Patients vaccinated repetitively with the natural Melan-AMART-126–35 decapeptide generated tumor-specific CD8 T cells with increased TCR–pMHC structural avidities as compared to vaccinations with the analog Melan-AMART-126–35 A27L peptide, even if the latter binds more strongly and stably to MHC as compared to the natural peptide. The gene discussed is CD8A; the disease is neoplasm.