Broadly neutralizing antibodies (bnAbs) hold great promise for the prevention and treatment of HIV infection, but this virus has evolved elaborate ways to evade effective neutralizing antibodies. One of these is the evasion of antibody avidity: Low Env density with spike distances surpassing the average ‘wingspan’ of an IgG impedes inter-spike crosslinking and Env structural constraints hamper intra-spike crosslinking; these limitations of bivalent binding may restrain bnAb potency. Here we hypothesized that bnAb neutralizing activity could be increased through a strategy that overcomes the evasion of Ab avidity by using bispecific Abs (BiAbs) targeting both Env and a host molecule known to be present on the viral surface, CD44.
BiAbs were engineered using the CrossMAb Technology. Neutralizing activity was assessed using the Tzm-bl assay for infectious viruses, including the deCamp global panel.
We engineered a prototype BiAb that combines the bnAb PGDM1400 (anti-V2 apex) with the anti-CD44 Ab RG7356 and assessed its neutralizing activity against diverse HIV-1 strains, including primary isolates and the deCamp global panel. As expected, RG7356 had no neutralizing activity. PGDM1400/RG7356 neutralized more potently than the parental bnAb, PGDM1400, for 14/16 of HIV-1 strains tested. The mean level of neutralization enhancement (defined as IC50 ratio of parental and bispecific Ab) was 8.6 (range 0.6 to 75.5). Mechanistically, the potency enhancement occurred irrespective of target cell CD44 expression but was critically dependent on presence of CD44 on the virion surface. Similar enhancement of virus neutralization was observed when PGDM1400 was replaced by other bnAbs (e.g., 10-074 and N6).
Our data provide strong evidence that bnAbs neutralize most HIV-1 strains through predominantly monovalent binding and increasing avidity via binding to a host protein on the virion surface could substantially enhance virus neutralization.