β IVS-2 PCR of transduced mouse spleen colonies. Two recipient mice were killed 12 days after transplantation with human β-globin transduced marrow. DNA samples were obtained from individual spleen colonies and PCR analysis performed using primers specific for the β-globin IVS-2 region (upper panel). Lanes 1 through 10, samples from individual spleen colonies; lane 11, producer cell DNA; lane 12, normal human DNA; lane 13, a size marker, φX. Indicated on the right of the figure are the predicted PCR bands for normal human β-globin (936 bp) and vector-derived human β-globin which contains a 372-bp deletion in IVS-2 (564 bp). Eight of 10 spleen colonies are strongly PCR-positive, the other two are weakly positive. As a control for DNA loading, PCR analysis using PDGF B primers was performed on each CFU-S sample as described in Materials and Methods (lower panel). DNA loading was approximately equal, except for the sample in lane 9.