Saturday, Mar 22, 2003

Preliminary Results from Open-Label Raptiva Study Suggest Continued Benefit with Long-Term Treatment

Over 64 Percent of Patients Continuing Treatment for 15 Months Showed PASI 75 or Greater Response with Weekly Raptiva Therapy

South San Francisco, Calif. -- March 22, 2003 --

SAN FRANCISCO, CA- March 22, 2003 - Genentech Inc. (NYSE: DNA) and XOMA Ltd. (Nasdaq: XOMA) today announced preliminary results from an open-label, multicenter trial evaluating the long-term safety and tolerability of continuous Raptiva™ (efalizumab) treatment in patients with moderate-to-severe psoriasis.

"The findings from this important open-label study on the long-term safety and efficacy of Raptiva are very encouraging and further support Raptiva's potential to address the unmet medical need of patients with moderate-to-severe psoriasis," said Hal Barron M.D., FACC, Genentech's vice president, Medical Affairs.

Alice Gottlieb, M.D., director of the Clinical Research Center at the Robert Wood Johnson Medical School at the University of Medicine and Dentistry of New Jersey presented data for patients receiving continuous Raptiva treatment for one year following an initial three months of treatment. The data were presented on Saturday, March 22 at the 61st annual American Academy of Dermatology meeting being held in San Francisco.

Response Rates with Continued Raptiva Treatment
A total of 339 patients were enrolled in this continuing open-label, multicenter study. 41 percent of patients (140/339) achieved 75 percent or greater improvement in Psoriasis Area and Severity Index (PASI) scores (PASI 75) and 82 percent (278/339) achieved PASI 50 or greater improvement after 12 weeks of 2 mg/kg/week Raptiva therapy. Patients who achieved a PASI 50 score or OLS (Overall Lesion Severity scale) of clear, minimal or mild at week 12 were eligible to enter the continuous treatment period. Of the original 339 patients, 290 patients who met the entry criteria for the maintenance period entered the continuous treatment phase of the study. For each successive three-month period of treatment, dropouts during that cohort period were counted as non-responders for that cohort, but were excluded from the subsequent cohorts.

Starting from week 13, the weekly subcutaneous dose in patients was reduced to 1 mg/kg Raptiva. At weeks 13-24 (n=290) more than 77 percent of patients who continued on therapy had 50 percent or greater PASI improvement (PASI 50) and more than 51 percent had 75 percent or greater PASI improvement (PASI 75). Of these patients, more than 22 percent achieved a 90 percent or greater improvement in their PASI score (PASI 90). At weeks 49-60 (n=228), more than 79 percent of patients who continued on therapy had a PASI 50 score and more than 64 percent of patients achieved a PASI 75 score. Of these patients, more than 31 percent achieved a 90 percent or greater improvement in their PASI score (PASI 90).

"The data from this study suggest that for some patients, Raptiva may present an option for continuous treatment of moderate-to-severe psoriasis," said Dr. Gottlieb. "As a chronic disease, the opportunity for an efficacious treatment with a favorable safety profile is of interest to clinicians as we explore potential therapies for this devastating disease."

The most common adverse events during the first 12 weeks of treatment were headache, non-specific infection (e.g., common colds), chills, pain, nausea, asthenia (weakness), and fever. These events principally occurred following the first two injections of Raptiva. No new adverse events emerged during continuous Raptiva therapy. Over time, among those patients who continued on therapy, the percentage of patients who experienced at least one adverse event decreased from 57 percent during weeks 13-24 to 47 percent during weeks 49-60. The occurrence of serious adverse events during the 15 months of treatment was infrequent, which is consistent with data from previous Raptiva Phase III studies.

About Raptiva™
As a targeted T-cell modulator, Raptiva is designed to block the activation of T-cells that cause psoriasis, without destroying them. Raptiva has been studied as a once-weekly therapy for the continuous treatment of moderate-to-severe plaque psoriasis. In clinical trials, Raptiva was administered via subcutaneous injection and in several of the trials was self-administered by some patients in their homes. In December 2002, Genentech and XOMA filed a Biologics License Application (BLA) with the U.S. Food and Drug Administration for Raptiva for the treatment of moderate-to-severe plaque psoriasis in patients 18 years or older. The BLA submission included data from over 2,100 patients treated with Raptiva.

About Psoriasis
Psoriasis occurs when new skin cells grow abnormally, resulting in thick, red, scaly, inflamed patches. Plaque psoriasis, the most common form of the disease, affects approximately 2.3 million Americans and is characterized by inflamed patches of skin ("lesions") topped with silvery white scales. Psoriasis can be limited to a few spots or involve extensive areas of the body, appearing most commonly on the scalp, knees, elbows and trunk. Although it is highly visible, psoriasis is not a contagious disease. While there are a number of medications that may help control the symptoms of psoriasis, there currently is no known cure.

About Genentech
Genentech is a leading biotechnology company that discovers, develops, manufactures and commercializes biotherapeutics for significant unmet medical needs. Fifteen of the currently approved biotechnology products originated from or are based on Genentech science. Genentech manufactures and commercializes ten biotechnology products directly in the United States. The company has headquarters in South San Francisco, California, and is traded on the New York Stock Exchange under the symbol DNA.

About XOMA
XOMA develops and manufactures antibody and other protein-based biopharmaceuticals for disease targets that include cancer, immunological and inflammatory disorders, and infectious diseases. XOMA's programs include collaborations: with Genentech, Inc. on the Raptiva™ antibody for psoriasis (BLA submission), rheumatoid arthritis (Phase II), psoriatic arthritis (Phase II) and other indications; with Baxter Healthcare Corporation to develop NEUPREX® (rBPI21) for Crohn's disease (Phase II) and other indications; with Millennium Pharmaceuticals, Inc. on two biotherapeutic agents, CAB2 and MLN01, for certain vascular inflammation indications (preclinical); and with Onyx Pharmaceuticals, Inc. on its ONYX-015 product for various cancers (current activities suspended, pending partnership discussions). Earlier-stage development programs include compounds to treat cancer, retinopathies, autoimmune diseases and infections. For more information about XOMA's pipeline and activities, please visit XOMA's website at http://www.xoma.com.

Regarding XOMA:
Statements made in this news release related to the regulatory process and collaborative arrangements, or that otherwise relate to future periods, are forward looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements are based on assumptions that may not prove accurate. Actual results could differ materially from those anticipated due to certain risks inherent in the biotechnology industry and for companies engaged in the development of new products in a regulated market. These risks include those related to safety and efficacy of the products being studied; action, inaction or delay by the Food and Drug Administration and European regulators; analysis, interpretation and submission of scientific data; changes in the status of existing collaborative relationships; the ability of collaborators to meet their obligations and market demand for products. These risks are discussed in XOMA's most recent annual report on Form 10K and in other SEC filings. Consider such risks carefully in evaluating XOMA's prospects.