C-KIT LIGAND COMBINED WITH GM-CSF AND OR IL-3 CAN EXPAND CD34+ HEMATOPOIETIC PROGENITOR SUBSETS FOR SEVERAL WEEKS IN-VITRO

It might be possible to facilitate engraftment after transplantation of purified hematopoietic progenitor cells if the cells are stimulated ex vivo prior to transplantation. The aim of this study was to analyze the potential of c-kit ligand (CKL) combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) and/or interleukin-3 (IL-3) to induce proliferation and differentiation of human bone marrow CD34+ cells in vitro. Particular attention was paid to the ability to expand populations that could maintain progenitor characteristics, i.e. CD34 expression and generation of colony forming cells (CFC), for a considerable period of time. Purified CD34+ cells were cultured in liquid medium for 42 days interrupted by immunophenotyping and CFC assays. In the presence of CKL combined with GM-CSF and/or IL-3, the total number of cells expressing CD34 increased significantly for several weeks after an initial decline. Further, CFC were continually recovered in these cultures. Based on the kinetics and the flow cytometry analysis, the expanding populations that continued to express CD34 probably originated from noncommitted, immature CD34+ cell subsets. CKL combined with GM-CSF and/or IL-3 also induced strong cell proliferation. The majority of the proliferating cells lost CD34 expression and acquired a series of mature myeloid cell surface markers associated with the monocytic, granulocytic and megakaryocytic lineages. These cells probably originated from committed CD34+ cell subsets. We conclude that CKL combined with GM-CSF and/or IL-3 can stimulate noncommitted, immature as well as committed CD34+ cell populations to expand and to differentiate. This property might be useful in a short-term ex vivo pretransplant stimulation of CD34+ cells in an attempt to facilitate rapid and stable engraftment after stem cell transplantation.