Outline of strategy used to transplant BM cells coexpressing NUP98-TOP1 and Meis1. Five-fluorouracil (5-FU) BM was harvested, transduced, and transplanted into primary mice as described in “Materials and methods.” Five weeks after transplantation, non-5-FU BM was harvested from the primary mice and transduced, and 1 × 10⁶ cells were transplanted into secondary mice along with 3 × 10⁵ helper cells. FACS profiles are representative of PB at 98 days after secondary transplantation. Top plot indicates NUP98-TOP1 BM infected with Meis1; bottom, Meis1 BM infected with NUP98-TOP1.