Obesity does not fully suppress the ability of Vγ9Vδ2 T cells to function, as the potent phosphoantigen, 1-Hydroxy-2-methyl—buten-4yl 4-diphosphate (HDMAPP), is able to stimulate IFN-γ production by Vγ9Vδ2 T cells isolated from obese patients. The gene discussed is IFNG; the disease is obesity due to melanocortin 4 receptor deficiency.