In vitro activity of candidate microbicides against cell-associated HIV

Most research on HIV transmission and microbicides focuses on the inhibition of cell-free virus (CFV) present in genital secretions. However, an effective microbicide should also block the transmission of cell-associated virus (CAV) originating from seminal T-cells and macrophages. Because inhibition of CAV remains controversial, especially for viral entry inhibitors, we developed a novel in vitro assay to evaluate the activity of different classes of candidate microbicides against cell-free HIV and HIV-infected leucocytes (i.e, resting PBMC, activated PBMC and monocyte-derived macrophages). The assay is based on two CD4+ CXCR4+ T-cell lines (R5MaRBLE and X4MaRBLE) that both contain a firefly luciferase reporter gene but differ in the expression of the CCR5 co-receptor. Consequently, the quantification of luciferase activity and Gag p24 concentration in co-cultures of R5-tropic HIV-infected leucocytes with each cell line separately allowed to discriminate between the infection of the cell-lines (i.e., target cells), the ongoing infection in the HIV-infected leucocytes (i.e., effector cells), and the total infection of the co-culture (i.e., effector + target cells). All fourteen antiretrovirals tested, were able to block target cell infection by all three sources of CAV, although a small decrease in activity (2 to 18-fold) was observed for all entry inhibitors. On the other hand, the production of Gag p24 by the infected effector cells could only be blocked by protease inhibitors. Overall, these results show that entry and protease inhibitors are eligible drug classes for inclusion in future combination microbicides.