CD226hiCD8+ T cells are a prerequisite for anti-TIGIT immunotherapy.

Clinical trials are evaluating the efficacy of anti-TIGIT for use as single-agent therapy or in combination with PD-1/PD-L1 blockade. How and whether a TIGIT blockade will synergize with immunotherapies is not clear. Here we show that CD226loCD8+ T cells accumulate at the tumor site and have an exhausted phenotype with impaired functionality. In contrast, CD226hiCD8+ tumor-infiltrating T cells possess greater self-renewal capacity and responsiveness. Anti-TIGIT treatment selectively affects CD226hiCD8+ T cells by promoting CD226 phosphorylation at tyrosine 322. CD226 agonist antibody-mediated activation of CD226 augments the effect of TIGIT blockade on CD8+ T-cell responses. Finally, mFOLFIRINOX treatment, which increases CD226hiCD8+ T cells in patients with pancreatic ductal adenocarcinoma, potentiates the effects of TIGIT or PD-1 blockade. Our results implicate CD226 as a predictive biomarker for cancer immunotherapy and suggest that increasing numbers of CD226hiCD8+ T cells may improve responses to anti-TIGIT therapy.