Analysis of bone marrow-derived colonies from two recipient animals. PCR amplification of the transgene using MDR1 specific primers and agarose gel electrophoresis are shown. Upper panel: recipient of fresh-untreated cells, tested 8 months after transplantation. Lane 1 represents the molecular size marker. Lane 2 represents the positive control (156-bp fragment). Lane 3 shows the negative control. Lanes 4 to 14 represent the BM-derived colonies. Three positive colonies were detected, as seen in lanes 7, 8, and 9. Lower panel: Recipient of ex vivo cultured cells, tested 14 months after transplant. Lane 1 represents the molecular size marker. Lane 2 represents the positive control. Lanes 3 to 13 represent the BM-derived colonies (pooled). Three positive samples were detected, as seen in Lanes 6, 11, and 12. Lane 14 shows the negative control (pooled colonies from normal, MDR-negative mouse).