Affinity Maturation and Light-Chain-Mediated Paratope Diversification Anticipate Viral Evolution.

Area of Science:

• Immunology
• Virology
• Structural Biology

Background:

• Vaccine development aims to induce immunity against existing pathogens and future variants.
• Anticipatory breadth, where antibodies neutralize evolved strains, is crucial for long-term vaccine efficacy.
• The SARS-CoV-2 ACE2 binding site is a key target for neutralizing antibodies.

Purpose of the Study:

• Investigate the mechanisms of anticipatory breadth in antibodies targeting the SARS-CoV-2 ACE2 binding site.
• Analyze the role of somatic hypermutation and antibody chain pairing in neutralization breadth.
• Understand how antibody responses adapt to viral evolution.

Main Methods:

• Isolation and characterization of IGHV3-53/66 antibodies from vaccinated individuals.
• Comparative analysis of antibodies from infection-naïve vaccinated individuals and those with Omicron breakthrough infections.
• Structural analysis of antibody-receptor binding domain complexes.

Main Results:

• Antibodies from mRNA-vaccinated individuals neutralized Omicron variants, showing hallmark mutations for breadth.
• Breadth-associated somatic hypermutation patterns emerged independently of variant exposure.
• Omicron infection influenced light chain pairing, suggesting selection for favorable light chains.
• Heavy chain mutations refined contacts with conserved viral residues, while light chain pairing shifted epitopes to accommodate viral mutations.

Conclusions:

• A model for anticipatory breadth involves targeting restricted epitopes, affinity maturation creating an 'affinity buffer,' and variable chain pairing for diversity.
• These mechanisms compensate for viral mutations, providing a framework for predicting and preparing for viral evolution.
• Understanding these antibody dynamics is key for designing next-generation vaccines against rapidly evolving viruses like SARS-CoV-2.