For those patients with aggressive prostate cancer there are a number of available therapies, including prostate gland removal, radioactive seed implants, and androgen deprivation therapy. Each of these has significant drawbacks. There is a vaccine, however, that has been developed for prostate cancer that may provide yet another modality to the treatment of this disease.
The first vaccine that directly treats cancer could be available soon if Seattle’s biotech company, Dendreon Corporation secures U.S. approval of its product called Provenge. The mechanism of action of this vaccine employs what is referred to as immunotherapy – the recruitment of the patient’s own immune system to preferentially destroy cancer cells. This approach has been used in the past to fight cancer with limited success. This particular application may prove to be more fruitful.
Dendritic cells which are found in the bloodstream play a key role in the immune response. They are referred to as Antigen Presenting Cells (APC). These cells interact with antigens – substances that induce the immune response – and by presenting these antigens to immunological T cells, trigger them to divide and find and destroy those cells carrying the antigen. For prostate cancer, the antigen is prostatic acid phosphatase (PAP). PAP is found predominantly on prostate cancer cells, and, therefore, would be the antigen of choice.
With this information in mind, the strategy used to produce the vaccine is the following:
•The patient’s Dendritic cells are harvested and stimulated to divide in the laboratory
•These APCs are then exposed to PAP, and bind to it
•These APCs armed with the antigen are then injected back into the patient.
Hopefully, these cells will then trigger the appropriate T Cells in the body to multiply, find and ultimately destroy the cancer cells carrying PAP. Initial clinical trials of this vaccine have proven quite promising. If successful, this would be very exciting news, for it would represent an essentially non-invasive technique to cure prostate cancer without any real risk to the patient, since it is the patient’s own cells that are used in the treatment.