Prostate Vaccine May Herald a New Era in Cancer Management

A vaccination scheme that alerts the immune system to defend itself against prostate stem cell antigen (PSCA) was shown to prevent the growth of prostate tumors in a line of mice genetically engineered to develop prostate cancer.

Investigators at the University of Southern California (Los Angeles, USA) worked with the transgenic adenocarcinoma mouse prostate (TRAMP) line of mice. Eight-week-old TRAMP mice were first injected with a fragment of PSCA DNA. Two weeks later, they were vaccinated with a modified virus, which carried the complete PSCA gene.

Results published in the February 1, 2008, issue of the journal Cancer Research revealed that the presence of excess PSCA protein caused a strong immune response in the mice. The prostates of the vaccinated mice were infiltrated by CD4-positive, CD8-positive, CD11b-positive, and CD11c-positive cells. Vaccination induced MHC class I expression and cytokine production 9IFN-gamma, tumor necrosis factor-alpha, interleukin 2 [IL-2], IL-4, and IL-5) within prostate tumors. This immune response led to a 90% survival rate at 12 months of age. In contrast, all control mice had succumbed to prostate cancer or had heavy tumor loads by 12 months of age. A further crucial finding was that this long-term protective immune response was not associated with any measurable induction of autoimmunity.

"We feel this is a very promising approach,” said senior author Dr. W. Martin Kast, professor of molecular microbiology and immunology at the University of Southern California. "With just two shots, the vaccine will prime immune cells to be on the lookout for any cell that over-expresses PSCA. By early vaccination, we have basically given these mice life-long protection against a disease they were destined to have. This has never been done before, and with further research, [it] could represent a paradigm shift in the management of human prostate cancer.”


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