Our studies with samples from melanoma patients vaccinated with gp100:209M peptide suggest that the GrB ELISPOT assay may be successfully applied to evaluate CTL precursor frequency, and reactivity in the GrB ELISPOT was more closely associated with cytotoxicity as determined by the 51Cr -release assay than either the tetramer or IFN-γ ELISPOT assays [35]. This evidence concerns the gene PMEL and melanoma.