Alemtuzumab is a recombinant humanized IgG1 monoclonal antibody directed against CD52, an antigen expressed on the surface of normal and malignant B and T lymphocytes. Alemtuzumab is approved for the treatment of B-cell chronic lymphocytic leukemia (B-CLL), but the exact mechanism by which the antibody depletes malignant lymphocytes in vivo is not clearly defined. To address this issue, the anti-tumor activity of alemtuzumab was studied in disseminated and subcutaneous xenograft tumor models. The density of CD52 target antigen on the surface of tumor cells appeared to correlate with the anti-tumor activity of alemtuzumab. Deglycosylation of alemtuzumab resulted in a loss of cytotoxicity in vitro and was found to abolish anti-tumor activity in vivo. Individual inactivation of effector mechanisms in tumor-bearing mice indicated that the protective activity of alemtuzumab in vivo was primarily dependent on ADCC mediated by neutrophils and to a lesser extent NK cells. Increasing the number of circulating neutrophils by treatment with G-CSF enhanced the anti-tumor activity of the antibody, thus providing further evidence for the involvement of neutrophils as effector cells in the activity of alemtuzumab.

The interaction between CXCR4 on the surface of tumor cells and CXCL12 in the stroma is believed to contribute to tumor cell survival and protection against drug treatment. Inhibition of stromal survival signals by CXCR4 antagonists has been reported to render tumor cells more sensitive to chemotherapy, but little is known about potential synergy with monoclonal antibodies. In this study, administration of the small molecule CXCR4 antagonists plerixafor and GENZ-644494 was found to enhance the anti-tumor activity of the monoclonal antibodies alemtuzumab and rituximab in disseminated lymphoma models. The observed enhancement in therapeutic efficacy by CXCR4 antagonists appeared to involve several factors, including interference with the tumor-promoting signals delivered by CXCL12, disruption of the tumor/stroma interaction and mobilization of effector neutrophils capable of mediating antibody-dependent cell-mediated cytotoxicity. The involvement of neutrophils was further supported by the observed reversal in therapeutic benefit upon neutrophil depletion.

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Immunization with the electrofusion product of tumor cells and dendritic cells (DCs) is a promising approach to cancer immunotherapy. Production of electrofusion vaccines currently requires the acquisition of tumor material and must be tailored to each individual. Alternative vaccine configurations were explored in this study. Results indicated that fusion vaccines with fully syngeneic, semi-allogeneic or fully allogeneic components, were all effective in inducing specific, long-lasting antitumor immunity. This previously undescribed activity of a fully allogeneic fusion product introduces the possibility of using defined allogeneic tumor and DC lines to simplify vaccine manufacturing.

2717 Poster Board II-693 Interactions between chemokines and their receptors play an important role in cancer biology and have been shown to influence several processes such as tumor growth and the development of metastatic lesions. Stromal cell derived factor-1 (SDF-1) is a chemokine that binds to the CXCR4 chemokine receptor and stimulates B cell growth. CXCR4 is frequently over-expressed on tumor cells and the SDF-1/CXCR4 axis has been reported to play a role in promoting survival, angiogenesis and metastasis. The role of the stroma, in particular SDF-1/CXCR4 interactions, in providing a “survival niche” for tumor cells is well described for both hematological and solid tumors. We hypothesized that disruption of the protective microenvironment of tumor cells through antagonism of the SDF-1/CXCR4 axis may enhance the sensitivity of the tumor cells to treatment with anti-cancer agents such as monoclonal antibodies. Mozobil (AMD3100) or its structurally related analog, AMD3465, were used in combination with either Campath (anti-CD52) or Rituxan (anti-CD20) in lymphoma xenograft models to determine whether enhanced tumor protection could be observed. Flow cytometry analysis of lymphoma cell lines confirmed the cell surface expression of high levels of CXCR4 as well as the CD20 and CD52 target antigens. Lymphoma cells were seeded by intravenous injection and tumor-bearing mice were treated with multiple injections of the CXCR4 antagonists AMD3465 or AMD3100 alone or in combination with monoclonal antibodies. Treatment with AMD3465 as a single agent was sufficient to increase survival of the animals compared to untreated controls. In addition, the combination of AMD3465 and Campath showed a synergistic effect with a prolongation of survival greater than that obtained with either agent alone (p<0.01). Similarly, combination of AMD3100 and Rituxan also resulted in a significantly prolonged survival compared to either agent alone (p=0.0340). In vivo imaging using a Raji-luciferase cell line also confirmed the impact of treatment on tumor burden. These results suggest that there is a potential role for CXCR4 antagonists in combination with a B-cell targeted therapy in the treatment of B-cell malignancies in the clinic. Disclosures: Siders: Genzyme Corporation: Employment. Hu:Genzyme: Employment. Gale:Genzyme: Employment. Jacques:Genzyme: Employment. Fogle:Genzyme: Employment. Shields:Genzyme: Employment. Garron:Genzyme: Employment. Kaplan:Genzyme: Employment.