CD274 and neoplasm: The ultimate functional competence of CART cells in solid tumors is determined by whether they can effectively penetrate into the tumor microenvironment, a complex and dense fibrotic matrix network orchestrated by both malignant and non-malignant cells, in which the infiltrated CART cells can be inhibited by immunosuppressive cells and molecules such as Tregs, myeloid derived suppressive cells (MDSCs), and programmed cell death protein ligand 1 (PD-L1) [21, 22], resulting in rapid loss of their cytolytic and cytokine secretion capacity and entering a state of hyporesponsiveness [23].