Mixed-mode size-exclusion silica resin for polishing human antibodies in flow-through mode

The polishing step in the downstream processing of therapeutic antibodies removes residual impurities from Protein A eluates. Among the various classes of impurities, antibody fragments are especially challenging to remove due to the broad biomolecular diversity generated by a multitude of fragmentation patterns. The current approach to fragment removal relies on ion exchange or mixed-mode adsorbents operated in bind-and-gradient-elution mode. However, fragments that bear strong similarity to the intact product or whose biophysical features deviate from the ensemble average can elude these adsorbents, and the lack of a chromatographic technology enabling robust antibody polishing is recognized as a major gap in downstream bioprocessing. Responding to this challenge, this study introduces size-exclusion mixed-mode (SEMM) silica resins as a novel chromatographic adsorbent for the capture of antibody fragments irrespective of their biomolecular features. The pore diameter of the silica beads features a narrow distribution and is selected to exclude monomeric antibodies, while allowing their fragments to access the pores where they are captured by the mixed-mode ligands. The static and dynamic binding capacity of the adsorbent ranged respectively between 30-45 and 25-33 gs of antibody fragments per liter of resin. Selected SEMM-silica resins also demonstrated the ability to capture antibody aggregates, which adsorb on the outer layer of the beads. Optimization of the SEMM-silica design and operation conditions - namely, pore size (10 nm) and ligand composition (quaternary amine and alkyl chain) as well as the linear velocity (100 cm/h), ionic strength (5.7 mS/cm), and pH (7) of the mobile phase - afforded a significant reduction of both fragments and aggregates, resulting into a final antibody yield up to 80% and monomeric purity above 97%.

Computational Engineering of Protein L to Achieve an Optimal Affinity Chromatography Resin for Purification of Antibody Fragments

Protein L affinity chromatography is a useful method for the purification of antibody fragments containing kappa light chains. In affinity chromatography, increasing the binding affinity leads to increased product purity, recovery, and dynamic binding capacity (DBC). In this study, molecular docking and molecular dynamics simulation techniques were used to design the engineered Protein L with higher affinity to the kappa light chain. Each engineered ligand was produced as a recombinant protein and coupled to a solid matrix. The purity, recovery, and DBC of the engineered resins were evaluated and then compared to those of a commercially available resin. The results showed important parameters for engineering more efficient Protein L ligands for affinity chromatography.

Chromatographic and adsorptive behavior of a bivalent bispecific antibody and associated fragments

The elution and adsorptive behavior of a bivalent bispecific antibody (BiSAb), comprising an IgG1 framework with a scFv domain genetically fused to each heavy chain C-terminus via flexible linkers, and of two associated fragments were studied on two cation exchange chromatography media - ProPac WCX-10, which is pellicular and suitable for analytical use, and Nuvia HR-S, which is macroporous and suitable for preparative and process scale uses. Both fragments were identified by MS as missing one of the two scFv domains and its flexible linker, but one of them also contains an additional C-terminal lysine. The separation of these fragments on both resins occurs as a result of differences in non-specific ligand-protein interactions that are modulated by the salt concentration. For the ProPac WCX-10 column, complex, multipeak elution behaviors are observed, since, as a result of the linker flexibility, both the intact molecule and the fragments appear to exist in multiple binding configurations with each scFv domains either collapsed onto the IgG framework or extended away from it. With a residence time of 2.5 min and at 21 °C, two peak elution is observed for the fragments which contain a single linked scFv and three peak elution for the intact molecule which contains two linked scFvs. This behavior is affected by residence time, temperature, and hold time. Increasing the residence time to 25 min or increasing temperature to 40°C results in elution of a single, merged peak for each of the protein species. For Nuvia HR-S, the broader peaks, obtained as a result of mass transfer limitations, tend to obscure the multipeak elution behavior. Nevertheless, even for this resin, the effects of configurational flexibility are still manifested at the single-particle scale and affect the evolution of the patterns of protein binding within individual resin particles as evident from confocal microscopy observations.

Method for studying immunoglobulin G binding on hydrophobic surfaces

We used a reactant adsorptive membrane bioreactor separator (or RAMBS) system to examine hydrophobic interaction based binding of human immunoglobulin G (HIgG) on synthetic microporous membranes possessing tunable hydrophobicity. Membrane bound HIgG on being pulsed with papain resulted in Fab being obtained in the flowthrough with Fc remaining bound to the membrane. On the other hand, when membrane bound HIgG was pulsed with pepsin, Fc subfragments were obtained in the flowthrough with F(ab')(2) remaining bound to the membrane. These product profiles suggest that HIgG bound to the membrane through its middle region. Enzyme linked immunoadsorbent assay (ELISA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and mass spectrometric analysis of eluate samples obtained from the RAMBS experiments provided evidence that the binding of HIgG took place primarily through the segment consisting of the hinge and C(H)2 domain of Fc. The experimental approach described in this paper could potentially be more widely applicable for studying protein interactions with membrane and surfaces in general.