Novel humanized anti‐ CD 20 antibody BM ‐ca binds to a unique epitope and exerts stronger cellular activity than others

Abstract

Cellular activity of BM ‐ca, a novel humanized anti‐ CD 20 antibody, was quantitatively compared with that of two other anti‐ CD 20 antibodies used for clinical practice, rituximab and ofatumumab. The results of a complement‐dependent cytotoxicity ( CDC ) assay revealed that the strongest antibody was ofatumumab, followed by BM ‐ca, with rituximab being the weakest. Ofatumumab and BM ‐ca were effective not only against rituximab‐sensitive SU ‐ DHL ‐4 cells but also against rituximab‐resistant RC ‐K8 cells. In an antibody‐dependent cell‐mediated cytotoxicity ( ADCC ) assay, although the effective concentrations against SU ‐ DHL ‐4 cells were almost the same among these three antibodies, the maximum cytotoxic level was the highest for BM ‐ca. In an anti‐cell proliferation assay using SU ‐ DHL ‐4 cells, BM ‐ca was the most effective and ofatumumab, the weakest. Against RC ‐K8 cells, only BM ‐ca was effective. When combined with each of four cancer chemotherapeutics (prednisolone, vincristine, hydroxydaunorubicin, and cisplatin), BM ‐ca exerted the most effective combinatorial anti‐cell proliferation activity. To assess the in vivo effect of BM ‐ca, we intravenously administered BM ‐ca into cynomolgus monkeys and found that the peripheral B ‐cell levels did not decrease in half of the animals. Sequencing of cDNA encoding CD 20 of cynomolgus monkeys revealed that the responders and nonresponders had Leu/Pro (hetero) and Leu/Leu (homo) at amino acid (a.a.) position 160, respectively, suggesting that the epitope recognized by BM ‐ca was around this a.a. By analyzing reactivity to synthetic peptides, the epitope recognized by BM ‐ca was estimated to be a.a.'s 156–166, not shared with rituximab and ofatumumab. These results suggest BM ‐ca to be a promising anti‐ CD 20 antibody having superior properties and recognizing a unique epitope.