This study describes the use of lentivirus-delivered RNA interference (RNAi) for stable gene silencing in primary cells. The authors developed a lentiviral vector system that expresses hairpin RNAs targeting green fluorescent protein (GFP) in HeLa cells and primary dendritic cells (DCs). The system, called Lentihair, was shown to effectively reduce GFP expression in both cell types, with stable silencing lasting for at least 4 weeks. The lentiviral vector was also tested in nondividing cells, demonstrating its potential for gene silencing in a wide range of cell types. The study highlights the utility of lentiviral RNAi for investigating gene function in primary cells and nondividing cells, providing a powerful tool for understanding biological processes and disease mechanisms.This study describes the use of lentivirus-delivered RNA interference (RNAi) for stable gene silencing in primary cells. The authors developed a lentiviral vector system that expresses hairpin RNAs targeting green fluorescent protein (GFP) in HeLa cells and primary dendritic cells (DCs). The system, called Lentihair, was shown to effectively reduce GFP expression in both cell types, with stable silencing lasting for at least 4 weeks. The lentiviral vector was also tested in nondividing cells, demonstrating its potential for gene silencing in a wide range of cell types. The study highlights the utility of lentiviral RNAi for investigating gene function in primary cells and nondividing cells, providing a powerful tool for understanding biological processes and disease mechanisms.