Pfenex Announces Strategic Collaboration With MedImmune for the Use of Pfenex Expression Technology(TM)

SAN DIEGO, May 10, 2011 - Pfenex Inc., an industry leader in protein expression through the Pfenex
Expression Technology(TM) platform, announced today a three year strategic
collaboration with MedImmune LLC, the global biologics business of
AstraZeneca. The agreement provides MedImmune with non-exclusive access to
Pfenex Expression Technology and scientific resources for the development of
bioprocesses for human therapeutic proteins and vaccines.

Pfenex Inc. will engineer production strains and develop early production
processes for MedImmune's proprietary molecules. A Joint Steering Committee
will be established to oversee the collaboration and facilitate the
decision-making process. This collaboration provides MedImmune with access to
an industry-leading expression platform and process development team that
will enable preclinical and clinical development for these molecules to
progress quickly and efficiently. MedImmune will provide annual technology
access fees, FTE resource funding and will also have pre-agreed commercial
license terms.

"This partnership with MedImmune will facilitate speed and reliability in
the development of protein therapeutics and vaccines to serve unmet medical
needs," said Dr. Bertrand Liang, CEO of Pfenex Inc. "Integrating our efforts
early will allow for the rapid progression of early stage candidate molecules
through discovery and development."

"We are very excited to initiate this collaboration with Pfenex" said Dr.
Gail Wasserman, Senior Vice President of Biopharmaceutical Development at
MedImmune. "Their scientific approach to strain development and protein
expression is robust and aligned with the way we work at MedImmune. Working
collaboratively with Pfenex by harnessing their novel platform will play an
important role in helping accelerate some of our early pipeline programs."

About Pfenex Inc.

Pfenex Inc. is a protein production company leveraging the unique and
powerful Pfenex Expression Technology(TM) 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 MedImmune, LLC

MedImmune, the global biologics unit for AstraZeneca PLC (LSE: AZN.L,
NYSE: AZN), has approximately 3,500 employees worldwide and is headquartered
in Gaithersburg, Maryland. For more information, visit MedImmune's website at
www.medimmune.com.

Cassidy Brady, Marketing Manager of Pfenex Inc., +1-858-344-7207, CBrady at pfenex.com