JAK2
abnormalities may serve as target for precision medicines in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In the current study we performed a screening forJAK2mutations and translocations, analyzed the clinical outcome and studied the efficacy of two JAK inhibitors in primary BCP-ALL cells. Importantly, we identify a number of limitations of JAK inhibitor therapy.JAK2mutations mainly occurred in the poor prognostic subtypesBCR-ABL1-like and non-BCR-ABL1-like B-other (negative for sentinel cytogenetic lesions).JAK2translocations were restricted toBCR-ABL1-like cases. Momelotinib and ruxolitinib were cytotoxic in bothJAK2translocated andJAK2mutated cells, although efficacy inJAK2mutated cells highly depended on cytokine receptor activation by TSLP. However, our data also suggest that the effect of JAK inhibition may be compromised by mutations in alternative survival pathways and microenvironment-induced resistance. Furthermore, inhibitors induced accumulation of phosphorylated JAK2Y1007, which resulted in a profound re-activation of JAK2 signaling upon release of the inhibitors. This preclinical evidence implies that further optimization and evaluation of JAK inhibitor treatment is necessary prior to its clinical integration in pediatric BCP-ALL.
