Dissection of these animals revealedblood in the stomach, suggestive of an excessive immune response leadingto colitis, an adverse event sometimes caused by ICI therapy.23 This large variability, along with the deathof some mice due to adverse immune events, suggests that, while IFNγdrives improved MHC expression and may be partially beneficial, leadingto a robust antitumor response in some mice, local IFNγ mayhave a narrow therapeutic index. This evidence concerns the gene HLA-C and colitis.