A cell-cell fusion assay reveals that the effective concentration for achieving 50% inhibition (IC50) of Enfuvirtide is 23 ± 6 nM. IFN-λs (1, 2, or 3) or the antiretrovirals (AZT, Efavirenz, Indinavir, and Enfuvirtide) significantly inhibita the expression of HIV p24 antigen and Gag gene in macrophages. IFN-λs (1, 2, or 3) also enhanced the anti-HIV (Bal) effect of AZT, Efavirenz, Indinavir, and Enfuvirtide.