ChemoCentryx Identifies Novel Small Molecule C5aR Antagonist

Development Candidate Triggers Milestone Payment from GlaxoSmithKline

Mountain View, CA — May 5, 2009 — ChemoCentryx, Inc., today announced that it has identified an orally bioavailable small molecule antagonist of the C5a receptor, CCX168, as a candidate for clinical development. The acceptance of the molecule as a development candidate triggered a $5.0 million milestone payment from the alliance with GlaxoSmithKline (NYSE: GSK). CCX168 is designed to specifically target the C5a receptor, a potent inflammatory mediator and component of the complement system, which is associated with the onset of autoimmune diseases such as lupus and certain types of vasculitis, among other diseases.

"In the quest to develop medicinally relevant inhibitor compounds, C5a receptor has been a target of epic difficulty in the pharmaceutical industry. CCX168 is a highly potent and specific C5a receptor small molecule antagonist, and unlike other compounds that have been developed to date. It adds another promising approach to addressing inflammatory and autoimmune diseases to ChemoCentryx's pharmaceuticals portfolio," said Thomas J. Schall, Ph.D., President and Chief Executive Officer. "I am gratified that the ChemoCentryx team has again demonstrated the broad capability of our proprietary technologies and our efficiency in developing a molecule with such excellent properties."

The complement system comprises a set of proteins that regulate certain types of inflammatory responses by the immune system. Fragments of these proteins, such as chemoattractant complement fragment C5a, work to recruit immune system cells including neutrophils and lymphocytes to the site of inflammation. The C5a receptor is highly expressed on innate immune cells, making it an attractive target for small molecule therapeutics. Given architectural similarities between the C5a receptor and chemokine receptors, ChemoCentryx researchers successfully applied the company's proprietary drug discovery technologies to identify and design small molecule C5aR antagonists and selected CCX168 based on its potency, selectivity and favorable pharmacokinetics. In preclinical models, C5a and its receptor C5aR have been shown to play a key role in the development of autoimmune disease. C5a also has been thought to play a role in age-related macular degeneration (AMD). C5aR is one of four defined chemokine and chemoattractant receptor targets covered under a 2006 alliance between ChemoCentryx and GlaxoSmithKline's Center of Excellence for External Drug Discovery (CEEDD), under which GSK has option rights to license certain product candidates.

About ChemoCentryx
ChemoCentryx, Inc., is a clinical-stage biopharmaceutical company focused on discovering, developing and commercializing orally-administered therapeutics that target the chemokine and chemoattractant systems in order to treat autoimmune diseases, inflammatory disorders and cancer. The chemokine system is a network of secreted chemokine molecules, or ligands, and cell surface receptors that regulates inflammation. Based on its proprietary drug discovery and drug development platform, ChemoCentryx has internally generated multiple clinical and preclinical-stage programs, each targeting distinct chemokine and chemoattractant receptors with different small molecule compounds. ChemoCentryx's lead compound, Traficet-EN, a specific CCR9 antagonist, is in a Phase II/III multi-national clinical trial, called PROTECT-1, in patients with moderate-to-severe Crohn's disease. CCX025, also a CCR9 antagonist, is in a Phase I clinical trial. Additional clinical programs include the development of CCX140, which targets the CCR2 receptor, currently in a Phase I clinical trial and intended for subsequent development to treat diseases such as Type 2 diabetes, multiple sclerosis and vascular restenosis, and CCX354, a CCR1 antagonist in a Phase I clinical trial, being developed for inflammatory diseases such as rheumatoid arthritis. ChemoCentryx also has several programs in preclinical development. ChemoCentryx is privately held. For more information, please refer to www.chemocentryx.com.

Any statements in this press release about ChemoCentryx's expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. These statements are often, but not always, made through the use of words or phrases such as may, believe, will, expect, anticipate, estimate, intend, predict, seek, potential, continue, plan, should, could and would or the negative of these terms or other comparable terminology. Forward-looking statements are not guarantees of performance. They involve known and unknown risks, uncertainties and assumptions that may cause actual results, levels of activity, performance or achievements to differ materially from any results, levels of activity, performance or achievements expressed or implied by any forward-looking statement. Some of the risks, uncertainties and assumptions that could cause actual results to differ materially from estimates or projections contained in the forward-looking statements include but are not limited to (i) the initiation, timing, progress and results of ChemoCentryx's preclinical studies and clinical trials, (ii) ChemoCentryx's ability to advance product candidates into clinical trials, (iii) GSK's exercise of its license options, (iv) the commercialization of ChemoCentryx's product candidates, (v) the implementation of ChemoCentryx's business model, strategic plans for its business, product candidates and technology, (vi) ChemoCentryx's ability to maintain and establish collaborations or obtain additional government grant funding, (vii) ChemoCentryx's estimates of its expenses, future revenues, capital requirements and its needs for additional financing, (viii) the timing or likelihood of regulatory filings and approvals, (ix) the availability of corporate partners, (x) the scope of protection ChemoCentryx is able to establish and maintain for intellectual property rights covering its product candidates and technology, (xi) the impact of competitive products and technological changes, (xii) the availability of capital and the cost of capital, (xiii) ChemoCentryx's financial performance, (xiv) developments relating to ChemoCentryx's competitors and other vagaries in the biotechnology industry and (xv) other risks.

You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement and ChemoCentryx undertakes no obligation to revise or update this press release to reflect events or circumstances after the date hereof. This caution is made under the safe harbor provisions of Section 21E of the Private Securities Litigation Reform Act of 1995.