Background:  HIV envelope gp120 binds to the chemokine co-receptor CXCR4 and induces apoptosis of CXCR4-expressing cells, including CD4 T cells. This cell death is one mechanism by which HIV depletes CD4 T cells during HIV infection. The HIV protease inhibitors are frequently used to treat HIV infection. This class of drug has also been found to have intrinsic anti-apoptotic properties. Therefore, we investigated whether an HIV protease inhibitor could block gp120/CXCR4-mediated CD4 T-cell apoptosis.

Methods:  Primary CD4 T cells were isolated from healthy donors, and pre-treated with 7 mM of nelfinavir (NFV) or control. The cells were then incubated, or not, with Lav-Bru (X4) gp120 (pre-treated with soluble CD4) for 24 hours. The cells were stained with fluorescently labeled anti-CXCR4 (12G5) or treated with DioC6 and analyzed by flow cytometry. Cells were incubated with SDF or control on opposite sides of a Transwell chemotaxis plate for 2 hours and then counted for percentage of chemotaxis. Cell death was determined by trypan dye exclusion and MTS viability.

Results:  Incubating CD4 T cells with NFV did not alter surface expression of CXCR4 (12% control treated, 12% NFV-treated cells) and did not inhibit SDF-induced chemotaxis of CD4 T cells (60% with control and 62% with NFV-treated cells). Pre-incubating the CD4 T cells with NFV did inhibit gp120-induced cell death, with 25% cell death in the cells pre-incubated with control and 1% death in cells pre-incubated with NFV before gp120 treatment. Gp120 caused a loss of mitochondrial transmembrane potential in CD4 T cells, indicating mitochondrial dependent apoptosis, which was blocked by NFV treatment.

Conclusions:  The HIV protease inhibitor NFV blocks gp120/CXCR4-mediated CD4 T-cell apoptosis and prevents mitochondrial membrane destabilization, but does not alter normal CD4 T-cell chemotactic function. Therefore, HIV protease inhibitors can protect CD4 T cells from gp120-mediated cell death, as well as block HIV replication.