CSF2 and chronic myelogenous leukemia, BCR-ABL1 positive: Consistent with our previous findings [10], Ser585 phosphorylation of the GM-CSF/IL-3 βc receptor was constitutive in primary AML blasts (Figure 1C) and K562 CML cells (Figure 1D) and was not affected by tyrosine kinase inhibitors (TKIs).