Mapping IgG Subunit Glycoforms Using HILIC and a Wide-Pore Amide Stationary Phase

Significance of the Topic

Therapeutic monoclonal antibodies (mAbs) dominate the biopharmaceutical market and their N-glycosylation critically influences effector functions, pharmacokinetics, safety, and efficacy. Domain-specific profiling of IgG subunit glycoforms enhances understanding of structure–function relationships and supports quality control and biosimilarity assessments.

Study Objectives and Overview

This application note presents a workflow to map IgG subunit glycoforms via hydrophilic interaction chromatography (HILIC) on a wide-pore amide stationary phase, coupled with mass spectrometry (MS). Key aims include:

• Achieving high-resolution HILIC separations of Fc/2, Fd′, and light chain (LC) subunits.
• Demonstrating orthogonal selectivity to conventional reversed-phase (RP) methods.
• Profiling glycoform heterogeneity in trastuzumab and cetuximab samples.
• Evaluating column performance, reproducibility, and lifetime.

Methodology and Instrumentation

Monoclonal antibodies were digested with IdeS (and carboxypeptidase B for cetuximab), denatured with guanidine HCl, and reduced with TCEP to yield three ~25 kDa subunits (two LC, two Fd′, two Fc/2). HILIC separations employed:

• ACQUITY UPLC Glycoprotein BEH Amide, 300 Å, 1.7 µm, 2.1 × 150 mm column.
• Mobile phases: 0.1% TFA in water (A) and 0.1% TFA in acetonitrile (B); gradient reversed from RP conditions.
• Flow rate 0.2 mL/min; column temperature 45–60 °C; sample temperature 5–10 °C.

MS detection was performed with Xevo G2 QTof and SYNAPT G2-S HDMS (ESI+, 500–4000 m/z), enabling deconvolution of individual subunit glycoforms. Released N-glycans were labeled with RapiFluor-MS and profiled by HILIC-FLR-MS on a Glycan BEH Amide, 130 Å, 1.7 µm, 2.1 × 50 mm column.

Main Results and Discussion

• HILIC separated ~10 peaks: early eluting LC and Fd′ subunits, followed by multiple Fc/2 glycoforms (A2, FA2, FA2G1, FA2G2, etc.). MS deconvolution provided accurate mass assignments for each glycoform.
• Batch-to-batch comparison of trastuzumab highlighted reproducible differences in Fc/2 galactosylation (FA2, FA2G1, FA2G2), consistent with released glycan assays.
• Column durability testing (300 consecutive injections) showed stable retention times, resolution (Rs≈2 for A2 vs FA2), low carryover (<0.2%), and consistent backpressure (~6000 psi).
• Benchmarking against a 130 Å Glycan BEH Amide column and two competitor amide phases demonstrated 48–261% improvement in peak-to-valley metrics for Fc/2 glycoform separation on the 300 Å phase.
• Cetuximab profiling revealed both Fc and Fd′ subunit glycosylation, including non-human immunogenic glycoforms (α-1,3-galactose, Neu5Gc) in Fd′, complementing RapiFluor-MS released glycan data.

Benefits and Practical Applications

• Provides MS-compatible, orthogonal selectivity to RP for hydrophilic protein modifications.
• Enables rapid, domain-specific glycoform profiling for quality control and biosimilar comparison.
• Delivers high resolution, reproducibility, and column robustness for routine laboratory use.
• Minimal sample preparation accelerates workflow and supports targeted MS strategies.

Future Trends and Applications

• Integration of HILIC subunit profiling with targeted MS (SRM/PRM) for low-abundance glycoforms.
• Extension to diverse antibody formats, Fc-fusion proteins, and other biotherapeutics.
• Automation and high-throughput platforms with advanced bioinformatics for glycoform data analysis.
• Development of new stationary phase chemistries to separate complex glycan isomers and larger biomolecules.

Conclusion

Wide-pore amide HILIC on the Glycoprotein BEH Amide, 300 Å, 1.7 µm column offers a complementary, MS-compatible approach to RP for IgG subunit glycoform mapping. It delivers high resolution, domain specificity, and robust performance, supporting therapeutic antibody characterization and quality assessment workflows.

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