Characterization of antibody-C1q interactions by Biolayer Interferometry

Area of Science:

• Immunology
• Biochemistry
• Drug Development

Background:

• Immunoglobulin G (IgG) antibodies mediate effector functions like complement-dependent cytotoxicity (CDC).
• Differential binding of IgG isotypes to C1q initiates the classical CDC pathway, varying CDC efficacy.
• Understanding IgG-C1q interactions is vital for optimizing antibody-based therapeutics.

Purpose of the Study:

• To develop and apply a label-free method for characterizing IgG-C1q binding affinities.
• To investigate the influence of antigen binding on the interaction between IgG antibodies and C1q.
• To assess the implications of these interactions for the CDC activity of antibody drugs.

Main Methods:

• Utilized a label-free technique to quantify binding affinities between various IgG isotypes (IgG1, IgG2, IgG4) and C1q.
• Assessed C1q binding to specific IgG1 monoclonal antibodies (Trastuzumab, Adalimumab) with and without their bound antigens.
• Compared C1q binding characteristics of antigen-free versus antigen-bound antibodies.

Main Results:

• Determined binding affinities of multiple IgG1, IgG2, and IgG4 antibodies to C1q.
• Demonstrated that antigen binding to the Fab region of IgG1 antibodies significantly impacts their Fc-mediated C1q binding.
• Observed similar C1q binding for two tested IgG1 monoclonal antibodies in their antigen-free state.

Conclusions:

• The characterized IgG-C1q interactions provide insights into variations in CDC induction among different IgG isotypes.
• Antigen binding to the Fab region can modulate the initiation of the complement cascade by affecting C1q binding to the Fc region.
• These findings highlight a critical factor influencing the CDC efficacy of antibody drugs, impacting therapeutic strategies.