Assessing bnAb potency in the context of HIV-1 Envelope conformational plasticity

The ability of broadly neutralizing antibodies (bnAbs) to interact with the closed, pre-fusion HIV-1 envelope (Env) trimer distinguishes them from weakly neutralizing antibodies (weak-nAbs) that depend on trimer opening to bind. Comparative analysis of neutralization data from the CATNAP database revealed a nuanced relationship between bnAb activity and Env conformational plasticity, with substantial epitope-specific variation of bnAb potency ranging from increased to decreased activity against open, neutralization-sensitive Env. To systematically investigate the impact of Env conformational dynamics on bnAb potency we screened 126 JR-CSF point mutants for generalized neutralization sensitivity to weak-nAbs and plasma from people with chronic HIV-1 infection. 23 mutations at highly conserved sites resulted in neutralization phenotype with high Tier 1 sensitivity, which was associated with de-stabilization of the closed, prefusion conformation. Including 19 of these mutants into a Sensitivity Env mutant panel (SENSE-19), we classified bnAbs according to potency variations in response to trimer opening. To verify that these sensitivity patterns are independent of the in vitro assay system, replication-competent SENSE-19 mutant viruses were tested on primary CD4 T cells. While loss of potency on SENSE-19 was registered for bnAbs recognizing quaternary epitopes on pre-triggered Env, structural destabilization benefitted MPER bnAbs and other inhibitors known to have post-CD4 attachment neutralization activity. Importantly, for certain bnAbs targeting CD4bs, V3-glycan and interface epitopes, particularly low potency variation was noted, suggesting that Env conformational tolerance can be achieved but is not the rule. In summary, SENSE-19 screens revealed distinct Env flexibility tolerance levels between bnAb types that provide mechanistic insights in their function and broaden current neutralization breadth assessments.