Consequently, the increase in PD-1+ CD8+ cells by diet-induced obesity resulted in reduced expression of cytotoxic genes such as IFN γ and granzyme B (GzB) (Kado et al., 2019), suggesting that obesity decreases anti-tumor cytotoxic activity by induction of T cell exhaustion. This evidence concerns the gene GZMB and obesity due to melanocortin 4 receptor deficiency.