In vitro expansion of CD34⁺ CD38^- cells under stimulation with hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia

Using serum-containing culture, we examined whether AGM-S3 stromal cells, alone or in combination with hematopoietic growth factor(s), stimulated the proliferation of CD34⁺ cells from patients with juvenile myelomonocytic leukemia (JMML). AGM-S3 cells in concert with stem cell factor plus thrombopoietin increased the numbers of peripheral blood CD34⁺ cells to approximately 20-fold of the input value after 2 weeks in nine JMML patients with either PTPN11 mutations or RAS mutations, who received allogeneic hematopoietic transplantation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) also augmented the proliferation of JMML CD34⁺ cells on AGM-S3 cells. The expansion potential of CD34⁺ cells was markedly low in four patients who achieved spontaneous hematological improvement. A large proportion of day-14-cultured CD34⁺ cells were negative for CD38 and cryopreservable. Cultured JMML CD34⁺CD38^- cells expressed CD117, CD116, c-mpl, CD123, CD90, but not CXCR4, and formed GM and erythroid colonies. Day-7-cultured CD34⁺ cells from two of three JMML patients injected intrafemorally into immunodeficient mice stimulated with human GM-CSF after transplantation displayed significant hematopoietic reconstitution. The abilities of OP9 cells and MS-5 cells were one-third and one-tenth, respectively, of the value obtained with AGM-S3 cells. Our culture system may provide a useful tool for elucidating leukemogenesis and for therapeutic approaches in JMML.