Exhibit 99.A

AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13D need be filed with respect to the ownership by each of the undersigned of Common Stock of Alpine Immune Systems, Inc.

Date: September 21, 2021	FRAZIER LIFE SCIENCES VIII, L.P.
	By FHM Life Sciences VIII, L.P., its general partner
	By FHM Life Sciences VIII, L.L.C., its general partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	FHM LIFE SCIENCES VIII, L.P.
	By FHM Life Sciences VIII, L.L.C., its general partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	FHM LIFE SCIENCES VIII, L.L.C.
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	FRAZIER LIFE SCIENCES PUBLIC FUND L.P.
	By: FHMLSP, L.P., its General Partner
	By: FHMLSP, L.L.C., its General Partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	FHMLSP, L.P.
	By: FHMLSP, L.L.C., its General Partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	FHMLSP, L.L.C.
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: September 21, 2021	By:	*
		James N. Topper

Date: September 21, 2021	By:	*
		Patrick J. Heron

Date: September 21, 2021	By:	**
		Albert Cha

Date: September 21, 2021	By:	**
		James Brush

Date: September 21, 2021	By:	/s/ Steve R. Bailey
		Steve R. Bailey, as Attorney-in-Fact

* This Agreement was executed by Steve R. Bailey on behalf of the individuals listed above pursuant to a Power of Attorney, a copy of which was filed with the SEC on July 31, 2017.

** This Agreement was executed by Steve R. Bailey on behalf of the individuals listed above pursuant to a Power of Attorney, a copy of which was filed with the SEC on August 16, 2021.