Confirmation of these data in a phase III trial is planned in this setting. The vaccine will also be evaluated in earlier stages of nonmetastatic CRPC by ECOG (E1805, Paradigm) in a phase III trial of PROSTVAC/GM-CSF versus GMCSF (Table 1). Measurement of Immune inhibitor licensed response With Vaccines The optimal measure of immune response is unclear. Correlation of immune response with clinical activity is vital to validate vaccine therapy. T-cell- and antibody-based immunoassays are used to determine

if a given vaccine can elicit an immune response. The ELISpot assay reproducibly measures Inhibitors,research,lifescience,medical cytokine (eg, IFN-γ) release from T cells and can detect a peptide-specific T-cell response.31 Recently, MHC-peptide tetramer (or pentamer) assays have been widely used Inhibitors,research,lifescience,medical to quantify the number of antigen-specific T cells in animal models.32 The intracellular cytokine FastImmune assay uses flow cytometry to detect intracellular cytokines and allows the examination of multiple cytokines within T cells.33 Pre- and posttreatment T-cell Inhibitors,research,lifescience,medical proliferation assays in response to specific antigens have also been used to measure cell-mediated immunity.34 Delayed-type hypersensitivity skin tests have been

used to crudely evaluate cell-mediated immunity to specific antigens. A humoral response is usually considered positive if a 4-fold increase in enzyme-linked immunosorbent assay (ELISA)-measured antigen-specific titer occurs Inhibitors,research,lifescience,medical compared with pretreatment levels with no cross reactivity against an unrelated patient antigen. Other nearly emerging Immunotherapeutic Agents for PCa Therapy Anti-CTLA-4 mAbs are emerging as active agents and single nucleotide polymorphisms (SNPs) within the CTLA-4 gene may predict responses.35 Inhibitors,research,lifescience,medical There are several antibodies (eg, ipilimumab, tremelimumab) in various stages of preclinical/clinical development that have the potential for clinical efficacy. These include antibodies to CD137, a costimulatory molecule that is induced on T cells after activation and enhances T-cell activation/proliferation on crosslinking;

programmed death (PD)-1 receptor, a receptor that binds to the negative T-cell costimulatory molecule; programmed death ligand-1, promoting T-cell apoptosis and dampening the immune response; Drug_discovery and OX-40 (CD134), expressed on Tregs and a negative regulator of their activity. The combination of such antibodies with vaccine as well as other modalities may merit further study to potentiate the immune response. Endpoints and Patient Selection in Trials Evaluating Immunotherapy for CRPC The choice of a primary endpoint for a phase II trial of CRPC is difficult, as advanced PCa is characterized by a poor ability to measure response due either to immeasurable bone-only metastases or PSA-only disease.