Murine systems to study host genetics of ICI response have, until recently, also been lacking due to the absence of genetic diversity.33 In a recent study, Hackett et al.62 identified a locus on mChr13 that modulated response of the transplantable B16 melanoma cell line to combined aPD1 and anti-CTLA4 (aCTLA4) treatment. This evidence concerns the gene CTLA4 and melanoma.