BM-ca is a newly defined type I/II anti-CD20 monoclonal antibody with unique biological properties

Rituximab (chimeric anti-CD20 mAb) is currently used in the treatment of B-NHL and B cell malignancies, alone or in combination with chemotherapy. However, subsets of patients do not initially respond and/or develop resistance to additional treatments. Hence, there is a need to develop more effective anti-CD20 mAbs that may improve clinical response. BM-ca is a novel humanized anti-CD20 mAb that was tested against several B-NHL cell lines and was compared to several anti-CD20 mAbs (Rituximab, ofatumumab, 2H7, B1 and B-Ly1). BM-ca was shown to strongly induce both homotypic cell aggregation and redistribution of CD20 to membrane lipid rafts. BM-ca was also able to induce programmed cell death (apoptosis) without the need for cross-linking and demonstrated potent complement-dependent cytotoxicity (CDC). BM-ca was more cytotoxic than rituximab even in malignant B cells expressing low amounts of membrane CD20. Type I anti-CD20 mAbs typically induce minimal levels of homotypic cell aggregation and apoptosis but strong localization of CD20 to lipid rafts and potent CDC. Type II anti-CD20 mAbs typically exert the reverse activities. Noteworthy, BM-ca exhibits properties that are shared by both type I and type II anti-CD20 mAbs, which may reflect the recognition of a new CD20 epitope and/or exhibit different molecular signaling. Overall, the present data show that BM-ca is a novel anti-CD20 mAb that may be classified as a type I/II. The therapeutics efficacy of BM-ca awaits its use in clinical trials.