In the mouse thymus, HES1 acts downstream of Notch signalling to repress Pten activity during T-cell differentiation (Wong et al. 2012), and the resistance of T-cell acute lymphoblastic leukemia cells to Notch inhibition depends on functional HES1 binding sites in the Pten promoter (Palomero et al. 2007). Here, PTEN is linked to T-cell acute lymphoblastic leukemia.