Antibody-receptor interactions mediate antibody-dependent cellular cytotoxicity

Area of Science:

• Immunology
• Biochemistry
• Structural Biology

Background:

• Antibody-Fc receptor interactions are vital for innate immunity and biotherapeutics.
• Afucosylation of monoclonal antibodies (mAbs) increases affinity for FcγRIIIa, boosting cellular cytotoxicity.
• Existing hypotheses on afucosylation's mechanism lack solution-phase validation and overlook potential Fab-receptor interactions.

Purpose of the Study:

• To provide solution-phase evidence for the mechanism of afucosylated IgG1 binding to FcγRIIIa.
• To investigate the role of the fragment antigen-binding (Fab) region in Fc receptor interactions.
• To elucidate the combined effects of Fc and Fab regions on antibody-dependent cellular cytotoxicity (ADCC).

Main Methods:

• Hydroxyl radical footprinting coupled with mass spectrometry (HRF-MS) to probe solvent accessibility differences.
• Extensive molecular dynamics (MD) simulations to model molecular interactions.
• MD-guided rational mutagenesis to assess functional impacts of identified interactions.

Main Results:

• Afucosylated IgG1 exhibits reduced conformational changes upon FcγRIIIa binding in solution.
• HRF-MS and MD simulations confirm steric hindrance from Fc fucose and support Fab-receptor interactions.
• Fab-receptor interactions were demonstrated to directly modulate ADCC activity.

Conclusions:

• Afucosylation facilitates FcγRIIIa binding by minimizing conformational changes.
• The Fab region contributes a third critical component to IgG-Fc receptor interactions beyond Fc and glycan effects.
• These findings offer a more comprehensive understanding of IgG-Fc receptor biology for improved biotherapeutic design.