High affinity mAb infusion can enhance maximum affinity maturation during HIV Env immunisation

Antigen-specific antibody infusion is known to enhance or suppress germinal centre (GC) responses depending on the affinity of the infusion. We hypothesised that infusing monoclonal antibodies (mAbs) of escalating affinity during an immunisation regimen may progressively escalate selection pressure on competing B cells, increasing their affinity. To test this, we immunised mice with HIV envelope gp120 and infused CD4 binding-site (CD4bs)-specific mAbs. While mAb infusion reduced somatic hypermutation (SHM) and affinity in most CD4bs-specific B cells, a sub-population was identified with greater SHM and affinity than control. High-throughput sequencing of plasma cells revealed that CD4bs-specific plasma cells possessed elevated SHM after mAb infusion, with phylogenetic tree topology that suggested more rapid differentiation. We therefore conclude, in accordance with other studies, that high-affinity mAb infusion primarily suppresses recruitment of most competing B cells but can increase and expedite affinity maturation of certain epitope-specific B cells.