Effect of anti-CD20 monoclonal antibody, Rituxan, on cynomolgus monkey and human B cells in a whole blood matrix.

Cynomolgus monkeys are widely used animal models in biomedical research. The differences between cynomolgus monkey and human B cells are not completely understood. However, these differences are of crucial importance for interpretation of data from studies on new therapeutic agents aimed at B-cell depletion, such as anti-CD20 monoclonal antibodies. Multicolor fluorescence-activated cell sorting analysis of peripheral blood B cells was performed on samples treated ex vivo with the anti-CD20 therapeutic monoclonal antibody, Rituxan, in a whole blood matrix. In contrast to humans, cynomolgus monkeys had two distinct B-cell subsets, CD20highCD40lowCD21- and CD20lowCD40highCD21+. These B-cell subsets had a 2.5-fold difference in the EC50 for Rituxan binding and differed significantly in their in vitro susceptibility to Rituxan depletion. Human B cells were similar to the CD20lowCD40highCD21+ cynomolgus monkey B cells with regard to their EC50 for Rituxan and response to Rituxan in a whole blood matrix assay. CD21 was upregulated, whereas CD40 was downregulated at incubation with Rituxan in the CD20lowCD40highCD21+ monkey and human B cells in a concentration-dependent manner. These findings have direct implications for in vivo studies of therapeutic agents that target B cells in cynomolgus monkeys and for extrapolation of the results to humans. In addition, our data are consistent with the model in which CD20, CD21, and CD40 exist in a supramolecular complex that is affected by anti-CD20 monoclonal antibodies.