High affinity is insufficient for strong B cell activation by HIV broadly neutralising antibodies

HIV broadly neutralizing antibodies (bnAbs) have been widely studied, and inducing a robust broadly neutralizing response remains a goal for many human vaccine studies. Much research focusses on creating higher affinity antigens to target bnAb precursors, however this ignores the role of non-neutralisers that are known to dominate HIV-specific responses. Furthermore, any effective vaccine will likely need to induce multiple bnAbs. Here, we question whether the previously postulated affinity ceiling of 10^-9M limits bnAb induction above a certain affinity. Using adeno-associated virus (AAV)-mediated CRISPR-Cas9 engineering to express HIV-specific bnAbs and non-bNAbs in Ramos B cells, we investigate antigen-specific activation by BCRs of known binding/neutralization potency, epitope and affinity. We found that between different bnAb epitopes affinity was not predictive of activation. However, within individual epitopes and across non-bnAb epitopes, increased affinity results in increased activation. We propose that at activation-resistant bnAb epitopes, affinity is overruled to an extent by the physical BCR-antigen interaction, while more 'simple' and immunogenic non-bnAb epitopes are more heavily dependent on BCR affinity. These findings may have significant consequences for vaccine development, as a high affinity BCR-antigen interaction at an epitope with poor activation potential may be unsuccessful at participating in the humoral response.