Human Monoclonal Antibodies to Sialyl-Lewisa (CA19.9) with Potent CDC, ADCC, and Antitumor Activity

Purpose: The carbohydrate antigen sialyl-Lewis(a) (sLe(a)), also known as CA19.9, is widely expressed on epithelial tumors of the gastrointestinal tract and breast and on small-cell lung cancers. Since overexpression of sLe(a) appears to be a key event in invasion and metastasis of many tumors and results in susceptibility to antibody-mediated lysis, sLe(a) is an attractive molecular target for tumor therapy. Experimental Design: We generated and characterized fully human monoclonal antibodies (mAb) from blood lymphocytes from individuals immunized with a sLe(a)-KLH vaccine. Results: Several mAbs were selected based on ELISA and FACS including two mAbs with high affinity for sLe(a) (5B1 and 7E3, binding affinities 0.14 and 0.04 nmol/L, respectively) and further characterized. Both antibodies were specific for Neu5Ac alpha 2-3Gal beta 1-3(Fuc alpha 1-4)GlcNAc beta as determined by glycan array analysis. Complement-dependent cytotoxicity against DMS-79 cells was higher (EC50 0.1 mu g/mL vs. 1.7 mu g/mL) for r7E3 (IgM) than for r5B1 (IgG1). In addition, r5B1 antibodies showed high level of antibody-dependent cell-mediated cytotoxicity activity on DMS-79 cells with human NK cells or peripheral blood mononuclear cells. To evaluate in vivo efficacy, the antibodies were tested in a xenograft model with Colo205 tumor cells engrafted into SCID (severe combined immunodeficient mice) mice. Treatment during the first 21 days with four doses of r5B1 (100 mu g per dose) doubled the median survival time to 207 days, and three of five animals survived with six doses. Conclusion: On the basis of the potential of sLe(a) as a target for immune attack and their affinity, specificity, and effector functions, 5B1 and 7E3 may have clinical utility. Clin Cancer Res; 17(5); 1024-32. (C)2011 AACR.