PROJECT SUMMARY Prostate cancer is a significant worldwide health problem for which new treatments are needed. The goal of our laboratory for the past twenty years has been to develop immunotherapy treatments for prostate cancer. We have evaluated multiple cancer-associated proteins as anti-tumor vaccine targets and have focused recent efforts on the ligand-binding domain of the androgen receptor (AR LBD) as a target. We demonstrated that a DNA vaccine encoding the AR LBD (pTVG-AR) can elicit epitope-specific cytolytic CD8+ T cells in HLA-A2 transgenic mice, and immunization of prostate tumor-bearing mice elicited anti-tumor responses and significantly prolonged their overall survival. Based on these results, we recently completed a multi-center phase I clinical trial using the pTVG-AR vaccine for patients with metastatic prostate cancer and demonstrated that vaccination is safe and immunologically active. Consistent with our preclinical studies, the development of T-cell immune response to the AR LBD was associated with a prolonged time to castration resistance. In preclinical studies, we have found that androgen deprivation (AD) leads to overexpression of the AR protein in prostate cancer cells, and this in turn makes them more recognized by CD8+ T cells activated by AR- targeted vaccination. We have subsequently demonstrated that AD can thus be used strategically with immunization. In other preclinical studies, we have further found that CD8+ T cells activated by vaccination express multiple immune checkpoint receptors (ICR), and that blockade of certain ICR with vaccination leads to greater anti-tumor effects. Together, these findings have led to the hypothesis to be tested in this proposal that combined AD, with AR-targeted vaccination and T-cell checkpoint blockade, will lead to increased tumor-specific CD8+ T cell infiltration, tumor eradication, and persistent immune memory. We will use relevant murine models of prostate cancer to conduct a mechanistic evaluation of the effects of AD with vaccination and ICR blockade on the development of T cell memory and antigen spread. This approach will also be evaluated in an investigator- initiated clinical trial in patients with high-risk prostate cancer prior to prostatectomy, with a design amenable to modification of study arms depending on the outcomes from the preclinical studies. This proposal, consequently, capitalizes on development of a novel anti-tumor vaccine that has now completed phase I clinical trial evaluation, and explores methods to increase its therapeutic effect in preclinical models and in a biomarker-driven clinical trial. Results from this proposal will identify optimal strategies and clinical scenarios for further clinical development of this treatment approach.

PROJECT NARRATIVE The ultimate goal of our research has been to develop effective anti-tumor vaccines as treatments for cancer, and prostate cancer in particular. We have studied the androgen receptor (AR) as a target for vaccination, and recently completed a phase I trial evaluating an AR-targeted vaccine. We have also recently identified that androgen deprivation, the cornerstone of therapy for men with recurrent prostate cancer, results in AR overexpression in prostate cancer cells, and this makes them more amenable to recognition by AR-specific CD8+ T cells. Combining these treatments results in a greater anti-tumor response in murine models. We have further found, in preclinical studies and clinical trials, that T-cell checkpoint blockade (notably targeting PD-1) with vaccination leads to greater anti-tumor effects. Together these findings form the basis for the current proposal using murine models and a pilot clinical trial to evaluate AR-targeted vaccination in combination with androgen deprivation and T-cell checkpoint blockade for their anti-tumor efficacy and establishment of immune memory. Thus, this application is directly relevant to the mission of the National Cancer Institute.