Exhibit C

Joint Filing Statement

I, the undersigned, hereby express my agreement that the attached Schedule 13D (and any amendments thereto) relating to the beneficial ownership by the undersigned of the equity securities of TCR² Therapeutics Inc. is filed on behalf of each of the undersigned.

Date: March 4, 2019

MPM BIOVENTURES 2014, L.P.
By:	MPM BioVentures 2014 GP LLC,
	its General Partner
By:	MPM BioVentures 2014 LLC,
	Its Managing Member
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Managing Director

MPM BIOVENTURES 2014 (B), L.P.
By:	MPM BioVentures 2014 GP LLC,
	its General Partner
By:	MPM BioVentures 2014 LLC,
	Its Managing Member
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Managing Director
MPM ASSET MANAGEMENT INVESTORS BV 2014 LLC
By:	/s/ Howard Rubin
Name:	Howard Rubin
Title:	Director

MPM ASSET MANAGEMENT LLC
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Member

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MPM BIOVENTURES 2014 GP, LLC
By:	MPM BioVentures 2014 LLC,
	Its Managing Member
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Managing Director
MPM BIOVENTURES 2014 LLC
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Managing Director
MPM SUNSTATES FUND, L.P.
By:	MPM SunStates GP LLC,
	its General Partner
By:	MPM SunStates GP Managing Member LLC,
	Its Managing Member

By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Member
MPM SUNSTATES GP LLC
By:	MPM SunStates GP Managing Member LLC,
	Its Managing Member
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Member
MPM SUNSTATES GP MANAGING MEMBER LLC
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Member
MPM ASSET MANAGEMENT INVESTORS SUNSTATES FUND LLC
By:	/s/ Howard Rubin
Name:	Howard Rubin
Title:	Director

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UBS ONCOLOGY IMPACT FUND, L.P.
By:	Oncology Impact Fund (Cayman) Management L.P.,
	its General Partner
By:	MPM Oncology Impact Management LP,
	Its General Partner
By:	MPM Oncology Impact Management GP LLC
	Its General Partner
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Managing Director
ONCOLOGY IMPACT FUND (CAYMAN) MANAGEMENT L.P.
By:	MPM Oncology Impact Management LP,
	Its General Partner
By:	MPM Oncology Impact Management GP LLC
	Its General Partner
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Managing Director
MPM ONCOLOGY IMPACT FUND MANAGEMENT LP
By:	MPM Oncology Impact Management GP LLC
	Its General Partner
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Managing Director
MPM ONCOLOGY IMPACT FUND MANAGEMENT GP LLC
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke
Title:	Managing Director
By:	/s/ Todd Foley
Name:	Todd Foley
By:	/s/ Luke Evnin
Name:	Luke Evnin
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke

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