HSF1A increased STAT3 function in AD-HIES patient PBMCs. PBMCs from a patient with STAT3 S mutation V463del or a healthy control were each preincubated in triplicate aliquots with HSF1A and stimulated with IL-21, as noted before (A). PBMCs from 3 patients with STAT3 S mutation V463del, 1 patient with STAT3 S mutation F621V, and 7 healthy controls were incubated with HSFA1 and stimulated with IL-21, as noted before, each on ≥4 occasions (B). Results shown are percentage of pY-STAT3–positive cells and MFI in CD4⁺ and CD8⁺ T cells determined by multiparametric flow cytometry ([A] ANOVA; [B] paired Student t test). ns, not significant.