CCR9 and acute lymphoblastic leukemia: It could thus be speculated that PTEN suppression together with NOTCH1 activation (frequently observed in human T-ALL) could cooperate to enhance migration to specific anatomical sites such as the intestine (through the increased expression of selected chemokine receptors such as CCR9) and confer a proliferative advantage in an otherwise non-supportive microenvironment (CCL25-expressing sites).