A pilot study of CTLA-4 blockade after cancer vaccine failure in patients with advanced malignancy

Purpose: Eleven patients with progressive advanced malignancy after administration of a cancer vaccine received a fully human anti-CTLA-4 monoclonal antibody (ipilimumab). The primary end point was to determine drug toxicity. Tumor response, tumor-specific CD8⁺ T-cell immune responses, and modulation of CD4⁺ CD25⁺ FoxP3⁺ regulatory T-cell (Treg) numbers were secondary end points. Experimental Design: Three patients with colon cancer, four with non - Hodgkin's lymphoma, and four with prostate cancer were treated. The first dose was given at 3 mg/kg and subsequent doses were administered monthly at 1.5 mg/kg for a total of four cycles. Results: Tumor regression was observed in two patients with lymphoma; one of which obtained a partial response of 14-month duration. Ipilimumab was well tolerated with predominantly grade 1/2 toxicities. One drug-related grade 3 toxicity was observed. One patient died within 30 days of treatment due to progressive colon cancer. No increase in vaccine-specific T-cell responses was observed after therapy. Tregs as detected by expression of CD4 ⁺CD25⁺CD62L⁺ declined at early time points but rebounded to levels at or above baseline values at the time of the next infusion. Conclusions: Ipilimumab treatment depressed Treg numbers at early time points in the treatment cycle but was not accompanied by an increase in vaccine-specific CD8⁺ T-cell responses in these patients previously treated with a variety of investigational anticancer vaccines. A partial response was observed in one patient with follicular lymphoma. A phase I/II trial evaluating ipilimumab in patients with follicular lymphoma is currently ongoing.