Griffithsin, Alone and Combined with All Classes of Antiretroviral Drugs, Potently Inhibits HIV Cell-Cell Transmission and Destruction of CD4+ T cells

Abstract

HIV spreads by cell-free virions but also efficiently through cell-cell mediated contacts. These cell-cell HIV transmission pathways have also been suggested as a mechanism of viral escape from neutralizing antibodies and antiretroviral (ARV) therapy. The carbohydrate-binding agent (CBA) griffithsin (GRFT) inhibits cell-free HIV replication in the pM range (43-630 pM). Here, we evaluated GRFT alone and in combination with compounds of four different classes of antiretroviral drugs (entry inhibitors, reverse transcriptase inhibitors, integrase inhibitors and protease inhibitors)in cell-cell HIV transmission routes and determined the combination index (CI) using the median effect principle. The activities of GRFT and antiretroviral drugs were evaluated in assays of inhibition of giant cell formation, HIV replication and target T cell destruction via light microscopy, multi-parameter flow cytometry and p24 HIV-1 Ag ELISA. GRFT potently inhibits (i) giant cell formation between persistently HIV-infected T cells and noninfected CD4+ target T cells (EC50: 87 ± 4 pM) and (ii) HIV transmission, CD4+ T-cell destruction and viral replication through the DC-SIGN mediated pathway (EC50:25 ± 3 pM).All GRFT/ARV drug combinations displayed synergistic or additive effects (CI95: 0.30-1.08) on inhibition of cell-cell fusion and on protection against target CD4+ T cell destruction. In addition, the GRFT/ARV combinations also potently inhibited short-term (20–24 h) viral replication in T-cells via the DC-SIGN mediated route of transmission. These in vitro data are very encouraging for GRFT as an ingredient in a multi-targeted microbicide.