In our study, we combined the epigenetic modulating drug HDACi Chidamide with CAR T immunotherapy for the first time and verified that Chidamide is able to enhance the efficacy of CD22 CAR T by upregulating CD22 expression on the surface of tumor cells in vitro and in vivo, providing a preclinical evidence to support the use of drug-mediated antigen density modulation to overcome such limitations for CAR T therapy. The gene discussed is CD22; the disease is neoplasm.