CRLF2r/JAK2-mutant PDX models engineered by Francis et al. (2016) to produce human TSLP may prove to be more clinically relevant models, enabling the in vivo efficacy of JAK2 inhibition for CRLF2r/JAK2-mutant ALL to be determined (Francis et al., 2016). Here, TSLP is linked to acute lymphoblastic leukemia.