Through a large serie of studies, we previously characterized the pathogenic effect of the highly conserved 3S epitope of gp41 during HIV infection. By analyzing the humoral immune response induced in asymptomatic long-term non-progressor (ALT) patients, we recently observed that up to 25% patients elicited efficient neutralizing responses directed against a point-mutated form of 3S (W614A-3S). Here we extensively characterized the neutralizing profile of this new family of neutralizing Abs.
Abs binding to 3S-WT (wild-type) or W614A-3S mutants were isolated from the sera of ALT patients. Abs were purified from heat-inactivated plasma of ALT patients by immunoprecipitation with synthetic W614A-3S peptides immobilized onto an amine-reactive agarose support, concentrated with Centicon filter, and dialyzed against PBS. The functional inhibitory profile of these Abs was defined using the well-standardized TZM-bl neutralization assay, the conventional neutralization assay on PBMCs, or the Fc-mediated inhibitory assay on macrophages.
We found that the anti-W614A-3S purified Abs display efficient and broad neutralizing activity. They inhibit transmitted founder Tier 2 viruses, neutralize primary isolates on primary cells and display Fc-mediated inhibitory functions at ng to µg/ml concentrations. The detection of anti-W614A-3S Abs was specifically correlated both with lower viral DNA (p<0.0001), viral load (p<0.0001), and other clinical parameters (CD4+ T cells, HLA protective alleles, …) suggesting that anti-W614A-3S neutralizing Abs participate in the control of HIV replication in ALT patients.
These results demonstrate that ALT patients develop efficient neutralizing Abs that can be purified using W614A-3S mutant protein capture assays. These Abs are distinct to that recently isolated from ELITE neutralizer patients. Abs directed against W614A-3S may therefore be considered as a new family of broadly neutralizing Abs, which need to be further characterized, considering their potential role on viral load and viral DNA.