University Of Michigan Researchers Zero-In On CD55

CD55 Is Over Expressed On Prostate Cancer, Promotes Cancer Cell Survival And Contributes To Metastatic Potential, According To New Data

London, UK, 27 March 2006: Onyvax Limited, the biotechnology company developing novel cancer therapies, today announced the publication of two key research papers by a group led by Professor Kenneth Pienta and Dr Robert Loberg at the University of Michigan, that validate the target of the Onyvax-105 vaccine in prostate cancer. The researchers report that CD55 is over-expressed in prostate cancer and that it is an important mediator of prostate cancer development, in particular by protecting tumour cells from immune attack. Furthermore, they showed that inhibition of CD55 expression in an in vivo model of prostate cancer resulted in a 76% decrease in overall tumor burden. Key findings from the research are summarized below.

CD55 is significantly over-expressed in prostate cancer
The first paper, published in December 2005, demonstrated that CD55 is consistently elevated in cancerous versus normal prostate tissue (Urology (2005)66:1321-1326). Furthermore, the molecule was shown to be functionally active and protected cells from immune attack.

Targeting CD55 reduces metastatic burden in prostate cancer models
In the second paper published in January 2006 (Neoplasia (2006) 8:69-70), the researchers used siRNA to compare the growth of prostate cancer cells that expressed CD55 versus those that did not in an in vivo mouse model of prostate cancer metastasis. The total tumor burden in mice injected with CD55 negative tumors was 76% lower than mice with CD55 positive tumors. This result provides further validation that an anti-CD55 therapy should be a valuable tool for the treatment of prostate cancer patients.

Dr Kenneth Pienta said “This laboratory research shows great promise for an anti-CD55 therapy, and we are looking forward to moving this therapy into the urology clinics under a clinical trial. There is a lack of effective therapies for metastatic prostate cancer and it is the metastases that kill patients. Any treatment that can help prevent the disease spreading would be very valuable.”

Onyvax’s anti-CD55 antibody
Onyvax-105 is a fully human monoclonal antibody that has been tested in clinical trials for colorectal cancer and osteosarcoma and has shown encouraging results to date. The company is planning new clinical trials of Onyvax-105, both as a monotherapy in a range of cancer types including prostate cancer and in combination with other treatment modalities, especially other immunotherapies.

In particular Onyvax is planning clinical trials of Onyvax-105 in combination with the company’s lead product, Onyvax-P, a cell-based vaccine in late stages of development and due to enter Phase IIb/III clinical trials in 2006. It is hoped that administration of Onyvax-105 will disrupt the metastasis of prostate cancer cells, unmask the tumor’s defensive shield and thus enhance the effectiveness of the broad immune responses generated by Onyvax-P.

For further information, please contact:

Onyvax
Dr Anthony Walker / Robert Johnson
+44 (0)208 682 9494

Financial Dynamics
Julia Philips
+44 (0)20 7831 3113

Notes to Editors:

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

Founded in 1998, Onyvax is developing products that use the power of the immune system to treat 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 tumor targets. Onyvax-P, a Cell Vaccine for prostate cancer, is due to enter Phase IIb/III clinical trials in early 2006. 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 standardized conditions. The Phase IIa trial for Onyvax-P demonstrated the product was safe and showed signs of efficacy with 40% patients showing statistically significant reductions of PSA velocity (a blood marker for prostate cancer) and median progression free survival of 58 weeks versus historical controls of 29-30 weeks.

Onyvax is also developing Onyvax-105, an antibody based therapy designed to target CD55. The product has shown promising results in early clinical trials in colorectal cancer and osteosarcoma. The company is intending to develop the antibody further, initially in prostate cancer.

Onyvax is committed to the commercialization 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