Exhibit A AGREEMENT REGARDING THE JOINT FILING OF SCHEDULE 13D

Exhibit A

AGREEMENT REGARDING THE JOINT FILING OF

SCHEDULE 13D

The undersigned, being duly authorized thereunto, hereby execute this agreement as an exhibit to this Schedule 13D Amendment No. 3 to evidence the agreement of the below-named parties, in accordance with the rules promulgated pursuant to the Securities Exchange Act of 1934, to file this Amendment No. 3 jointly on behalf of each such party.

Date: February 4, 2019

POLARIS VENTURE PARTNERS V, L.P.
By:		Polaris Venture Management Co. V, L.L.C.
By:		*
		Managing Member
POLARIS VENTURE PARTNERS ENTREPRENEURS’ FUND V, L.P.
By:		Polaris Venture Management Co. V, L.L.C.
By:		*
		Managing Member
POLARIS VENTURE PARTNERS FOUNDERS’ FUND V, L.P.
By: Polaris Venture Management Co. V, L.L.C.
By:		*
		Managing Member
POLARIS VENTURE PARTNERS SPECIAL FOUNDERS’ FUND V, L.P.
By:		Polaris Venture Management Co. V, L.L.C.
By:		*
		Managing Member
POLARIS VENTURE MANAGEMENT CO. V, L.L.C.
By:		*
		Managing Member
XXXXXXXX X. XXXXX
By:		*
Xxxxxxxx X. Xxxxx
XXXXXXXX X. XXXXXXX
By:		*
Xxxxxxxx X. XxXxxxx

XXXX XXXXXX
By:		*
		Xxxx Xxxxxx

*By:		/s/ Xxx Xxxxxxxxx
Name:		Xxx Xxxxxxxxx
		Attorney-in-Fact

[This Exhibit A to Schedule 13D Amendment No. 3 was executed pursuant to Powers of Attorney. Note that copies of the applicable Powers of Attorney are already on file with the appropriate agencies.]