Hydrophobic interaction chromatography as polishing step enables obtaining ultra-pure recombinant antibodies

Host cell proteins in monoclonal antibody processing: Control, detection, and removal

Host cell proteins (HCPs) are process-related impurities in a therapeutic protein expressed using cell culture technology. This review presents biopharmaceutical industry trends in terms of both HCPs in the bioprocessing of monoclonal antibodies (mAbs) and the capabilities for HCP clearance by downstream unit operations. A comprehensive assessment of currently implemented and emerging technologies in the manufacturing processes with extensive references was performed. Meta-analyses of published downstream data were conducted to identify trends. Improved analytical methods and understanding of "high-risk" HCPs lead to more robust manufacturing processes and higher-quality therapeutics. The trend of higher cell density cultures leads to both higher mAb expression and higher HCP levels. However, HCP levels can be significantly reduced with improvements in operations, resulting in similar concentrations of approx. 10 ppm HCPs. There are no differences in the performance of HCP clearance between recent enhanced downstream operations and traditional batch processing. This review includes best practices for developing improved processes.

Parameter-by-parameter estimation method for adsorption isotherm in hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) is used as a critical polishing step in the downstream processing of biopharmaceuticals. Normally the process development of HIC is a cumbersome and time-consuming task, and the mechanical models can provide a powerful tool to characterize the process, assist process design and accelerate process development. However, the current estimation of model parameters relies on the inverse method, which lacks an efficient and logical parameter estimation strategy. In this study, a parameter-by-parameter (PbP) method based on the theoretical derivation and simplifying assumptions was proposed to estimate the Mollerup isotherm parameters for HIC. The method involves three key steps: (1) linear regression (LR) to estimate the salt-protein interaction parameter and the equilibrium constant; (2) linear approximation (LA) to estimate the stoichiometric parameter and the maximum binding capacity; and (3) inverse method to estimate the protein-protein interaction parameter and the kinetic coefficient. The results indicated that the LR step should be used for dilution condition (loading factor below 5%), while the LA step should be conducted when the isotherm is in the transition or nonlinear regions. Six numerical experiments were conducted to implement the PbP method. The results demonstrated that the PbP method developed allows for the systematic estimation of HIC parameters one-by-one, effectively reducing the number of parameters required for inverse method estimation from six to two. This helps prevent non-identifiability of structural parameters. The feasibility of the PbP-HIC method was further validated by real-world experiments. Moreover, the PbP method enhances the mechanistic understanding of adsorption behavior of HIC and shows a promising application to other stoichiometric displacement model-derived isotherms.

Selectivity and Resolving Power of Hydrophobic Interaction Chromatography Targeting the Separation of Monoclonal Antibody Variants

This study presents a comprehensive investigation of the mechanistic understanding of retention and selectivity in hydrophobic interaction chromatography. It provides valuable insights into crucial method-development parameters involved in achieving chromatographic resolution for profiling molecular variants of trastuzumab. Retention characteristics have been assessed for three column chemistries, i.e., butyl, alkylamide, and long-stranded multialkylamide ligands, while distinguishing column hydrophobicity and surface area. Salt type and specifically chloride ions proved to be the key driver for improving chromatographic selectivity, and this was attributed to the spatial distribution of ions at the protein surface, which is ion-specific. The effect was notably more pronounced on the multialkylamide column, as proteins intercalated between the multiamide polymer strands, enabling steric effects. Column coupling proved to be an effective approach for maximizing resolution between molecular variants present in the trastuzumab reference sample and trastuzumab variants induced by forced oxidation. Liquid chromatography-mass spectrometry (LC-MS)/MS peptide mapping experiments after fraction collection indicate that the presence of chloride in the mobile phase enables the selectivity of site-specific deamidation (N30) situated at the heavy chain. Moreover, site-specific oxidation of peptides (M255, W420, and M431) was observed for peptides situated at the Fc region close to the CH2-CH3 interface, previously reported to activate unfolding of trastuzumab, increasing the accessible surface area and hence resulting in an increase in chromatographic retention.

Production of full-length SARS-CoV-2 nucleocapsid protein from Escherichia coli optimized by native hydrophobic interaction chromatography hyphenated to multi-angle light scattering detection

The nucleocapsid protein (NP) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical for several steps of the viral life cycle, and is abundantly expressed during infection, making it an ideal diagnostic target protein. This protein has a strong tendency for dimerization and interaction with nucleic acids. For the first time, high titers of NP were expressed in E. coli with a CASPON tag, using a growth-decoupled protein expression system. Purification was accomplished by nuclease treatment of the cell homogenate and a sequence of downstream processing (DSP) steps. An analytical method consisting of native hydrophobic interaction chromatography hyphenated to multi-angle light scattering detection (HIC-MALS) was established for in-process control, in particular, to monitor product fragmentation and multimerization throughout the purification process. 730 mg purified NP per liter of fermentation could be produced by the optimized process, corresponding to a yield of 77% after cell lysis. The HIC-MALS method was used to demonstrate that the NP product can be produced with a purity of 95%. The molecular mass of the main NP fraction is consistent with dimerized protein as was verified by a complementary native size-exclusion separation (SEC)-MALS analysis. Peptide mapping mass spectrometry and host cell specific enzyme-linked immunosorbent assay confirmed the high product purity, and the presence of a minor endogenous chaperone explained the residual impurities. The optimized HIC-MALS method enables monitoring of the product purity, and simultaneously access its molecular mass, providing orthogonal information complementary to established SEC-MALS methods. Enhanced resolving power can be achieved over SEC, attributed to the extended variables to tune selectivity in HIC mode.