RET and skin neoplasm: In wild type mice, the frequencies of tetramer-positive CTLs within total mononuclear spleen cells ranged from 0.3% to 1.2% upon immunization with the TRP-2 peptide, whereas spleens of immunized ret transgenic mice without macroscopic skin tumors contained from 0.3% to 0.4% TRP-2-reactive T cells (Figure 5a).