Dependence on a variable residue in its epitope limits the breadth of an HIVMPER neutralizing antibody, despite convergent evolution with geneticallysimilar bNAbs

BNAbs that target the MPER of HIV, such as VRC42 and 4E10 are capable of neutralizing of viruses. These two antibodies share germline antibody genes ,IGHV1-69 and IGKV3-20, forming a bNAb class. Furthermore, previous studies have revealed convergent evolution within these two bNAb lineages towards a GA/WGW motif in the CDRH3, which enhances neutralization potency. We have previously isolated an MPER NAb, CAP206-CH12, that also uses these germline genes but lacks breadth. Longitudinal antibody gene sequencing of the CAP206-CH12 lineage from 10 - 198 weeks post-infection revealed similar convergent evolution towards a GW motif in the CDRH3. However, none of the clonally related antibodies contained the double GA/WGW motif as seen in VRC42 and 4E10. Mutagenesis of CAP206-CH12 from GL to GW improved neutralization breadth and potency, but failed to reach the levels of breath and potency shown by VRC42 and 4E10. To explore the lack of potency/breadth, viral mutagenesis was performed to map the CAP206-CH12 epitope. This indicated that CAP206-CH12 is dependent on D674, a highly variable residue at the solvent exposed elbow of MPER. In contrast, VRC42 and 4E10 are dependent on highly conserved residues facing the hydrophobic patch of the C-terminal helix. Therefore, while CAP206-CH12, VRC42and 4E10 show some convergent evolution, and fall within the same class of antibodies, their varying epitopes and orientation of binding to the MPER likely distinguish their differences in breadth and potency