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Analog peptides represent a promising tool to further optimize peptide-based vaccines in promoting the expansion of tumor antigen-specific cytotoxic T lymphocytes. Here, we report the results of a pilot trial designed to study the immunogenicity of the analog peptide NY-ESO-1 157-165V in combination with CpG 7909/PF3512676 and Montanide ISA 720 in patients with stage III/IV NY-ESO-1–expressing melanoma. Eight patients were immunized either with Montanide and CpG (arm 1, 3 patients); Montanide and peptide NY-ESO-1 157-165V (arm 2, 2 patients); or with Montanide, CpG, and peptide NY-ESO-1 157-165V (arm 3, 3 patients). Only the 3 patients immunized with Montanide, CpG, and peptide NY-ESO-1 157-165V in arm 3 developed a rapid increase of effector-memory NY-ESO-1–specific CD8+ T cells, detectable ex vivo. The majority of these cells exhibited an intermediate/late-stage differentiated phenotype (CD28−). Our study further demonstrated that our vaccine approach stimulated spontaneous tumor-reactive NY-ESO-1–specific CD8+ T cells in 2 patients with advanced disease, but failed to prime tumor-reactive NY-ESO-1–specific T cells in 1 patient with no spontaneously tumor-induced CD8+ T-cell responses to NY-ESO-1. Collectively, our data support the capability of the analog peptide NY-ESO-1 157-165V in combination with CpG and Montanide to promote the expansion of NY-ESO-1–specific CD8+ T cells in patients with advanced cancer. They also suggest that the presence of tumor-induced NY-ESO-1–specific T cells of well-defined clonotypes is critical for the expansion of tumor-reactive NY-ESO-1–specific CD8+ T cells after peptide-based vaccine strategies.