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Genetically Targeted T Cells Eradicate Systemic Acute Lymphoblastic Leukemia Xenografts

Authors' Affiliations: Departments of ¹ Medicine and ² Radiology; ³ Research Animal Resource Center; ⁴ Immunology Program; and ⁵ Gene Transfer and Somatic Cell Engineering Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York

Requests for reprints: Renier J. Brentjens, Department of Medicine, Memorial Sloan Kettering Cancer Center, Box 242, 1275 York Avenue, New York, NY 10021. Phone: 212-639-7053; E-mail: brentjer{at}mskcc.org.

Purpose: Human T cells targeted to the B cell–specific CD19 antigen through retroviral-mediated transfer of a chimeric antigen receptor (CAR), termed 19z1, have shown significant but partial in vivo antitumor efficacy in a severe combined immunodeficient (SCID)-Beige systemic human acute lymphoblastic leukemia (NALM-6) tumor model. Here, we investigate the etiologies of treatment failure in this model and design approaches to enhance the efficacy of this adoptive strategy.

Experimental Design: A panel of modified CD19-targeted CARs designed to deliver combined activating and costimulatory signals to the T cell was generated and tested in vitro to identify an optimal second-generation CAR. Antitumor efficacy of T cells expressing this optimal costimulatory CAR, 19-28z, was analyzed in mice bearing systemic costimulatory ligand-deficient NALM-6 tumors.

Results: Expression of the 19-28z CAR, containing the signaling domain of the CD28 receptor, enhanced systemic T-cell antitumor activity when compared with 19z1 in treated mice. A treatment schedule of 4 weekly T-cell injections, designed to prolong in vivo T-cell function, further improved long-term survival. Bioluminescent imaging of tumor in treated mice failed to identify a conserved site of tumor relapse, consistent with successful homing by tumor-specific T cells to systemic sites of tumor involvement.

Conclusions: Both in vivo costimulation and repeated administration enhance eradication of systemic tumor by genetically targeted T cells. The finding that modifications in CAR design as well as T-cell dosing allowed for the complete eradication of systemic disease affects the design of clinical trials using this treatment strategy.

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