Detection of human cells in mouse blood soon after injection. BV173 cells were injected in the tail vein at a dose expected to give 50% of human cells in mouse blood. Mice were bled 1, 6, and 24 hours after injection. Quantification of human cells was assessed by staining with human CD45 MoAbs. Bars refer to standard deviations (SD). The same findings were observed using peripheral blood CD34⁺ cells from CML patients and healthy subjects.