Defects in CD8+ T cell suppression by Foxp3-dE2 regulatory T cells 2257749

Abstract Introduction Regulatory T-cells (Tregs) prevent autoimmunity through suppressive functions which are largely programmed by the transcription factor FOXP3. Healthy humans express two major alternatively spliced isoforms of FOXP3: One full-length version containing all coding exons (FOXP3-FL) and one version lacking the second exon (FOXP3-α”E2). Although healthy humans have Tregs programmed by either or both isoforms, humans with sole FOXP3-α”E2 expression develop lethal autoimmunity. The overall goal of this study is to identify the defects in suppression by FOXP3-α”E2 Tregs. Methods This study used novel mouse models including Foxp3-α”E2 mice, influenza A viral infection, RNA-seq, ATAC-seq, spectral flow cytometry, confocal microscopy, and standard molecular biology techniques. Results Foxp3-α”E2 Tregs have reduced expression of core Treg signature genes, including CD25 and IL-2/STAT5 signaling targets. Reduced CD25 expression on Foxp3-α”E2 Tregs leads to lowered pSTAT5 responsiveness to IL-2 stimulation in vitro. Diminished regulation of IL-2 by Foxp3-α”E2 Tregs associates with enhanced CD8+ T-cell expansion, activation, and memory formation in response to influenza viral infection. These defects in T cell restraint are intrinsic to Foxp3-α”E2 Tregs as the phenotype is maintained in a Foxp3-FL-DTR/α”E2 mouse model where WT Tregs are depleted immediately prior to infection. These phenotypic and functional defects in Foxp3-α”E2 Tregs are putatively driven by impaired binding of the Foxp3-α”E2 isoform to Runx1 which is the only transcription factor with enriched promoter binding motifs amongst differentially expressed genes and differentially accessible chromatin. Conclusion Reduced expression of key inhibitory molecules on Foxp3-α”E2 Tregs results in diminished IL-2 regulation and enhanced CD8+ T-cell activation and memory formation. These findings are critical for understanding the defects in suppression by Foxp3-α”E2 Tregs and how these cells may contribute to aberrant immune responses. Funding Source NIAID 1R01AI188364-01 awarded to Steven Ziegler & NSF-GRF DGE-2140004 awarded to Kristin Weinstein Topic Categories Immune Response Regulation: Cellular Mechanisms (IRC)