Immunostaining demonstrates FLAG expression in rat BMMNCs transduced with SV(Nef-FLAG) in vitro. Rat BMMNCs were selected by centrifugation over Ficoll-Hypaque and transduced with SV(Nef-FLAG) or SV(BUGT) (negative control) as described in “Materials and methods.” FLAG expression in transduced rat BMMNCs was analyzed by intracellular immunostaining. (A) Seven days after transduction; (B) 21 days after transduction. Original magnification, × 200.