Furthermore, the dependence of JAK2 mutations on human TSLPR activation suggests that conventional patient-derived xenograft (PDX) models of CRLF2r/JAK2-mutant ALL are not suitable to assess the efficacy of JAK2 inhibition (Francis et al., 2016; Steeghs et al., 2017; Kim et al., 2018). Here, JAK2 is linked to acute lymphoblastic leukemia.