Characterization of the interactions between stromal and haematopoietic progenitor cells in expansion cell culture models

Development of the long-term culture models of haematopoietic stem cells (HSCs) is one of the important tasks in modern biotechnology. It has been suggested that stromal presence is important for haematopoiesis in vitro and in vivo, but the question remains: whether diffusible factors produced by stromal cells are sufficient for the regeneration of primitive and definitive haematopoietic cells, or direct cell-to-cell contacts of the cultured material with underlying stromal base would be required. During present studies, influence of various feeder layers and feeder layer conditioned media on proliferative, differentiative and clonogenic activity of human AC133+ derived from human umbilical cord blood was investigated. Cell extracts for feeder layers were prepared from 4-6 weeks old human embryos and co-cultured feeder cells. Effects of the conditioned media were also determined. Culture and feeder layer media were additionally supplemented with commonly implemented factors such as GM-CSF, IL-3 and LIF. Estimation of morpho-functional properties of AC133+ cultivated suspension cultures was performed in subculture experiments using semisolid agar culture conditions. Multipotential CFU-MIX (CFU-GEMM) and unipotential progenitor cells CFU-GM, BFU-E and CFU-E were observed and analyzed. Our data suggest that haematopoiesis can be sustained for prolonged cultivation periods in the presence of feeder layer cells or conditioned media supported culture models. Prolonged support of primitive haematopoietic cells and their clonogenic capacity and functional characteristics in feeder layer positive cultures, indicates that diffusible factors are sufficient for haematopoiesis and suggests that direct cell-to-cell contacts may not be exclusively required for successful long-term in vitro haematopoiesis.     

Bone marrow stromal culture from patients with myelodysplastic syndromes and patients at different stages of acute nonlymphocytic leukaemia

The haematopoietic microenvironment or stroma plays a decisive role for the proliferation and differentiation of haemopoietic cells. We studied if bone marrow cells from patients with myelodysplastic syndromes (MDS) and acute nonlymphocytic leukaemias (ANLL) are altered in their ability to form adherent stromal layer with active haemopoiesis in the Dexter liquid culture. Bone marrow cells were obtained from 24 normal volunteers, 28 patients with ANLL in different stages of the disease and 9 patients with MDS. There are no differences between the stromal layers of patients with ANLL in complete remission and those of normal volunteers after two weeks of cultivation. However, bone marrow cells from patients with ANLL before treatment and from patients in relapse formed a poor adherent stromal layer in most cases. In 6 of 9 cases we found the normal stromal grade of bone marrow cells from patients with MDS. There were qualitative differences in the nonadherent cell population between normal and ANLL patients in complete remission. In most cases we found morphologically recognizable erythroid cells after two-weeks Dexter liquid culture of bone marrow cells from patients with ANLL in complete remission, which were not seen with normal volunteers. This could be an indication of harmful effects on the balance of haematopoiesis caused by previous infiltration with leukaemic cells or/and high-dose chemotherapy.     

The influence of 3,3',5-triiodo-L-thyronine on human haematopoiesis

OBJECTIVES: Thyroid hormones mediate many physiological and developmental functions in humans. The role of the 3,3',5-triiodo-L-thyronine (T3) in normal human haematopoiesis at the cellular and molecular levels has not been determined. In this study, it was revealed that the human haematopoietic system might be directly depended on T3 influence. MATERIALS AND METHODS: We detected the TRalpha1 and TRbeta1 gene expression at the mRNA level in human cord blood, peripheral blood and bone marrow CD34(+)-enriched progenitor cells, using the RT-PCR method. Furthermore, we performed Western blotting to prove TRalpha1 and TRbeta1 expression occurs at the protein level in human cord blood, peripheral blood and bone marrow CD34(+) cells. In addition, the examined populations of cells were exposed in serum-free conditions to increasing doses of T3 and were subsequently investigated for clonogenic growth of granulocyte-macrophage colony-forming unit and erythrocyte burst-forming unit in methylcellulose cultures, and for the level of apoptosis, by employing annexin V staining and the terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling method. We investigated expression levels of apoptosis-related Bax and antiapoptotic Bcl-2 and Bcl-x(L) genes in the examined cells. RESULTS: We found that exposure to higher and lower than normal concentration of thyroid hormone significantly influenced clonogenecity and induced apoptosis in human haematopoietic progenitor cells. CONCLUSIONS: This study expands the understanding of the role of thyroid disorders in normal human haematopoiesis and indicates a direct influence of T3 on this process.     

Stromal cells from murine developing hemopoietic organs: comparison of colony-forming unit of fibroblasts and long-term cultures.

The adherent stromal layer in long-term marrow cultures is essential to the proliferation and differentiation of hemopoietic cells. Adhering cells are heterogeneous and morphologically not adequately characterized. Comparative morphological studies were conducted on adherent cells in short-term clonal assays and long-term cultures derived from liver and bone marrow. Liver and bone marrow at different developmental ages have different hemopoietic activities in vivo and in vitro, as tested via CFU-GM recovery in long-term cultures. Adherent cells from each organ were recovered at an age with high hemopoietic activity (fetal liver and adult bone marrow) and at an age with low hemopoietic activity (neonatal liver and bone marrow). The presence of macrophages, alkaline phosphatase, acid phosphatase, myeloperoxidase, sulfated and non-sulfated glycosaminoglycans (GAGs) and fibronectin was compared. For a given organ, CFU-f colonies showed characteristics similar to those of the confluent adherent stromal layer in long-term cultures. The presence of macrophages and GAGs (sulfated and non-sulfated) in the adherent layer were directly related to the hemopoietic activity. The amount of alkaline phosphatase-positive cells and the amount of fibronectin showed no correlation with the hemopoietic activity of the cultures.     

Changes in the haematopoietic progenitor cell compartment in the acquired immunodeficiency syndrome

In order to elucidate the mechanisms responsible for the disturbances of haematopoiesis in HIV-infected individuals, bone marrow from 25 patients with either ARC or AIDS was studied. There is a stage-related decrease in CFU-GEMM, CFU-MK, BFU-E and CFU-GM, with the latter being least affected. This decrease is inversely correlated with the number of circulating CD4 cells and the CD4/CD8 ratio. Immunohistochemical and in situ hybridization studies of haematopoietic colonies failed to demonstrate HIV infection of haematopoietic cells. Neither the depletion of adherent mononuclear cells from haematopoietic cell cultures nor the addition of plasma containing antibodies against HIV gp120 could demonstrate an inhibitory effect of HIV-infected macrophages or immune-mediated progenitor cell lysis, respectively. Hence, imbalances of T-cell subpopulations appear to be mainly responsible for the progressive impairment of proliferation and differentiation of bone marrow progenitor cells observed in HIV-infected individuals.     

Growth and cell kinetics of human hair papilla cells in vitro. An autoradiographic and flow cytometric study

Hair papilla, a distinct specialized dermal compartment, plays a fundamental role in the biology of hair growth. Recently some attention has been focused on hair papilla cells (HPC) as possible targets for drugs influencing the hair growth. Isolation and cultivation of the HPC facilitates screening for such drugs. In the present work, growth and cell kinetics of human occipital scalp follicle HPC have been studied in vitro. HPC grow according to a Gompertz function, i.e. with considerable growth delay long before becoming confluent cultures, due probably to elongation of the potential doubling time (Tpot) and to a parallel increasing cell loss rate. The [3H]dT labelling index of the HPC strongly depends on the age of the subculture; the cycle time being about 4 days. A potential doubling time of about 93 h, indicative of growth fraction (GF) = 1, and a duration of S phase and G2 + M phase of about 8 h each were found by the combined application of continuous labelling with [3H]dT and DNA flow cytometry.     

Characterization of the in vitro stromal microenvironment of human bone marrow

Utilizing long-term in vitro culture techniques, we characterized the cellular composition and functional attributes of the human in vitro bone marrow stromal microenvironment. Morphologic, specific cytochemical and immunologic methods demonstrated that the marrow stromal adherent layer (AL) reached confluency at two to three weeks, and was comprised of 60%-70% fibroblastic cells, 10%-20% endothelial cells, 10%-20% monocyte/macrophages and 5%-10% fat-laden adherent cells. These proportions of cell types persisted for at least three months concomitant with proliferation of CFU-gm and BFU-e. In contrast, umbilical cord blood cells did not form a stromal AL despite persistence of hemopoietic progenitor cell proliferation. These findings provide a basis for improved understanding of cellular interactions regulating hemopoiesis.     

Stromal cell-derived factor-1 (SDF-1)\CXCR4 couple plays multiple roles on haematopoietic progenitors at the border between the old cytokine and new chemokine worlds: survival, cell cycling and trafficking

Generation of haematopoietic cells is regulated by cellular and humoral interactions in which stromal cells, adhesion molecules, cytokines and chemokines play a crucial role. Among the chemokines, SDF-1 and its CXCR4 receptor have been reported to be key players in the nesting of haematopoietic progenitors within the bone marrow. Disruption of the SDF-1\CXCR4 axis results in cell mobilization and may participate in leukaemia extramedullary infiltration. In this review we will discuss the manifold roles of the SDF-1 chemokine and of its receptor in haematopoiesis regulation. By recruiting quiescent progenitors, by participating in their survival\cycling and by sensitizing them to further cytokine synergistic action, SDF-1 likely contributes to haematopoiesis homeostasis under physiological conditions and in stress situations. The complexity of the SDF-1\CXCR4 interactions in the regulation of haematopoiesis illustrates a dynamic and sequential cross-talk between chemokine and cytokine\growth factor worlds. Because of their pleiotropic effects on haematopoietic progenitor trafficking, survival and proliferation, the SDF-1\CXCR4 couple could be considered as promising molecules for improvement of cell-based therapy protocols in haematopoietic transplantation.     

Haemopoietic long-term bone marrow cultures from adult mice show osteogenic capacity in vitro on 3–dimensional collagen sponges

Abstract. Adult murine bone marrow cells, cultured under conditions for long-term haemopoietic marrow cultures, produce bone matrix proteins and mineralized tissue in vitro , but only after the adherent stromal cells were loaded on a 3-dimensional collagen sponge. Provided more than 8 × 10⁶ cells are loaded, mineralization as measured by ⁸⁵Sr uptake from the culture medium, occurred in this 3-dimensional configuration (3-D) within 6 days. In contrast if undisrupted marrow fragments (containing more than 10⁷ cells) are placed directly on a collagen sponge, then it requires more than 10 days before significant mineralization can similarly be detected. The 2-dimensional (2-D) long-term marrow culture system allows prior expansion of the stromal cells and some differentiation in an osteogenic direction within the adherent stromal layer. This is suggested by the presence of type I collagen and alkaline phos-phatase positive cells. However, synthesis of osteonectin and a bone specific protein, osteocalcin, as well as calcification are only observed in 3-D cultures. Electron microscopy demonstrated hydroxyapatite mineral on collagen fibres, osteoblast-like cells, fibroblasts, cells which accumulated lipids, and macrophages which were retained on the collagen matrices. Irradiation of confluent long-term bone marrow cultures, prior to their loading on the collagen sponge showed that haemopoietic stem cells are not necessary for the mineralization.     

A stromal cell line from myeloid long-term bone marrow cultures can support myelopoiesis and B lymphopoiesis

The production of B lymphocytes and myeloid cells occurs in the bone marrow in association with a supporting population of stromal cells. To determine whether these processes are dependent upon the same or different populations of stromal cells, stromal cell lines were generated from the adherent layer of a Dexter type long-term bone marrow culture. These cultures support myeloid cells and their precursors, a B cell precursor, and the adherent layer cells with support B cell differentiation under appropriate conditions. Two of the lines examined, S10 and S17, express class I histocompatibility antigens but not other hemopoietic cell surface determinants such as Thy-1, Lyt-1, Ig, Ia, Mac-1, or BP-1. Both lines could support myelopoiesis under Dexter conditions upon seeding with nylon wool-passed bone marrow. The nylon wool passage depletes stromal cells capable of forming adherent layers in vitro but retains hemopoietic precursors. The number of cells and colony-forming units-granulocytes/macrophages in the nonadherent cell population recovered 3 wk post-seeding had increased 19-fold and 10-fold, respectively, in the reseeded cultures of S10 and S17. After 3 wk of growth in Dexter conditions, the reseeded cultures were transferred to conditions optimal for B cell differentiation described by Whitlock and Witte. After 4 wk of growth, hemopoietic cells were consistently recovered from S17 cultures but not those of S10. A proportion of these cells from S17 cultures expressed the 14.8 antigen and were surface IgM positive. Surviving hemopoietic cells present in cultures of S10 were primarily macrophages. These findings indicate that S17 but not S10 can support both myelopoiesis and B lymphopoiesis and suggest that one stromal cell population has the capacity to form a hemopoietic microenvironment for both lineages.     

The kinetics of granulopoiesis in long-term mouse bone marrow culture. Part I

The spontaneous stratification in long-term bone marrow cultures was illustrated and quantified. The cultures were separated into three hematopoietic layers: nonadherent cells in the supernatant medium, lightly adherent cells on top of the stromal layer, and remaining cells buried within the stromal layer. The cells of each layer were subcultured for 10 days in plastic tubes that inhibit the formation of a stromal layer. Daily samplings with absolute and differential cell counts were obtained. We identified three families of cell disappearance curves and cell types: CFU-s, hemocytoblasts, myeloblasts, and promyelocytes (G1, 2); myelocytes (G3); and postmitotic granulocytes (G4). Also, the numbers of mitotic and necrotic cells were determined. The longest half-time of CFU-s was 2.5 days. Lacking stromal support, CFU-s disappeared faster than other differentiated cells. Generally, these cells maintained their numbers for the first week of subcultures, which was attributable to a temporarily maintained balance of cell death and fresh cell production. After more than 7 days, there was a rapid decline of all differentiated cell types.     

Identification of a clonally expanding haematopoietic compartment in bone marrow

In mammals, postnatal haematopoiesis occurs in the bone marrow (BM) and involves specialized microenvironments controlling haematopoietic stem cell (HSC) behaviour and, in particular, stem cell dormancy and self‐renewal. While these processes have been linked to a number of different stromal cell types and signalling pathways, it is currently unclear whether BM has a homogenous architecture devoid of structural and functional partitions. Here, we show with genetic labelling techniques, high‐resolution imaging and functional experiments in mice that the periphery of the adult BM cavity harbours previously unrecognized compartments with distinct properties. These units, which we have termed hemospheres, were composed of endothelial, haematopoietic and mesenchymal cells, were enriched in CD150+ CD48? putative HSCs, and enabled rapid haematopoietic cell proliferation and clonal expansion. Inducible gene targeting of the receptor tyrosine kinase VEGFR2 in endothelial cells disrupted hemospheres and, concomitantly, reduced the number of CD150+ CD48? cells. Our results identify a previously unrecognized, vessel‐associated BM compartment with a specific localization and properties distinct from the marrow cavity.     

Persistent production of colony-stimulating factor (CSF-1) by cloned bone marrow stromal cell line D2XRII after X-irradiation

The adherent stromal layer in long-term bone marrow cultures (LTBMC) provides the cellular environment necessary for the in vitro proliferation and differentiation of pluripotential hematopoietic stem cells. The role of humoral hematopoietic growth factors, colony-stimulating factors (CSF) in the regulation of hematopoietic cell production in this system is poorly understood. We have recently isolated and cloned an adherent cell line, D2XRII, derived from murine LTBMC. Plateau phase 25 cm2 cultures of 2 X 10(6) D2XRII cells in 8.0 ml produced CSF-1 (M-CSF) at around 100-150 units/0.1 ml medium. Following X-irradiation there was a dose-dependent decrease in the production of CSF-1 to a plateau of 50% of control levels at 10,000 rad. Higher doses did not produce a further decrease. The X-ray dose reducing CSF-1 production to 50% was 100-fold above the lethal dose as measured by clonagenic survival following trypsinization and replating. Trypsinized replated viable adherent but nondividing X-irradiated D2XRII cells were maintained for up to 8 weeks after irradiation and demonstrated continuous production of CSF-1. The data indicate significant divergence of two biologic effects of X-irradiation on plateau-phase marrow stromal cells: physiologic function of adherence and CSF-1 production, versus proliferative integrity. This divergence of effects may be very relevant to understanding the mechanism of X-irradiation-associated marrow suppression and leukemogenesis.     

The xid mutation affects hemopoiesis in long term cultures of murine bone marrow

Cells of the humoral immune system are particularly affected by a mutation at the X chromosome linked immunodeficiency disease (xid)locus. Although B cells are made in normal numbers, they fail to become phenotypically and functionally diverse. Consequently, poor antibody responses are mounted to certain types of Ag. There have been some indications that other types of hemopoietic cells may be influenced by the mutation and development of the humoral immune system is unusually dependent on the presence of T lymphocytes. We now describe an analysis of the lympho-hemopoietic environment studied with long term bone marrow cultures. Contrary to expectations, cultures initiated with cells from homozygous female or hemizygous male mice with the mutant allele established more quickly than normal. The accelerated initial growth pattern was clearly linked to the xid mutation. Artificial mixtures of marrow exhibited intermediate growth kinetics. Experiments with H-2 congenic and T6 chromosome marked cells did not reveal an intrinsic dominance of growth in nonadherent xid cells. Similar results were obtained with culture conditions which favored production of myeloid or lymphoid cells. These findings would be consistent with subtle changes in the bone marrow microenvironment resulting from the xid mutation. The pedigree of the mouse strains had a significant influence on lymphopoiesis in long term bone marrow cultures. Lymphocytes of BALB/c origin dominated over CBA/H background cells in cultures established from mixtures of the two, but this did not correlate with any functional deficiency in CBA/H stromal cells. In fact, establishment of an adherent layer was a rate-limiting step in initiating long term cultures and this could be achieved with a low dose inoculum of CBA/H marrow. Even more dramatic effects were found in hemopoietic cells from doubly defective C3H.nu/nu-xid mice. The bone marrow of these athymic animals contained normal numbers of granulocyte/macrophage progenitors. However, lymphoid cultures could not be reproducibly established with their cells and myelopoiesis was never observed in vitro. The relatively simple conditions which pertain in culture make it possible to appreciate effects of mutations and pedigree on hemopoiesis which are unremarkable in intact animals.     

Phosphate and the regulation of DNA replication in normal and virus-transformed 3T3 cells.

3T3 cells were cultured in media with different phosphate concentrations and the effects on DNA synthesis were examined. Even a modest phosphate depletion markedly inhibited DNA synthesis and cell multiplication in proliferating cultures. Furthermore, the decrease in the proportion of DNA-synthesizing cells observed after phosphate starvation followed the same time-course as the decrease seen after serum starvation. Cells starved to quiescence in a medium with a 100-fold decrease in phosphate concentration remained viable but non-proliferating for up to 3 weeks, i.e. they had entered a state of quiescence comparable with that seen after serum starvation. Addition of phosphate to phosphate-depleted cultures restored DNA synthesis within 24h. Furthermore, the kinetics of [3H]thymidine labelling after phosphate addition were nearly identical with the labelling kinetics following addition of serum to serum-depleted cultures. In contrast, phosphate deprivation had no inhibitory effects on DNA synthesis in simian-virus-40-transformed 3T3 cells. Furthermore, the inhibitory effects on DNA synthesis in such cells caused by a complete removal of serum could not be further enhanced by decreasing the phosphate concentration in the culture medium.     

cAMP analogues downregulate the expression of granulocyte macrophage colony-stimulating factor (GM-CSF) in human bone marrow stromal cells in vitro.

The stimulation of granulocyte macrophage-colony stimulating factor (GM-CSF) by interleukin-1 (IL-1) has been shown to be counteracted in different mesenchymal cell systems by cyclic adenosine monophosphate (cAMP) agonists. The aim of this study was the evaluation of different cAMP agonists on GM-CSF expression in human bone marrow stromal cells. Incubation of secondary haematopoietic progenitor cell deprived human stromal cell cultures with IL-1 or TNF-alpha induced GM-CSF protein expression in culture supernatants and GM-CSF-mRNA in adherent stromal cells. The coincubation with 8-bromo-cAMP (8BrcAMP), a water soluble cAMP analogue, inhibited this GM-CSF stimulation at the protein and the mRNA level. This effect was dose dependent with a maximal inhibition of about 65% occurring at a 8BrcAMP concentration of 0.75 mM. In addition to 8BrcAMP, other cAMP agonists such as dibutyryl-cAMP, forskolin, pertussis toxin, or prostaglandin E2 (PGE2) had the same inhibitory effect on GM-CSF stimulation by IL-1. Coincubation with the cyclooxygenase inhibitor indomethacin had no significant influence on GM-CSF expression in stromal cells. Our results provide evidence that the previously described inhibitory effect of cAMP agonist PGE2 on haematopoietic progenitor cells in vivo is, at least in part, mediated by modulating the expression of GM-CSF in bone marrow stromal cells.     

Pattern of cytokine expression by rat liver epithelial cells supporting long-term culture of human CD34(+)umbilical cord blood cells

Fetal liver is the main site of haematopoiesis during mid-gestation. The adult liver still provides a favourable environment for extramedullary haematopoiesis. Nevertheless, regulation of liver haematopoiesis by cell-cell contacts or by cytokines remains poorly understood. Recently, we have shown that rat liver epithelial cells (RLECs) support long-term survival and multilineage differentiation of adult human CD34(+)and CD34(+)/CD38(-)haematopoietic cells obtained from granulocyte-colony stimulating factor mobilized peripheral blood and from bone marrow respectively. In addition, the importance of physical proximity between haematopoietic cells and RLECs was clearly demonstrated. Here, our findings give evidence that RLECs belonging to the epithelial but non-parenchymal liver compartment also sustain the long-term production of progenitors from human CD34(+)umbilical cord blood cells. Moreover, to better analyse the regulation of haematopoiesis in this RLEC coculture model, we have investigated the cytokine expression by RLECs alone and by RLECs coming from coculture with CD34(+)cells from umbilical cord blood. We demonstrated that a broad spectrum of cytokines acting at different stages of haematopoiesis is produced by RLECs. Interestingly, an upregulation of leukemia inhibitory factor expression by RLECs in presence of CD34(+)haematopoietic cells was observed. These data suggest an important role of cell-cell interactions in the regulation of haematopoiesis.     

Rate of Non-Adherent Cell Loss From Long-Term Cultures of Murine Bone Marrow: Effect of Medium Conditioned By the Adherent Cell Population

Abstract. The rate of random spontaneous cell loss from the non-adherent cell population of long-term cultures of murine bone marrow was determined. the measured rate of non-adherent cell loss is affected by previous conditioning of the medium in which the non-adherent cells are suspended. Specifically, the measured rate of non-adherent cell loss is significantly slowed when the non-adherent cells are suspended in medium conditioned in long-term haematopoietic cultures instead of fresh medium. It appears that a subset of the adherent cell population is the source of the factor or factors within the medium which result in this slower measured rate of non-adherent cell loss. This effect may be due to the stimulation to division of haematopoietic progenitor cells, offsetting the lysis of other non-adherent cells.     

Rate of non-adherent cell loss from long-term cultures of murine bone marrow: effect of medium conditioned by the adherent cell population

The rate of random spontaneous cell loss from the non-adherent cell population of long-term cultures of murine bone marrow was determined. The measured rate of non-adherent cell loss is affected by previous conditioning of the medium in which the non-adherent cells are suspended. Specifically, the measured rate of non-adherent cell loss is significantly slowed when the non-adherent cells are suspended in medium conditioned in long-term haematopoietic cultures instead of fresh medium. It appears that a subset of the adherent cell population is the source of the factor or factors within the medium which result in this slower measured rate of non-adherent cell loss. This effect may be due to the stimulation to division of haematopoietic progenitor cells, offsetting the lysis of other non-adherent cells.     

Effects of lipoxygenase metabolites of arachidonic acid on the growth of human mononuclear marrow cells and marrow stromal cell cultures.

The effects of various lipoxygenase metabolites of arachidonic acid (AA) were investigated on the growth of freshly isolated human bone marrow mononuclear cells and marrow stromal cell cultures. LTB4, LXA4, LXB4, 12-HETE and 15-HETE (1 microM) decreased [3H]-thymidine incorporation on marrow stromal cell cultures without affecting cell number. Only 12-HETE showed a dose-response effect on [3H]-thymidine incorporation. While LTB4 (1 microM) decreased thymidine incorporation on marrow mononuclear cells, LTC4, LXA4, LXB4, 12-HETE and 15-HETE had no effect. The lipoxygenase inhibitor NDGA had no effect on both cell types suggesting no role of endogenous lipoxygenase metabolites on cell growth. These results suggest no important role of lipoxygenase metabolites of AA on the proliferation of human marrow mononuclear cells and marrow stromal cell cultures.