CD34+ progenitor cells in idiopathic (primary) myelofibrosis: a comparative quantification between spleen and bone marrow tissue.

Previous studies on idiopathic (primary) myelofibrosis (IMF) are in keeping with the finding of an increased number of circulating CD34+ progenitor cells. However, dependent on the fibrosclerotic changes, little knowledge exists about quantitative relationships of this precursor cell population in spleen and bone marrow. The purpose of this study was to determine the number of CD34+ cells at these sites by applying immunohistochemistry and morphometry. In seven patients with IMF and a control group without hematopathology (14 patients), CD34+ progenitors were identified in the red pulp of the spleen and also in bone marrow trephine biopsies by the monoclonal antibody QBEND10. Histological analysis showed no differences regarding size or cytological details of these cells at both sites in patients with IMF as well as in the controls. On the other hand, in the IMF group there was an unequal distribution with an approximate twofold increase in precursor cells in the spleen compared to the bone marrow. This result is opposed to corresponding values of the control group. Considering the quantity of progenitor cells in the normal bone marrow, no significant increase was revealed in IMF, but a marked pooling (more than fourfold of the normal value) in the spleen. In conclusion, our findings are in keeping with a increased number of splenic CD34+ progenitor cells and therefore support the hypothesis of a pronounced filtration and trapping of this precursor cell population by the spleen in IMF.