Addition of Hepatitis C Treatment to Ongoing Oncology Program for MDX-1106

PRINCETON, NJ, USA | October 29, 2007 | Ono Pharmaceutical Co., Ltd. and Medarex, Inc. (Nasdaq: MEDX) announced today the allowance of an investigational new drug application (IND) filed with the U.S. Food & Drug Administration (FDA) for MDX-1106 (ONO-4538: development code of Ono Pharmaceutical Co., Ltd.), a fully human anti-PD-1 antibody being investigated for the treatment of chronic viral infections, with the first trial to target hepatitis C. MDX-1106 was developed under the May 2005 collaborative research agreement between Ono and Medarex, and currently is in a separate ongoing Phase I clinical study in patients with recurrent or treatment- refractory cancer.

The new Phase I single-dose, dose-escalation trial with MDX-1106/ONO-4538 is expected to enroll up to 34 patients with active hepatitis C genotype 1 infection (HCV). The study is intended to evaluate the safety, pharmacokinetics, and preliminary efficacy of single doses of MDX-1106/ONO- 4538.

"Recently, involvement of PD-1 in hepatitis C has been reported in the scientific literature," said Shozo Matsuoka, Ph.D., Senior Managing Director of Ono Pharmaceutical, Co., Ltd. "ONO-4538/MDX-1106 aims to improve the immune capacity of the body and treat hepatitis C with a novel mechanism of action which inhibits the involvement of PD-1. We are seeking to develop ONO- 4538/MDX-1106 to be a new treatment for hepatitis C."

"We value our partnership with Ono and are pleased with the progress to study the potential of MDX-1106 in both oncology and infectious diseases," said Howard Pien, President and CEO of Medarex. "We believe that our ongoing program in patients with cancer is currently progressing well and that this exploratory Phase I study in HCV may be a step toward potentially adding new infectious disease indications for therapeutic blockade of this important T cell regulatory molecule."

About MDX-1106/ONO-4538

PD-1 (programmed cell death 1) is one of the receptors expressed on the surface of activated lymphocytes (T-cells) and is involved in the system of negative regulation for the suppression of activated lymphocytes. An increasing number of studies have reported that tumor cells and certain chronic viruses, including HCV, may use the PD-1 pathway to evade host adaptive immune responses (which protect the host from both harmful pathogens and tumors), suggesting that blockade of the negative regulatory signal mediated by PD-1 may promote the host immune response to recognize tumor cells as foreign and eliminate viral pathogens. Preclinical studies suggest that blockade of the PD-1 signaling pathway by MDX-1106/ONO-4538, a fully human anti-PD-1 antibody, activates T-cell responses and promotes an immune response to fight tumors and infectious diseases. Medarex and Ono Pharmaceutical continue to investigate the potential of MDX-1106/ONO-4538 for cancer in an ongoing Phase I clinical trial and for hepatitis C.

About Medarex

Medarex is a biopharmaceutical company focused on the discovery, development and potential commercialization of fully human antibody-based therapeutics to treat life-threatening and debilitating diseases, including cancer, inflammation, autoimmune disorders and infectious diseases. Medarex applies its UltiMAb(R) technology and product development and clinical manufacturing experience to
generate, support and potentially commercialize a broad range of fully human antibody product candidates for itself and its partners. More than 30 of these therapeutic product candidates derived from Medarex technology are in human clinical testing or have had INDs submitted for such trials, with seven of the most advanced product candidates currently in Phase III clinical trials. Medarex is committed to building value by developing a diverse pipeline of antibody products to address the
world’s unmet healthcare needs. For more information about Medarex, visit its website at www.medarex.com.

Medarex(R), the Medarex logo and UltiMAb(R) are registered trademarks of
Medarex, Inc. All rights are reserved.

SOURCE: Medarex, Inc.