Decreased Generation and Function of CD4+CD25^hi T Regulatory Cells in Human STAT5b Deficiency.

CD4+ CD25+ regulatory T cells (Tregs) are a well characterized population of cells that play an important role in limiting inflammation and in the maintenance of tolerance to self. Here we describe a patient with a homozygous missense mutation (A630P) in the STAT5b gene who clinically displays immune dysregulation in association with decreased numbers and function of Tregs. Freshly isolated or in vitro-derived CD4+CD25^high Treg cells from this patient had low Foxp3 expression, did not suppress non Treg T-cell proliferation, and were unable to kill autologous CD4+CD25^neg T cells compared to controls. CD25 expression in response to IL-2 did not increase on freshly isolated CD4 T cells and was decreased on T-cell blasts derived from the patient. The patients mother who was heterozygous for this mutation had an intermediate phenotype for all of these immune abnormalities, indicating a gene dosage effect. In contrast, IL-2 upregulated expression of the common gamma chain (γc) cytokine receptor and perforin by T cells normally. Activation-induced T-cell expression of CD40-ligand (CD154) and interferon-gamma (IFN-γ) were also normal in the patient. These results suggest that the STAT5 pathway propagates an important IL-2 mediated signal that is necessary for Treg generation and function in humans in vivo.