Self-renewal of factor-dependent hemopoietic progenitor cell-lines derived from long-term bone marrow cultures demonstrates significant mouse strain genotypic variation

Increased longevity of hematopoiesis in continuous bone marrow cultures and adipocytogenesis in marrow stromal cells derived from Smad3(-/-) mice

OBJECTIVE

To determine the role of Smad3 in modulating hematopoiesis, continuous bone marrow cultures were established from Smad-/- mice, and the longevity of hematopoiesis and extent of adipogenesis in the supportive hematopoietic microenvironment were compared to those from cultures of control, Smad3+/+ or heterozygous Smad3+/- mice.

MATERIALS AND METHODS

Long-term bone marrow cultures (LTBMCs) were established from Smad3+/+, Smad3+/-, or Smad3-/- mice. On a weekly basis, the number of cobblestone islands, number of nonadherent cells, confluence of the adherent cells, or CFU-GEMM colonies was determined. Bone marrow stromal cell lines were established and cobblestone island production on these cell lines determined in the presence of nonadherent cells from week-42 Smad3-/- or week-4 C57BL/6J LTBMCs.

RESULTS

Initial proliferative capacity of the LTBMCs was similar in all groups through week 20, at which time there was an increase in cobblestone islands and production of nonadherent cells and CFU-GEMM colonies in the Smad3-/- group. By week 28, only the Smad3-/- LTBMCs had significantly maintained increased production of these parameters. Maintenance of cobblestone islands indicative of the most primitive hematopoietic progenitor cells persisted past 45 weeks in Smad3-/- cultures. The Smad3-/- stromal cell line also demonstrated increased support of cobblestone island production when incubated with nonadherent cells from week-42 Smad3-/- or week-4 C57BL/6J LTBMCs. Evaluation of adipocytogenesis in stromal cells showed significantly greater accumulation of adipocytes in lines from Smad3-/- than from Smad3+/+ mice.

CONCLUSIONS

These data provide evidence for a significant effect of deletion of the Smad3 signaling pathway in increased hematopoiesis in LTBMCs and support the negative regulatory influence of TGFbeta signaling on adipocytogenesis and long-term hematopoiesis in vitro.

Metabolically inactive 3T3 cells can substitute for marrow stromal cells to promote the proliferation and development of multipotent haemopoietic stem cells

When highly enriched multipotential spleen colony forming cells (CFU-S) obtained following fluorescence activated cell sorting (FACS-CFU-S) are cultured on marrow stromal cells, they undergo proliferation and development to produce mature haemopoietic cells (Spooncer et al., Nature, 316:62-64, 1985). We now show that FACS-CFU-S behave in a similar way when cultured on monolayers of 3T3 cells, indicating that the 3T3 cells can supply at least part of the environment which is representative of marrow stromal cells and provide, therefore, a system for studying stromal cell: haemopoietic cell interactions. We also demonstrate that IL-3-dependent multipotential stem cell lines (FDCP-Mix), but not a variety of other "committed" IL-3-dependent cell lines, resemble FACS-CFU-S in terms of their ability to proliferate and differentiate when cultured on 3T3 cells in the absence of IL-3. In this system, attachment of the FDCP-Mix to the 3T3 cells is critical for the subsequent maintenance of viability and stimulation of development of the cells. When the FDCP-Mix cells are physically separated from the 3T3 cells, they die and their death cannot be prevented by using 3T3-cell-conditioned medium. The extracellular matrix generated by 3T3 cells is not sufficient for promoting attachment or viability of the FDCP-Mix cells, indicating the importance of integral membrane components. However, attachment and development of FDCP-Mix cells occurs on 3T3 cells that have been lightly fixed with glutaraldehyde indicating that active metabolism is not essential for the effects promoted by the 3T3 cells. We suggest that the ability of FACS-CFU-S and FDCP-Mix cells to respond to 3T3 cells involves specific ligand/receptor interactions.

Self-renewal and differentiation of interleukin-3-dependent multipotent stem cells are modulated by stromal cells and serum factors

Interleukin-3 (IL-3)-dependent cell lines (FDCP-mix) were cloned and isolated from long-term bone-marrow cultures infected with src-MoMuLV. These cell lines have many of the characteristics of hematopoietic stem cells. Early isolates of the FDCP-mix cells form spleen colonies in irradiated mice and establish long-term hematopoiesis on irradiated marrow stroma in vitro in the absence of IL-3. These two properties of the cells are lost within 15 weeks of establishing the cell lines, but the cell lines retain their ability to differentiate in a multilineage response to hematopoietic growth factors and to hematopoietic stromal cells, as well as to self-renew in the presence of IL-3. The choice between differentiation and self-renewal in FDCP-mix cells can clearly be modified by culture conditions: in particular, cultures containing horse serum preferentially promote self-renewal, whereas cultures containing fetal calf serum preferentially promote differentiation. The FDCP-mix cell lines are not leukemic, nor do they contain the src oncogene. Their ability to respond to hematopoietic growth factors and stroma in a similar manner to normal hematopoietic cells makes them a valuable model for studying the regulation of hemopoietic cell self-renewal and differentiation.

Multipotential hemopoietic cell lines isolated from stem cell cultures infected with Friend virus complex (MuLV + F-SFFV) show presence of MuLV but not F-SFFV

The only factor-dependent or factor-independent hemopoietic murine stem cell lines which can be permanently maintained in vitro are cell lines which originate from bone marrow cultures of congenic mice differing in the Fv-2 locus infected with Friend spleen focus forming virus (F-SFFV) in conjunction with either Rauscher or Friend helper virus (R-MuLV or F-MuLV). We determined the viral state of these cells by restriction enzyme analysis, measurement of SFFV and MuLV related RNA, immunoprecipitation analysis of viral related proteins and biological activity to test whether integration and expression of R-MuLV or F-SFFV are obligatory. All stem cell lines (SUT, JUT, 416B) showed expression of MuLV coded proteins or virus but SFFV was not found in these cell lines. A two-fold difference of RNA hybridizing with SFFV-specific cDNAs observed in stem cells of Fv-2rr and of Fv-2ss genotype is in agreement with data published earlier.

A self-renewing, bipotential erythroid/mast cell progenitor in continuous cultures of normal murine bone marrow

We have established permanent lines of nonadherent cells from fresh normal mouse bone marrow in media containing pokeweed mitogen-stimulated spleen cell conditioned medium (PWSCM). These lines continuously produced erythropoietic progenitor cells (detected by their ability to form erythroid bursts in semi-solid medium containing erythropoietin) together with cells having characteristics of the mast cell lineage (as demonstrated by metachromatic staining with toluidine blue, histamine content and membrane receptors for IgE). Sixteen such cell lines have been established in sixteen attempts. Cloning experiments were carried out to determine the nature of the progenitor cell(s) responsible for the permanence of these cultures. When cells were cultured in methylcellulose medium containing PWSCM, colonies were observed which reached macroscopic size after 4 weeks of incubation. Replating of individual primary colonies resulted in secondary colony formation, indicating the presence of progenitor cells with self-renewal potential. Forty-seven primary colonies were picked and their cells were suspended in liquid culture medium containing PWSCM. Of these, twenty-one could be expanded to establish permanently growing sublines. Sixteen of these sublines were found to be composed of both erythroid progenitors and mast cells. In five sublines only mast cells could be seen; none of the sublines appeared to be purely erythroid. Karyotypic analysis of mast cells and of erythroid cells of seven sublines derived from individual colonies which arose in cocultures of male and female cells revealed that the mast cells and erythroid cells were both of the same sex in each of the seven sublines; this demonstrates the single cell origin of each colony and of the two lineages derived from it. We conclude that these nonadherent, factor-dependent cell lines are maintained by self-renewal and differentiation of bipotential progenitor cells apparently restricted to the erythroid and mast cell lineages.

Established leukemia cell lines: their role in the understanding and control of leukemia proliferation

For investigation of mechanisms of leukemogenesis and control of proliferation of leukemia cells, various preleukemic hematopoietic progenitor cell lines and leukemia cell lines have been established. The role of these established cell lines in understanding leukemogenesis and control of leukemia cell proliferation is described. The results of studies on biological characteristics of numerous human leukemia-lymphoma cell lines suggest that the heterogeneity in various markers of the cell lines reflects different patterns of normal hematopoietic cell differentiation. Then, recent studies on the control of proliferation of leukemia cells by induction of terminal differentiation with the use of established leukemia cell lines both in vitro and in vivo are described. Therapeutic significance of the results obtained with these leukemia cell lines is also discussed.

Role of a single haemopoietic growth factor in multiple proliferative disorders of haemopoietic and related cells

Activated T cells secrete a glycoprotein (P-cell-stimulating factor; PSF) that stimulates the proliferation of many types of haemopoietic progenitor cells and the pluripotential haemopoietic stem cells. Based on experiments in mice, it is proposed that some proliferative disorders of the pluripotential haemopoietic stem cell or its progeny may result from the abnormal production and secretion of PSF by these cells themselves. The secreted PSF binding to specific receptors on the surface of these cells causes autostimulation and uncontrolled proliferation. Acute non-lymphocytic leukaemias and the late stages of Hodgkin's disease might be due to such autostimulation. More chronic proliferative diseases (eg, chronic myeloid leukaemia and the early stages of Hodgkin's disease) may involve the expansion of an abnormal, immortalised, clone of pluripotential haemopoietic stem cells or committed haemopoietic progenitor cells that are not autonomous but remain strictly dependent for their proliferation and survival on the presence of exogenous PSF.

Continuous in vitro generation of multipotential stem cell clones from src-infected cultures

A molecular recombinant of Rous sarcoma virus and murine amphotropic leukaemia virus, src(MoMuLV), where the avian src oncogene has been placed under the influence of a murine virus promoter sequence, has been reported. Infection of long-term marrow cultures with this virus led to a dramatic change in the relative numbers of stem cells, granulocyte-macrophage progenitor cells and mature cells found in normal haematopoietic cell development. However, although the balance between self-renewal, differentiation and development was disturbed, injection of the cultured cells into irradiated syngeneic recipients did not lead to the development of leukaemia. Thus, although the control had been 'loosened', the host regulatory mechanisms were sufficient to impose a restraint on unlimited growth of the cells. We now show that the stem cells from the src-infected cultures show a remarkably increased capacity for self-renewal in vitro in situations which are inimical to the maintenance of self-renewal in normal uninfected stem cells and that self-renewal/differentiation can be modified by the culture conditions.

Biologic properties of factor-independent nonadherent hematopoietic and adherent preadipocyte cell lines derived from continuous bone marrow culture

Cell lines dependent for growth upon an inducer T-cell synthesized glycoprotein factor interleukin-3 have been derived from continuous mouse bone marrow cultures. These factor-dependent (FD) lines have been shown to be multipotential (erythroid/basophil/neutrophil) or (eosinophil/basophil/neutrophil); or are unipotent basophil or neutrophil granulocyte cell lines. Both classes of cloned FD lines have maintained self-renewal in vitro for several years with absolute growth dependence on freshly added IL-3. In four instances, factor-independent (FI) variant cell lines were derived, one by subculture in medium containing hydrocortisone and 25% horse serum and three by evolution of variants from cloned FD lines. One class of (FI) lines demonstrated adherent fibroblast-like morphology with differentiation to differentiated adipocytes in medium containing 10(-5) hydrocortisone. A second class of cell lines evolved from cloned FD lines and each grew in suspension culture to a saturation density over 10-fold greater than that for the parent FD line (greater than 10(7)/ml) and each contained no detectable hematopoietic cellular differentiation markers by histochemistry or cell surface receptors. In contrast to IL-3 dependent cell lines, (FI) cell lines failed to differentiate to mature granulocyte morphology in diffusion chambers in vivo. The FI cell lines formed no detectable CFUs in vivo, did not reconstitute hematopoiesis in irradiated mice and did not form tumors in vivo. The failure of the (FI) lines to form tumors and lack of detectable hematopoietic differentiation capacity indicates that these lines may represent an intermediate state between normally regulated hematopoietic cellular self-renewal and malignant transformation.

The regulation of growth and development of normal and leukaemic cells

Numerous significant advances have been made in recent years in understanding those factors and conditions which influence the growth and differentiation of haemopoietic cells. This communication is primarily concerned with defining lineage-independent and lineage-restricted growth factors and some of the aberrations which may be involved in leukaemia.

Studies on the in vivo production of a lymphokine activity, interleukin 3 (IL-3) elaborated by lymphocytes and a myeloid leukaemic line in vitro and the fate of IL-3 dependent cell lines

Interleukin 3 (IL-3) is produced constitutively by WEHI-3b leukaemic cells and stimulated lymphoid cell populations in vitro. We have investigated the in vivo production of IL-3 in mice rendered leukaemic with WEHI-3b cells and mice stimulated by acute graft versus host disease (GVHD). In leukaemic mice, IL-3 was not found in serum or sonicates of 18-day spleens or bone marrow, although cells from the leukaemic organs were fully competent to elaborate IL-3 in vitro. Further, elaboration of IL-3 by WEHI cells in vitro was not affected by co-culture with normal haemopoietic cells. However, intracellular IL-3 was detected in leukaemic nodules isolated from the liver. Inhibitors specific for IL-3 were not found, although liver-cell conditioned medium and leukaemic nodule sonicates contained potent non-specific inhibitors of cell growth. At 21 days, intracellular IL-3 was also present in spleens and correlated with the presence of non-specific inhibitors. In GVHD, no evidence for IL-3 elaboration in vivo was found, nor did lymphoid populations affected by GVHD spontaneously elaborate it in vitro; however, their competence to produce it was unaffected, as IL-3 was elaborated on subsequent mitogen stimulation in vitro. We also investigated the recovery and circulation of in vitro 111Indium-labelled IL-3 dependent cells after injection in vivo and the half-life of semi-purified IL-3. Dependent cells were not recovered after injection into irradiated recipients, although the cells recirculated for at least 24 hours. Inability to recover dependent cells was explicable on general cytotoxicity which masked potential recovery. The serum half-life of injected partially purified material with IL-3 activity was short (less than 30 min). We conclude that the elaboration of IL-3 by leukaemic WEHI-3b is not an in vitro artifact and these results are discussed in relationship to other growth factors and the leukaemic state, and the origin of IL-3 dependent lines.

Demonstration of permanent factor-dependent multipotential (erythroid/neutrophil/basophil) hematopoietic progenitor cell lines

Multipotential hematopoietic progenitor cell lines have been established from nonadherent cell populations removed from continuous mouse bone marrow cultures. Clonal sublines of lines B6SUtA or B6JUt derived from single cells formed mixed colonies containing erythroid cells, neutrophil-granulocytes, and basophil/mast cells in semisolid medium containing erythropoietin and conditioned medium from pokeweed mitogen-stimulated spleen cells. Each of several subclones of cell line Ro cl formed colonies containing eosinophils, neutrophil-granulocytes, and basophil/mast cells in semisolid medium. Multipotentiality was maintained in vitro for over 2 1/2 years. In contrast, cell line 32D formed basophil/mast cell colonies with no detectable differentiation to other pathways. Multipotential cell lines did not produce detectable spleen colonies (CFUs) in vivo, nor did intravenous inoculation of up to 5 X 10(7) cells protect lethally irradiated mice from bone marrow failure. Newborn and adult mice inoculated with 5 X 10(7) cells showed no detectable leukemia or solid tumors after one year. Both multipotential and committed basophil/mast cell lines demonstrated absolute dependence upon a source of a growth factor(s) found in medium conditioned by WEHI-3 cells. These cell lines should be of value in studies of the regulation of hematopoietic stem cell differentiation in vitro.

Role of stromal and hematopoietic stem cells in Friend spleen focus forming virus effects in continuous bone marrow culture

Replication of the Friend spleen focus forming virus (SFFV) in C3H/HeJ or C57BL/6J mouse continuous bone marrow cultures is associated with an increased cumulative production of pluripotential/hematopoietic stem cells (CFUs), granulocyte-macrophage progenitor cells (GM-CFUc), and total granulocytes, compared to uninfected or helper virus infected control cultures. The site(s) of action of the virus are not known. To determine whether viral effect(s) occurred in adherent stromal and/or non-adherent hematopoietic stem cells, purified cell populations, comprised exclusively of cells from each compartment, were separated from C57BL/6J (Fv-1bb) or C3H/HeJ (Fv-1nn) marrow cultures and were left uninfected or were infected with host range replication restricted B-tropic or N-tropic helper pseudotype viruses of SFFV respectively. Cell populations were then mixed to establish continuous hematopoiesis in allogeneic or syngeneic combinations. Virus host range restriction between compartments was maintained in allogeneic reconstituted cultures which showed active hematopoiesis for 16-17 weeks and no significant differences between: (1) virus infected and uninfected groups or (2) groups comprised of stromal cells from one or the other strain. Thus, these data indicate that the prolongation of hematopoiesis in undisturbed long-term marrow cultures by SFFV occurs through an interaction of adherent hematopoietic stem cells with the marrow stroma.

In vitro quantitation of lethal and physiologic effects of total body irradiation on stromal and hematopoietic stem cells in continuous bone marrow cultures from Rf mice

The role of stromal-supportive cells in hematopoietic stem cell responses to irradiation is poorly understood. The effects of in vivo total body irradiation (TBI) and interval from TBI to explant of marrow on: stromal cell proliferation in vitro; stromal cell support of hematopoiesis in continuous bone marrow culture; and generation of WEHI-3 growth factor (GF)-dependent lines of hematopoietic progenitor cells were evaluated. Continuous marrow cultures from non-irradiated control RfM/UN, C57BL/6J, C3H/HeJ, and N:NIH (Swiss) mice generated pluripotential hematopoietic stem cells (CFUs) and committed granulocyte-macrophage progenitor cells (GM-CFUc) for over 20 weeks. Explant of marrow at 2, 4, 5, or 6 months after single fraction TBI (300-800 rad) was associated with decreased longevity of hemopoiesis (2-12 weeks), and a decrease in the proliferative capacity of fibroblastic adherent-stromal colony forming cells (CFUf) as measured by colony size at 14 days and number of colonies per 10(6) cells plated. In contrast, explant of marrow 8 to 24 months after TBI produced cultures with longevity that was indistinguishable from age-matched control cultures (19-24 weeks). Marrow from irradiated first and second generation recipients of serially transferred marrow demonstrated a similar 7-month in vivo recovery period; however, the plateau maximum duration of hemopoiesis did not return to control levels. Purified stromal cell cultures were prepared by corticosteroid-deprivation of explanted marrow for 28 days and were then engrafted in vitro with marrow from C57BL/6J or RfM/UN mice that had been irradiated 1 month previously. Hemopoiesis in these cultures was restored, and they produced GM-CFUc and granulocytes for 15-24 weeks. Thus, healthy stroma supported growth of recently irradiated hemopoietic cells in vitro. Nonadherent cells removed from the above continuous marrow cultures generated clonal non-leukemogenic WEHI-3 GF-dependent hemopoietic progenitor cell lines with a frequency concordant with radiation effects on culture longevity, and this was increased by the presence of purified healthy stromal cultures. Indirect effects of x-irradiation on hemopoietic stem cells through damage and repair in the stromal cell compartment can be effectively studied with the present bone marrow culture system.

Continuous lines of basophil/mast cells derived from normal mouse bone marrow

Nonadherent tissue culture cell lines were established from normal bone marrow of a variety of mouse strains. The lines possessed morphological and histochemical markers of the basophil/mast cell and contained committed stem cells for metachromatic cells. Their derivation from normal marrow and their lack of tumorigenicity despite long-term culture makes these cell lines potentially important for studies of the mechanisms of allergic reactions and inflammation as well as the differentiation pathways involving this subset of hematopoietic cells.