Chicken-derived CD20 antibodies with potent B-cell depletion activity

We report four novel anti-human CD20 (hCD20) monoclonal antibodies (mAbs) discovered from a phylogenetically distant species-chickens. The chicken-human chimaeric antibodies exhibit at least 10-fold enhanced antibody-dependent cellular cytotoxicity (ADCC) and 4-8-fold stronger complement-dependent cytotoxicity (CDC) relative to the clinically used mouse-human chimaeric anti-hCD20 antibody rituximab (RTX). Thus, to our knowledge these mAbs are the first to significantly outperform RTX in both Fc-mediated mechanisms of action. The antibodies show 20-100-fold superior depletion of B cells in whole blood from healthy humans relative to RTX and retain efficacy in vivo. One of the mAbs, AC1, can bind mouse CD20, indicating specificity for a novel hCD20 epitope inaccessible to current (mouse-derived) anti-hCD20 mAbs. A humanized version of one antibody, hAC11-10, was created by complementarity-determining region (CDR) grafting into a human variable region framework and this molecule retained the ADCC, in vitro human whole-blood B-cell depletion, and in vivo lymphoma cell depletion activities of the parent. These mAbs represent promising monotherapy candidates for improving upon current less-than-ideal clinical outcomes in lymphoid malignancies and provide an arsenal of biologically relevant molecules for the development of next-generation CD20-mediated immunotherapies including bispecific T-cell engagers (BiTE), antibody-drug conjugates (ADC) and chimaeric antigen receptor-engineered T (CAR-T) cells.