FLT-1 neutralization increases leukemia apoptosis within the BM. Results show the percentage of TUNEL-positive leukemia cells (of a total of 200 cells counted/BM area). Note the increase in TUNEL-positive cells in the BM of mice treated with the neutralizing Ab to FLT-1 (in the diaphysis and the epiphysis). Results shown are representative of 3 independent determinations/experiments.