Characterization of native reversible self-association of a monoclonal antibody mediated by Fab-Fab interaction

The native reversible self-association of monoclonal antibodies has been associated with high viscosity, liquid-liquid and liquid-solid phase separation. We investigated the native reversible self-association of an IgG1, which exerts this association even at low protein concentrations, in detail to gain further understanding of this phenomenon by extensive characterization of the association as a function of multiple factors, namely pH, temperature, salt concentration and protein concentration. The nature of the self-association of the full-length IgG1 as well as the corresponding Fab and Fc fragment was studied by viz. SEC-MALS, DLS, SLS, AUC, SAXS, AF4-MALS and intrinsic fluorescence. We rationalized the self-association as a combination of hydrophobic and electrostatic interactions driven by the Fab fragments. Finally, we investigated the long-term stability of the IgG1 molecule.