For example, in human PV, BFU-E heterozygous for JAK2V617F were responsive in vitro to erythropoietin in a manner similar to normal BFU-E [60] and HPC hematopoietic growth factor-responsiveness was also observed in vitro with MPL [38] and CALR [4,31] mutations. Here, MPL is linked to acquired polycythemia vera.