Specific peptide inhibition of HIV-1 Env-mediated fusion with primary target cell types. Designated primary target cells infected with vCB-21R-LacZ were preincubated with peptides at the indicated concentrations for 1 hour at 37°C. Target cells were then mixed with HeLa effector cells coinfected with vTF7-3 and vCB43 (Ba-L) or vCB-41 (LAV). Effector 89.6 Env-expressing HeLa cells were prepared by transfection of pSC59/89.6 and infection with vTF7-3. Fusion assay was performed as described in “Materials and methods.” (A) PBMC targets. (B) Primary macrophage targets. Error bars indicate SD of mean values obtained from duplicate fusion assays.