Both HEK293TEnv cells and HeLaT4Tru cells were detached with 0.05% EDTA in
PBS (pH7.4), and co-cultured (3 x 104 cells/well each) in wells of a 96-well plate. Various
concentrations of T20, a known HIV-1 fusion inhibitor, were added. As positive and negative
controls, the wells containing no fusion inhibitor and mock transfected cells, respectively,
were included. Co-cultured cells were incubated for 1-5 days at 37C in 5% CO2. At
indicated time, cell-cell fusions were observed under the inverted fluorescent microscope
(Nikon, Japan). The GFP signals were quantified by using a fluorescent microplate reader
(Wallac 1420-018 Victor 2, Perkin Elmer) with excitation and emission wavelengths at 485
nm and 510 nm, respectively. The data obtained from measurement of copGFP intensity were
analyzed by the program Microsoft Excel to calculate for percent cell-cell fusion and 50%
inhibitory concentration (IC50). GFP generated in wells containing no fusion inhibitor was
set as 100% while those generated by the co-cultured cells of target cells and mock
transfected cells was set as 0%. The percent fusions of each concentration of T20 were
plotted to calculate the IC50 of T20