Exhibit A LOCK-UP LETTER AGREEMENTLock-Up Letter Agreement • November 29th, 2011 • MPM BioVentures IV QP LP • Pharmaceutical preparations
Barclays Capital Inc. Jefferies & Company, Inc. As Representatives of the several Underwriters named in Schedule I of the Underwriting Agreement, c/o Barclays Capital Inc. 745 Seventh Avenue New York, New York 10019 Ladies and Gentlemen:
