While the link between IL21R signaling and CD8 bTRM differentiation has not been clearly established, it is worth noting that the effector functions of CD8 T cells, such as granzyme B expression and IFNγ production, have been correlated with the CD8 TRM phenotype, suggesting that the changes in CD8 T cells observed during IL-21 deficiency may be due to alterations in CD8 TRM differentiation (Figure 2A) [19,53,55,60,88]. The gene discussed is CD8A; the disease is hyperinsulinemic hypoglycemia, familial, 4.