Engraftment of the PB of NOD/SCID recipients over time. The PB of 5 chimeric recipient mice was sampled at 4, 8, 16, and 24 weeks after in utero transplantation of Ly5.1 lineage-depleted progenitor cells. Total nucleated cells were analyzed for the presence of either the Ly5.1⁺ (donor) cells or the Ly5.2⁺ (host) cells. The percentage of Ly5⁺ cells that were of donor origin in 5 individual animals is shown.