ICOS limits memory-like properties and function of exhausted PD-1+ CD8 T cells [RNA-seq]

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 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), Tpex (CD39neg PD1+), effector-like Tex (CD39+ CX3CR1+ PD1+) and terminal Tex (CD39+ CX3CR1neg PD1+) P14 control or sgICos were sorted for gene expression analysis of bulk RNAsequencing to understand the molecular impact of ICOS on differentiation of PD-1+ virus-specific CD8 T cells.