STIM1-mediated NFAT signaling synergizes with STAT1 to control T-bet expression and TH1 differentiation

Stromal interaction molecule 1 (STIM1) is critical for store-operated Ca²⁺ entry (SOCE) and T cell activation. T helper 1 (T_H1) cells, which express T-bet (encoded by TBX21), mediate immunity to intracellular pathogens. Although SOCE is known to regulate other T_H lineages, its role in Th1 differentiation remains unclear. Here, we report a patient with an intronic loss-of-function mutation in STIM1, which abolishes SOCE and causes immunodeficiency. We demonstrate that SOCE promotes nuclear factor of activated T cells (NFAT) binding to conserved noncoding sequence (CNS)-12 in the TBX21 enhancer and enables NFAT to synergize with STAT1 to mediate TBX21 expression. While SOCE-deficient CD4⁺ T cells have reduced expression of TBX21 in the absence of interleukin-12 (IL-12), their expression of IL-12 receptors β1 and β2 is increased, sensitizing them to IL-12 signaling and allowing IL-12 to rescue T-bet expression. Our study reveals that the STIM1-SOCE–NFAT signaling axis is essential for the differentiation of Th1 cells depending on the cytokine milieu.