Characteristics of circulating megakaryocyte progenitors (CFU-MK) in patients with primary myelofibrosis.

Characteristics of circulating CFU-MK and the effect of serum and plasma on CFU-MK growth were studied in 14 patients with primary myelofibrosis (MF) using short- and long-term culture methods. The number of CFU-MK in short-term cultures was significantly increased in the non-splenectomized patient group (p less than 0.01). Without added PHA-LCM and normal serum, spontaneous colony formation was found in 9 out of 10 patients. In long-term blood cultures from 6 MF patients, 3 untreated patients formed confluent adherent layers and produced in suspension an equal number or an even greater number of nucleated cells, megakaryocytes and CFU-MK than those obtained in long-term bone marrow culture from normal individuals. 2 splenectomized patients showed neither an increased numbers of CFU-MK nor the capacity to develop an adherent layer. The serum and plasma of MF patients failed to stimulate megakaryocyte colony formation by normal bone marrow in a normal fashion. These findings indicate a megakaryocytopoietic abnormality, and a central role of the spleen in extramedullary haematopoiesis in MF.