A signaling-optimized TIGIT chimeric switch receptor promotes metabolic fitness and antitumor efficacy of TCR/CAR T cells

Adoptive T cell therapies have revolutionized the treatment of hematological malignancies, however, their efficacy against solid tumors often remains limited. Lack of activation and overabundance of immune checkpoint-mediated inhibitory signals from cancer cells drive T cell dysfunction and limit persistence. To circumvent this imbalance towards inhibitory factors, we engineered a chimeric switch receptor (CSR) that repurposes the immunosuppressive TIGIT extracellular domain by fusing it to a CD28-derived stimulatory signaling tail. Here we show that while the prototype CSR design enhances immediate cytolytic activity, it also induces premature proliferative arrest and terminal differentiation due to excessive tonic signaling. By introducing a strategic point mutation within the CD28 cytoplasmic domain, we "fine-tuned" the activation threshold of the CSR for optimal functional properties. Engineered T cells with 'fine-tuned' CSR exhibit superior mitochondrial bioenergetics and sustained metabolic flux in an in vitro system of chronic antigen exposure. In preclinical xenograft models, fine-tuned CSR-expressing T cells demonstrated robust expansion and durable persistence, leading to complete tumor eradication. These findings provide a scalable strategy to rewire inhibitory checkpoints into tailored costimulatory signals, offering a potent approach to enhance the metabolic fitness and persistence of therapeutic T cells, in suppressive tumor microenvironments, in particular.