Aiolos represses CD4(+) T cell cytotoxic programming via reciprocal regulation of T-FH transcription factors and IL-2 sensitivity

During intracellular infection, T follicular helper (T-FH) and T helper 1 (T(H)1) cells promote humoral and cell-mediated responses, respectively. Another subset, CD4-cytotoxic T lymphocytes (CD4-CTLs), eliminate infected cells via functions typically associated with CD8(+) T cells. The mechanisms underlying differentiation of these populations are incompletely understood. Here, we identify the transcription factor Aiolos as a reciprocal regulator of T-FH and CD4-CTL programming. We find that Aiolos deficiency results in downregulation of key T-FH transcription factors, and consequently reduced T-FH differentiation and antibody production, during influenza virus infection. Conversely, CD4-CTL programming is elevated, including enhanced Eomes and cytolytic molecule expression. We further demonstrate that Aiolos deficiency allows for enhanced IL-2 sensitivity and increased STAT5 association with CD4-CTL gene targets, including Eomes, effector molecules, and IL2Ra. Thus, our collective findings identify Aiolos as a pivotal regulator of CD4-CTL and T-FH programming and highlight its potential as a target for manipulating CD4(+) T cell responses. The regulation and direction of CD4(+) T cells into phenotypic and functional lineages is coordinated by a complex set of mechanisms. Here the authors show a role for Aiolos as a regulator of the CD4(+) cytotoxic and T follicular helper lineages.