The disclosure provides a method of treatment of a B-cell lymphoma or leukemia, including diffuse large B-cell lymphoma (DLBCL) comprising a CD19-directed chimeric antigen receptor (CAR) genetically modified T-cell immunotherapy in combination with a 4-1BB (CD137) agonist. Some aspects of the disclosure relate to methods of treatment and monitoring following infusion of T-cell therapy provided herein.