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Mesenchymal stem cells (MSC) represent a mixture of different cell types, of which only a minority is therapeutically relevant. Surface markers specifically identifying non-differentiated MSC from their differentiated progeny have not been described in sufficient detail. We here compare the gene expression profile of the in vivo bone-forming bone marrow-derived MSC (BM-MSC) with non-bone-forming umbilical vein stromal cells (UVSC) and other non-MSC. Clustering analysis shows that UVSC are a lineage homogeneous cell population, clearly distinct from MSC, other mesenchymal lineages and hematopoietic cells. We find that 89 transcripts of membrane-associated proteins are represented more in cultured BM-MSC than in UVSC. These include previously identified molecules, but also novel markers like NOTCH3, JAG1, and ITGA11. We show that the latter three molecules are also expressed on fibroblast colony-forming units (CFU-F). Both NOTCH3 and ITGA11, but not JAG1, further enrich for CFU-F when combined with CD146, a known marker of cells with MSC activity in vivo. Differentiation studies show that NOTCH3+ and CD146+ NOTCH3+ cells sorted from cultured BM-MSC are capable of adipogenic and osteogenic progeny, while ITGA11-expressing cells mainly show an osteogenic differentiation profile with limited adipogenic differentiation. Our observations may facilitate the study of lineage relationships in MSC as well as facilitate the development of more homogeneous cell populations for mesenchymal cell therapy., (2010 Elsevier Inc. All rights reserved.)

The purpose of this study was to evaluate the growth patterns and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) when seeded onto new biodegradable chitosan/polyester scaffolds. Scaffolds were obtained by melt blending chitosan with poly(butylene succinate) in a proportion of 50% (wt) each and further used to produce a fiber mesh scaffold. hBMSCs were seeded on those structures and cultured for 3 weeks under osteogenic conditions. Cells were able to reduce MTS and demonstrated increasing metabolic rates over time. SEM observations showed cell colonization at the surface as well as within the scaffolds. The presence of mineralized extracellular matrix (ECM) was successfully demonstrated by peaks corresponding to calcium and phosphorus elements detected in the EDS analysis. A further confirmation was obtained when carbonate and phosphate group peaks were identified in Fourier Transformed Infrared (FTIR) spectra. Moreover, by reverse transcriptase (RT)-PCR analysis, it was observed the expression of osteogenic gene markers, namely, Runt related transcription factor 2 (Runx2), type 1 collagen, bone sialoprotein (BSP), and osteocalcin. Chitosan-PBS (Ch-PBS) biodegradable scaffolds support the proliferation and osteogenic differentiation of hBMSCs cultured at their surface in vitro, enabling future in vivo testing for the development of bone tissue engineering therapies.

We have previously described a culture system for human bone marrow endothelial cells that organize into capillary tubes associated to pericytes. In the present work, we used this model to assess the angiogenic properties of tachykinins, which have been demonstrated to be involved in neuro-immuno-haematopoietic interactions. The substance P (SP) and neurokinin A (NKA) were similarly potent at increasing in vitro angiogenesis, via NK1 and NK2 receptors respectively. These mediators were not produced by cells in culture, suggesting that in vivo they may be released by nerve fibres in the bone marrow. Therefore, we looked for in situ innervation of the human bone marrow, unknown to date, using immunohistochemistry techniques. As in rodents, arterioles were largely innervated, associated with between one and 10 nerve fibres. Capillary innervation was more restrictive as a unique thin nerve fibre was found in the vicinity of only 6% of these vessels. Finally, no nerve fibres were observed in the vicinity of sinus walls. In conclusion, both in vitro results and the anatomical display of nerve fibres suggest a role in human bone marrow for the vasoactive neuropeptides SP and NKA, which were secreted into a perivascular location. These neural mediators might modulate blood flow in the bone marrow both in the short term by adjusting vascular tone and in the long term by inducing angiogenesis.

This study was performed to evaluate the role of human microenvironmental cells in the metabolism of AcSDKP, a physiological inhibitor of hematopoietic stem cells. Using long-term marrow cultures (LTMCs), whose medium already contained a baseline value of AcSDKP, we found after 2 weeks a net output in the culture supernatant indicating that release by cells from the adherent layer was superior to consumption of the peptide. Since human microenvironmental cells consist of macrophages and vascular smooth-muscle-like stromal cells we generated pure populations of macrophages (by culturing cord blood cells in the presence of granulomonocytic colony-stimulating factor) and of stromal cells (generated by stromal colonies). We found in supernatants of macrophage cultures a significantly (p < 0.01) increased level of AcSDKP (compared with value in medium) while in supernatants of stromal cell cultures the level was decreased. Cell content of angiotensin-converting enzyme (ACE) in stromal cells was higher than in macrophages, which suggests a degradation of AcSDKP by stromal cells because of their higher amount of ACE. Finally, we analyzed the content of AcSDKP in adherent layers of LTMCs (with or without extracellular matrix [ECM] components), macrophages, and stromal cells. We found levels of AcSDKP of 1.5 pMol per 106 cells in extracts from macrophages or from stromal cells. On the contrary, extracts from primary layers of LTMCs contained 3 times more AcSDKP; however, after treatment of primary layers by collagenase, AcSDKP level fell to 1 pMol per 10(6) cells. Immunofluorescence using an anti-AcSDKP monoclonal antibody showed an extracellular network in certain areas of LTMCs. This study shows that 1) macrophages synthesize and release in the supernatant AcSDKP, 2) stromal cells probably degrade the peptide via ACE, and 3) components of the ECM from LTMCs serve as a reservoir for the peptide. These results are reminiscent of what has been described for growth factors, produced by microenvironmental cells, and stored in the ECM in close vicinity to hematopoietic precursors.

We describe an assay that makes possible the observation of granulomonocytic colonies grown on allogeneic stromal layers and the quantification of the stroma-adherent colony-forming cells (CFC). Stromal layers were generated from Stro-1 positive cells isolated from adherent layers of primary long-term marrow cultures using magnetic beads coated with the Stro-1 antibody. The stromal layers consisted mainly of myofibroblastic cells. Marrow fractions depleted of cells bearing receptors for soybean agglutinin (SBA) and enriched in CD34+ cells were obtained by panning. SBA-, CD34+ marrow cells were seeded onto stromal cells grown in 96-well plates. After four weeks, a mixture of cytokines was added (granulocyte-macrophage colony-stimulating factor [GM-CSF]: 25 U/ml, interleukin [IL]-3: 4 ng/ml, Steel factor: 5 ng/ml and growth factors provided by 3% conditioned medium from the 5637 cell line). Wells with large colonies (containing 10(3) to 10(4) cells) were scored after 14 days. Limiting dilution analysis of data revealed a Poisson distribution of the stroma-adherent CFC. There was an average of one stroma-adherent CFC per 167 CD34+ enriched marrow cells, which gave an estimated frequency of one CFC per 10(5) unfractionated bone marrow cells. Colonies contained cells that gave rise to CFU-GM after replating in agar (5-40 CFU-GM were provided per each stroma-adherent CFC), but not cells with self-renewal ability (as indicated by negative results after replating single colonies onto secondary adherent layers). Colonies usually formed from a cobblestone-area and developed in intimate contact with alpha SM actin positive stromal cells. Some of the stromal cells were located above granulocytic cells, corresponding to the description of "blanket cells." This assay should allow the study of colony-formation on marrow stroma without disrupting the hemopoietic niche.

In human long-term marrow cultures granulomonopoiesis is maintained for several weeks. Studies on granulomonocytic progenitors (CFU-GM) and their progeny have shown that survival, proliferation, differentiation and maturation of these cells are controlled by a set of glycoproteins, the colony-stimulating factors (CSFs) and the Steel factor. We have studied the expression of these factors using reverse transcriptase polymerase chain reaction (RT-PCR) in 17 adherent layers of normal bone marrow at 3, 5 or 7 weeks of culture. We have taken the 5637 bladder carcinoma cell line as a control for expression of GM-CSF, M-CSF, G-CSF and Steel factor, and PHA-activated T lymphocytes as a control for expression of multi-CSF (interleukin 3, IL-3). We have found that GM-CSF was expressed in the 17 adherent layers without induction by interleukin 1 beta (IL-1 beta). M-CSF was also detected in all cases, but in two early-stage (week 3 and week 5) cultures only after stimulation by IL-1 beta. G-CSF was detected in only 11 cases (three without IL-1 beta, and eight after addition of IL-1 beta). Steel factor was detected in 14 cases (ten without IL-1 beta, and four after addition of IL-1 beta). IL-3 was not detected even by means of nested RT-PCR. These data indicate in six late-stage (week 5 or week 7) cultures G-CSF messenger concentrations 10(3)-fold less than in 5637 control cells (for an identical amount of total cellular RNA). A similar conclusion may be drawn for Steel factor in three late-stage cultures. For IL-3 our negative results indicate a messenger concentration 10(5)-fold less than in activated T lymphocytes. These results suggest a crucial role for GM-CSF and M-CSF in the maintenance of granulomonopoiesis in human long-term cultures. The role of G-CSF and Steel factor may be more marginal. Eventually IL-2 may not be involved in the regulatory process.

Fibronectin is a major component of the extracellular matrix of adherent layers of human long-term marrow cultures where it may stabilize the extracellular matrix network and provide adhesion sites for primitive hemopoietic cells. This study was devised to analyze the role of adherent cell populations in fibronectin synthesis, matrix assembly, and degradation. In cultures performed under the conditions described by Gartner and Kaplan, immunoprecipitation after metabolic labeling showed that adherent cells synthesized a fibronectin variant comprising the EDa domain and lacking the EDb one. Vascular smooth muscle-like stromal cells were the cell subset responsible for this synthesis. Once synthesized by stromal cells, EDa+fibronectin was secreted into the supernatant and incorporated into the extracellular matrix. The cumulation in the extracellular matrix was predominant by weeks 5 and 6 of culture, when a decrease in the stromal cell intracytoplasmic content of fibronectin was observed. Stromal cells from a transformed cell line, L2Ori-, were also able to synthesize the EDa+fibronectin variant, although for these cells the assembly into the extracellular matrix was partly impaired. Besides stromal cells, other cell types participated in fibronectin synthesis: early-adhering granulomonocytic cells and macrophages appearing later in culture were able to synthesize an EDa-, EDb- fibronectin variant, clearly distinct from the EDa+ variant produced by stromal cells. Studies on cultures in which macrophage growth was stimulated at the expense of stromal cells by adding granulocyte-macrophage colony-stimulating factor (50 ng/mL) to the culture medium showed a striking decrease in amounts of fibronectin measured in the adherent layer. This decrease was caused by a lack of incorporation of fibronectin in the extracellular matrix, disclosing a major difference between stromal cells and macrophages in terms of matrix assembly. This study confirms the similarity between stromal cells and vascular smooth muscle cells, because in vivo subendothelial intimal aortic smooth muscle cells and cultured smooth muscle cells from the aortic media express the EDa+, EDb- fibronectin variant. Furthermore, our results suggest that the level of fibronectin in adherent layers is regulated by stromal cells and macrophages. The balance between these two cell populations may therefore be crucial for the local control of hemopoiesis by regulating the extracellular fibronectin available for the adhesion of hematopoietic cells. Our data indicate that it may be essential to study the adhesion of stem cells to EDa+, EDb- fibronectin instead of EDa-, EDb- soluble fibronectin, as found in human plasma.

This report describes the effects of cryopreservation on the adherent layer of human long-term bone marrow cultures (HLTBMC). Stromal cells are believed to be the most important cells of medullar microenvironment to regulate hematopoiesis. To study effects of cryopreservation, we compared the cell phenotypes of adherent layers of fresh and frozen-thawed bone marrows. To characterize stromal cells we used monoclonal antibodies reacting with components of these cells (CGA-7 alpha SM and gamma SM actin isoforms; HHF-35, all muscle actin isoforms; BMS-1, stromal cell lysosomes). The other components studied were: fibronectin (BMS-2 monoclonal antibody) and hematopoietic cells (monoclonal antibodies against CD45, CD33, and CD14). Results show a decrease of cells positive for CGA-7, HHF-35, and BMS-1, in adherent layer of HLTBMC of frozen-thawed bone marrows. Expression of BMS-2 is unchanged, and CD45 and CD14-positive cells proportionately increased. These results are consistent with an impairment of stromal cell proliferation in frozen-thawed marrows, without impairment of most stromal cell functions. The difference between stromal cell and hematopoietic cell kinetics seems to be an additional fact suggesting a different origin for both cell populations.

We have investigated the distribution of membrane molecules on CD34+ hematopoietic cells isolated from human bone marrow (BM) and cord blood (CB). A distinct CD10+ population was present in BM, but it was not detected in CB. Most CD34+ CD10+ cells in BM were B-cell precursors (BCP), because they expressed CD19. However, CD40 and CD37 were found on the majority of CD34+ cells from either BM or CB, demonstrating that these antigens are not restricted to B-lineage CD34+ cells. CD40 and CD37 were lost during culture of CD34+ cells in the presence of interleukin 3 (IL-3), indicating transient expression early in myeloid development. CD13 antigen was detected on virtually all CD34+ cells from BM and CB. Accordingly, CD13 was present on CD34+ CD10+ cells, demonstrating that this structure is not restricted to myeloid CD34+ cells. In contrast, myeloid CD33 antigen was not detected on CD34+ CD10+ cells. Expression levels of CD13 and of CD33 were heterogeneous in BM, reflecting diversity within the resident CD34+ population. CD25 and CD71 were found on a proportion of CD34+ cells from either BM or CB and maintained during culture in IL-3, consistent with a distribution on activated cells. Finally, a variety of adhesion receptors were present on CD34+ cells. These included the alpha 4 beta 1 (VLA-4), alpha 5 beta 1 (VLA-5), and alpha L beta 2 (LFA-1) integrins, as well as ICAM-1, LFA-3, H-CAM, and LAM-1. Expression of adhesion receptors was remarkably similar in BM and CB, and it followed an all-or-nothing pattern that failed to delineate CD34+ subsets. Taken together, our data show that although CD34+ cells from BM constitute a more heterogeneous population, resident and circulating CD34+ cells largely display the same cell-surface molecules.

This study was designed to assess the presence of endogenous granulocyte-macrophage colony-stimulating factor (GM-CSF) within adherent layers of human Dexter-type cultures and to investigate the effect on granulomonopoiesis of adding exogenous GM-CSF to the culture medium. The presence of GM-CSF was demonstrated using a bioassay, in which adherent layers from normal bone marrows gave rise to endogenous granulocyte-macrophage colony-forming units (CFU-GM) that were specifically inhibited by increasing amounts of an anti-GM-CSF neutralizing antibody. Using an immunoassay, the estimated amounts of GM-CSF were less than or equal to 40 pg per flask in adherent layers, while remaining undetectable in supernatants. The addition of 10 ng or purified recombinant GM-CSF per milliliter of culture medium increased slightly the CFU-GM output over a 5-week culture period. The addition of 50 ng/mL decreased significantly the CFU-GM output after 5 weeks of culture. This decrease was associated with major modifications of the adherent layer cell composition. Large round or ovoid macrophages were generated at the expense of the interdigitated and elongated stromal cells and the extracellular fibronectin network was no longer observed. These studies suggest that GM-CSF production by accessory cells (stromal cells and/or monocytes) is almost equal to its consumption by hematopoietic cells, a situation similar to that found in long-term cultures of murine marrows. They also show that the maintenance of granulomonopoiesis is decreased by adding more than 10 ng/mL of exogenous GM-CSF to the culture medium, which is related to the induction of adherent macrophages, the disappearance of the major smooth-muscle-like stromal cell component of the adherent layer, and that of the fibronectin extracellular matrix.

A suicide technique applicable to human bone marrow granulocytic progenitor cells has been previously described (3). This study discusses the conditions for its use on bone marrow aspirates poor in cells. When the number of cells exposed to hydroxyurea (HU) is proportional to the quantity of HU it is possible to avoid artifacts due to HU toxicity. This technique can repeatedly reproduce a 40--50% suicide. To obtain this result we suggest using a 6.10(-6) mM/ml/cell HU concentration.

We report a case of splenectomized spent polycythemia, where under the influence of alkylating agents (busulfan or chlorambucil), a true redistribution of granulopoiesis appeared. Before treatment, granulopoiesis was confined to the liver (within the portal spaces and the sinusoids), whereas bone marrow was depleted of any hematopoiesis, being the site of a mutilating fibrosis; the blood concentration of granulomonocytic colony-forming cells (GM-CFCs) was high. After a year of discontinuous treatment an intense granulopoiesis was present in bone marrow, comprising more than 90% of the hematopoietic cells, whereas circulating colony-forming cells were low to nil. This phenomenon was long-lasting, since after another year of treatment, a third bone marrow biopsy revealed the persistence of an active granulopoiesis. During the last year of treatment, the treatment was continuous with chlorambucil. After 6 months a decrease in polymorph and platelet values appeared and treatment had to be interrupted. Death supervened one month after treatment interruption. Histological examination revealed the lack of any intrahepatic hematopoiesis whereas bone marrow granulopoiesis was active but presented gross maturation abnormalities. The results obtained in this case permit discussion of some aspects of the physiopathology of myelofibrosis, and particularly the genesis of extramedullary hematopoiesis in this clonal disease.

Eight patients presenting primary myelofibrosis or spent polycythemia were submitted to a ferrokinetic study, a triphine bone marrow biopsy and a bone marrow puncture. In all cases before treatment (splenic radiotherapy) ferrokinetic measurements demonstrated an ineffective erythropoiesis, the intensity of which was precised on bone marrow biopsies, in numbering the erythroblasts per surface unit. Bone marrow biopsies permitted also, through a semiquantitative estimate of the bone marrow cellularity, to evaluate an aplasia component not always expected with ferrokinetic study. Study of bone marrow allowed to precise the site of the erythroblastic abortion; cellular death might occur during the last nitosis of the erythroblastic series (transition from the polychromatophil erythroblasts to the acidophil erythroblasts). In order to delineate the general pattern of erythropoiesis before treatment and when assessing the results of a treatment, besides ferrokinetic measurements, the study of bone marrow biopsy and smears appears relevant.

The action of human serum on granulocyte-macrophage progenitors (CFC-gm) from normal human bone marrow has been studied. When human serum was added to a culture of nonadherent bone marrow cells, no colony formation was observed in the absence of exogenous colony-stimulating factor (CSF); however, the number of colonies increased with the addition of exogenous CSF. When serum was added to a culture of unseparated bone marrow buffy coat cells, colony formation appeared even in the absence of exogenous CSF. These results show a synergic effect of serum and exogenous CSF and suggest that adherent cells, when stimulated by a serum component, secrete endogenous CSF.

Background Mesenchymal stromal cells (MSC) have become the focus of cellular therapeutics but little is known regarding bone marrow (BM) MSC derived from children. As MSC constitute part of BM stroma, we examined their properties in children with hematologic diseases. Methods BM MSC from children with non-malignant hematologic disorders and acute lymphoblastic leukemia (ALL) were isolated and expanded. MSC were immunophenotypically characterized and their functional characteristics were assessed by CFU-F assay and cell doubling time calculation. Their ability for trilineage differentiation was verified by molecular and histochemical methods. Apoptosis was evaluated and clonal analysis was performed. Results MSC were isolated from BM of all groups. They acquired the mesenchymal-related markers from the first passage, with a simultaneous decrease of hematopoietic markers. A very low percentage of apoptotic cells was detected in all passages. The proliferative and clonogenic capacity did not differ among groups, with the exception of ALL at diagnosis, in which they were defective. Histochemical and molecular analysis of differentiated MSC yielded characteristics for adipocytes, osteoblasts and chondrocytes. Clonal analysis in a number of BM samples revealed a highly heterogeneous population of cells within each clone. Discussion MSC from BM of children with hematologic disorders, with the exception of ALL at diagnosis, can be isolated in sufficient number and quality to serve as a potential source for clinical applications. [ABSTRACT FROM AUTHOR]