Effective therapy for a murine model of adult T-cell leukemia with the humanized anti-CD52 monoclonal antibody, Campath-1H.

Adult T-cell leukemia (ATL) develops in a small proportion of human T-cell leukemia virus I-infected individuals. Presently, there is no effective therapy for ATL. A murine model of ATL was produced by introducing leukemic cells (MET-1) from an ATL patient into nonobese diabetic/severe combined immunodeficient mice. The MET-1 cells are activated T cells that express CD2, CD3, CD4, CD25, CD122, and CD52. We evaluated the efficacy of Campath-1H (alemtuzumab; a humanized monoclonal antibody directed to CD52), alone and in combination with humanized anti-Tac (HAT) directed to CD25 (interleukin 2 receptor alpha) or with MEDI-507 directed to CD2. We observed that four weekly treatments with 4 mg/kg HAT significantly prolonged survival of MET-1-bearing mice. However, the survival of mice receiving 4 weeks of 4 mg/kg Campath-1H was significantly longer than that of the group receiving four weekly treatments with HAT (P < 0.001). Treatment with Campath-1H for 4 weeks led to a striking prolongation of the survival of MET-1 ATL-bearing mice that was comparable with that of tumor-free nontreated controls. Using Fc receptor (FcR) gamma(-/-) mice, we found that FcRgammas on polymorphonuclear leukocytes and monocytes are required for Campath-1H-mediated tumor killing in vivo. These results demonstrate that Campath-1H has therapeutic efficacy on ATL in vivo in that the life span of the Campath-1H treatment group was comparable with that of mice that did not receive a tumor or therapy. The main tumor killing mechanism with Campath-1H in vivo involves FcRgamma-containing receptors (e.g., FcRgammaIII) on polymorphonuclear leukocytes and macrophages that mediate antibody-dependent cellular cytotoxicity and/or trigger cross-linking induced apoptosis. This study provides support for a clinical trial of Campath-1H in the treatment of patients with T-cell leukemias and lymphomas.