Peptide vaccination of patients with metastatic melanoma: Improved clinical outcome in patients demonstrating effective immunization

OBJECTIVES: Therapeutic peptide vaccines for melanoma continue to only demonstrate anecdotal success. We set out to evaluate the impact of low-dose GM-CSF emulsified in Montanide ISA-51 on the immunogenicity of HLA-A2 restricted melanoma differentiation antigen peptide vaccines (MART-1, gp100 and tyrosinase) administered in separate subcutaneous injections. METHODS: We conducted a randomized phase II clinical trial of HLA-A2+ patients with metastatic melanoma that were immunized every 3 weeks with one of the following vaccine preparations: (A) peptides + Montanide ISA-51; (B) peptides + Montanide ISA-51 + GM-CSF (10 μg); (C) peptides + Montanide ISA-51 + GM-CSF (50 μg). Immunization efficacy was determined by quantification of vaccine specific tetramer positive cytotoxic T cells in peripheral blood. Global assessment of immune competence was ascertained using DTH testing to common recall antigens as well as peripheral blood immunophenotyping. RESULTS: Twenty-five eligible patients were equally distributed across all 3 treatment groups. Only 9 patients demonstrated evidence of immunization. Most commonly, immune response was achieved to the gp100 peptide. The addition of low-dose GM-CSF did not impact immunization efficacy. DTH reactivity to Candida appeared predictive of successful immunization. Successful immunization with the peptide vaccines was associated with improved clinical outcomes. CONCLUSIONS: The addition of low dose GM-CSF to peptide vaccines did not enhance immunogenicity. Higher doses of GM-CSF may be needed to achieve this effect and this is a testable hypothesis. Likewise, better patient selection based on immunologic status (DTH reactivity) may be helpful to better understand the clinical impact of therapeutic cancer vaccines.