Regrowth of granulocyte-macrophage progenitor cells (GM-CFC) in suspension cultures of bone marrow depleted of GM-CFC with 4-hydroperoxycyclophosphamide (4-HC)

Growth regulation of hematopoietic cells. An overview

The production of mature blood cells is absolutely dependent on a small pool of pluripotent stem cells with high proliferative and self-renewal capacities. The hematopoietic stem cells develop gradually from pluripotent to unipotent, committed progenitor cells during which process they lose their self-renewal capacity. This development is dependent on interactions with specific hematopoietic growth factors, which by binding to surface receptors on the stem cells stimulate them to proceed to the next step of differentiation. During recent years several of the hematopoietic growth factors have been purified to homogeneity, their primary protein as well as genetic structures have been determined and today they are available for clinical trials as recombinant proteins produced in bacteria, yeast or mammalian cells. Our present knowledge sustains the notion that IL-3, and to a lesser extent GM-CSF, play a major role in multipotent hematopoietic stem cell survival, proliferation and differentiation into stem cells with restricted maturation programs. The programmed unipotent stem cells need stimulation by erythropoietin, G-CSF, M-CSF and IL-5 to proliferate and mature into their end stage products erythrocytes, neutrophils, monocytes and eosinophils respectively. Other cytokines such as IL-1, IL-4 and IL-6 fulfil important functions as cofactors in these processes and several others play the part of tentative physiological inhibitors. During the past decade major progress has been made in our understanding of the complex interplay between stem cells, accessory cells, growth factors, and their receptors, and the clinical trials now undertaken will certainly bring even more basic knowledge to the field of hematopoietic growth regulation.

Cell-mediated inhibition of granulopoiesis in vitro in patients with acute myeloid leukemia in remission

We investigated the in vitro granulopoiesis in 11 patients with acute myeloid leukemia (AML) in complete remission 3-80 months after diagnosis (median 8.5 months). 3 of the patients had subnormal levels of bone marrow-derived CFU-GM. 6 of 10 patients tested had defective recloning capacity of d-7 CFU-GM, suggesting a stem cell defect. Most patients (7/11) showed an increased colony growth of bone marrow-derived CFU-GM after T-cell depletion by E-rosetting, while readdition of isolated autologous T cells to T-cell depleted marrow caused a dose-dependent inhibition of colony formation; bone marrow T cells were more effective in this inhibition than peripheral blood T cells. Experiments using cells depleted of either CD4- or CD8-positive cells and CD4/CD8-enriched cell populations showed that both CD4- and CD8-positive cells had the capacity to inhibit colony growth. Long-term culture of bone marrow cells in suspension showed that the production of CFU-GM declined at about the same rate as in normal controls. Our findings suggest that there are persisting stem cell defects in patients with AML in remission and that the cell growth regulatory systems may be altered. These abnormalities could possibly be an effect of residual damage to the hematopoietic system caused by intensive chemotherapy.