PDCD1 and neoplasm: The mannose-modified macrophage-derived microparticles (Man-MPs) loading metformin (Met@Man-MPs) targeted M2-like TAMs to repolarize into M1-like phenotype, increase the recruitment of CD8+ T cells into tumor tissues, and boost anti-PD-1 antibody therapy in H22 tumor-bearing BALB/c mice [83].