An experimental dendritic vaccine has shown significant prognosis and extension of lifetime of men with prostate cancer. The vaccine Provenge is based on dendritic cells, which help the immune system recognize tumors. "If these results are true, this represents the first proof of principle of a dendritic cell vaccine altering the natural history of a solid tumor", says Philip Kantoff, Chief of solid tumor oncology at the Dana-Farber Cancer Institute in Boston.
Provenge carries the patients own dendritic cells engineered to express a protein found on about 95% of prostate cancer cells. It is one of more than 15 vaccines in trials for a range of cancers, including lymphoma, melanoma, breast, lung and colorectal cancers, but the first to increase lifespan in advancer cancer patients.
There are also questions about which cells are antigens to use in vaccines and the mode and frequency with which they should be administered. For example, mature dendritic cell vaccines seem to produce the best immune response when given either subcutaneously or intradermally, but not intravenously. Researchers are trying to determine whether vaccines will be need to be designed for specific cancers, or whether a universal vaccine could produce a robust immune response.
The provenge trial has raised several questions of its own: 34% of men given provenge, compared with 11% on placebo, were alive three years on, and lived 4.5 months on average longer. "Because of this, we were all somewhat pleasantly surprised that Provenge showed a survival benefit, says E. Roy Berger, director of the Prostate Cancer Consultation and Treatment service in East Setauket, New York.
"Cancer vaccines prime the immune system to attack cancer, a slower, more indirect process,' he says. This may mean that survival, and not time to progression is a better measure of efficacy for cancer vaccines, Berger suggests.
Source: Nature Medicine