Transduction of human CD34⁺ HSCs by pseudotyped vectors. Resting CD34⁺ cells display the ASCT-1 and ASCT-2 proteins that serve as receptors for the BaEV envelope glycoprotein, and retroviral or lentiviral vectors pseudotyped with the BaEV envelope can bind to the receptors and transduce the cells. Resting CD34⁺ cells lack expression of the LDL-R that serves as the receptor for VSV-G-pseudotyped vectors and thus are not effectively transduced by them. Activated CD34⁺ cells, prestimulated with HGFs, such as ckit ligand, flt-3-ligand, and thrombopoietin, express the LDL-R and can bind and be transduced by VSV-G-pseudotyped vectors. The levels of the ASCT-1 and ASCT-2 receptors increase further in activated CD34⁺ cells, and transduction by the BaEV-pseudotyped vectors also increases.