Background:
HIV-1 gp120 is a viral envelope glycoprotein (Env) expressed on the surface of infected cells which renders it an attractive target for the clearance of the infected cells. However, Env is metastable and presents in multiple conformations, making it challenging for antibody-mediated clearance. Temsavir (TMR), the active form of the HIV-1 attachment inhibitor fostemsavir, binds to and stabilizes Env in a ‘closed’ conformation that may allow better targeting by broadly neutralizing antibodies (bnAbs).
Methods:
To understand whether TMR can modulate bnAb binding to Env on the infected cells, we conducted experiments with primary CD4+T cells isolated from HIV negative donors infected with a broad panel of viruses that includes 26 clinical HIV isolates. Antibody binding to Env on the infected cell surface was determined after 24h treatment with a serial titration of TMR ranging from 0 to 25µM.
Results:
We found that TMR treatment significantly enhances binding of bnAbs, including N6, to HIV-1 infected cells and leads to increased clearance of infected cells through antibody dependent cellular cytotoxicity (ADCC). This synergistic effect of N6 and TMR is most prominently observed on infected cells that maintain CD4 expression, the cells that are otherwise difficult to target by N6 and other bnAbs alone. The enhanced bnAb binding is diminished when tested against strains with reduced TMR sensitivity (clade AE), suggesting that it is an on-target MOA. We observed decreased bnAb binding to CD4 downregulated infected cells with some viruses. However, this effect only occurs at much higher TMR concentrations than required for neutralization and is not consistent across the panel. Alternatively, we saw significantly increased bnAb binding to the CD4 downregulated cells in 1/3 of isolates that are tested. Further analysis of HIV Env from infected cells demonstrated that the altered bnAb binding is not attributed to the modified gp160/gp120 processing by TMR.
Conclusions:
We have demonstrated for the majority of viruses tested that TMR treatment leads to enhanced bnAb binding to the infected cells that maintain CD4 expression, and the reduced bnAb binding to the CD4 downregulated infected cells occurs at much higher concentrations than neutralization. These results suggest that combination of bnAb and TMR can expand the population of HIV-1 infected cells susceptible to bnAb mediated clearance and may increase the likelihood of reservoir reduction in the clinical setting.