Pfenex Inc. Announces Strategic Agreement with SAFC

San Diego, California June 7, 2011 – Pfenex Inc., an industry leader in protein expression through the Pfenex Expression Technology™ platform, announced today that it has entered into a non-exclusive strategic partnership with SAFC®, a unit of the Sigma-Aldrich Corporation (NASDAQ:SIAL) and a global leader in biopharmaceutical contract manufacturing. Under the agreement, Pfenex Inc. will engineer production strains and processes for SAFC’s contract manufacturing customers, and the developed processes will ultimately be transferred to SAFC’s recently expanded fermentation facility in Jerusalem, Israel for cGMP production.

In addition, the companies plan to work together to combine Pfenex’s Reagent Proteins product offerings in the area of vaccine components with SAFC’s expertise and facilities for bioconjugation to support development of conjugate vaccines.

This collaboration is expected to provide SAFC and the biotechnology community with access to an industry-leading expression platform, a comprehensive range of vaccine carrier proteins, and enable preclinical and clinical development to progress much more quickly and efficiently.

“Our partnership agreement with SAFC combines a cutting edge expression technology and a broad offering of vaccine components with a world class contract manufacturing services provider, facilitating the speed and reliability with which important new drugs can be brought to patients.” said Dr Bertrand Liang, CEO of Pfenex Inc.

“Providing our customers access to Pfenex’s expression system is a valuable addition to our complex technology portfolio,” said Mark Cassidy, Vice President of SAFC’s Contract Manufacturing Services. “This alliance reinforces SAFC’s commitment to bringing our customers the latest technological solutions in the advancement of biopharmaceutical manufacturing.”

About Pfenex Inc.

Pfenex Inc. is a protein production company leveraging the unique and powerful Pfenex Expression Technology™ platform based on the microorganism, Pseudomonas fluorescens, for the production of research proteins, reagent proteins, biosimilars and innovator biopharmaceuticals. For more information please visit www.pfenex.com

About Reagent Proteins

Reagent Proteins is a leading supplier of reagent, pre-clinical and cGMP grade proteins to the biopharmaceutical and vaccine development community. We ensure that scientists have ready access to a comprehensive offering of high quality proteins to enable their development efforts to proceed efficiently. For more information please visit www.reagentproteins.com

SAFC and Sigma-Aldrich are registered trademarks of Sigma-Aldrich Biotechnology L.P. and Sigma-Aldrich Co.

Pfenex Contact:

Cassidy Brady

Marketing Manager

858-344-7207

cbrady@pfenex.com