Bivalent binding on cells varies between anti-CD20 antibodies and is dose-dependent
Bondza S, Ten Broeke T, Nestor M, Leusen JHW, Buijs J.
MAbs. 2020. 12(1):1792673.
In this paper LigandTracer Green was used to investigate the binding mechanism of the type I CD20 antibodies Rituximab and Ofatumumab, as well as the type II CD20 antibody Obinutuzumab on live cells. With a series of real-time binding assays on the human B-cell line Daudi, the authors show that the therapeutic antibodies differ in their binding stability and binding dynamics. Control experiments with Fab and F(ab’)2 lead to the conclusion that differences in binding stability were due to that the degree in bivalent target engagement differed for the antibodies. For Rituximab and Obinutuzumab stabilization of the interaction due to bivalency decreased with increasing antibody concentration, resulting in dose-dependent apparent affinities. A plausible explanation for the decrease in bivalent stabilization is a concentration-dependent crowding effect at the cell surface. The authors concluded that the degree of bivalent binding for the investigated CD20 antibodies correlated positively with their known complement recruiting capacity.