CD4 and HIV infectious disease: Although direct GS-9620 treatment had no major effect on de novo HIV infection of isolated CD4+ T cells (EC50 > 7 μM), the addition of conditioned medium from GS-9620-treated PBMC cultures strongly inhibited (99%) de novo HIV infection in isolated CD4+ T cells (EC50 = 1.6 ± 0.5 nM), indicating that the antiviral activity of GS-9620 is mostly mediated by a soluble PBMC-derived antiviral factor(s) (Fig. 2).