β IVS-2 PCR of 5-month peripheral blood samples. DNA samples were obtained from mice transplanted with human β-globin transduced marrow (β-mice) and from mice transplanted with neomycin resistance gene-transduced marrow (neo^R mice). PCR analysis was performed using primers specific for the β-globin IVS-2 region (upper panel). Lane 1, a size marker (φX); lane 2, a normal human DNA sample; lanes 3 through 5 represent dilutions of producer cell DNA (lane 3, 100%; lane 4, 10%, lane 5, 1%); lanes 6 and 7, samples from two neo^R mice; and lanes 8 through 12, samples from β-mice. Indicated at the left of the figure are the predicted PCR bands for human β-globin (936 bp) and vector-derived human β-globin (564 bp). Three of 5 mice (lanes 9, 11, and 12) are positive. As a control for DNA loading, PCR analysis using PDGF B primers was performed on each sample as described in Materials and Methods (lower panel). Apart from lane 10, DNA loading was approximately equal.