Together, these results show that the quiescent CD44high cells described in human T-ALL PDX models are also detected in T-ALL patient samples, these cells have a specific gene signature, and CD44 expression levels are enriched in Immature T-ALL subgroups that are associated with a poor prognosis, maybe in relation with an immaturity/progenitor cell state. This evidence concerns the gene CD44 and acute lymphoblastic leukemia.