Differences among myeloproliferative disorders in the behavior of their restricted progenitor cells in culture

We have studied the behavior in culture of circulating restricted hemopoietic progenitor cells from patients with idiopathic myelofibrosis (IMF), polycythemia vera (PV), and essential thrombocytopenia (ET). We have found differences in circulating granulocyte-macrophage, erythroid, and megakaryocytic progenitors that appear to be specific for these chronic myeloproliferative disorders. In IMF, most affected were granulocyte-macrophage progenitor cells (CFU-C), which circulated in increased numbers and were heterogeneous in their sensitivity to the regulatory factor(s) present in phytohemagglutinin (PHA) stimulated T-lymphocyte conditioned medium (CM). Most CFU-C were either highly sensitive to, or independent from, stimulatory factors, while others showed normal sensitivity. In some IMF patients, circulating megakaryocytic progenitors (CFU-M) were present that were capable of giving rise to colonies in the absence of added CM or erythropoietin (EPO). In PV, we confirmed the presence of circulating erythroid progenitor cells that give rise to colonies in culture without the addition of EPO. The number of circulating CFU-C was normal and they responded normally to CM. In ET, failure to detect 7-day circulating restricted progenitor cells was a common observation; the level of other circulating restricted progenitors was in the low normal range. Thus, despite certain common features, including a primary lesion at the level of the pluripotential hemopoietic stem cell, the myeloproliferative disorders differ with respect to the behavior in culture of their circulating restricted progenitor cells. These results have led us to postulate a second regulatory lesion in the pluripotential stem cell that differs in these disorders and is expressed at the level of the respective restricted progenitor cells.