A decisive answer to the question of which cells serve as targets for Ipilimumab (trade name Yervoy, developed by Bristol-Myers Squibb) in cancer immunotherapy can be obtained by immunophenotyping of CTLA-4(+) cells with an anti-CTLA-4 antibody of the same clone as a monoclonal anti-CTLA-4 therapeutic antibody Ipilimumab. This evidence concerns the gene CTLA4 and cancer.