Exhibit 99.1

Joint Filing Agreement

In accordance with Rule 13d-1(f) under the Securities and Exchange Act of 1934, the persons or entities named below agree to the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the Shares of the Issuer and further agree that this joint filing agreement be included as an exhibit to this Schedule 13D. In evidence thereof, the undersigned, being duly authorized, have executed this Joint Filing Agreement as of September 29, 2017.

	ATLAS VENTURE FUND IX, L.P.

	By:	Atlas Venture Associates IX, L.P., its general partner
	By:	Atlas Venture Associates IX, LLC, its general partner

	By:	/s/ Frank Castellucci
		Name: Frank Castellucci
		Title: Secretary

	ATLAS VENTURE ASSOCIATES IX, L.P.

	By:	Atlas Venture Associates IX, LLC, its general partner

	By:	/s/ Frank Castellucci
		Name: Frank Castellucci
		Title: Secretary


	ATLAS VENTURE ASSOCIATES IX, LLC

	By:	/s/ Frank Castellucci
		Name: Frank Castellucci
		Title: Secretary

SYNLOGIC OPERATING CO INC SC 13D