Single cell analysis of splenic control and ICOS deficient P14 cells from LCMV chronically infected mice

During persistent antigen stimulation, PD-1+CD8 T cells are maintained by progenitor exhausted PD-1+TCF-1+CD8 T cells (Tpex). Tpex respond to PD-1 blockade, and regulation of Tpex differentiation into more functional Tex is of major interest for cancer immunotherapies. Tpex express high levels of Inducible T-cell Costimulator (ICOS), but the role of ICOS for PD-1+CD8 T cell responses has not been addressed. In chronic infection, ICOS-deficiency increased both number and quality of virus-specific CD8 T cells, with accumulation of effector-like Tex due to enhanced survival. Mechanistically, loss of ICOS signaling potentiated FoxO1 activity and memory features of Tpex. In mice with established chronic infection, ICOS-Ligand blockade resulted in expansion of effector-like Tex and reduction in viral load. In a mouse model of hepatocellular carcinoma, ICOS inhibition improved cytokine production by tumor-specific PD-1+CD8 T cells and delayed tumor growth. Overall, we show that ICOS constrains CD8 T cell responses during chronic antigen exposure. P14 (LCMV-specific CD8 T cell) electroporated with Cas9/gRNA control or targeting Icos were transfered into mice prior to LCMV c13 infection. Once mice are chronically infected (>42DPI), P14 control and sgICos were sorted for scRNA-sequencing (10x) to understand the molecular impact of ICOS on differentiation of virus-specific PD-1+ CD8 T cells.