Onyvax Presents Preliminary Phase II Data on its Prostate Cancer Vaccine at American Association of Immunologists Annual Meeting

Denver, CO, 6th May 2003 – Onyvax Ltd (London, UK), the vaccine therapy company, today presented preliminary data from its Phase IIa clinical trial in prostate cancer at Immunology 2003, the 90th Anniversary Annual Meeting of the American Association of Immunologists (AAI).

Onyvax reported preliminary findings from the first 15 patients in its Phase IIa study of Onyvax-P, a therapeutic cancer vaccine designed to stimulate an immune response against tumour cells. Immune activation in response to treatment was detected both by an increase in cytokine production and by evidence of T-cell proliferation.

Data presented at AAI show several patients with a statistically significant decrease in the rate of Prostate Specific Antigen (PSA) release, the widely used blood marker of disease progression. The clinical study started in January 2002 and targets a total of 48 patients with prostate cancer who failed hormone therapy and have rising PSA levels. No approved treatment is currently available for patients who have failed hormone therapy. All study participants receive the vaccine therapy for a period of 12 months and are followed for 12 months after. So far, two patients have completed the 12 month treatment period without any sign of disease progression. These are early findings and Onyvax expects to publish more data later in 2003.

Onyvax-P contains three cell lines that represent different stages of prostate cancer. The cell lines are irradiated and so cannot grow or divide. Onyvax designed its vaccine to induce a powerful immune response against a broad range of prostate cancer-associated antigens without the severe side effects often associated with conventional cancer therapies.

Onyvax will present pre-clinical data at the Annual Meeting of the International Society for Cellular Therapy in Phoenix, May 29th-June 1st, and further clinical data at the British Cancer Research meeting July 2nd-5th in Bournemouth, UK.

“We are pleased to be presenting our data to these prestigious scientific audiences,” said Anthony Walker, CEO of Onyvax. “We are encouraged by the positive results we have seen so far and anticipate releasing further data later this year.”

According to the American Cancer Society, prostate cancer is the most common cancer among men in the US, with an estimated 220,900 new cases diagnosed each year. It is the second leading cause of cancer death in American men, with about 28,900 deaths per year, exceeded only by lung cancer. In the UK, some 21,000 men are diagnosed with prostate cancer per year and about 9,500 die of the disease annually. If detected early enough, prostate cancer can be treated effectively by surgery or radiotherapy while hormone therapy can control later stages of the disease. No treatment is currently available for patients who have failed hormone therapy, and median survival time for these patients is approximately 13 months.

About Onyvax

Onyvax is a biotechnology company developing novel cancer therapies that harness the selective power of the immune system to seek and destroy tumour cells.

Founded in 1997, Onyvax has three product candidates in clinical trials designed for the treatment of prostate and other cancers. Onyvax’s lead products are based on combinations of inactivated cell lines that induce immune responses to a broad spectrum of tumour targets. For each cancer type, Onyvax generates banks of proprietary cell lines representative of different stages of the disease. The vaccines are manufactured in bulk under standardised conditions.

Onyvax is committed to the commercialisation of new therapies that significantly prolong survival while maintaining a high quality of life for cancer patients. The Company is based in London and has collaborations with leading institutions in Europe and the US.

Further information on Onyvax can be found at www.onyvax.com.

About AAI

The American Association of Immunologists is the world’s largest and most prestigious professional association of immunologists. Its mission is to advance knowledge of immunology and related disciplines, to foster interchange of ideas and information among investigators in the various disciplines and to promote understanding of the field of immunology. The AAI’s annual scientific meeting draws thousands of delegates from around the world.