Immunization with mutant p53- and K-ras-derived peptides in cancer patients: Immune response and clinical outcome

Purpose: To determine the ability to induce tumor-specific immunity with individual mutant K-ras- or p53-derived peptides and to monitor clinical outcome. Patients and Methods: Patients in varying stages of disease underwent genetic analysis for mutations in K-ras and p53. Thirty-nine patients were enrolled. Seventeen-mer peptides were custom synthesized to the corresponding mutation. Baseline immunity was assessed for cytotoxic T-lymphocyte (CTL) response and interferon gamma (IFN-γ) release from mutant peptide-primed lymphocytes. Patients' peripheral-blood mononuclear cells were pulsed with the corresponding peptide, irradiated, and applied intravenously. Patients were observed for CTL, IFN-γ, interleukin (IL)-2, IL-5, and granulocyte-macrophage colony-stimulating factor responses, for treatment-related toxicity, and for tumor response. Results: No toxicity was observed. Ten (26%) of 38 patients had detectable CTL against mutant p53 or K-ras, and two patients were positive for CTL at baseline. Positive IFN-γ responses occurred in 16 patients (42%) after vaccination, whereas four patients had positive IFN-γ reaction before vaccination. Of 29 patients with evident disease, five experienced a period of stable disease. Favorable prognostic markers were detectable CTL activity and a positive IFN-γ reaction but not IL-5 release. Median survival times of 393 v 98 days for a positive versus negative CTL response (P = .04), respectively, and of 470 v 88 days for a positive versus negative IFN-γ response (P = .02), respectively, were detected. Conclusion: Custom-made peptide vaccination is feasible without any toxicity. CTL and cytokine responses specific to a given mutation can be induced or enhanced with peptide vaccines. Cellular immunity to mutant p53 and K-ras oncopeptides is associated with longer survival.