Low avidity CD8⁺ T cells are less exhausted than their high avidity counterparts and provide superior anti-tumor immunity

Abstract The interaction of T cell receptors (TCRs) on T cells with MHC I-peptide complexes on cancer cells elicits the cytotoxic activity of CD8 +T cells. Here we analyze how the strength of this interaction, or T cell avidity, shapes the exhaustion of CD8 +TILs and dictates anti-tumor immunity. We developed a novel tetramer decay assay to isolate T cells based on their TCR avidities. We used this method to study low and high avidity CD8 +TILs responding to the tumor neoantigen PDPR MUTof the murine sarcoma Meth A. Single cell sequencing reveals that high avidity CD8 +TILs are more terminally exhausted (51.41% vs 27.21%) and less effector-like (28.39% vs. 60.0%) than low avidity CD8 +TILs. We used flow cytometry to analyze PDPR MUT-specific CD8 +TILs with low or high avidity from 28 day-old Meth A tumors. There were significantly more TIM3 +PD-1 +cells (Paired t-test; P < 0.0001) and TOX +PD-1 +cells (Paired t-test; P < 0.05) in the high avidity CD8 +TILs than the low avidity CD8 +TILs. We adoptively transferred 1,000 PDPR MUT-specific low or high avidity CD8 +T cells, or control CD8 +T cells into tumor-bearing mice 10 days after tumor challenge. Low avidity T cells significantly improved the survival of mice (Mantel-Cox; P = 0.0044), while high avidity t cells did not do so (Mantel-Cox; P = 0.7081). These results establish a novel correlation between avidity, exhaustion and T cell-mediated tumor control in vivo.