Tribulations or triumphs in prostate cancer immunotherapy: on the road to victory?

Toward maximizing immunotherapy in metastatic castration-resistant prostate cancer - rationale for combinatorial approaches using chemotherapy

Prostate cancer is particularly suited for active immunotherapy because of the expression of a distinctive number of antigens which are overexpressed on prostate cancer cells and cell lines. There is evidence in this disease that tumors promote immune tolerance starting early in the disease course. As such, chemotherapy, by suppressing tumors and activating immune system homeostatic mechanisms, may help overcome this tumor-induced immune tolerance. Sipuleucel-T which has recently been approved in the US, is an autologous cellular product immunotherapy that induces immune activity likely through activation of dendritic cells. This was associated with a survival benefit in the absence of significant toxicity. However, a post hoc analysis of phase III trial participants found a substantial survival benefit to receiving docetaxel some months after sipuleucel-T. However, another phase III immunotherapy trial combining a prostate cancer therapeutic vaccine GVAX plus docetaxel versus standard docetaxel therapy in advanced prostate cancer, observed a lower overall survival with the vaccine regimen. These trials highlight major unresolved questions concerning the optimum choice, dosing, and timing of chemotherapy relative to active immunotherapy and the overall merits of considering this approach. The ideal treatment approach remains unclear; advances in biomarker validation and trial design may likely improve our ability to assess biologic benefit irrespective of the development of true antitumor immunity.

HLA Class II Antigen Presentation in Prostate Cancer Cells: A Novel Approach to Prostate Tumor Immunotherapy

Prostate cancer is a deadly disease that is in drastic need of new treatment strategies for late stage and metastatic prostate cancer. Immunotherapy has emerged as a viable option to fill this void. Clinical trials have been conducted that induce tumor clearance through cytotoxic T lymphocyte (CTL) activation, these studies have had mixed outcomes with the overlying problem being the lack of a complete immune response with sustained killing and the formation of tumor specific memory cells. To overcome this, we have outlined the need for activating the HLA class II pathway in inducing a sustained CD8+ T cell response and the development of effective memory. We have also discussed the ability of prostate cancer cells to express stable HLA class II molecules that can be manipulated for tumor antigen (Ag) processing and presentation. This review also sets to outline new directions that exist for the use of class II-restricted Ags/peptides in devising cancer vaccines as well as combined chemoimmunotherapy. A better understanding of these concepts will improve future cancer vaccine studies and further the field of cancer immunobiology.