Dissecting the heterogeneity and specificity of regulatory CD8 T cells 3127

Abstract Description Regulatory CD8 T cells (8Tregs) were first described two decades ago, as a counterpart to regulatory CD4 T cells. Since then, multiple groups have published on 8Tregs that can suppress an overexuberant immune response and ultimately prevent autoimmunity during inflammation. The consensus is that 8Tregs have a memory phenotype (“MP”, CD44hi CD122+) in unimmunized mice and express one or both markers: Ly49, an NK receptor, and Helios, a transcription factor. However, important questions remain unanswered regarding the definitive markers, specificity, and functional mechanism of these 8Tregs. To address these questions, we performed single-cell RNA sequencing on Ly49+ or Helios+ cells, revealing multiple subsets, and indicating that true 8Tregs may be within the Ly49+/Helios+ subpopulation. We also conducted TCR repertoire analysis on cells from mice with a fixed TCRβ chain. These studies showed that Helios+ and Ly49+Helios+ populations have an overlapping repertoire which is distinct from the “conventional” MP population. Interestingly, TCRs enriched in Helios+ MP CD8 T cells were previously defined as being prominent among prostate tumor-infiltrating lymphocytes (TRAMP TILs) in the same fixed TCRβ transgenic model. These results lead us to speculate that the TCR specificity drives the phenotype of these cells and raise the possibility that TCRs from 8Tregs recognize self-antigens expressed in tumors. Funding Sources Supported by NIH AI38903 Topic Categories Lymphocyte Differentiation and Peripheral Maintenance (LYM)