CCR9 and acute lymphoblastic leukemia: The described therapeutic tools that specifically target human CCR9+-tumors and have been tried in xenogeneic models are limited to the use of the CCR9-ligand coupled to a cytotoxic agent (CCL25-PE38 fusion protein) (33), the use of ligand-specific antibodies, alone or in combination with etoposide (25), or the mAb 91R that selectively inhibited growth of a human acute T lymphoblastic leukemia (T-ALL) cell line in Rag2−/− xenografts (34).