PTEN and acute lymphoblastic leukemia: One good example is the Pten-null T-ALL model that we have generated by the conditional deletion of the Pten tumor suppressor gene in fetal liver hematopoietic stem cells (Guo et al., 2008). In this model, LSCs are enriched in the Lin-CD3+KITmid cell subpopulation; these cells are self-renewable and responsible for T-ALL initiation and drug resistance (Guo et al., 2008; Guo et al., 2011; Schubbert et al., 2014).