Sipuleucel-T With Immediate vs. Delayed Cytotoxic T-Lymphocyte-Associated Protein 4 (CTLA-4) Blockade for Prostate Cancer

This is an open-label randomized multicenter Phase 2 clinical trial combining SipT with ipilimumab in patients with chemotherapy-naïve metastatic castration resistant prostate cancer (CRPC). All patients will be treated with standard SipT (Q2wks x 3). Patients will be randomized to one of two arms: Arm 1 (Immediate Treatment): Ipilimumab Q3wks x 4 started 1 day following the final dose of SipT (Day 0). Arm 2 (Delayed Treatment): Ipilimumab Q3wks x 4 started 3 weeks following the final dose of SipT (Day 0). Following this ipilimumab treatment, patients will then be followed monthly for 3 months and then quarterly until disease progression. The definition of unacceptable toxicity is grade 3 or higher treatment-related toxicities (NCI CTCAE v4) excluding immune-related adverse events (irAEs). The study will assess for the immunogenicity and clinical activity of sequential sipuleucel-T treatment followed by ipilimumab. Patients who experience an initial clinical response to ipilimumab followed by subsequent disease progression will be offered reinduction treatment with ipilimumab.