No abstract

No abstract

Characteristics of murine megakaryocytic colonies and their progenitor cells (CFU-m) were studied in vitro in agar gel. Colony growth required the presence of poke-weed-mitogen-stimulated spleen-conditioned medium. The number of colonies formed was linearly related to both the number of marrow cells plated and the amount of conditioned medium added. In addition, CFU-m were found in both the spleen and peripheral blood. Conditioned medium was also made without plasma, and this resulted in a cloning efficiency greater than that of conditioned medium prepared with plasma. The percentage of CFU-m in DNA synthesis was low (10%), as determined both in vivo and in vitro. Velocity sedimentation revealed that the majority of CFU-m sedimented at 4.3 mm/hr and had a tritiated thymidine (3H-TdR) suicide rate of 1.5 +/- 1.5%. A shoulder on the profile of CFU-m sedimented at approximately 6 mm/hr, with a suicide rate of 79 +/- 2%. Analysis of these data indicated that the majority of CFU-m were not in cycle or were in a long G1 period. The results suggest that CFU-m is a primitive progenitor, possibly closely related to murine splenic colony-forming units (CFU-s), analogous to erythroid bursts and granulocytic colony-forming units.

Human cord blood was used as a source of progenitor and stem cells to evaluate the effect of recombinant human stem-cell factor (SCF) on colony formation and the generation of colony-forming cells (CFC) under highly defined, serum-deprived conditions. SCF interacted with a number of hematopoietic growth factors to stimulate colony growth and was particularly effective in stimulating the formation of mixed-cell colonies from CD34+ soybean agglutinin negative (SBA-) cells. In suspension culture of CD34+, SBA- cells, SCF alone was unable to maintain cell numbers or CFC but, in combination with interleukin-3 (IL- 3), increased input numbers of cells by 10-fold and increased CFC of all kinds by nearly 20-fold. This included erythroid burst-forming cells (BFU-E), granulocyte/macrophage (GM) CFC, and mixed-cell CFC. In contrast, CD34- SBA- cells neither gave rise to CFC nor were maintained by combinations of growth factors including SCF. SCF interacted with erythropoietin (Epo) and granulocyte colony-stimulating factor (G-CSF) to maintain large numbers of cells as well as to generate a twofold to threefold increase in CFC in the case of Epo, and a 10-fold increase in CFC in the case of G-CSF. With Epo, the predominant CFC generated were BFU-E and erythroid CFC and many of the cells in suspension were erythroblasts. In contrast, SCF plus G-CSF resulted in large numbers of granulocytes at various stages of maturation and the CFC generated were almost exclusively granulocytic-CFC. IL-1 and IL-6, alone or in combination with SCF, showed little or no ability to increase cell numbers or generate CFC. In summary, SCF interacts with a variety of hematopoietic growth factors to promote colony formation, particularly mixed-cell colony formation, and also, in suspension culture, SCF interacts with IL-3, G-CSF, and Epo to generate large numbers of differentiated cells as well as a variety of CFC for up to 1 month.

Four patients with acute nonlymphocytic leukemia who were heterozygous for the X-chromosome-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) were studied to determine the numbers and types of progenitor cells in which the disease arose. Both forms of enzyme were found in normal tissues, but the malignant blast cells showed only one G6PD, indicating that the disease was clonal at the time of testing. The observations that normal erythroid cells were present in two young patients at diagnosis and relapse indicate that the clone suppressed expression of normal granulopoiesis but did not prevent normal erythroid differentiation. In contrast to this situation, in two elderly patients, the disease involved stem cells multipotent for granulocytes, red cells, and platelets. These results indicate that acute nonlymphocytic leukemia is heterogeneous. In some patients, the disease is expressed in cells with differentiation restricted to the granulocyte-monocyte pathway; in others, it involves stem cells capable of differentiating to granulocytes-monocytes, platelets, and erythrocytes. This heterogeneity may reflect differences in causation and could have prognostic and therapeutic importance.