Ibalizumab shows in-vitro activity against group A and group B HIV-2 clinical isolates.

Objective: Treatment of multidrug-resistant HIV-2 is an emerging issue, because of the rapid selection of mutations at time of virological failure and the low number of antiretrovirals active on HIV-2. The aim of this study was to determine the susceptibility of HIV-2 primary isolates to ibalizumab, a long-acting monoclonal antibody that binds to CD4 that is approved for the treatment of MDR HIV-1.

Methods: In-vitro phenotypic susceptibility of 16 HIV-2 primary isolates was measured using a modified version of the ANRS peripheral blood mononuclear cells (PBMC) assay. Susceptibility to ibalizumab was assessed through 50% inhibitory concentrations and maximum percentage inhibitions (MPI), and gp105 was sequenced to look for determinants of reduced susceptibility.

Results: Ibalizumab inhibited viral replication of all 16 isolates, with a median IC 50 value of 0.027 μg/ml (range = 0.001-0.506 μg/ml), and a median MPI of 93%. Although two isolates presented higher IC 50 (above 0.1 μg/ml), they did not exhibit a loss of potential N-linked glycosylation sites in V5 loop, as reported in HIV-1 strains with reduced susceptibility. However, both presented shorter V1 and V2 loops than the HIV-2 reference strain.

Conclusion: Ibalizumab inhibits HIV-2 replication, with IC 50 and MPI in the range of those reported for HIV-1. These in vitro data support the use of ibalizumab in patients with MDR HIV-2, in combination with an optimized background regimen.