No abstract

By using static and dynamic light scattering (SLS and DLS), we investigate the effect of ion specificity and solution conditions on the solution behavior of monoclonal antibodies (mAbs). The extracted second virial coefficient, a global measure of the strength of protein-protein interactions, shows a complicated, nonmonotonic behavior. It can be connected on one side with the Hofmeister effect, and on the other with the interplay of screening and charge fluctuations in inhomogeneous, patchy charge distribution of these particular proteins. Although direct quantification in terms of the underlying long and short-range potentials is out of reach, the observed effects do point toward important features of mAbs solution aggregation processes that are governed by the identity of the solution ions as well as by details of the charge distribution of interacting proteins.

Ultrafiltration/diafiltration (UF/DF) operations are employed for achieving the desired therapeutic monoclonal antibody (mAb) formulations. Due to electrostatic interactions between the charged proteins, solute ions, and uncharged excipients, the final pH and concentration values are not always equal to those in the DF buffer. At high protein concentrations, typical for industrial formulations, this effect becomes predominant. To account for challenges occurring in industrial environments, a robust mathematical framework enabling the prediction of pH and concentration profiles throughout the UF/DF process is provided. The proposed mechanistic model combines a macroscopic mass balance approach with a molecular approach based on a Poisson–Boltzmann equation dealing with electrostatic interactions and accounting for protein exclusion volume effect. The mathematical model was validated with experimental data of two commercially relevant mAbs obtained from an industrial UF/DF process using scalable laboratory equipment. The robustness and flexibility of the model were tested by using proteins with different isoelectric points and net charges. The latter was determined via a titration curve, enabling realistic protein charge‐pH evaluation. In addition, the model was tested for different DF buffer types containing both monovalent and polyvalent ions, with various types of uncharged excipients. The model generality enables its implementation for the UF/DF processes of other protein varieties.