The cell-cell fusion assay described in this study is easy, quantitative, and can be
served as a tool for determining novel HIV-1 CXCR4-related entry inhibitors. Although other
fusion assays such as the enzyme-based systems and the recombinant virus systems have
been developed, our assay is simpler because the process is virus-free, no cell lysate
preparation is needed, and cell-cell fusion is directly detected without additional step of
adding enzyme substrates. However, this assay does not rule out the possibility of generating
false-positive results if a tested compound is Tat inhibitor. One approach to solve this
problem is to incubate the compound with a cell line transfected with plasmids encoding Tat
and a different reporter gene under HIV-1 LTR promoter. Future work to improve our assay
is to shorten the incubation time required for the measurement of copGFP signal as a readout
of fusion event.