Early identification of unusually clustered mutations and root causes in therapeutic antibody development

Design of next-generation therapeutic IgG4 with improved manufacturability and bioanalytical characteristics

Manufacturability of immunoglobulin G4 (IgG4) antibodies from the Chemistry, Manufacture, and Controls (CMC) perspective has received little attention during early drug discovery. Despite the success of protein engineering in improving antibody biophysical properties, a clear gap still exists between rational design of IgG4 candidates and their manufacturing suitability. Here, we illustrate that undesirable two-peak elution profiles in cation-exchange chromatography are attributed to the S228P mutation (in IgG4 core-hinge region) intentionally designed to prevent Fab-arm exchange. A new scaffolding platform for engineering IgG4 antibodies amenable to bioprocessing and bioanalysis is proposed by introducing an “IgG1-like” single-point mutation in the hinge or CH1 region of IgG4S228P. This work offers insight into the design, discovery, and development of innovative therapeutic antibodies that are well suited for robust biomanufacturing and quality control.

Computational insights into O-glycosylation in a CTLA4 Fc-fusion protein linker and its impact on protein quality attributes

The hinge region of immunoglobulin G1 (IgG1) is used as a common linker for Fc-fusion therapeutic proteins. With the advances of high-resolution mass spectrometry and sample treatment strategies, unexpected O-linked glycosylation has been observed in the linker. However, the molecular mechanism involved in this unusual posttranslational modification is unknown. In this study, we applied site-direct mutagenesis, mass spectrometry, analytical chromatography, and computational modeling to investigate O-glycosylation processes in a clinically used CTLA4 Fc-fusion protein and its impacts on protein quality attributes. Surprisingly, O-glycans could be formed at new sites when an initial O-glycosylation site was eliminated, and continued to occur until all potential O-glycosylation sites were nulled. Site-preference of O-glycosylation initiation was attributed to the complex formation between the linker peptide and glycan transferase whereas the O-glycosylating efficiency and the linker flexibility were correlated using molecular modeling and simulations. As predicted, O-glycan-free CTLA4 Fc-fusion proteins were more homogenous for sialylation, and interestingly less prone to protein aggregation. Attenuating protein aggregation was a desirable effect, and could be related to the reduced presence of linker O-glycans that hindered inter-chain disulfide bond reformation. Findings from this study shed light on new therapeutic protein design and development.