Self-renewal, maturation, and differentiation of the rat myelomonocytic hematopoietic stem cell

Hematopoiesis is viewed as a differentiating system emanating from a plurip otent hematopoietic stem cell capable of both self-renewal and differentiat ion. By identifying and characterizing a novel and highly specific in vitro mitogenic response to the N-acetyl glucosamyl/sialic acid specific, stem c eh-binding lectin wheat perm agglutinin (WGA), we demonstrate the existance of a rare (0.1%), plastic adherent precursor in rat bone marrow capable of proliferation (two to seven divisions) in response to WGA. Stimulated cell s possess a lineage (lin)(low/-) immunophenotype and immature blastoid morp hology (WGA blasts). A subsequent proliferative response-to stem cell facto r (SCF), the ligand for the proto-oncogene receptor tyrosine kinase c-kit, is characterized by an initial maturation in immunophenotype and subsequent self-renewal of cells (SCF blasts) without differentiation for at least 50 generations. Although granulocyte colony-stimulating factor (G-CSF), inter leukin (IL) -6, IL-7, and IL-11 synergize with SCF to increase blast colony formation, cytokines such as granulocyte-macrophage CSF or IL-3 are withou t significant effect. At all time points in culture, however, cells rapidly differentiate to mature neutrophils with dexamethasone or to mainly monocy tes/macrophages in the presence of 1 alpha,25-dihydroxyvitamin D-3, charact erized by cell morphology and cytochemistry. Removal of SCF during blast ma turation, self-renewal, or induction of differentiation phases results in a poptotic cell. death. Data indicate a pivotal role for SCF/c-kit interactio n during antigenic maturation, self-renewal, and apoptotic protection of th ese lineage-restricted progenitors during non-CSF-mediated induction of dif ferentiation. This approach provides a source of many normal, proliferating myelomonocytic precursor cells, and introduces possible clinical applicati ons of ex vivo expanded myeloid stem cells.