Ability of antibodies specific to the HIV-1 envelope glycoprotein to block the fusion inhibitor T20 in a cell–cell fusion assay

The anti-HIV peptide T20 is able to inhibit the syncytia formation between CHO-WT and HeLa CD4+cells. We found that several sera of HIV-infected patients have the capacity to block the inhibition of fusion by T20. Suggesting that these sera may contain antibody which can block T20 access and prevent membrane fusion, we studied the ability of a panel of antibodies directed to different regions of HIV-1 envelope glycoprotein to block the inhibition of fusion by T20. We found that the C1 and V3 loop regions of gp120 and the heptad repeat 1, the immunodominant C–C region and the Kennedy epitope of gp41 located in the intracytoplasmic tail were the target for antibodies capable to block the inhibition of syncytia formation by T20. We suggest that these antibodies have the capacity to counteract the anti-fusion effect of T20 by preventing its binding to the interaction sites. Further studies are needed to determine if some of them recognize new T20 interaction sites.