Chromatographic behavior of IgM:DNA complexes

Factors affecting product association as a mechanism of host-cell protein persistence in bioprocessing

Product association of host-cell proteins (HCPs) to monoclonal antibodies (mAbs) is widely regarded as a mechanism that can enable HCP persistence through multiple purification steps and even into the final drug substance. Discussion of this mechanism often implies that the existence or extent of persistence is directly related to the strength of binding but actual measurements of the binding affinity of such interactions remain sparse. Two separate avenues of investigation of HCP-mAb binding are reported here. One is the measurement of the affinity of binding of individual, commonly persistent Chinese hamster ovary (CHO) HCPs to each of a set of mAbs, and the other uses quantitative proteomic measurements to assess binding of HCPs in a null CHO harvested cell culture fluid (HCCF) to mAbs produced in the same cell line. The individual HCP measurements show that the binding affinities of individual HCPs to different mAbs can vary appreciably but are rarely very high, with only weak pH dependence. The measurements on the null HCCF allow estimation of individual HCP-mAb affinities; these are typically weaker than those seen in affinity measurements on isolated HCPs. Instead, the extent of binding appears correlated with the initial abundance of individual HCPs in the HCCF and the forms of the HCPs in the solution, i.e., whether HCPs are present as free molecules or as parts of large aggregates. Separate protein A chromatography experiments performed by feeding different fractions of a mAb-containing HCCF obtained by size-exclusion chromatography (SEC) showed clear differences in the number and identity of HCPs found in the protein A eluate. These results indicate a significant role for HCP-mAb association in determining HCP persistence through protein A chromatography, presumably through binding of HCP-mAb complexes to the resin. Overall, the results illustrate the importance of considering more fully the biophysical context of HCP-product association in assessing the factors that may affect the phenomenon and determine its implications. Knowledge of the abundances and the forms of individual or aggregated HCPs in HCCF are particularly significant, emphasizing the integration of upstream and downstream bioprocessing and the importance of understanding the collective properties of HCPs in addition to just the biophysical properties of individual HCPs.

Anti-DNA-IgM Favors the Detection of NET-Associated Extracellular DNA

During inflammatory responses, neutrophils enter the sites of attack where they execute various defense mechanisms. They (I) phagocytose microorganisms, (II) degranulate to release cytokines, (III) recruit various immune cells by cell-type specific chemokines, (IV) secrete anti-microbials including lactoferrin, lysozyme, defensins and reactive oxygen species, and (V) release DNA as neutrophil extracellular traps (NETs). The latter originates from mitochondria as well as from decondensed nuclei. This is easily detected in cultured cells by staining of DNA with specific dyes. However, in tissues sections the very high fluorescence signals emitted from the condensed nuclear DNA hamper the detection of the widespread, extranuclear DNA of the NETs. In contrast, when we employ anti-DNA-IgM antibodies, they are unable to penetrate deep into the tightly packed DNA of the nucleus, and we observe a robust signal for the extended DNA patches of the NETs. To validate anti-DNA-IgM, we additionally stained the sections for the NET-markers histone H2B, myeloperoxidase, citrullinated histone H3, and neutrophil elastase. Altogether, we have described a fast one-step procedure for the detection of NETs in tissue sections, which provides new perspectives to characterize neutrophil-associated immune reactions in disease.

Multivalent IgM scaffold enhances the therapeutic potential of variant-agnostic ACE2 decoys against SARS-CoV-2

As immunological selection for escape mutants continues to give rise to future SARS-CoV-2 variants, novel universal therapeutic strategies against ACE2-dependent viruses are needed. Here we present an IgM-based decavalent ACE2 decoy that has variant-agnostic efficacy. In immuno-, pseudovirus, and live virus assays, IgM ACE2 decoy had potency comparable or superior to leading SARS-CoV-2 IgG-based mAb therapeutics evaluated in the clinic, which were variant-sensitive in their potency. We found that increased ACE2 valency translated into increased apparent affinity for spike protein and superior potency in biological assays when decavalent IgM ACE2 was compared to tetravalent, bivalent, and monovalent ACE2 decoys. Furthermore, a single intranasal dose of IgM ACE2 decoy at 1 mg/kg conferred therapeutic benefit against SARS-CoV-2 Delta variant infection in a hamster model. Taken together, this engineered IgM ACE2 decoy represents a SARS-CoV-2 variant-agnostic therapeutic that leverages avidity to drive enhanced target binding, viral neutralization, and in vivo respiratory protection against SARS-CoV-2.

Conjugated Detergent Micelles as a Platform for IgM Purification

Immunoglobulin M (IgM) antibodies hold promise as anticancer drugs and as agents for promoting immune homeostasis. This promise has not been realized due to low expression levels in mammalian cells producing IgM class antibodies, and the failure of protein A chromatography for IgM purification. Here, we describe a nonchromatographic platform for quantitatively capturing IgMs at neutral pH, which is then recovered with 86%–94% yield and >95% purity at pH 3. The platform contains micelles conjugated with the [(bathophenanthroline)₃:Fe²⁺] amphiphilic complex. Inclusion of amino acid monomers, for example, phenylalanine or tyrosine, during conjugation of detergent micelles, allows subsequent extraction of IgMs at close to neutral pH. With the successful implementation of this purification platform for both polyclonal humans and bovine IgMs, we anticipate similar results for monoclonal IgMs, most relevant for the pharmaceutical industry.

Structure, Function, and Therapeutic Use of IgM Antibodies

Natural immunoglobulin M (IgM) antibodies are pentameric or hexameric macro-immunoglobulins and have been highly conserved during evolution. IgMs are initially expressed during B cell ontogeny and are the first antibodies secreted following exposure to foreign antigens. The IgM multimer has either 10 (pentamer) or 12 (hexamer) antigen binding domains consisting of paired µ heavy chains with four constant domains, each with a single variable domain, paired with a corresponding light chain. Although the antigen binding affinities of natural IgM antibodies are typically lower than IgG, their polyvalency allows for high avidity binding and efficient engagement of complement to induce complement-dependent cell lysis. The high avidity of IgM antibodies renders them particularly efficient at binding antigens present at low levels, and non-protein antigens, for example, carbohydrates or lipids present on microbial surfaces. Pentameric IgM antibodies also contain a joining (J) chain that stabilizes the pentameric structure and enables binding to several receptors. One such receptor, the polymeric immunoglobulin receptor (pIgR), is responsible for transcytosis from the vasculature to the mucosal surfaces of the lung and gastrointestinal tract. Several naturally occurring IgM antibodies have been explored as therapeutics in clinical trials, and a new class of molecules, engineered IgM antibodies with enhanced binding and/or additional functional properties are being evaluated in humans. Here, we review the considerable progress that has been made regarding the understanding of biology, structure, function, manufacturing, and therapeutic potential of IgM antibodies since their discovery more than 80 years ago.

Analysis of Product Quality of Complex Polymeric IgM Produced by CHO Cells

Immunoglobulin M (IgM) antibodies are considered as promising biopharmaceutical drugs in the future despite recombinant production is quite challenging as incomplete polymer formation or nucleic acid adherence can decrease the quality of the IgM preparation. Therefore, we defined densitometric and chromatographic methods as suitable tools to analyze the polymer distribution and the remaining nucleic acid content after initial IgM purification. Additionally, the quality of the glycosylation pattern is an important parameter for biological safety and efficacy.

Exploring the Unique Selectivity of Hydrophobic Cation Exchanger Nuvia cPrime for the Removal of a Major Process Impurity: A Case Study with IgM

BACKGROUND

Mixed-mode chromatography is becoming an important tool for downstream process purification, as it provides the selectivity and robustness unmatched by conventional singlemode chromatographic methods. The joint action of multiple functionalities present on the ligands of mixed-mode chromatography matrices effectively enhances the separation of target molecules from impurities.

MATERIAL AND METHODS

Using Nuvia cPrime as an example, we elucidate the separation principles of hydrophobic cation exchange mixed-mode chromatography and its difference from traditional strong cation exchangers. We have developed a Nuvia cPrime based polish purification step specifically for the removal of a major process contaminant, which has an isoelectric point similar to that of the target monoclonal IgM molecule. Additional purification was accomplished using a second mixed-mode chromatography column packed with Ceramic Hydroxyapatite.

CONCLUSION

The monoclonal IgM prepared with this new process fully retained its biological activity and was free of high molecular weight aggregates, a product quality that was not achievable in previous attempts using traditional ion exchange or hydrophobic interaction chromatography.

Receptor-ligand interactions: Advanced biomedical applications

Receptor-ligand interactions (RLIs) are at the base of all biological events occurring in living cells. The understanding of interactions between complementary macromolecules in biological systems represents a high-priority research area in bionanotechnology to design the artificial systems mimicking natural processes. This review summarizes and analyzes RLIs in some cutting-edge biomedical fields, in particular, for the preparation of novel stationary phases to separate complex biological mixtures in medical diagnostics, for the design of ultrasensitive biosensors for identification of biomarkers of various diseases at early stages, as well as in the development of innovative biomaterials and approaches for regenerative medicine. All these biotechnological fields are closely related, because their success depends on a proper choice, combination and spatial disposition of the single components of ligand-receptor pairs on the surface of appropriately designed support.

Host cell protein testing by ELISAs and the use of orthogonal methods

Host cell proteins (HCPs) are among the process-related impurities monitored during recombinant protein pharmaceutical process development. The challenges of HCP detection include (1) low levels of residual HCPs present in large excess of product protein, (2) the assay must measure a large number of different protein analytes, and (3) the population of HCP species may change during process development. Suitable methods for measuring process-related impurities are needed to support process development, process validation, and control system testing. A multi-analyte enzyme-linked immunosorbent assay (ELISA) is the workhorse method for HCP testing due to its high throughput, sensitivity and selectivity. However, as the anti-HCP antibodies, the critical reagents for HCP ELISA, do not comprehensively recognize all the HCP species, it is especially important to ensure that weak and non-immunoreactive HCPs are not overlooked by the ELISA. In some cases limited amount of antibodies to HCP species or antigen excess causes dilution-dependent non-linearity with multi-product HCP ELISA. In our experience, correct interpretation of assay data can lead to isolation and identification of co-purifying HCP with the product in some cases. Moreover, even if the antibodies for a particular HCP are present in the reagent, the corresponding HCP may not be readily detected in the ELISA due to antibody/antigen binding conditions and availability of HCP epitopes. This report reviews the use of the HCP ELISA, discusses its limitations, and demonstrates the importance of orthogonal methods, including mass spectrometry, to complement the platform HCP ELISA for support of process development. In addition, risk and impact assessment for low-level HCPs is also outlined, with consideration of clinical information.

Principles and applications of steric exclusion chromatography

We introduce a chromatography method for purification of large proteins and viruses that works by capturing them at a non-reactive hydrophilic surface by their mutual steric exclusion of polyethylene glycol (PEG). No direct chemical interaction between the surface and the target species is required. We refer to the technique as steric exclusion chromatography. Hydroxyl-substituted polymethacrylate monoliths provide a hydrophilic surface and support convective mass transport that is unaffected by the viscosity of the PEG. Elution is achieved by reducing PEG concentration. Selectivity correlates with molecular size, with larger species retained more strongly than smaller species. Retention increases with PEG size and concentration. Salts weaken retention in proportion to their concentration and Hofmeister ranking. Retention is enhanced near the isoelectric point of the target species. Virus binding capacity was measured at 9.9×10(12) plaque forming units per mL of monolith. 99.8% of host cell proteins and 93% of DNA were eliminated. Mass recovery exceeded 90%. IgM capacity was greater than 60 mg/mL. 95% of host cell proteins were eliminated from IgM produced in protein-free media, and mass recovery was up to 90%. Bioactivity was fully conserved by both viruses and antibodies. Process time ranged from less than 30 min to 2 h depending on the product concentration in the feed stream.