Hematopoiesis In Long-term Cultures Research Articles

Transformed Phenotype of Bone Marrow Stromal Cell Lines Derived from K14E7 Fancd2-/- mice

To determine whether cytokeratin 14 promoter linked expression of the Human Papilloma Virus (HPV) oncogene detectably influenced biologic parameters of cell phenotypes other than squamous epithelium, continuous bone marrow cultures were derived from K14E7 Fancd2-/- mice (Park, et al., Cancer Research, 70(23): 9959-9968, 2010). Long-term bone marrow cultures derived from K14E7 Fancd2-/-, control Fancd2-/- (129/Sv), K14E7 (FVB/N), and wild type 129/Sv X FVB/N F1 mice were evaluated for longevity of hematopoiesis in long-term cultures and stromal cell lines were derived from each. Similar to Fancd2-/- mouse, long-term marrow cultures, K14E7 Fancd2-/- marrow cultures demonstrated decreased longevity of hematopoiesis with cessation of production of multi-lineage colony forming progenitor cells after 14 weeks. In contrast, wild type F1 and K14E7 long-term marrow cultures continued to produce hematopoietic cells for a significantly longer duration 25 weeks (p=0.0257). Bone marrow stromal and IL-3 dependent hematopoietic cell lines were derived from each genotype marrow culture. K14E7 Fancd2-/- hematopoietic cells showed reversal of the radiation resistance of Fancd2-/- IL-3 dependent cell lines (D0 of 1.34 ± 0.197Gy, ñ 4.0 ± 0.9 compared to D02.213 ± 0.124 Gy (p = 0.0284), ñ 3.3 ± 0.8. Thus, one phenotypic difference associated with K14E7 oncogene expression was reversal of radioresistance of Fancd2-/- hematopoietic cells. In contrast, bone marrow stromal cell lines from K14E7 Fancd2-/- remained radiosensitive similar to those from Fancd2-/- mice. K14E7 and wild type F1 marrow stromal cell lines showed intermediate radioresistance (p= 0.1759). To determine whether the E6/E7 oncogene had a biological effect in tissues other than squamous epithelium, tissue analysis for cytokeratins 13, 14, 6, and 10 was carried out. Cytokeratin 14 was detected only in squamous cells of the esophagus and oral cavity, not in bone marrow. E6/E7 oncogene was detected only in squamous cell lines expressing cytokeratin 14. However, bone marrow stromal cell lines from K14E7 Fancd2-/- marrow cultures demonstrated a unique phenomenon of cellular density, piling up and formation of tumors in vitro. Each of 22 single cell derived clonal sub-lines of K14E7 Fancd2-/- stromal cell lines demonstrated the same transformed phenotype. These data provide support for indirect effects of the E7 oncogene linked to the K14 promoter in Fancd2-/- hematopoietic and mesenchymal stem cell tissues.Supported by research grant NIAID/NIH, U19A168021. DisclosuresNo relevant conflicts of interest to declare.

Functional characteristics of mesenchymal stem cells derived from bone marrow of patients with myelodysplastic syndromes

Mesenchymal stem cells (MSCs) have emerged as excellent candidates for clinical application because of their capabilities of immunomodulatory and supporting hematopoiesis. Nevertheless, it is unclear whether the characteristics of MSCs are altered in diseased states. In this study, we obtained and expanded MSCs from bone marrow of patients with myelodysplastic syndromes (MDS). Our results showed that MSCs derived from MDS (MDS–MSCs) were similar to normal adult bone marrow derived MSCs in morphology, growth property, surface epitopes, and differentiation ability in vitro. In addition, MDS–MSCs had normal karyotype and ultrastructure. However, MDS–MSCs appeared to be impaired in immunomodulatory and supporting hematopoiesis function. Although, MDS–MSCs could express hematopoietic cytokines and support hematopoiesis in long term culture, Real time quantitative polymerase chain reaction showed that the expression of hematopoietic cytokines in MDS–MSCs was much lower than that of normal adult derived MSCs. Moreover, MDS–MSCs showed reduced hematopoiesis support function, as compared to their normal counterparts. Lastly, the capacity of MDS–MSCs to inhibit T lymphocyte activation and proliferation was impaired in vitro. These results indicate that MDS–MSCs have impaired immunomodulatory and hematopoiesis support functions, suggesting their critical role in the pathogenesis of MDS.

Phenotypic and Functional Comparison of Mesenchymal Stem Cells Derived from the Bone Marrow of Normal Adults and Patients with Hematologic Malignant Diseases

Mesenchymal stem cells (MSCs) have received much attention for their ability to differentiate into various cell types under specific conditions and to support the proliferation of hematopoietic stem cells. However, it is unclear whether the characteristics of MSCs are altered in different disease states. In this study, we obtained and expanded MSCs from bone marrow of patients with acute lymphoblastic leukemia (ALL), Hodgkin disease (HD), and non-Hodgkin lymphoma (NHL). Our results showed that MSCs derived from ALL, HD, and NHL were similar to normal adult bone marrow-derived MSCs in morphology, growth properties, surface epitopes, and differentiation ability in vitro. Moreover, MSCs derived from ALL, NHL, and HD had a normal karyotype and ultrastructure. These cells could express hematopoietic cytokines and support hematopoiesis in long-term culture. However, adherent cells isolated from bone marrow of patients with acute myeloid leukemia (AML) showed abnormal biological properties, including heterogeneity in morphology, limited proliferation capacity, and impaired differentiation and hematopoiesis support ability. These results indicate that there are differences in the characteristics of adherent cells derived from different disease states, which may be important for reasonable MSC selection in stem cell-based therapy.

Human marrow-derived mesenchymal stem cells (MSCs) express hematopoietic cytokines and support long-term hematopoiesis when differentiated toward stromal and osteogenic lineages.

Human mesenchymal stem cells (MSCs), bone marrow-derived pluripotent adherent cells of mesenchymal origin can differentiate along the osteogenic, chondrogenic, adipogenic, and tendonogenic lineages. In this report we characterize cytokine and growth factor gene expression by MSCs and investigate the modulation of cytokine expression that occurs during osteogenic and stromal differentiation. MSCs constitutively expressed mRNA for interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF), macrophage colony-stimulating factor (M-CSF), and stem cell factor (SCF). MSCs treated with IL-1alpha upregulated mRNA levels of IL-6, IL-11, and LIF, and began to express detectable levels of granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF). mRNA levels of M-CSF and SCF did not change. MSCs cultured in osteogenic medium differentiated along the osteogenic lineage and downregulated mRNA levels of IL-6, IL-11 and LIF whereas, M-CSF and SCF expression were unchanged and G-CSF and GM-CSF remained undetectable. IL-3 was not detected in MSC culture under any conditions. MSCs precultured in control medium, IL-1alpha, or osteogenic medium maintained similar capacity to support long-term culture initiating cell (LT-CIC). Thus, primary and osteogenic differentiated MSCs produce important hematopoietic cytokines and support hematopoiesis in long-term cultures, suggesting that these cells may provide an excellent ex vivo environment for hematopoiesis during progenitor cell expansion and may be important for in vivo cell therapy.

In vitro growth of mobilized peripheral blood progenitor cells is significantly enhanced by stem cell factor.

The existence of primitive hematopoietic progenitors in mobilized peripheral blood is suggested by clinical, phenotypic and in vitro cell culture evidences. In order to quantify primitive progenitors, 32 leukaphereses from 15 patients with lymphoid malignancies were investigated for the growth of multilineage colony-forming units (CFU-Mix), erythroid burst-forming units (BFU-E) and granulocyte-macrophage colony-forming units (CFU-GM) in the absence or presence of recombinant stem cell factor (SCF), a cytokine which selectively controls stem cell self-renewal, proliferation and differentiation. Primitive progenitors were also quantitated by means of a long-term assay which allows the growth of cells capable of initiating and sustaining hematopoiesis in long-term culture (LTC-IC). Addition of SCF (50 ng/ml) to methyl-cellulose cultures stimulated with maximal concentrations of G-CSF, GM-CSF, interleukin 3 and erythropoietin significantly increased the growth (mean +/- SE) of CFU-Mix (7.7 +/- 1.7 versus 2.4 +/- 0.6, p < or = 0.0001), BFU-E (47 +/- 10 versus 32 +/- 6, p < or = 0.002) and CFU-GM (173 +/- 31 versus 112 +/- 20, p < or = 0.0001). Mean (+/- SE) percentages of SCF-dependent CFU-Mix, BFU-E and CFU-GM were 60 +/- 5%, 19 +/- 5%, and 33 +/- 4%, respectively. Mean (+/- SE) LTC-IC growth per 2 x 10(6) nucleated cells was 221 +/- 53 (range, 2 to 704). Linear regression analysis demonstrated a statistically significant correlation (r = .87; p < or = 0.0001) between LTC-IC and SCF-dependent progenitors. In conclusion, our data suggest that: A) the optimal quantification of mobilized progenitors requires supplementation of methylcellulose cultures with SCF, and B) in vitro detection of SCF-dependent progenitors might represent a reliable and technically simple method to assess the primitive progenitor cell content of blood cell autografts. Such in vitro evaluation of immature hematopoietic progenitors might be clinically relevant for predicting the reconstituting potential of autografts.

Phenotypic and Functional Characterization of Long-Term Culture-Initiating Cells Present in Peripheral Blood Progenitor Collections of Normal Donors Treated With Granulocyte Colony-Stimulating Factor

Granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood progenitor cells (PBPC) have successfully been used as stem cells for both autologous and allogeneic transplants. However, little is known concerning the absolute number and phenotype of primitive progenitors, such as long-term culture-initiating cells (LTC-IC) in mobilized PBPC. The aim of our study was to evaluate the capacity of G-CSF to mobilize LTC-IC in the PB of normal individuals and to evaluate the phenotypic and functional characteristics of G-CSF mobilized LTC-IC. G-CSF was administered to 29 healthy volunteers at 7.5 micrograms or 10 micrograms/kg/d subcutaneously (SC) for 5 consecutive days and PBPC were harvested on day 6. Mobilization with G-CSF increased the absolute number of week 5 LTC-IC in PB 60-fold, while the number of CD34+ cells and committed colony forming cells (CFC) was increased sevenfold to 12-fold. The frequency of CFC and week 5 LTC-IC in CD34+ cells selected by fluorescence-activated cell sorter (FACS) from mobilized PBPC was 2 +/- 0.3-fold and 9 +/- 2.2-fold higher respectively than in CD34+ cells selected from unmobilized PBMNC. CFC were enriched in the CD34+ CD38+ and CD34+ HLA-DR+ populations. The absolute number of LTC-IC present in CD34+ CD38- and CD34+ HLA-DR- cells selected by FACS from either mobilized PBPC, unmobilized PBMNC or steady state bone marrow (BM) was similar (0.5% to 2%). In contrast to unmobilized PBMNC or steady state BM CD34+ CD38+ and CD34+ HLA-DR+ cells, which contain less than 0.1% LTC-IC, CD34+ CD38+ and CD34+ HLA-DR+ cells sorted from mobilized PBPC contained 0.5% to 5% of cells capable of sustaining hematopoiesis in long-term cultures for 5 weeks. However, 90% to 95% of LTC-IC present in mobilized CD34+ CD38+ and CD34+ HLA-DR+ cells were not able to sustain hematopoiesis for 8 weeks, while 30% of CD34+ CD38- and CD34+ HLA-DR- LTC-IC present in mobilized PBPC could sustain hematopoiesis for at least 8 weeks. This suggests that the majority of CD34+ CD38+ and CD34+ HLA-DR+ week 5 LTC-IC represent progenitors at an intermediate state of differentiation. We conclude that G-CSF effectively mobilizes LTC-IC in the blood of normal individuals. Although a fraction of these cells has functional characteristics similar to those of steady state PBMNC or BM LTC-IC, more than 85% of mobilized PBPC LTC-IC are CD34+ CD38+ and CD34+ HLA-DR+, capable of sustaining hematopoiesis for 5 weeks, but not for 8 weeks. The functional and phenotypic characterization of primitive and more mature populations of LTC-IC in mobilized PBPC should prove extremely useful in future studies examining the role of these progenitors in engraftment following transplantation.

Transplantation Potential of Hematopoietic Cells Released Into the Circulation During Routine Chemotherapy for Non-Hodgkin's Lymphoma

Primitive hematopoietic cells released into the peripheral blood (PB) were studied in 50 patients with high-grade non-Hodgkin's lymphoma enrolled in a phase III trial of intensive weekly chemotherapy (VAPEC-B) alone or with granulocyte colony-stimulating factor (G-CSF). Mononuclear cells numbers were monitored and their in vitro growth potential assessed in clonogenic progenitor cell assays and in long-term culture. Total colony-forming cells (granulocyte-macrophage [GM], burst-forming unit, erythroid [BFU-E], Mix-CFC) were increased 40-fold (median) over baseline with chemotherapy alone and 106-fold with chemotherapy and G-CSF after the final dose. CD34+ cells were increased to a median of 4%, equivalent to that in normal bone marrow (BM) controls. Circulating colony-forming cell levels were maximal when the recovering total white blood cell (WBC) count reached 5 to 10 x 10(9)/L. The timing of the maximum was reproducible in individual patients. Therefore the WBC count can be used as a guide to the timing of leukapheresis. PB cells from normal controls' and patients' prechemotherapy were unable to sustain hemopoiesis in two-stage long-term cultures. In contrast, PB cells collected from patients primed with chemotherapy alone or chemotherapy with G-CSF at the time of predicted maximal colony-forming cell release were able to generate and sustain hematopoiesis in long-term cultures at a level comparable or superior to normal BM. These findings indicate that the use of G-CSF after routine outpatient chemotherapy stimulates maximal release of primitive hemopoietic cells into the circulation, including colony-forming cells and long-term culture-initiating cells. Their numbers are comparable with those in normal BM and are such that a single leukapheresis will usually yield enough cells for hemopoietic reconstitution after myeloablative chemotherapy.

Transplantation potential of hematopoietic cells released into the circulation during routine chemotherapy for non-Hodgkin's lymphoma [see comments

Primitive hematopoietic cells released into the peripheral blood (PB) were studied in 50 patients with high-grade non-Hodgkin's lymphoma enrolled in a phase III trial of intensive weekly chemotherapy (VAPEC- B) alone or with granulocyte colony-stimulating factor (G-CSF). Mononuclear cells numbers were monitored and their in vitro growth potential assessed in clonogenic progenitor cell assays and in long- term culture. Total colony-forming cells (granulocyte-macrophage [GM], burst-forming unit, erythroid [BFU-E], Mix-CFC) were increased 40-fold (median) over baseline with chemotherapy alone and 106-fold with chemotherapy and G-CSF after the final dose. CD34+ cells were increased to a median of 4%, equivalent to that in normal bone marrow (BM) controls. Circulating colony-forming cell levels were maximal when the recovering total white blood cell (WBC) count reached 5 to 10 x 10(9)/L. The timing of the maximum was reproducible in individual patients. Therefore the WBC count can be used as a guide to the timing of leukapheresis. PB cells from normal controls' and patients' prechemotherapy were unable to sustain hemopoiesis in two-stage long- term cultures. In contrast, PB cells collected from patients primed with chemotherapy alone or chemotherapy with G-CSF at the time of predicted maximal colony-forming cell release were able to generate and sustain hematopoiesis in long-term cultures at a level comparable or superior to normal BM. These findings indicate that the use of G-CSF after routine outpatient chemotherapy stimulates maximal release of primitive hemopoietic cells into the circulation, including colony- forming cells and long-term culture-initiating cells. Their numbers are comparable with those in normal BM and are such that a single leukapheresis will usually yield enough cells for hemopoietic reconstitution after myeloablative chemotherapy.

Differential effects of drugs upon hematopoiesis can be assessed in long-term bone marrow cultures established on nylon screens.

Hematotoxicity is associated with exposure to chemotherapeutic drugs and numerous other agents. Most measurements of the hematopoietic effects of prospective therapeutic drugs and environmental agents have been made in animal models. We tested the influence of various drugs on hematopoiesis in long-term cultures of Long-Evans rat bone marrow cells. These cultures were established on nylon screen-bone marrow stromal cell templates that were suspended in liquid medium. Previous phenotypic analyses of adherent zone cells of suspended nylon screen bone marrow cultures (NSBMC) using monoclonal antibodies and flow cytometry indicated that they maintain a multilineage character for extended periods in culture and display continuous proliferation of hematopoietic progenitors (colony-forming unit culture [CFU-C]). NSBMC of various ages were incubated for 21 hr with several concentrations of beta-D-cytosine arabinofuranoside, 5-fluorouracil, cyclophosphamide, or methotrexate. Adherent zone cells were dissociated enzymatically, phenotyped by flow cytometry, and assayed for colony-forming unit culture content. beta-D-cytosine arabinofuranoside, 5-fluorouracil, and methotrexate treatment of bone marrow cultures resulted in a dose-related diminution in colony-forming unit culture numbers in the adherent zones of NSBMC. Phenotypic analyses revealed similar trends but certain of these drugs manifested lineage specificities. Toxicity was also related to cyclophosphamide dose, but the presence of bone marrow stroma was necessary to demonstrate this effect in vitro. A subpopulation of these cells was found to metabolize ethoxyfluorescein ethyl ester to fluorescein after induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin, an effect which was quantified by flow cytometry. NSBMC may be used to ascertain lineage-specific toxicities and evaluate the effects of drugs on the proliferation of hematopoietic progenitor cells.

Differential effects of microenvironmentally presented interleukin 3 versus soluble growth factor on primitive human hematopoietic cells.

The effect of IL-3 on hematopoiesis in long-term culture (LTC) was studied by cocultivating normal human marrow cells with human marrow fibroblast feeders engineered to constitutively produce IL-3 and by adding soluble IL-3 to LTC according to a variety of dose-time schedules. Feeders stably producing 7 ng/ml IL-3, or LTC to which 10 ng/ml IL-3 was added daily for 5 wk, but not once or twice weekly for the same time period, increased the output of mature nonadherent cells and progenitors from LTC as compared to control cultures. At the time of the weekly half-medium change, when primitive clonogenic progenitors in the adherent layer of standard LTC are quiescent, such cells were actively cycling in cultures containing a continuous source of an adequate dose of IL-3. In LTC, where the proportion of IL-3-producing cells in the feeder layer was diluted to 10% and no IL-3 was detectable in culture medium, primitive adherent layer progenitors were, nevertheless, maintained as a population of continuously proliferating cells. Thus, the presence of IL-3 in LTC can enhance the proliferation and differentiation of very early human hematopoietic cells, but the concentration, duration of exposure, and method of IL-3 presentation are important determinants of the ultimate effects observed.

Differential and Synergistic Effects of Human Granulocyte-Macrophage Colony-Stimulating Factor and Human Granulocyte Colony-Stimulating Factor on Hematopoiesis in Human Long-Term Marrow Cultures

The ability of granulocyte-macrophage colony-stimulating factor (GM-CSF) and G-CSF to influence hematopoiesis in long-term cultures (LTC) of human marrow was studied by cocultivating light density normal human marrow cells with human marrow fibroblast feeders engineered by retroviral infection to constitutively produce one of these growth factors. Feeders producing stable levels of 4 ng/mL GM-CSF or 20 ng/mL G-CSF doubled the output of mature nonadherent cells. The numbers of both colony forming unit-GM (CFU-GM) and erythroid burst forming unit (BFU-E) in the G-CSF LTC were also increased (twofold and fourfold, respectively, after 5 weeks in culture), but this effect was not seen with the GM-CSF feeders. At the time of the weekly half medium change 3H-thymidine suicide assays showed primitive adherent layer progenitors in LTC to be quiescent in both the control and GM-CSF cultures. In contrast, in the G-CSF cultures, a high proportion of primitive progenitors were in S-phase. A single addition of either recombinant GM-CSF or G-CSF to LTC in doses as high as 80 ng/mL and 150 ng/mL, respectively, failed to induce primitive progenitor cycling. However, three sequential daily additions of 150 ng/mL G-CSF did stimulate primitive progenitors to enter S-phase and a single addition of 5 or 12.5 ng/mL of G-CSF together with 10 ng/mL GM-CSF was able to elicit the same effect. Thus, selective elevation of G-CSF in human LTC stimulates proliferation of primitive clonogenic progenitors, which may then proceed through to the terminal stages of granulopoiesis. In contrast, the effects of GM-CSF in this system appear limited to terminally differentiating granulopoietic cells. However, when both GM-CSF and G-CSF are provided together, otherwise biologically inactive doses show strong stimulatory activity. These findings suggest that the production of both of these growth factors by normal stromal cells may contribute to the support and proliferation of hematopoietic cells, not only in LTC, but also in the microenvironment of the marrow in vivo.

Differential and synergistic effects of human granulocyte-macrophage colony-stimulating factor and human granulocyte colony-stimulating factor on hematopoiesis in human long-term marrow cultures

The ability of granulocyte-macrophage colony-stimulating factor (GM- CSF) and G-CSF to influence hematopoiesis in long-term cultures (LTC) of human marrow was studied by cocultivating light density normal human marrow cells with human marrow fibroblast feeders engineered by retroviral infection to constitutively produce one of these growth factors. Feeders producing stable levels of 4 ng/mL GM-CSF or 20 ng/mL G-CSF doubled the output of mature nonadherent cells. The numbers of both colony forming unit-GM (CFU-GM) and erythroid burst forming unit (BFU-E) in the G-CSF LTC were also increased (twofold and fourfold, respectively, after 5 weeks in culture), but this effect was not seen with the GM-CSF feeders. At the time of the weekly half medium change 3H-thymidine suicide assays showed primitive adherent layer progenitors in LTC to be quiescent in both the control and GM-CSF cultures. In contrast, in the G-CSF cultures, a high proportion of primitive progenitors were in S-phase. A single addition of either recombinant GM- CSF or G-CSF to LTC in doses as high as 80 ng/mL and 150 ng/mL, respectively, failed to induce primitive progenitor cycling. However, three sequential daily additions of 150 ng/mL G-CSF did stimulate primitive progenitors to enter S-phase and a single addition of 5 or 12.5 ng/mL of G-CSF together with 10 ng/mL GM-CSF was able to elicit the same effect. Thus, selective elevation of G-CSF in human LTC stimulates proliferation of primitive clonogenic progenitors, which may then proceed through to the terminal stages of granulopoiesis. In contrast, the effects of GM-CSF in this system appear limited to terminally differentiating granulopoietic cells. However, when both GM- CSF and G-CSF are provided together, otherwise biologically inactive doses show strong stimulatory activity. These findings suggest that the production of both of these growth factors by normal stromal cells may contribute to the support and proliferation of hematopoietic cells, not only in LTC, but also in the microenvironment of the marrow in vivo.

Differential Effects of TGF- β1 on Lymphohemopoiesis in Long-TermBone Marrow Cultures

Latent transforming growth factors beta (TGF-beta) are easily detectable in embryonic and adult hematopoietic tissues and in vitro studies show that they are potent antagonists of lymphopoiesis and myelopoiesis when converted to biologically active form. To learn more about possible roles in hematopoiesis, active TGF-beta 1 was added to cultures prepared to support myeloid cells (Dexter conditions) or B lineage lymphocytes (Whitlock-Witte conditions) and studied in detail. Hematopoiesis was permanently arrested in Dexter cultures treated with 40 pmol/L (1 ng/mL) of active TGF-beta from initiation. In addition, adipogenesis was inhibited in a dose-dependent manner, and adherent layers from treated cultures were defective when recharged with fresh bone marrow cells. Ongoing neutrophil production was terminated in established cultures when addition of the factor was delayed for 8 weeks. In contrast, in experiments with Whitlock-Witte cultures, some of the flasks produced lymphocytes in the continuous presence of TGF-beta 1 (40 pmol/L). Lymphopoiesis was completely arrested by ten-fold higher concentrations, and this was most effective when added at the beginning of culture. Precursors of lymphocytes as well as the microenvironmental elements necessary for supporting their growth survived 2 weeks of cytokine treatment (400 pmol/L) in Dexter cultures. Normal outgrowth of lymphocytes occurred when the cultures were switched to Whitlock-Witte conditions. Surface marker expression on lymphocytes growing in TGF-beta resistant or previously treated cultures was not unusual. These studies demonstrate that TGF-beta is a negative regulator of hematopoiesis in long-term cultures and show that this includes effects on microenvironmental elements. At low concentrations, production of myeloid cells was preferentially affected.

Differential effects of TGF-beta 1 on lymphohemopoiesis in long-term bone marrow cultures

Latent transforming growth factors beta (TGF-beta) are easily detectable in embryonic and adult hematopoietic tissues and in vitro studies show that they are potent antagonists of lymphopoiesis and myelopoiesis when converted to biologically active form. To learn more about possible roles in hematopoiesis, active TGF-beta 1 was added to cultures prepared to support myeloid cells (Dexter conditions) or B lineage lymphocytes (Whitlock-Witte conditions) and studied in detail. Hematopoiesis was permanently arrested in Dexter cultures treated with 40 pmol/L (1 ng/mL) of active TGF-beta from initiation. In addition, adipogenesis was inhibited in a dose-dependent manner, and adherent layers from treated cultures were defective when recharged with fresh bone marrow cells. Ongoing neutrophil production was terminated in established cultures when addition of the factor was delayed for 8 weeks. In contrast, in experiments with Whitlock-Witte cultures, some of the flasks produced lymphocytes in the continuous presence of TGF- beta 1 (40 pmol/L). Lymphopoiesis was completely arrested by ten-fold higher concentrations, and this was most effective when added at the beginning of culture. Precursors of lymphocytes as well as the microenvironmental elements necessary for supporting their growth survived 2 weeks of cytokine treatment (400 pmol/L) in Dexter cultures. Normal outgrowth of lymphocytes occurred when the cultures were switched to Whitlock-Witte conditions. Surface marker expression on lymphocytes growing in TGF-beta resistant or previously treated cultures was not unusual. These studies demonstrate that TGF-beta is a negative regulator of hematopoiesis in long-term cultures and show that this includes effects on microenvironmental elements. At low concentrations, production of myeloid cells was preferentially affected.

Different stimulative effects of human bone marrow and fetal liver stromal cells on erythropoiesis in long-term culture

The factors determining the predominantly erythroid direction of human fetal liver hematopoiesis are unknown. We compared the capacities of human fetal liver and bone marrow stromas to sustain fetal and adult hematopoiesis in long-term cultures. In various marrow-fetal liver combinations of stroma and recharge, the maintenance of erythroid (BFU- e) and myeloid (CFU-GM) precursors in the nonadherent phase was determined. The morphology of the fetal liver nucleated cells during culture was also examined. This study shows that fetal liver stromas efficiently support fetal BFU-e for 6 to 7 weeks in vitro. Bone marrow stromas were not able to maintain fetal BFU-e beyond 4 weeks. Significant numbers of marrow BFU-e were not sustained in vitro on either source of stroma. On the other hand, the stroma layers of fetal liver and marrow origin were equally effective in maintaining fetal CFU- GM and adult CFU-GM in long-term culture. These findings show that the human embryonic liver stroma is a preferential site for stimulating fetal erythropoiesis. They do not demonstrate differences in stroma function to explain the relative paucity of myelopoiesis in the fetal liver.

Different Stimulative Effects of Human Bone Marrow and Fetal Liver Stromal Cells on Erythropoiesis in Long-Term Culture

The factors determining the predominantly erythroid direction of human fetal liver hematopoiesis are unknown. We compared the capacities of human fetal liver and bone marrow stromas to sustain fetal and adult hematopoiesis in long-term cultures. In various marrow-fetal liver combinations of stroma and recharge, the maintenance of erythroid (BFU-e) and myeloid (CFU-GM) precursors in the nonadherent phase was determined. The morphology of the fetal liver nucleated cells during culture was also examined. This study shows that fetal liver stromas efficiently support fetal BFU-e for 6 to 7 weeks in vitro. Bone marrow stromas were not able to maintain fetal BFU-e beyond 4 weeks. Significant numbers of marrow BFU-e were not sustained in vitro on either source of stroma. On the other hand, the stroma layers of fetal liver and marrow origin were equally effective in maintaining fetal CFU-GM and adult CFU-GM in long-term culture. These findings show that the human embryonic liver stroma is a preferential site for stimulating fetal erythropoiesis. They do not demonstrate differences in stroma function to explain the relative paucity of myelopoiesis in the fetal liver.