Because CTL response to vaccinations was not readily detectable ex vivo in the blood, even in those patients who showed tumor regressions, sensitive and quantitative approaches were set up allowing the detection of frequencies of CTL precursors specific for a MAGE-3 peptide presented by HLA-A1 (anti-MAGE-3.A1) as low as one precursor per million CD8 blood T cells [22,23]. This evidence concerns the gene MAGEA3 and neoplasm.