Dendritic cell-based multi-epitope immunotherapy of hormone-refractory prostate carcinoma

Background: Dendritic cell (DC)-based immunotherapy is a promising approach to augment tumor antigen-specific T cell responses in cancer patients. However, tumor escape with down-regulation or complete loss of target antigens may limit the susceptibility of tumor cells to the immune attack. Concomitant generation of T cell responses against several immunodominant antigens may circumvent this potential drawback. In this trial, we determined the immunostimulatory capacity of autologous DC pulsed with multiple T cell epitopes derived from four different prostate-specific antigens in patients with advanced hormone-refractory prostate cancer.Patients and methods:Autologous DC of HLA-A*0201+ patients with hormone-refractory prostate cancer were loaded with antigenic peptides derived from prostate stem cell antigen (PSCA14–22), prostatic acid phosphatase (PAP299–307), prostate-specific membrane antigen (PSMA4–12), and prostate-specific antigen (PSA154–163). DC were intradermally applied six times at biweekly intervals followed-in the case of an enhanced immune response-by monthly booster injections. Immune monitoring during the time of ongoing vaccinations (12–59 weeks) included ex vivo ELISPOT measurements, MHC tetramer analysis and in vitro cytotoxicity assays.Results: Of the initial six patients, three qualified for long-term multi-epitope DC vaccination. This regime was tolerated well by all three patients. The vaccination elicited significant cytotoxic T cell responses against all prostate-specific antigens tested. In addition, memory T cell responses against the control peptides derived from influenza matrix protein and tetanus toxoid were efficiently boosted. Clinically, the long-term DC vaccination was associated with an increase in PSA doubling time.Conclusions: DC-based multi-epitope immunotherapy with repeated boosting in men with hormonerefractory prostate carcinoma is feasible and generates efficient cellular antitumor responses