Analysis of host bone marrow DNAs for vector DNA. Bone marrow DNA from transplant recipients and controls was analyzed by PCR for the presence of the MDR18.1 vector DNA. For each reaction, 250 ng of template DNA was amplified with the human MDR1 primers and the murine β-globin primers using the same PCR reaction conditions as the MDR1 colony RT-PCR assay. The murine β-globin serves as an internal standard for copy number and quality of template. The MDR1 fragment is the upper band, and the β-globin is 100 bases shorter and runs below the MDR1. This assay is capable of detecting 1 copy of the transgene per haploid genome in <1% of the cells as determined by a standard dilution curve. None of the transplant recipients showed detectable amounts of MDR1 DNA using this assay. The templates assayed are (from left to right) two no-template negative control reactions; NIH3T3 (murine cell line; negative control for human MDR1 gene); MDR18.1 (the retroviral producing murine cell line; positive control, producer line contains the proviral genome); male murine spleen DNA (negative control); TX40 and TX60 bone marrow DNAs (negative control; these mice received no MDR-transduced cells, only phosphate-buffered saline); and TX1, TX2, TX5, TX6 bone marrow DNAs (transplant recipients).