Defective regulatory and effector T cell functions in patients with FOXP3 mutations

The autoimmune disease immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) is caused by mutations in the forkhead box protein P3 (FOXP3) gene. In the mouse model of FOXP3 deficiency, the lack of CD4(+)CD25(+) Tregs is responsible for lethal autoimmunity, indicating that FOXP3 is required for the differentiation of this Treg subset. We show that the number and phenotype of CD4(+)CD25(+) T cells from IPEX patients are comparable to those of normal donors. CD4(+)CD25(high) T cells from IPEX patients who express FOXP3 protein suppressed the in vitro proliferation of effector T cells from normal donors, when activated by weak TCR stimuli. In contrast, the suppressive function of CD4(+)CD25(high) T cells from IPEX patients who do not express FOXP3 protein was profoundly impaired. Importantly, CD4(+)CD25(high) T cells from either FOXP3(+) or FOXP3(-) IPEX patients showed altered suppression toward autologous effector T cells. Interestingly, IL-2 and IFN-gamma production by PBMCs from IPEX patients was significantly decreased. These findings indicate that FOXP3 mutations in IPEX patients result in heterogeneous biological abnormalities, leading not necessarily to a lack of differentiation of CD4(+)CD25(high) Tregs but rather to a dysfunction in these cells and in effector T cells.