PDCD1 and neoplasm: a. The PD-1-TREM2 scFv antibody effectively inhibited the activation of the PD-1/PD-L1 pathway and reduced the proportion of MDSCs and TAMs.b. The modified CAR-T cells significantly enhanced effector T cell function and increased the infiltration and cytotoxic activity of CD8+ T cells within the tumour.c. Compared with conventional CAR-T cell therapy secreting PD-1 scFv alone, PD-1-TREM2 scFv-secreting CAR-T cells demonstrated stronger anti-tumour effects and more pronounced inhibition of tumour growth in the CRC mouse model.