Fig. 1

Schematic representation of the three generations of lentiviral vectors. A First generation vector systems include all HIV-1 genes, except env, in a single packaging plasmid. The env gene is replaced with VSV-G and provided in a separate plasmid. The vector plasmid contains an internal promotor-driven transgene cassette flanked by the HIV-1 LTRs. B In second-generation lentiviral vector systems, genes encoding accessory proteins Vif, Vpr, Vpu, and Nef are removed from the packaging plasmid. C In third-generation lentiviral vector system, the rev gene is placed on a separate plasmid, giving rise to a total of four separate plasmids required for production. Replacement of the U3 with a heterologous promoter (usually CMV or RSV) in the 5′ LTR allows the tat gene to be removed from the packaging plasmid, while a partial deletion of the U3 region from the 3′ LTR results in so-called ‘self-inactivating’ (SIN) lentiviral vectors. State-of-the art third-generation lentiviral transfer vectors usually also contains additional cis-acting elements such as cPPT/FLAP and WPRE for increased transduction efficiency and transgene expression, respectively. All vectors are shown schematically, and elements such as genes and promoters are not shown to scale