Furthermore, treating the Pten-null T-ALL model with PI3K inhibitors is effective only before the onset of leukemia, not after leukemia is already underway (Guo et al., 2011; Schubbert et al., 2014), suggesting that this driver mutation is not responsible for the maintenance of LSC ‘stemness’ once it has been generated. Here, PTEN is linked to acute lymphoblastic leukemia.