Human Mesenchymal Stem Cells as Precursors of Functional Fibroblastic Reticular Cells: Implications for the Physiopathology of Secondary Lymphoid Organs.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2310-2310
Author(s):  
Karin Tarte ◽  
Patricia Ame-Thomas ◽  
Hélène Maby ◽  
Sylvie Caulet-Maugendre ◽  
Rachel Jean ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Lymph Node ◽  
Stromal Cells ◽  
Stromal Cell ◽  
Lymphoid Organs ◽  
Tnf Α ◽  
Reticular Cells ◽  
Secondary Lymphoid Organs

Abstract Several subsets of stromal cells are found among secondary lymphoid organs where they play a key role in the initiation and maintenance of immune response. In particular, fibroblastic reticular cells (FRC) of the paracortex secrete extracellular matrix (ECM) components that constitute a dense network of conduits allowing antigens carried within the subcapsular afferent lymph to reach the lumen of the medullary high endothelial venules. FRC produce also several chemokines that recruit T, B, and dendritic cells from blood and favour their reciprocal interactions. In addition, follicular dendritic cells (FDC) are located exclusively into germinal centers and allow normal B-cell selection through a complex set of survival signals, including BCR-mediated signal, chemokines and adhesion molecules. FRC and FDC networks are phenotypically and probably functionally altered during development of follicular lymphomas and diffuse large B cell lymphomas, the two most frequent Non-Hodgkin Lymphomas. FRC and FDC are supposed to be of mesenchymal origin even if no conclusive work has been conducted to date in human. We have obtained 15 tonsil-derived stromal cell lines, that displayed all the morphologic, phenotypic, and functional characteristics of FRC, including synthesis of inflammatory (CXCL10, CXCL9, CCL5) and lymph-node specific (CCL19, CCL21) chemokines, and secretion of ECM organized in a reticular meshwork after long-term culture in the presence of TNF-α and lymphotoxin-α1β2 (LT). These cells induced tonsil leukocyte migration and adhesion in vitro. Tonsil-derived stromal cells expressed LTβR, TNFR, and CD40 but were negative for FDC specific markers, such as CD21 or CXCL13, even following in vitro stimulation by TNF-α, LT, and trimeric CD40L. Interestingly, such TNF and LT-dependent FRC differentiation could also be induced in adult bone marrow-derived mesenchymal stem cells (MSC). In addition, MSC-like cells able to differentiate along osteogenic, adipogenic, and chondrogenic lineages at the clonal level were found in normal tonsils. These data shed new lights on our current understanding of lymph node stromal cell origin and strongly suggest that MSC are the precursors of FRC in secondary lymphoid organs, and perhaps in bone marrow in case of FL involvement where ectopic lymph node-like stromal cells are detected in close association with tumor cells. In conclusion, MSC and their progeny trigger differential immune effects, depending on cytokine context, localization and cell contact with immune cells. These properties are probably modified during lymphomas where the contact between malignant B cells and stromal cells is crucial for tumor development.

Human Mesenchymal Stem Cells Isolated from Bone Marrow and Lymphoid Organs Support Tumor B-Cell Growth: Implications in Follicular Lymphoma Pathogenesis.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2409-2409
Author(s):  
Karin Tarte ◽  
Patricia Ame-Thomas ◽  
Hélène Maby-El Hajjami ◽  
Céline Monvoisin ◽  
Rachel Jean ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Mesenchymal Stem Cells ◽  
Cell Migration ◽  
Cell Growth ◽  
B Cell ◽  
Stromal Cells ◽  
Lymphoid Organs ◽  
Reticular Cells ◽  
Secondary Lymphoid Organs

Abstract There is accumulating evidence that cellular microenvironment plays a key role in follicular lymphoma (FL) pathogenesis, both within tumor lymph nodes (LN) and in infiltrated bone marrow (BM) where ectopic LN-like reticular cells are integrated within malignant B-cell nodular aggregates. In normal secondary lymphoid organs, specific stromal cell subsets provide a highly specialized microenvironment that supports immune response. In particular, fibroblastic reticular cells (FRC) mediate immune cell migration, adhesion, and reciprocal interactions. The role of FRC and their postulated progenitors, i.e. bone marrow mesenchymal stem cells (MSC), in FL remains unexplored. In this study, we have investigated the relationships between FRC and MSC and their capacity to sustain malignant B-cell growth. Our findings strongly suggest that secondary lymphoid organs contain bona-fide MSC able to give rise at single-cell level to adipocytes, chondrocytes, and osteoblasts. These LN-derived MSC could also differentiate, in response to a combination of tumor necrosis factor-α (TNF) and lymphotoxin-α1β2 (LT), into fully functional FRC, able to construct a dense extracellular reticular meshwork positive for transglutaminase and fibronectin staining, to produce inflammatory (CXCL9, CXCL10, CCL5, CCL2) and LN-specific (CCL19) chemokines, and to favour lymphoma B-cell growth. Bone marrow-derived MSC (BM-MSC) acquire in vitro a complete FRC phenotype in the same culture conditions. As an exemple, BM-MSC had a strong, although not complete, protective effect on serum deprivation-induced apoptosis of BL2 cell line (mean percentage of CD20posCaspase-3pos cells: 24.8 +/− 17.5% in coculture with BM-MSC versus 80.7 +/- 10.4% in medium alone; P < .05; n =5) and pretreatment with TNF/LT fully restored BL2 viability (mean percentage of CD20posCaspase-3pos cells: 7.4 +/− 4.7%; P < .05; n = 5). Moreover, stimulation of stromal cells by TNF/LT before coculture enhanced the number of viable CD19pos primary FL B cells by 2.4-fold for BM-MSC and 2.3 fold for LN-MSC compared with the culture without stromal cells (P < .05; n = 6). Interestingly, cell contact with lymphoma B-cell lines or purified FL B cells trigger the differentiation of BM-MSC into FRC that, in turn, support malignant B-cell migration, adhesion and survival. Altogether, these new insights into the interactions between lymphoma cells and their microenvironment could offer original therapeutic strategies.

Human mesenchymal stem cells isolated from bone marrow and lymphoid organs support tumor B-cell growth: role of stromal cells in follicular lymphoma pathogenesis

Blood ◽  
2006 ◽  
Vol 109 (2) ◽  
pp. 693-702 ◽  
Author(s):  
Patricia Amé-Thomas ◽  
Hélène Maby-El Hajjami ◽  
Céline Monvoisin ◽  
Rachel Jean ◽  
Delphine Monnier ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Mesenchymal Stem Cells ◽  
Cell Growth ◽  
Follicular Lymphoma ◽  
B Cell ◽  
Lymphoid Organs ◽  
Reticular Cells ◽  
Secondary Lymphoid Organs

Abstract Accumulating evidence indicates that the cellular microenvironment plays a key role in follicular lymphoma (FL) pathogenesis, both within tumor lymph nodes (LNs) and in infiltrated bone marrow where ectopic LN-like reticular cells are integrated within malignant B-cell nodular aggregates. In normal secondary lymphoid organs, specific stromal cell subsets provide a highly specialized microenvironment that supports immune response. In particular, fibroblastic reticular cells (FRCs) mediate immune cell migration, adhesion, and reciprocal interactions. The role of FRCs and their postulated progenitors, that is, bone marrow mesenchymal stem cells (MSCs), in FL remains unexplored. In this study, we investigated the relationships between FRCs and MSCs and their capacity to sustain malignant B-cell growth. Our findings strongly suggest that secondary lymphoid organs contain MSCs able to give rise to adipocytes, chondrocytes, osteoblasts, as well as fully functional B-cell supportive FRCs. In vitro, bone marrow–derived MSCs acquire a complete FRC phenotype in response to a combination of tumor necrosis factor-α and lymphotoxin-α1β2. Moreover, MSCs recruit primary FL cells that, in turn, trigger their differentiation into FRCs, making them able to support malignant B-cell survival. Altogether, these new insights into the cross talk between lymphoma cells and their microenvironment could offer original therapeutic strategies.

scholarly journals A Method for Measurement of Drug Sensitivity of Myeloma Cells Co-Cultured with Bone Marrow Stromal Cells

2013 ◽  
Vol 18 (6) ◽  
pp. 637-646 ◽  
Author(s):  
Kristine Misund ◽  
Katarzyna A. Baranowska ◽  
Toril Holien ◽  
Christoph Rampa ◽  
Dionne C. G. Klein ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Survival ◽  
Stromal Cells ◽  
Bone Marrow Stromal Cells ◽  
Large Scale ◽  
Stromal Cell ◽  
Marrow Stromal Cells ◽  
Cell Nuclei ◽  
Myeloma Cells

The tumor microenvironment can profoundly affect tumor cell survival as well as alter antitumor drug activity. However, conventional anticancer drug screening typically is performed in the absence of stromal cells. Here, we analyzed survival of myeloma cells co-cultured with bone marrow stromal cells (BMSC) using an automated fluorescence microscope platform, ScanR. By staining the cell nuclei with DRAQ5, we could distinguish between BMSC and myeloma cells, based on their staining intensity and nuclear shape. Using the apoptotic marker YO-PRO-1, the effects of drug treatment on the viability of the myeloma cells in the presence of stromal cells could be measured. The method does not require cell staining before incubation with drugs, and less than 5000 cells are required per condition. The method can be used for large-scale screening of anticancer drugs on primary myeloma cells. This study shows the importance of stromal cell support for primary myeloma cell survival in vitro, as half of the cell samples had a marked increase in their viability when cultured in the presence of BMSC. Stromal cell–induced protection against common myeloma drugs is also observed with this method.

scholarly journals Maintenance of high levels of pluripotent hematopoietic stem cells in vitro: effect of stromal cells and c-kit

Blood ◽  
1993 ◽  
Vol 81 (2) ◽  
pp. 365-372 ◽  
Author(s):  
JP Wineman ◽  
S Nishikawa ◽  
CE Muller-Sieburg
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Cell Line ◽  
Stromal Cells ◽  
Stromal Cell ◽  
Hematopoietic Stem ◽  
Stem Cell Maintenance ◽  
Stromal Cell Line ◽  
Cell Maintenance

We show here that mouse pluripotent hematopoietic stem cells can be maintained in vitro on stroma for at least 3 weeks at levels close to those found in bone marrow. The extent of stem cell maintenance is affected by the nature of the stromal cells. The stromal cell line S17 supported stem cells significantly better than heterogeneous, primary stromal layers or the stromal cell line Strofl-1. Stem cells cultured on S17 repopulated all hematopoietic lineages in marrow-ablated hosts for at least 10 months, indicating that this culture system maintained primitive stem cells with extensive proliferative capacity. Furthermore, we demonstrate that, while pluripotent stem cells express c-kit, this receptor appears to play only a minor role in stem cell maintenance in vitro. The addition of an antibody that blocks the interaction of c-kit with its ligand essentially abrogated myelopoiesis in cultures. However, the level of stem cells in antibody-treated cultures was similar to that found in untreated cultures. Thus, it seems likely that the maintenance of primitive stem cells in vitro depends on yet unidentified stromal cell-derived factor(s).

scholarly journals In Vitro Murine Hematopoiesis Supported by Signaling from a Splenic Stromal Cell Line

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Hong Kiat Lim ◽  
Pravin Periasamy ◽  
Helen C. O’Neill
Keyword(s):  
Bone Marrow ◽  
Cell Line ◽  
Stromal Cell ◽  
Hematopoietic Cells ◽  
Model Systems ◽  
Hematopoietic Stem ◽  
Cell Production ◽  
Stromal Cell Line ◽  
Reticular Cells

There are very few model systems which demonstrate hematopoiesis in vitro. Previously, we described unique splenic stromal cell lines which support the in vitro development of hematopoietic cells and particularly myeloid cells. Here, the 5G3 spleen stromal cell line has been investigated for capacity to support the differentiation of hematopoietic cells from progenitors in vitro. Initially, 5G3 was shown to express markers of mesenchymal but not endothelial or hematopoietic cells and to resemble perivascular reticular cells in the bone marrow through gene expression. In particular, 5G3 resembles CXCL12-abundant reticular cells or perivascular reticular cells, which are important niche elements for hematopoiesis in the bone marrow. To analyse the hematopoietic support function of 5G3, specific signaling pathway inhibitors were tested for the ability to regulate cell production in vitro in cocultures of stroma overlaid with bone marrow-derived hematopoietic stem/progenitor cells. These studies identified an important role for Wnt and Notch pathways as well as tyrosine kinase receptors like c-KIT and PDGFR. Cell production in stromal cocultures constitutes hematopoiesis, since signaling pathways provided by splenic stroma reflect those which support hematopoiesis in the bone marrow.

scholarly journals Stromal cells in myeloid and lymphoid long-term bone marrow cultures can support multiple hemopoietic lineages and modulate their production of hemopoietic growth factors

Blood ◽  
1986 ◽  
Vol 68 (6) ◽  
pp. 1348-1354 ◽  
Author(s):  
A Johnson ◽  
K Dorshkind
Keyword(s):  
Bone Marrow ◽  
Stromal Cells ◽  
Stromal Cell ◽  
Culture Conditions ◽  
B Lymphopoiesis ◽  
Bone Marrow Cultures ◽  
Factor Secretion ◽  
Marrow Cultures

Abstract Hemopoiesis in long-term bone marrow cultures (LTBMC) is dependent on adherent stromal cells that form an in vitro hemopoietic microenvironment. Myeloid bone marrow cultures (MBMC) are optimal for myelopoiesis, while lymphoid bone marrow cultures (LBMC) only support B lymphopoiesis. The experiments reported here have made a comparative analysis of the two cultures to determine whether the stromal cells that establish in vitro are restricted to the support of myelopoiesis or lymphopoiesis, respectively, and to examine how the different culture conditions affect stromal cell physiology. In order to facilitate this analysis, purified populations of MBMC and LBMC stroma were prepared by treating the LTBMC with the antibiotic mycophenolic acid; this results in the elimination of hemopoietic cells while retaining purified populations of functional stroma. Stromal cell cultures prepared and maintained under MBMC conditions secreted myeloid growth factors that stimulated the growth of granulocyte-macrophage colonies, while no such activity was detected from purified LBMC stromal cultures. However, this was not due to the inability of LBMC stroma to mediate this function. Transfer of LBMC stromal cultures to MBMC conditions resulted in an induction of myeloid growth factor secretion. When seeded under these conditions with stromal cell- depleted populations of hemopoietic cells, obtained by passing marrow through nylon wool columns, the LBMC stromal cells could support long- term myelopoiesis. Conversely, transfer of MBMC stroma to LBMC conditions resulted in a cessation of myeloid growth factor secretion; on seeding these cultures with nylon wool-passed marrow, B lymphopoiesis, but not myelopoiesis, initiated. These findings indicate that the stroma in the different LTBMC are not restricted in their hemopoietic support capacity but are sensitive to culture conditions in a manner that may affect the type of microenvironment formed.

Leishmania donovani infection of bone marrow stromal macrophages selectively enhances myelopoiesis, by a mechanism involving GM-CSF and TNF-α

Blood ◽  
2000 ◽  
Vol 95 (5) ◽  
pp. 1642-1651 ◽  
Author(s):  
Sara E. J. Cotterell ◽  
Christian R. Engwerda ◽  
Paul M. Kaye
Keyword(s):  
Infectious Disease ◽  
Bone Marrow ◽  
Stromal Cell ◽  
Leishmania Donovani ◽  
Protozoan Parasite ◽  
Gm Csf ◽  
Tnf Α ◽  
Macrophage Colony

Alterations in hematopoiesis are common in experimental infectious disease. However, few studies have addressed the mechanisms underlying changes in hematopoietic function or assessed the direct impact of infectious agents on the cells that regulate these processes. In experimental visceral leishmaniasis, caused by infection with the protozoan parasite Leishmania donovani, parasites persist in the spleen and bone marrow, and their expansion in these sites is associated with increases in local hematopoietic activity. The results of this study show that L donovani targets bone marrow stromal macrophages in vivo and can infect and multiply in stromal cell lines of macrophage, but not other lineages in vitro. Infection of stromal macrophages increases their capacity to support myelopoiesis in vitro, an effect mediated mainly through the induction of granulocyte macrophage-colony stimulating factor and tumor necrosis factor-. These data are the first to directly demonstrate that intracellular parasitism of a stromal cell population may modify its capacity to regulate hematopoiesis during infectious disease.

scholarly journals Phenotypic Characterization of Bone Marrow Mononuclear Cells and Derived Stromal Cell Populations from Human Iliac Crest, Vertebral Body and Femoral Head

2019 ◽  
Vol 20 (14) ◽  
pp. 3454 ◽  
Author(s):  
Marietta Herrmann ◽  
Maria Hildebrand ◽  
Ursula Menzel ◽  
Niamh Fahy ◽  
Mauro Alini ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Femoral Head ◽  
Cell Surface ◽  
Cell Cultures ◽  
Vertebral Body ◽  
Stromal Cells ◽  
Stromal Cell ◽  
Iliac Crest ◽  
Surface Marker

(1) In vitro, bone marrow-derived stromal cells (BMSCs) demonstrate inter-donor phenotypic variability, which presents challenges for the development of regenerative therapies. Here, we investigated whether the frequency of putative BMSC sub-populations within the freshly isolated mononuclear cell fraction of bone marrow is phenotypically predictive for the in vitro derived stromal cell culture. (2) Vertebral body, iliac crest, and femoral head bone marrow were acquired from 33 patients (10 female and 23 male, age range 14–91). BMSC sub-populations were identified within freshly isolated mononuclear cell fractions based on cell-surface marker profiles. Stromal cells were expanded in monolayer on tissue culture plastic. Phenotypic assessment of in vitro derived cell cultures was performed by examining growth kinetics, chondrogenic, osteogenic, and adipogenic differentiation. (3) Gender, donor age, and anatomical site were neither predictive for the total yield nor the population doubling time of in vitro derived BMSC cultures. The abundance of freshly isolated progenitor sub-populations (CD45−CD34−CD73+, CD45−CD34−CD146+, NG2+CD146+) was not phenotypically predictive of derived stromal cell cultures in terms of growth kinetics nor plasticity. BMSCs derived from iliac crest and vertebral body bone marrow were more responsive to chondrogenic induction, forming superior cartilaginous tissue in vitro, compared to those isolated from femoral head. (4) The identification of discrete progenitor populations in bone marrow by current cell-surface marker profiling is not predictive for subsequently derived in vitro BMSC cultures. Overall, the iliac crest and the vertebral body offer a more reliable tissue source of stromal progenitor cells for cartilage repair strategies compared to femoral head.

Donor Origin of Multipotent Adult Progenitor Cells in Radiation Chimeras.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1395-1395
Author(s):  
Morayma Reyes ◽  
Jeffrey S. Chamberlain
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Progenitor Cells ◽  
Y Chromosome ◽  
Stromal Cells ◽  
Mononuclear Cells ◽  
Multipotent Adult Progenitor Cells

Abstract Multipotent Adult Progenitor Cells (MAPC) are bone marrow derived stem cells that can be extensively expanded in vitro and can differentiate in vivo and in vitro into cells of all three germinal layers: ectoderm, mesoderm, endoderm. The origin of MAPC within bone marrow (BM) is unknown. MAPC are believed to be derived from the BM stroma compartment as they are isolated within the adherent cell component. Numerous studies of bone marrow chimeras in human and mouse point to a host origin of bone marrow stromal cells, including mesenchymal stem cells. We report here that following syngeneic bone marrow transplants into lethally irradiated C57Bl/6 mice, MAPC are of donor origin. When MAPC were isolated from BM chimeras (n=12, 4–12 weeks post-syngeneic BM transplant from a transgenic mouse ubiquitously expressing GFP), a mixture of large and small GFP-positive and GFP-negative cells were seen early in culture. While the large cells stained positive for stroma cell markers (smooth muscle actin), mesenchymal stem cell makers (CD73, CD105, CD44) or macrophages (CD45, CD14), the small cells were negative for all these markers and after 30 cell doublings, these cells displayed the classical phenotype of MAPC (CD45−,CD105−, CD44−, CD73−, FLK-1+(vascular endothelial growth factor receptor 2, VEGFR2), Sca-1+,CD13+). In a second experiment, BM obtained one month post BM transplant (n=3) was harvested and mononuclear cells were sorted as GFP-positive and GFP-negative cells and were cultured in MAPC expansion medium. MAPC grew from the GFP-positive fraction. These GFP positive cells displayed the typical MAPC-like immunophenotypes, displayed a normal diploid karyotype and were expanded for more than 50 cell doublings and differentiated into endothelial cells, hepatocytes and neurons. To rule out the possibility that MAPC are the product of cell fusion between a host and a donor cell either in vivo or in our in vitro culture conditions, we performed sex mismatched transplants of female GFP donor BM cells into a male host. BM from 5 chimeras were harvested 4 weeks after transplant and MAPC cultures were established. MAPC colonies were then sorted as GFP-positive and GFP- negative and analyzed for the presence of Y-chromosome by FISH analysis. As expected all GFP-negative (host cells) contained the Y-chromosome whereas all GFP-positive cells (donor cells) were negative for the Y-chromosome by FISH. This proves that MAPC are not derived from an in vitro or in vivo fusion event. In a third study, BM mononuclear cells from mice that had been previously BM-transplanted with syngeneic GFP-positive donors (n=3) were transplanted into a second set of syngeneic recipients (n=9). Two months after the second transplant, BM was harvested and mononuclear cells were cultured in MAPC medium. The secondary recipients also contained GFP-positive MAPC. This is the first demonstration that BM transplantation leads to the transfer of cells that upon isolation in vitro generate MAPCs and, whatever the identity of this cell may be, is eliminated by irradiation. We believe this is an important observation as MAPC hold great clinical potential for stem cell and/or gene therapy and, thus, BM transplant may serve as a way to deliver and reconstitute the MAPC population. In addition, this study provides insight into the nature of MAPC. The capacity to be transplantable within unfractionated BM transplant renders a functional and physiological distinction between MAPC and BM stromal cells. This study validates the use of unfractionated BM transplants to study the nature and possible in vivo role of MAPC in the BM.

Perivascular/Mesenchymal Stem Cells from Multiple Human Tissues Support Hematopoiesis in Vitro.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1361-1361
Author(s):  
Elisa Montelatici ◽  
Gabriella Andriolo ◽  
Mihaela Crisan ◽  
Rosaria Giordano ◽  
Paolo Rebulla ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Stem Cells ◽  
Bone Marrow ◽  
Mesenchymal Stem Cells ◽  
Stromal Cells ◽  
Marrow Stromal Cells ◽  
Hematopoietic Cell ◽  
Human Tissues

Abstract Mesenchymal stem cells (MSC) can be derived selectively in culture from multiple organs, an omnipresence we have recently suggested to be explained by the perivascular location of native MSC ancestors within intact tissues (Crisan et al. 2008, in press). We have now analyzed the ability of MSC extracted pro- or retrospectively from different human tissues to support hematopoiesis. MSC were either classically derived in primary cultures of umbilical cord blood (UCB) lineage-depleted mononuclear cells (n=3) or enzymatically dissociated adult adipose tissue (n=3), or grown as CD146+ NG2+ CD34-CD56- CD45- pericytes (n=2) purified by flow cytometry from fetal skeletal muscle and cultured over the long term. In both settings, identical MSC were obtained that maintained a stable CD146+ CD90+ CD73+ CD105+ CD34- CD45- surface phenotype and could differentiate into skeletal muscle, fat, bone and cartilage. CD34+ hematopoietic progenitors (n=3) immunoselected from term UCB were seeded (5×10e3cells/cm2 in triplicate) onto confluent irradiated layers of MSC derived from UCB, adipose tissue or fetal muscle pericytes (MSCu, MSCa and MSCmp, respectively) or, as a control, MS5 bone marrow stromal cells that allow the proliferation of very primitive human progenitor cells. All studies were approved by the relevant institutional regulatory board. The cells were cocultured for 5 weeks in a classical long-term culture-initiating cell assay in a complete medium (MyeloCult H5100, Stem Cell Technologies) containing hydrocortisone but no added cytokine. Wells were scored daily for the presence of cobblestone areas (CA) and half of the medium was replaced every week. Eventually, trypsinized cells from each well were characterized by flow cytometry for the expression of hematopoietic cell markers and assayed for CFC potential. After 14 days of incubation, colonies grown in semi-solid medium were scored as derived from colony forming units (CFU)-granulocyte, erythroid, macrophage, megakaryocyte (GEMM) and as high-proliferative-potential colony precursors (HPPC), the most primitive hematopoietic cell so far identified in a clonogenic assay in vitro. Within the CD45+ gate, all trypsinized cultures contained comparable percentages of CD34+lin- cells (MSCu: 51±9%; MSCa: 58±14%; MSCmp: 61±19%; MS5: 59±18%), the most immature hematopoietic cell compartment maintained during the long-term coculture. MSCu and MSCmp supported a similar cell proliferation during the whole culture while on MSCa, CA formed very rapidly and consistently but eventually decreased over the long-term culture. Interestingly, MSCu and MSCmp supported the development of the highest numbers of HPPC and of CFU giving rise to the largest GEMM colonies, as compared to MSCa that gave the same results as the control MS5 cell line. In summary, all MSCs tested were able to support hematopoiesis and CA formation, albeit with differences in growth kinetics and morphology of the colonies. Herein we show for the first time that purified human perivascular cells exhibit robust hematopoiesis support in vitro, in addition to multilineage mesodermal developmental potential. In conclusion, we demonstrate that MSC from novel sources distinct from the bone marrow are able to support hematopoiesis. These results further sustain the identity, beyond acronyms, between marrow stromal cells, long known for their support of hematopoiesis, and mesenchymal stem cells that gained more recent credit in the field of regenerative medicine because of their multilineage differentiation potential.

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