Share-based compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based compensation

Schedule of share based compensation expense

The Company recorded share‑based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):

	Year Ended
	December 31,
	2019		2018		2017
Research and development expenses	$	1,286	$	513	$	241
General and administrative expenses		1,797		510		274
	$	3,083	$	1,023	$	515

Schedule of share option activity

				Weighted
		Weighted		Average	Aggregate
	Number of	Average		Contractual	Intrinsic
	Shares	Exercise Price		Term	Value
				(in years)	(in thousands)
Outstanding as of December 31, 2018	863,712	$	1.01	8.75	$	3,292
Granted	2,134,538		12.01	—		—
Exercised	(85,839)		1.67	—		—
Forfeited	(278,065)		4.21	—		—
Outstanding as of December 31, 2019	2,634,346	$	9.57	9.04	$	6,107
Vested and expected to vest as of December 31, 2019	2,634,346	$	9.57	9.04	$	6,107
Options exercisable as of December 31, 2019	647,901	$	6.81	8.49	$	2,868

Schedule of assumptions used to determine the fair value of share options granted

	Year Ended
	December 31,
	2019		2018		2017
Risk-free interest rate	2.1	%	2.7	%	2.0	%
Expected volatility	77.9	%	78.6	%	79.7	%
Expected dividend yield	—		—		—
Expected term (in years)	5.86		6.07		6.07

Schedule of restricted ordinary share award activity

		Weighted Average
		Grant-Date
	Shares	Fair Value
Unvested restricted ordinary shares as of December 31, 2018	83,947	$	1.93
Issued	—		—
Forfeited	—		—
Vested	(83,947)		1.93
Unvested restricted ordinary shares as of December 31, 2019	—	$	—