Use of Debye–Hückel–Henry charge measurements in early antibody development elucidates effects of non-specific association

The diffusion interaction parameter (k(D)) has been demonstrated to be a high-throughput technique for characterizing interactions between proteins in solution. k(D) reflects both attractive and repulsive interactions, including long-ranged electrostatic repulsions. Here, we plot the mutual diffusion coefficient (D(m)) as a function of the experimentally determined Debye–Hückel–Henry surface charge (Z(DHH)) for seven human monoclonal antibodies (mAbs) in 15 mM histidine at pH 6. We find that graphs of D(m) versus Z(DHH) intersect at Z(DHH), ~ 2.6, independent of protein concentration. The same data plotted as k(D) versus Z(DHH) show a transition from net attractive to net repulsive interactions in the same region of the Z(DHH) intersection point. These data suggest that there is a minimum surface charge necessary on these mAbs needed to overcome attractive interactions.