Chimeric antigen receptor (CAR) T cells targeting CD19 will be evaluated for safety and efficacy in patients with B cell lymphoma or leukemia. The CAR consists of a CD19 targeting antibody scFv with three intracellular signaling domains derived from CD3 zeta, CD28 and 4-1BB. Autologous T cells will be gene engineered with the CAR gene using a retrovirus vector. Prior to T cell infusion, the patients will be subjected to preconditioning treatment. After T cell infusion, the patients will be evaluated for 24 months for adverse reactions, persistence of CAR T cells and efficacy.