Serum-free culture of enriched murine haemopoietic stem cells. II: Effects of growth factors and haemin on development

Murine long-term repopulating ability is compromised by ex vivo culture in serum-free medium despite preservation of committed progenitors

Hematopoietic progenitor cells can be maintained and expanded ex vivo in standard or serum-free culture medium supplemented with a variety of stimulatory cytokines. The use of serum-free medium allows specification of reproducible and precise growth conditions optimal for various applications and is more acceptable from a safety and regulatory point of view. Human and murine committed progenitor cells have been shown to be equivalently ro better supported by serum-free culture conditions in the presence of multicytokine combinations, but there is little information on the effects of such culture conditions on repopulating stem cells. We used a murine competitive repopulation model to assess the effect of serum-free versus serum-containing ex vivo culture on long-term reconstituting cells. Despite equivalent numbers of committed CFU-C and day 12 CFU-S present after 4 days of culture of murine marrow in serum-free or serum-containing conditions in the presence of IL-3, IL-6, and SCF, long-term reconstituting activity was significantly impaired by serum-free culture. These findings may have important implications for transplantation and gene therapy applications.

Anemia and perinatal death result from loss of the murine ecotropic retrovirus receptor mCAT-1

The mCAT-1 gene encodes a basic amino acid transporter that also acts as the receptor for murine ecotropic leukemia viruses. Targeted mutagenesis in embryonic stem cells has been used to introduce a germ-line null mutation into this gene. This mutation removes a domain critical for virus binding and inactivates amino acid transport activity. Homozygous mutant pups generated from these cells were approximately 25% smaller than normal littermates, very anemic, and died on the day of birth. Peripheral blood from homozygotes contained 50% fewer red blood cells, reduced hemoglobin levels, and showed a pronounced normoblastosis. Histological analyses of bone marrow, spleen, and liver showed a decrease in both erythroid progenitors and mature red blood cells. Mutant fetal liver cells behaved normally in in vitro hematopoietic colony-forming assays but generated an anemia when transplanted into irradiated C.B.-17 SCID mice. Furthermore, reconstitution of the white cell compartment of SCID mice by mutant fetal liver cells was less complete than that observed with a mixed population of wild-type and heterozygous fetal liver cells. Primary embryo fibroblasts from mutant mice were completely resistant to ecotropic retrovirus infection. Thus, mCAT-1 not only appears to be the sole receptor for a group of murine ecotropic retroviruses associated with hematological disease but also plays a critical role in both hematopoiesis and growth control during mouse development.

Erythroid development of the FDCP-Mix A4 multipotent cell line is governed by the relative concentrations of erythropoietin and interleukin 3

Conditions are described which promote the erythroid development of the FDCP-Mix A4 (A4) cell line with accompanying proliferation of the cells. The requirements for this development are low concentrations of interleukin 3 (IL-3) plus the presence of erythropoietin (epo) and haemin. When high concentrations of IL-3 are added with erythropoietin and haemin the cells do not differentiate and maintain their blast cell morphology. Addition of haemin, in the absence of erythropoietin, does not promote erythroid development, but the presence of haemin with erythropoietin promotes increased proliferation and maturation. The morphological maturation of A4 cells along the erythroid lineage is accompanied by a gradual loss of clonogenic potential, loss of A4 cell multipotency, increased erythropoietin receptor expression, and an increased expression of the beta-globin gene. An initial increase in mitogenic responsiveness to erythropoietin is followed by a decrease as the cells become refractory to all mitogenic stimuli with the acquisition of a postmitotic, mature erythroid cell phenotype.

The cellular basis for enhancement interactions between stem cell factor and the colony stimulating factors

In cultures of normal mouse fetal liver cells, combination of stem cell factor (SCF) with erythropoietin enhanced erythroid colony formation and, in bone marrow cultures, combination of SCF with interleukin 6 (IL-6) enhanced megakaryocyte colony formation. Combination in marrow cultures of SCF and granulocyte colony stimulating factor (G-CSF) increased cell numbers more than tenfold in developing granulocytic and blast cell colonies. Combination with G-CSF enhanced progenitor cell numbers five-fold in developing blast colonies, but a majority of these were committed macrophage progenitor cells not able to proliferate further with SCF plus G-CSF. Similarly, many of the granulocyte progenitor cells could not proliferate further with this combination of stimuli. This process of amplified but abortive formation of progenitor cells was also noted with use of the combination of SCF plus IL-6 but not with combination of SCF with granulocyte-macrophage CSF (GM-CSF) or Multi-CSF (IL-3). Analysis indicated that where colony size was amplified by combination of a factor with SCF, quantitatively the more important process was amplification of progenitor cell formation rather than amplification of the number of progeny formed by individual committed progenitor cells.