Overall retroviral marking levels. The arrow indicates the time of 3 Gy TBI. The upper line corresponds to animal 96E019 and the lower line, to animal 96E025. The marking was stable in both animals after low-dose 3 Gy TBI, despite marked clonal fluctuation. The marking level for the animal 96E025 was 4% to 10% and for the animal 96E025, 1.5% to 3%.