Phase I Clinical Trial for CHIR-12.12

Chiron Corporation and XOMA Ltd. today announced the initiation of a second clinical trial of CHIR-12.12, a novel, fully human, antagonist antibody that targets the CD40 antigen. The Phase I trial is for patients with multiple myeloma, a type of cancer that is associated with expression of the CD40 antigen on the cancer cell surface. Chiron and XOMA announced the initiation of a Phase I clinical trial of CHIR-12.12 in patients with chronic lymphocytic leukemia in April 2005.

"We're pleased to move CHIR-12.12 into clinical studies in a second B-cell oncology indication," said John C. Castello, XOMA's chairman, president and chief executive officer. "Our collaboration with Chiron enables both companies to advance promising antibodies more quickly than either could alone."

The single-agent, open-label Phase I study of CHIR-12.12 is designed to evaluate the safety, dose tolerability and pharmacokinetic profile of CHIR-12.12 in patients with multiple myeloma. Translational medicine will be used to monitor biomarkers and allow correlation of these markers with response to CHIR-12.12 therapy, guiding the dosing regimen and the selection of responsive patient populations. The study is expected to enroll up to 40 patients at four leading cancer centers in the United States.

About CHIR-12.12

CHIR-12.12 is a fully human, antagonist antibody that targets the CD40 antigen. As shown in vitro in cell lines, in vivo in animal models and ex vivo in patient cells, CHIR-12.12 binds to tumor cells that express CD40 and antagonizes (prevents) CD40 ligand-mediated growth and survival of malignant B cells. Based on preclinical data, CHIR-12.12 also induces antibody-dependent cellular cytotoxicity (ADCC), killing CD40 expressing tumor cells by immune effector cells. This dual mechanism of action makes CHIR-12.12 a drug candidate with potential for the treatment of B-cell malignancies.