CUSIP No. 28106W103

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 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 Schedule jointly on behalf of each such party.

Date: September 18, 2017

POLARIS VENTURE PARTNERS VI, L.P.
By:	Polaris Venture Management Co. VI, L.L.C.
By:	*
	Authorized Signatory
POLARIS VENTURE PARTNERS FOUNDERS’ FUND VI, L.P.
By:	Polaris Venture Management Co. VI, L.L.C.
By:	*
	Authorized Signatory
JONATHAN A. FLINT
By:	*
Jonathan A. Flint
TERRANCE G. MCGUIRE
By:	*
Terrance G. McGuire
BRIAN CHEE
By:	*
Brian Chee
DAVID BARRETT
By:	*
David Barrett

AMIR NASHAT
By:	*
Amir Nashat
BRYCE YOUNGREN
By:	*
Bryce Youngren
KEVIN BITTERMAN
By:	*
Kevin Bitterman

*By:	/s/ Max Eisenberg
Name:	Max Eisenberg
	Attorney-in-Fact

[This Schedule 13D was executed pursuant to a Power of Attorney. Note that copies of the applicable Powers of Attorney are already on file with the appropriate agencies.]