Further Characterization of the Bifunctional HIV Entry Inhibitor sCD4-FI T45

Abstract

HIV entry into target cells is a highly sequential and time-sensitive process. In recent years, potent HIV Env-targeting antibodies, such as VRC01, have been identified. However, antibodies bind only to a single epitope, and mutations that confer resistance to antibody-mediated inhibition of HIV entry have been detected. In contrast, HIV cannot escape from binding to soluble CD4 (sCD4) without a fitness disadvantage. sCD4 has the unique ability to induce conformational changes within the HIV envelope glycoproteins (Env) that allow fusion inhibitors to bind. We have previously linked sCD4 to the fusion inhibitor FIT45 (sCD4-FIT45) and examined delivery of the bifunctional entry inhibitor via gene therapy. Here, we extend our studies and analyze the ability of sCD4-FIT45 to inhibit HIV Env-mediated cell fusion and HIV entry of several primary isolates. sCD4-FIT45 inhibited both cell fusion and HIV entry with remarkable antiviral activity. The mean 50% inhibitory concentrations (IC50) for sCD4-FIT45 were <0.2 μg/mL in both assays. Importantly, inhibition by sCD4-FIT45 was more potent than by VRC01, sCD4, or the previously described bifunctional protein sCD4-scFv17b. In contrast to sCD4, sCD4-FIT45 as well as VRC01 and sCD4-scFv17b did not mediate cell fusion between HIV Env+ and CD4−CCR5+ cells. The results presented here provide further evidence for the testing of sCD4-FIT45 and development of bifunctional proteins based on the sCD4-fusion inhibitor architecture.

Control of HIV Infection In Vivo Using Gene Therapy with a Secreted Entry Inhibitor

“…We and other groups have shown that sCD4 can be covalently linked to synergistic inhibitors, such as sCD4-induced epitope-targeting antibody fragments (e.g., sCD4-scFv 17b ), CCR5-mimicking peptides (e.g., eCD4-immunoglobulin [Ig]), or fusion inhibitors (e.g., 2DLT or sCD4-FI T45 ). 37 , 68 , 69 , 70 , 71 The resulting bifunctional proteins drastically improved the antiviral effect of sCD4 without enabling infection of CD4-negative cells. Furthermore, bifunctional inhibitors should also minimize the emergence of escape mutants.…”

Genetic Strategies for HIV Treatment and Prevention

“… 100 , 101 To overcome the limitations of single inhibitors, several inhibitors have also been combined, e.g., sCD4 was fused to a co-receptor-mimicking peptide or fusion inhibitors. 102 , 103 , 104 , 105 Aside from inhibiting HIV entry, several AVPs have the advantage that they can also reduce the cytopathic effects of HIV replication and mediate the elimination of infected cells. For example, antibodies and sCD4 can neutralize free gp120 in the serum of HIV-positive individuals or gp120 on the surface of infected cells.…”

HIV Entry and Its Inhibition by Bifunctional Antiviral Proteins

“…The resulting fusion protein sCD4-FI T45 was a potent inhibitor of HIV entry and neutralized isolates that were resistant to sCD4, FI T20 , or VRC01. 164 , 165 Lu et al. 166 have also fused sCD4 to the second-generation FI T1144 by using a seven-repeat GGGGS linker (2DLT).…”

“… 177 In contrast, the bAVPs eCD4-Ig and sCD4-FI T45 are significantly more effective against HIV strains that are relatively resistant to CD4-binding site bnAbs; the eCD4-Ig and sCD4-FI T45 IC 50 s for the same clade C isolate are below 0.1 μg/mL. 158 , 165 …”