Peripheral blood analysis of the eight transplant survivors. PCR amplification with MDR1 specific primers and Southern blot hybridization with a ³²P-labeled human MDR1 cDNA probe were performed 2 to 4 months after transplantation. Lanes A and B represent negative controls: normal mouse spleen DNA. Lanes C and D represent positive controls: placental DNA MDR1 positive at 1:1,000 and 1:100 dilutions, respectively. Lanes E, F, H, I, and K represent the animals that received fresh-untreated donor cells. Lanes G, L, and M represent the animals that received ex vivo–cultured cells.