Lymphopoiesis in

eng^−/− cells appears normal. Sorted Flk1⁺ cells from day-6eng^+/− andeng^−/− ES-cell/OP9 cocultures were reseeded onto OP9 cells and analyzed by flow cytometry on day 16 and day 19 for surface expression of CD45, CD19, and CD11b. The total number of cells obtained from each coculture is indicated in parentheses.