Very recently, a high throughput screen of the effects of 313 human cytokines on the growth of CD34+CD38– cells isolated from CML patients has confirmed the previously reported regulatory effects of IL-3, IL-1a/b, GM-CSF and IFNg but has also identified myostatin propeptide (MSTNpp; produced by muscle cells and secreted into the bloodstream where it binds and regulates the myokine myostatin) as a novel positive regulator [117]. This evidence concerns the gene MSTN and chronic myelogenous leukemia, BCR-ABL1 positive.