Abundant Yet Aberrant T Helper Cell Responses to Candida albicans Underlie Mucosal Candidiasis in Humans and Mice

T helper cell subsets—Th1, Th2, and Th17—coordinate pathogen-specific immune responses. Candida albicans-specific T cells include protective Th17 cells alongside other Th subsets. However, the role of alternative Th subsets remains unclear, particularly in individuals with impaired Th17 responses and recurrent candidiasis. Here, we show that patients with STAT1 gain-of-function mutations and chronic mucocutaneous candidiasis have a numerically normal but functionally altered pool of C. albicans-specific Th cells, skewed toward Th1 and Th2. This imbalance persisted even when assessing responses to the known and the newly identified immunodominant C. albicans antigens MP65 (65-kilodalton mannoprotein), HYR1 (hyphally regulated cell wall protein 1), and SAP4-6 (secreted aspartic proteinases 4–6), suggesting that antigen recognition and priming remain intact despite qualitative defects in T cell polarization. Using mucosal infection mouse models, we demonstrate that C. albicans-specific transgenic Th17 cells are sufficient to control infection, whereas Th1 and Th2 cells fail to protect, even in high numbers. Moreover, co-transfer of Th2 cells with Th17 cells impaired fungal control via an IL-4-dependent mechanism. These findings highlight the essential role of Th17 cells in protective immunity against C. albicans and reveal that non-Th17 responses are ineffective and may contribute to susceptibility in both humans and mice.