PDCD1 and neoplasm: To some extent, our poor clinical response implies that CAR-T cell-intrinsic modification alone, for example, knocking out PD-1 in CAR-T cells, may not be enough to induce promising outcomes in the treatment of patients with solid tumors, highlighting that more endeavors are needed to explore cell-intrinsic and cell-extrinsic combinational therapy approaches to affect infused CAR-T cells, the innate immune system, and the tumor milieu.