Effective therapy for a murine model of adult T-cell leukemia with the humanized anti-CD2 monoclonal antibody, MEDI-507

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Abstract
Adult T-cell leukemia (ATL) develops in a small proportion of individuals infected with the retrovirus human T-cell leukemia virus (HTLV-1). We evaluated the efficacy of MEDI-507 (a humanized monoclonal antibody directed against CD2) alone and in combination with humanized anti-Tac (HAT) directed toward CD25, the interleukin-2 receptor α (IL-2Rα) using a human adult T-cell leukemia xenograft model. Weekly treatments (4) with HAT significantly prolonged the survival of the ATL-bearing mice when compared with phosphate-buffered saline (PBS)–treated controls (P < .0001). Mice treated with MEDI-507 (100 μg/wk for 4 weeks) survived longer than those treated with HAT (P < .0025). Furthermore, prolonged treatment (6 months) of ATL with MEDI-507 significantly improved the outcome when compared with a short course (4 weeks) of therapy (P < .0036). Such treatment with weekly MEDI-507 for 6 months led to a prolonged survival of the ATL-bearing mice that was comparable with the survival observed in the control group of mice that did not receive a tumor or therapeutic agent. We also found that the expression of Fcγ receptors (FcRγ) on polymorphonuclear leukocytes and monocytes was required for MEDI-507–mediated tumor killing in vivo. Thus, the tumor-killing mechanism with MEDI-507 in vivo required the expression of the receptor FcRγIII on polymorphonuclear leukocytes and monocytes, suggesting that it is mediated by a form of antibody-dependent cellular cytotoxicity. These results demonstrate that MEDI-507 has therapeutic efficacy on ATL in vivo and provides support for a clinical trial involving this monoclonal antibody in the treatment of patients with CD2-expressing leukemias and lymphomas. (Blood. 2003; 102:284-288)