PI3K shapes Th2 lineage restriction through coordination of IL-2 signaling, Foxo1 inactivation and epigenetic remodeling

Abstract Activated PI3K-delta syndrome (APDS) is a primary immunodeficiency caused by heterozygous activating mutations in PI3Kδ, resulting in recurrent infections as well as allergic diseases. Given that APDS patients show an inability to clear respiratory pathogens (Th1) and development of allergic diseases (Th2), we hypothesized that hyperactivated PI3Kδ (Pik3cd E1020K) may alter CD4 T cell differentiation. Using in vitro polarization of murine naïve CD4 T cells, we observed increased production of IFNγ from Pik3cd E1020Kmice under Th1 inducing conditions and marked increases in IL-4 and IL-13 production under Th2 conditions. However, Pik3cd E1020KTh2 cells also expressed high levels of Tbet and aberrantly produced IFNγ. Strikingly, this dysregulation was also observed in vivo; Pik3cd E1020KCD4 cells show pronounced alterations following house dust mite induced airway inflammation, with impaired Th2 and inappropriate polarization to Th1 responses as visualized by scRNAseq. We linked this unstable Th1 and Th2 differentiation in Pik3cd E1020KCD4 T cells in vitro to hyper-responsiveness to IL-2, associated with increased phosphorylation and inactivation of transcription factor Foxo1. CRISPR-mediated targeting of Foxo1 in naïve WT CD4 cells recapitulated the Pik3cd E1020Kphenotype. Transcriptomic analysis of Pik3cd E1020KCD4 T cells revealed differential expression of genes involved in histone methylation. Accordingly, Pik3cd E1020KCD4 exhibit altered chromatin modifications, including H3K27 and H3K4 trimethylation. Together these data suggest that balanced regulation of PI3Kδ plays a critical role in enforcing Th1 and Th2 lineage identity. This research was supported by the Intramural Research Program of NIAID, NIH