The impact of forced degradation conditions on mAb dimer formation and subsequent influence on aggregation propensity

Monoclonal antibody (mAb) aggregation can present major challenges for the development of biotherapeutics. An understanding of the molecular mechanisms of mAb aggregation is highly desirable both because it allows the performance of informed risk assessments regarding the criticality of mAb aggregates and because it may facilitate rational stabilization of aggregation prone regions. Here, we report the generation and isolation of dimer species of an IgG4 mAb (mAb1) that were present in stressed material under differing levels of temperature stress. We demonstrate the power of combining established higher order techniques with non-routine analysis, such as small-angle X-ray scattering, hydrogen/deuterium exchange mass spectrometry (HDX-MS), and protein conformational array enzyme-linked immunosorbent assay (PCA ELISA), and show that dimer species formed under temperature stress are structurally distinct from those present in unstressed mAb1. Specifically, stress-induced dimers are shown to adopt a more elongated conformation with a greater degree of unfolding when compared to native dimers. Analysis by HDX-MS and PCA ELISA, supported by in silico shape and charge molecular docking, enabled the identification of residues in both the variable and constant domains that appear to play a significant role in the dimerization of mAb1. Furthermore, we show that dimers formed under temperature stress are significantly more long-lived than those present in unstressed mAb1. We also present evidence that mAb1 dimers can behave as aggregation nuclei, and that dimers produced under high-temperature stress do so to a greater extent. This work presents an advancement in our understanding of the molecular mechanisms of mAb aggregation and highlights the importance of structural characterization of dimer species during the development of mAb biotherapeutics. Abbreviations: 2DSA: 2-Dimensional Spectrum Analysis; CD: Circular Dichroism; CDR: Complementarity-Determining Region; CQA: Critical Quality Attribute; DSC: Differential Scanning Calorimetry; FTIR: Fourier Transform Infrared spectroscopy; HDX-MS: Hydrogen/Deuterium Exchange Mass Spectrometry; HIC: Hydrophobic interaction chromatography; HMWS: High Molecular Weight Species; HOS: Higher Order Structure; mAb: Monoclonal Antibody; MD: Molecular Dynamics PCA; ELISA: Protein Conformational Array Enzyme-Linked Immunosorbent Assay; Rg: Radius of Gyration; SAXS: Small Angle X-ray Scattering; SE-HPLC: Size Exclusion High Performance Liquid Chromatography; SV-AUC: Sedimentation Velocity-Analytical Ultracentrifugation