For an adoptive T cell immunotherapy to successfully treat cancer, T cells must be able to recognize tumor antigen, expand and persist in the tumor microenvironment, and deliver its effector function. Treatment of B cell acute lymphoblastic leukemia (B-ALL) using human T cells modified to express a “second generation” CD19-targeted chimeric antigen receptor (CAR), which includes the CD28 co-stimulatory signaling domain (19-28z) along with the CD3 zeta chain signaling domain, has been successfully demonstrated in both the pre-clinical and clinical settings. However, application of CAR therapy for the treatment of B cell chronic lymphocytic leukemia (B-CLL) and solid tumors remains a challenge. Here, we present preclinical studies demonstrating that further modifying 19-28z CAR T cells to additionally secrete a recombinant fusion protein of the pro-inflammatory interleukin 12 (IL-12) (19-28z/mIL-12 CAR T cells) enhances the potency of adoptive T cell immunotherapy. We demonstrate that these 19-28z/mIL-12 “armored” CAR T cells display increased proliferation, up-regulation of perforin and granzyme B, as well as a central memory-like phenotype when compared to T cells transduced to express the 19-28z CAR alone. In vivo, treatment of systemic NALM-6 B-ALL tumor-bearing SCID-Beige mice with 19-28z/mIL-12 CAR T cells significantly improved survival when compared to mice treated with T cells modified to express the 19-28z CAR alone. Furthermore, in contrast to T cells modified to express the 19-28z CAR alone, 19-28z/mIL-12 CAR T cells resist CD4+CD25hiFOXP3+ Treg-mediated immunosuppression in vitro and successfully eradicate Raji Burkitt’s lymphoma tumor in SCID-Beige tumor-bearing mice previously infused with CD19-targeted CAR modified Tregs. These findings have important implications for future clinical trials with CAR T cells designed to enhance the clinical outcomes of relapsed B-CLL as well as solid tumor malignancies.