Cell Genesys reported positive results from a phase II trial of GVAX for the treatment of prostate cancer. GVAX is a cell vaccine that is also being evaluated for the treatment of leukemia and pancreatic cancer.  The autologous vaccine is made by removing a sample of the patient's own tumor and coaxing it into producing granulocyte-macrophage colony stimulating factor (GM-CSF). The vaccine is then re-administered into the patient via injection, which initiates a potent immune response against the tumor.

The trial analysis was designed to evaluate the potential association between immune responses to GVAX and increased survival. The study enrolled 80 subjects, including 65 who had their serum evaluated to determine each subjects' immune response to two specific antigens, HLA-A24 and FLJ14668, following GVAX treatment. Of the 65 subjects, 34 demonstrated FLJ14668-specific antibody immune response and had a median survival of 43 months. 

The median survival of subjects who did not generate the anti-FLJ14668 antibodies was 21 months (p=0.002). Twenty-two of the 65 subjects received a dose of GVAX comparable to that being evaluated in ongoing phase III prostate cancer trials. Of the 22 subjects, 16 (73%) mounted an immune response to FLJ14668.

These 16 subjects achieved a median survival of 44.9 months. The median survival for all 22 subjects in this treatment group was 35 months. Of the 58 subjects who were HLA-A24 genotype negative and therefore potentially able to mount anti-HLA-A24 specific antibody responses, 30 subjects were found to be anti-HLA-A24 antibody positive. These 30 had a median survival of 43 months, compared with a median survival of 18 months in the subjects who did not generate anti-HLA-A24 antibodies (p=0.05).

"The findings being reported today indicate a potential association between two specific GVAX-induced antibody responses and patient survival, an association consistent with the proposed mechanism of action for this product. We look forward to expanding these findings in a prospective analysis of the sera of patients treated in our two randomized controlled phase III trials," stated Peter Working, Ph.D., senior vice president of research and development at Cell Genesys.

The results will be presented by Thomas Harding, Ph.D, and colleagues from Cell Genesys at the American Society of Clinical Oncology's Genitourinary Cancer Symposium held in San Francisco. Phase III trials are currently underway.