EXHIBIT A

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Vaccinogen, Inc. and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.

In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf this 10^th day of February, 2017.

MPM BIOVENTURES III, L.P.
By:	MPM BioVentures III GP, L.P.,
	its General Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM BIOVENTURES III-QP, L.P.
By:	MPM BioVentures III GP, L.P.,
	its General Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM BIOVENTURES III, L.P.
By:	MPM BioVentures III GP, L.P.,
	its General Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM BIOVENTURES III-QP, L.P.
By:	MPM BioVentures III GP, L.P.,
	its General Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM BIOVENTURES III PARALLEL FUND, L.P.
By:	MPM BioVentures III GP, L.P.,
	its General Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG
By:	MPM BioVentures III GP, L.P.,
	in its capacity as the Managing Limited Partner
By:	MPM BioVentures III LLC,
	its General Partner
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Series A Member

MPM ASSET MANAGEMENT INVESTORS 2003 BVIII LLC
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Manager

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MPM BIOVENTURES III GP, L.P.		MPM BIOVENTURES III LLC
By:	MPM BioVentures III LLC,	By:	/s/ Luke Evnin
	its General Partner	Name:	Luke Evnin
		Title:	Series A Member
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Series A Member
By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke
	Name: Luke Evnin		Name: Ansbert Gadicke

By:	/s/ Nicholas Galakatos	By:	/s/ Dennis Henner
	Name: Nicholas Galakatos		Name: Dennis Henner
By:	/s/ Kurt Wheeler	By:	/s/ Nicholas Simon III
	Name: Kurt Wheeler		Name: Nicholas Simon III

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MPM BIOVENTURES III GP, L.P.		MPM BIOVENTURES III LLC
By:	MPM BioVentures III LLC,	By:
	its General Partner	Name:	Luke Evnin
		Title:	Series A Member
By:
Name:	Luke Evnin
Title:	Series A Member

By:		By:
	Name: Luke Evnin		Name: Ansbert Gadicke

By:		By:
	Name: Nicholas Galakatos		Name: Dennis Henner

By:		By:
	Name: Kurt Wheeler		Name: Nicholas Simon III

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