Similar to ICOS deficiency, IL-2/IL-15Rβ deficiency does not cause decreases of stages 1 and 2 MAIT cells, suggesting that IL-2/IL-15R signal does not play an important role for early MAIT cell development, which is consistent with the lack of expression of this receptor in these MAIT cells. This evidence concerns the gene ICOS and hyperinsulinemic hypoglycemia, familial, 4.