Blood and spleen haematopoiesis in patients with myelofibrosis.

Blood nucleated cells collected by leukapheresis and spleen cell suspension from patients with myelofibrosis with myeloid metaplasia (MMM) were studied for their haematopoietic capacity. Using committed progenitor cell assays (CFU-GM, BFU-e) and a one-stage long-term liquid stem cell system, we have shown: (1) a preferential expansion of the circulating committed progenitor cell pool above the more primitive stem cell compartment; (2) the absence of any development of a stromal adherent layer in long-term cultures of peripheral blood nucleated cells suggesting the self-sustaining capacity of the circulating primitive stem cells; (3) that the spleen is only a production site of committed progenitor cells but does not generate primitive stem cells; (4) the presence, in the spleen, of stromal progenitor cells. We conclude that the peripheral blood primitive stem cells in patients with MMM are not of splenic origin.