Vaccines Approaches

Vaccines are designed to foster an immune response against prostate cancer cells.  Current theories suggest that, as cancer progresses it somehow disrupts one or more of the many steps required for proper immune recognition of cancer cells.  Loss of this immune recognition is referred to as tolerance.  Therefore, vaccine approaches are designed to help the immune system overcome this tolerance.  There are several approaches currently in clinical trials and most of these approaches fall into one of two general categories: tumor-based vaccine approaches or immune cell-based vaccines.

Tumor vaccines attempt to expose proteins specific to the cancer, in this case prostate cancer, to the immune system in order to generate an immune response against them.  Proteins that elicit an immune response are called antigens. By stimulating an immune response against one or more tumor antigens, these vaccines attempt to overcome tolerance.  Examples of these types of approaches include vaccines of viruses engineered to express prostate-specific antigen (PSA) or prostate-specific membrane antigen (PSMA) as well as vaccines with irradiated tumor cells designed to express GM-CSF or other immune stimulating chemicals.  In the first case, viruses that elicit a robust immune response are “labeled” with a prostate antigen and injected into the patient to create a cross-reactive immune response against prostate cancer.  In the second case, prostate cancer cells, either from the same patient (autologous) or from another prostate cancer patient (allogeneic), are engineered to express a cytokine that attracts a brisk immune response. Then, the cancer cells are irradiated, so not to cause any risk to the patient, and injected into the patient to create an immune response against a number of tumor antigens expressed on the cancer cell.  

Immune cell-based vaccines attempt to directly stimulate the immune system by removing a subset of immune cells from the patient and stimulating them in the laboratory to recognize and react against the cancer cells.  Dendritic cells, which function like scouts to recognize tumor cells, can be removed from the peripheral blood and stimulated in the laboratory to recognize certain antigens.  When re-injected into the patient these immune cells can then elicit local immune responses against the tumor.  Other immune cells, including CD40 B cells can function similarly, while cytotoxic killer T cells can also be removed and stimulated to create a more direct anti-tumor response.