CSF2 and juvenile myelomonocytic leukemia: We recently demonstrated that the hypersensitivity of JMML cells harboring the most prevalent JMML-causing Cbl mutation, Y371H, to GM-CSF is due to the defective E3 ligase function of mutant Cbl(Y371H) towards Src family kinases that in turn hyper-phosphorylate and activate GMR to promote GMR hypersensitivity [5].