PDCD1 and neoplasm: As reported, a differentiated T-cell phenotype, the expression of immune checkpoints (programmed cell death protein-1, PD-1; T cell immunoglobulin and mucin-domain containing-3, TIM-3; lymphocyte activation gene-3, LAG-3) as well as immune microenvironment can influence the anti-tumor activity, proliferation, and persistence of CAR-T cells (33, 34).