The T-box transcription factors T-bet and Eomes repress protective Th17 CD4 T cell responses against Influenza A Virus

Abstract

Abstract Promoting strong CD4 cell immunity is an attractive strategy to generate a universal Influenza A Virus (IAV) vaccine. Though most CD4 cell responses against IAV are classified as Th1, Th17 and cytotoxic CD4 cells (ThCTL) may also contribute to viral clearance. Interestingly, we find the transcription factor T-bet (Tbx21), the ‘master regulator’ of Th1 differentiation, to be dispensable for protective CD4 responses against IAV. Surprisingly, Tbx21−/− cells develop Th17 characteristics but retain Th1 functionality, highlighted by strong IFN-γ production. While the transcription factor Eomesodermin (Eomes) can compensate for loss of T-bet to promote antiviral CD8 responses, its roles in CD4 cells is still unclear. Here we analyze Eomes−/−, Tbx21−/− and Tbx21−/−Eomes−/− CD4 cell responses against IAV using an adoptive transfer model to determine the extent to which Eomes regulates antiviral CD4 functions. Eomes−/− cells mirrored the prototypical Th1 responses of WT CD4 cells. Strikingly, Tbx21−/−Eomes−/− cells exhibited near complete loss of both Th1 responses and ThCTL function. In contrast, Tbx21−/− Eomes−/− developed stronger Th17 attributes than Tbx21−/− cells. We assessed protection provided by transfer of in vitro Th17-primed WT, Eomes−/−, Tbx21−/− and Tbx21−/−Eomes−/− cells to unprimed WT mice infected with lethal IAV. While WT and Eomes−/− effectors gained Th1 characteristics in vivo, Tbx21−/−Eomes−/− cells strengthened their Th17 phenotype. Remarkably, all of the Th17 effectors were equally protective. Our observations reinforce the concept that Th17 cells can provide strong protection against IAV, independently of Th1 and ThCTL responses, and suggest Th17 cells use unique pathways to do so.