Considering T-bet does not appear regulate GzmB expression and the high levels of Prdm1 mRNA observed in CD4+ Th-ctx cells post-αCTLA-4 treatment, we explored whether Blimp-1 contributed to the acquisition of a cytotoxic phenotype by CD4eff T cells and to the overall anti-tumor activity of αCTLA-4. This evidence concerns the gene PRDM1 and neoplasm.