TIGIT and PD-L1 co-blockade promotes clonal expansion of multipotent, non-exhausted anti-tumor T cells by facilitating costimulation

Abstract Blockade of the immune checkpoints PD-1 and TIGIT has demonstrated activity in mouse tumor models and human cancer patients. Although these coinhibitory receptors can restrict signaling in CD8⁺ T cells by regulating their associated costimulatory receptors CD28 and CD226, the functional consequences of combining PD-1 and TIGIT blockade remain poorly characterized. In mouse tumor models, combination blockade elicited CD226-driven clonal expansion of tumor antigen-specific CD8⁺ T cells. The expanded clones emerged from a population of stem-like cells in draining lymph nodes (dLN), entering the blood as a previously unidentified single-phenotype, multi-clonal population. Upon reaching the tumor, these tumor antigen-specific transiting cells expanded further and differentiated into effector or exhausted T cells, with combination blockade restricting entry into the exhaustion pathway by favoring costimulation. Thus, PD-1 and TIGIT inhibition helps shape the repertoire of tumor-reactive CD8⁺ T cells in dLN and determines their immunological fate in the tumor to enhance therapeutic benefit. Analysis of clinical trial samples suggests a similar mechanism may also occur in cancer patients.