PDCD1 and gastric cancer: Modified CAR-T on the basis of the original target can play a role in increasing the efficacy, such as EGFR-CAR-T that secretes PD-1 scFv, c-Met CAR-T that adds PD-1/CD28 chimeric switch receptor (CSR), and bispecific human trophoblast cell surface antigen 2/PD-L1 CAR-T, which all have been proven to increase the efficacy of the original CAR-T therapy in mouse GC models (114–116).