Transfusion-dependent beta-thalassemia: in vitro characterization of peripheral blood multipotential and committed progenitor cells.

Conditions for the in vitro culture of multipotential and committed progenitor cells obtained from the peripheral blood of transfusion-dependent beta-thalassemic individuals have been determined. When stimulated by either human placental-conditioned medium (HPCM), phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM), or U5637-conditioned medium and erythropoietin, colonies containing neutrophils, neutrophils and macrophages, macrophages, eosinophils, erythroid cells, or mixtures of erythroid cells and neutrophils, eosinophils, or macrophages were obtained in cultures of beta-thalassemic mononuclear cells. Removal of adherent cells from beta-thalassemic peripheral blood demonstrated the presence of cells capable of the autostimulation of all of the above colony types in the presence of erythropoietin. In addition, adherent cells also appeared to inhibit erythropoiesis in cultures stimulated with HPCM. In cultures of nonadherent beta-thalassemic mononuclear cells, one population of BFU-E was stimulated by erythropoietin and a second required both erythropoietin and HPCM. Titration of erythropoietin, in the presence of optimal stimulation by HPCM, showed that beta-thalassemic peripheral blood BFU-E were more responsive to erythropoietin than was normal peripheral blood BFU-E. Stimulation of multipotential cells in cultures of nonadherent mononuclear cells was dependent upon HPCM. Using these culture conditions, the studies show that, compared with normals, the peripheral blood of transfusion-dependent beta-thalassemic patients contain elevated numbers of multipotential and committed progenitor cells, and that splenectomy did not account for the elevated numbers of these cells.