Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock^F1,F2,F3	Feb 12, 2019	C	1,525,164	—	A	1,847,227	I	See Footnote
Common Stock^F1,F3,F4	Feb 12, 2019	C	1,578,751	—	A	3,425,978	I	See Footnote
Common Stock^F1,F3,F5	Feb 12, 2019	C	417,852	—	A	3,843,830	I	See Footnote
Common Stock^F3,F7	Feb 12, 2019	X	432,119	$0.0492	A	4,275,949	I	See Footnote
Common Stock^F3,F8	Feb 12, 2019	S	1,524	$14.00	D	4,274,425	I	See Footnote
Common Stock^F3,F9	Feb 12, 2019	P	250,000	$14.00	A	4,524,425	I	See Footnote

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	D/I
Series A Preferred Stock^F10,F1	—	Feb 12, 2019	C	1,525,164	D	—	—	Common Stock	1,525,164	I
Series B Preferred Stock^F10,F1	—	Feb 12, 2019	C	1,578,751	D	—	—	Common Stock	1,578,751	I
Series C Preferred Stock^F10,F1	—	Feb 12, 2019	C	417,852	D	—	—	Common Stock	417,852	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	25,418	D	Mar 24, 2015	Mar 24, 2025	Common Stock	25,418	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	57,192	D	Jul 23, 2015	Jul 23, 2025	Common Stock	57,192	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	171,579	D	Aug 19, 2015	Aug 19, 2025	Common Stock	171,579	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	50,837	D	Dec 16, 2015	Dec 16, 2025	Common Stock	50,837	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	76,256	D	Nov 1, 2016	Nov 1, 2026	Common Stock	76,256	I
Common Stock Warrant (Right to Buy)^F10	$0.0492	Feb 12, 2019	X	50,837	D	Jan 10, 2017	Jan 10, 2027	Common Stock	50,837	I

Explanation of responses

F1All series of convertible preferred stock automatically converted into the number of shares of the Issuer's common stock on a 1-for-1 basis, for no additional consideration, immediately prior to the closing of the Issuer's initial public offering and had no expiration date.
F10No securities held by the Reporting Persons.
F2The shares are held as follows: 1,382,777 by MPM BioVentures 2014, L.P. ("BV 2014"), 92,229 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 50,158 by MPM Asset Management Investors BV2014 LLC ("AM BV2014") and 322,063 by MPM Asset Management LLC ("AM LLC"). MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("BV LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B). Luke Evnin, Ansbert Gadicke and Todd Foley are the members of BV LLC and Luke Evnin and Anbert Gadicke are the members of AM LLC.
F3Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its pecuniary interest therein.
F4The shares are held as follows: 2,814,142 by BV 2014, 187,696 by BV 2014(B), 102,077 by AM BV2014 and 322,063 by MPM LLC.
F5The shares are held as follows: 3,192,985 by BV 2014, 212,964 by BV 2014(B), 115,818 by AM BV2014 and 322,063 by MPM LLC.
F6On February 12, 2019, BV 2014, BV 2014(B) and AM BV2014 exercised warrants to purchase an aggregate of 432,119 shares of the Issuer's common stock for $0.0492 per share. The warrants were exercised as follows: 391,784 by BV 2014, 26,129 by BV 2014(B) and 14,206 by AM BV2014. The exercise price was paid on a cashless basis, resulting in the Issuer's withholding of an aggregate of 1,524 of the warrant shares to pay the exercise price and issuing to the respective Reporting Persons the remaining 430,595 shares.
F7The shares are held as follows: 3,584,769 by BV 2014, 239,093 by BV 2014(B), 130,024 by AM BV2014 and 322,063 by MPM LLC.
F8The shares are held as follows: 3,583,391 by BV 2014, 238,998 by BV 2014(B), 129,973 by AM BV2014 and 322,063 by MPM LLC.
F9The shares are held as follows: 3,810,051 by BV 2014, 254,116 by BV 2014(B), 138,195 by AM BV2014 and 322,063 by MPM LLC.