CTLA4 and obesity due to melanocortin 4 receptor deficiency: Positive associations between obesity, as defined by BMI, and increased responsiveness to immune checkpoint inhibitor (ICI) therapies (i.e., antibodies blocking the interaction of PD-1 with its ligand PD-L1, or the interaction of CTLA-4 with its ligands B7-1 and B7-2) have been observed in cancer patients with varying tumor types.