Human TSLPR cannot be activated by mouse TSLP (Van Bodegom et al., 2012; Francis et al., 2016) yet despite this dependence, patient-derived xenograft (PDX) models of CRLF2r/JAK2-mutant ALL cells have been generated in NSG mice (Maude et al., 2012; Suryani et al., 2015; Tasian SK. Here, CRLF2 is linked to acute lymphoblastic leukemia.