Surface marker analysis of leukemic cells in 4-5 and 4-5-6 that developed ALL and MPD, respectively. Open histograms are for a negative control and marker staining is indicated by closed histograms. Lymphoblasts in the thymus of 4-5 expressed Thy1.2 at a high intensity (left), whereas proliferating granulocytes in the peripheral blood of 4-5-6 are positive for Gr-1 (right).