Cotransduction of K562 and human peripheral blood CD34⁺ cells with FeLV-C and GALV or RD114 and GALV-pseudotyped retrovirus particles. Slot blot analysis of 1.0 mL and 0.1 mL virus-containing medium was used to compare the titer of the different virus preparations (A). These titers were used to adjust the volumes of supernatants to ensure that equivalent numbers of each pseudotype were used. Human CD34⁺ peripheral blood CD34⁺ cells were cotransduced with FeLV-C and GALV or RD114 and GALV-pseudotyped virus preparations over a 4-day period. Parallel cultures of K562 cells were cotransduced with the same virus preparations each day (d1, d2, d3, d4). One culture was cotransduced over the 4-day period (d1-4). DNA was extracted from the K562 cultures and a portion of the CD34⁺ cells for analysis of the integration of the FeLV-C or RD114 and GALV-pseudotyped viruses by PCR using primers that span the nls in the MFG-nlsLacZ vector. (B) The analysis of FeLV-C/GALV- and RD114/GALV-transduced K562 cells is shown in the left and center panels. Sequences from the human β-globin were amplified in the same samples as a control. The analysis of FeLV-C/GALV (G/F)– and RD114/GALV (G/R)–transduced CD34⁺ cells used for transplantation into fetal sheep is shown in the right panel.