Wright-stained peripheral blood smears from mice displaying an abnormal cell population and elevated leukocyte counts. (A) A normal untransplanted mouse blood smear at the indicated magnifications is shown in the top panel. (B) The middle panel shows the most common phenotype seen with MDR1 expanded cells, which includes a large number of cells with a granulocytic morphology. (C) In a few cases, a leukemic blast phenotype was seen (4 of 24 mice), indicating possible transformation from a myeloproliferative disorder into a less differentiated leukemia.