3 Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Affirmative vote of outstanding shares percentage							75.00%

Convertible Redeemable Prefer_4

Convertible Redeemable Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018
Redeemable Convertible Preferred Stock [Line Items]
Preferred Stock Authorized	40,618,706		37,695,912
Preferred Stock Issued and Outstanding	40,618,706		31,225,324
Carrying Value	$ 467,253		$ 312,253
Series A-1 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred Stock Authorized	14,225,324		14,225,324
Preferred Stock Issued and Outstanding	14,225,324		14,225,324
Carrying Value	$ 142,253	$ 142,253	$ 142,253	$ 142,253	$ 142,253
Series A-2 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred Stock Authorized	17,000,000		17,000,000
Preferred Stock Issued and Outstanding	17,000,000		17,000,000
Carrying Value	$ 170,000	170,000	$ 170,000	$ 140,000	$ 140,000
Series A-3 Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred Stock Authorized	4,705,882		6,470,588
Preferred Stock Issued and Outstanding	4,705,882
Carrying Value	$ 80,000
Series B Preferred Stock
Redeemable Convertible Preferred Stock [Line Items]
Preferred Stock Authorized	4,687,500		0
Preferred Stock Issued and Outstanding	4,687,500
Carrying Value	$ 75,000	$ 75,000

Asset Acquisition - Additional

Asset Acquisition - Additional Information (Details) - In-process Research and Development - AZ Parties $ in Thousands	1 Months Ended
	Feb. 28, 2018USD ($)
Finite Lived Intangible Assets [Line Items]
Purchase price of asset acquisition	$ 142,253
Direct and incremental transaction expenses	$ 1,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options vested or exercisable	391,720		0
Weighted average grant date fair value per share of options granted	$ 8.51	$ 1.99
Aggregate intrinsic value of options vested and expected to vest	$ 39,505
Aggregate intrinsic value of options vested and exercisable	6,330
Total unrecognized compensation expense related to unvested stock options	$ 13,071
Unvested stock option recognized over period	2 years 11 months 26 days
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, number of common stock shares for issuance under plan	5,541,224
Stock Option | 2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, vesting period	4 years	4 years
Stock Option | 2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, contractual term	10 years	10 years
Restricted Stock Awards (RSA)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, vesting period	2 years
Unvested stock option recognized over period	5 months 8 days
Shares granted	0
Total unrecognized compensation expense related to restricted stock grants	$ 463
Restricted Stock Awards (RSA) | Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock vesting percentage	50.00%
Restricted Stock Awards (RSA) | Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock vesting percentage	50.00%
Restricted Stock Awards (RSA) | 2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, vesting period	2 years
Shares granted	0		757,577

Stock-based compensation - Sche

Stock-based compensation - Schedule of Company's Stock Option Activity (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019$ / sharesshares	Dec. 31, 2018$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of options, Outstanding at December 31, 2018 | shares	2,485,650
Number of options, Granted | shares	1,242,700
Number of options, Exercised | shares	(493,525)
Number of options, Cancelled | shares	(92,000)
Number of options, Outstanding at September 30, 2019 | shares	3,142,825	2,485,650
Number of options, Exercisable at September 30, 2019 | shares	391,720	0
Number of options, Vested and expected to vest at September 30, 2019 | shares	3,142,825
Weighted-average exercise price, Outstanding at December 31, 2018 | $ / shares	$ 2.84
Weighted-average exercise price, Granted | $ / shares	11.92
Weighted-average exercise price, Exercised | $ / shares	2.84
Weighted-average exercise price, Cancelled | $ / shares	2.84
Weighted-average exercise price, Outstanding at September 30, 2019 | $ / shares	6.43	$ 2.84
Weighted-average exercise price, Exercisable at September 30, 2019 | $ / shares	2.84
Weighted-average exercise price, Vested and expected to vest at September 30, 2019 | $ / shares	$ 6.43
Weighted-average remaining contractual term, Outstanding	9 years	9 years 3 months
Weighted-average remaining contractual term, Exercisable at September 30, 2019	8 years 4 months 24 days
Weighted-average remaining contractual term, Vested and expected to vest at September 30, 2019	9 years

Stock-based compensation - Summ

Stock-based compensation - Summary of Restricted Stock Awards (RSA) Outstanding (Details) - Restricted Stock Awards (RSA)	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, Unvested as of December 31, 2018	757,577
Shares granted	0
Number of shares, Vested/Released	(378,789)
Number of shares, Cancelled	(6,258)
Number of shares, Unvested as of September 30, 2019	372,530
Grant-date fair value, Unvested as of December 31, 2018 | $ / shares	$ 2.84
Grant-date fair value, Vested/Released | $ / shares	2.84
Grant-date fair value, Cancelled | $ / shares	2.84
Grant-date fair value, Unvested as of September 30, 2019 | $ / shares	$ 2.84

Stock-based compensation - Sc_2

Stock-based compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 931	$ 580	$ 2,218	$ 1,268
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	460	297	1,100	621
Selling, General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 471	$ 283	$ 1,118	$ 647

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0
Deferred tax assets, valuation allowance	0		$ 0
Accrued interest or penalties related to uncertain tax positions	0		0
Amount of accrued interest or penalties recognized	0		0
Unrecognized tax benefits	$ 0		$ 0

Benefit Plan - Additional Infor

Benefit Plan - Additional Information (Details) - 401(k) Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Contribution Plan Disclosure [Line Items]
Automatic matching contribution of employer ($1.00 per $1.00 of employee contribution)			100.00%
Maximum contribution by employee, percentage			4.00%
Company contributions to 401 (k) plan	$ 110	$ 59	$ 353	$ 111

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jul. 01, 2018
Loss Contingencies [Line Items]
Regulatory milestone payments	$ 19,800
Additional regulatory expected payments				$ 20,000
Operating lease effective date				Jul. 1, 2018
Operating lease expiration date				2021-06
Lessee, Operating Lease, Existence of Option to Extend [true false]				true
Operating lease, option to extend				option to extend it by one year
Operating lease term of extension				1 year
Total lease payment under lease for 2018						$ 300
Lease payment under lease for 2019						365
Lease payment under lease for 2020						376
Lease payment for remainder of lease						$ 191
Rent expense		$ 64	$ 51	$ 167	$ 119
Research and Development Expense
Loss Contingencies [Line Items]
Regulatory milestone payments		$ 19,800		$ 19,800

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Related party liability	$ 13,100		$ 12,054
AZ Parties
Related Party Transaction [Line Items]
Costs under agreements	28,805	$ 23,254
Related party liability	$ 13,100

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Details) - USD ($)	May 24, 2019	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognized associated revenue					$ 20,000,000
Revenue from Contract with Customer, Product and Service [Extensible List]			us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Commercial License And Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payments received		$ 15,000,000
Additional upfront non-refundable amount payment payable		5,000,000	$ 5,000,000		$ 5,000,000
Upfront payment	$ 20,000,000
Upfront payment yet to be received	5,000,000
Recognized associated revenue	$ 20,000,000
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:LicenseMember
Commercial License And Collaboration Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional payments under agreement ability to receive		203,000,000
Commercial milestone payments		180,000,000
Development milestone payments		5,000,000
Commercial License And Collaboration Agreement | Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone payments		$ 2,000,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event - Mitsubishi Tanabe Pharma Corporation $ in Thousands	Oct. 08, 2019USD ($)
Subsequent Event [Line Items]
Upfront licensing fees receivable	$ 30,000
Supply agreement description	The Company will be responsible for supplying inebilizumab to MTPC pursuant to a supply agreement that it expects to enter into. On a country-by-country and product-by-product basis, the licenses will become perpetual, non-exclusive and fully paid-up upon the later of (a) the expiration of the last valid claim of a Company patent covering the product; (b) the expiration of any regulatory exclusivity with respect to the product; or (c) 10 years after the first commercial sale of the product in such country.
Number of years considered after first commercial sale of product in country	10 years
License agreement termination period	180 days