Exhibit B LOCK-UP LETTER AGREEMENTLock-Up Letter Agreement • February 18th, 2011 • MPM BioVentures IV QP LP • Pharmaceutical preparations
BARCLAYS CAPITAL INC. PIPER JAFFRAY & CO. 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
