PMEL and melanoma: Others have questioned the ability of single Ag-based vaccines to elicit a broadly reactive CD8+ T cell repertoire capable of mediating therapy benefits against antigenically heterogeneous populations of tumor clones in the setting of visceral disease.41 43 To determine whether skin immunization leads to Ag spreading in the antimelanoma CD8+ T cell repertoire, single-cell suspensions of spleens were isolated from treated mice and then restimulated in vitro with MHC class I-presented peptide epitopes derived from vaccine Ag TRP2 or non-vaccine (but melanoma-associated) Ags gp100 and TRP1.