IPEX patients harbor activated T cells including Tfh-like cells. Increased expression of CD40L, ICOS, and PD-1 but not CD69 on total (A) CD3⁺CD4⁺ cells and (B) CD3⁺CD4⁺FOXP3⁺ cells in IPEX patients (solid gray) compared with healthy donors (bold). (C) Increased PD-1 expression on circulating CD4⁺CXCR5⁺ cells reveals Tfh-like cells in IPEX patients.