exhibit 10. 21 confidential material omitted and filed separately with the securities and exchange commission. asterisks denote such omissions. master agreement relating to the production of clarified goat ’ s milk containing recombinant human alpha fetoprotein by and between gtc biotherapeutics, inc. and merrimack pharmaceuticals, inc. september 9, 2005 this agreement ( the “ master agreement ” ) is made this 9th day of september, 2005 ( the “ effective date ” ), by and between merrimack pharmaceuticals, inc., a massachusetts corporation ( “ merrimack ” ) located at 101 binney street, cambridge, ma 02142 and gtc biotherapeutics, inc., a massachusetts corporation ( “ gtc ” ) located at 175 crossing boulevard, framingham, ma 01702. ( gtc and merrimack each individually a “ party ” and collectively the “ parties ” ). whereas, merrimack is a biotechnology company actively involved in the development of recombinant human alpha fetoprotein ) ; and whereas, gtc is a leader in the development of therapeutic proteins in the milk of transgenic animals ; and whereas, on may 11, 1999, merrimack ( then known as atlantic biopharmaceuticals, inc. ) and gtc entered into an agreement under which gtc was to conduct a mouse feasibility study of human alpha fetoprotein ( the “ may 1999 agreement ” ) ; and whereas, on february 12, 2001, merrimack and gtc entered into an agreement for the generation of goats transgenic for human alpha fetoprotein expressed in milk ( the “ february 2001 agreement ” and together with the may 1999 agreement, the “ initial agreements ” ) ; and whereas, on june 27, 2003, in order to more fully exploit the opportunities for the commercialization of transgenic rhafp, merrimack and gtc entered into the first definitive ( stage i ) agreement for the purpose of producing transgenic rhafp in the milk of transgenic animals for merrimack ’ s use in pre - clinical studies, clinical trials and commercial distribution, to be implemented in three stages through a series of definitive agreements between the parties ( the “ 2003 agreement ” ) ; and whereas, the 2003 agreement has been successfully completed to the satisfaction of the parties, and the parties wish to enter into this master agreement to provide for continued production of transgenic