Development of B cells stably expressing transgene from SB100X-transfected CD34⁺ HPCs. CD34⁺ cells were nucleofected with SB transposon alone or with SB transposon + SB100X, or with piggyBac transposon + piggyBac, transposase or without DNA, respectively. Transfected cells were cocultured with MS-5 in medium supplemented with SCF and G-CSF. At day 28, cells were collected and analyzed for expression of CD19 and DsRed by flow cytometry.