Abnormalities of bone marrow mesenchymal cells in multiple myeloma patients

In vitro growth of hematopoietic progenitors and stromal bone marrow cells from patients with multiple myeloma

In the present study we have determined the content of hematopoietic and stromal progenitors in multiple myeloma (MM) bone marrow, and assessed their in vitro growth. Marrow cells were obtained from 17 MM patients at the time of diagnosis, and from 6 hematologically normal subjects. When mononuclear cells (MNC) from MM marrow were cultured, reduced numbers of hematopoietic progenitors were detected and their growth in long-term cultures was deficient, as compared to cultures of normal cells. When cell fractions enriched for CD34(+) Lin(-) cells were obtained, the levels of hematopoietic progenitors from MM marrow were within the normal range, and so was their growth kinetics in liquid suspension cultures. The levels of fibroblast progenitors in MM were not statistically different from those in normal marrow; however, their proliferation potential was significantly reduced. Conditioned media from MM-derived MNC and stroma cells contained factors that inhibited normal progenitor cell growth. Our observations suggest that hematopoietic progenitors in MM marrow are intrinsically normal; however, their growth in LTMC may be hampered by the presence of abnormal accessory and stroma cells. These results suggest that besides its role in the generation of osteolytic lesions and the expansion of the myeloma clone, the marrow microenvironment in MM may have a negative effect on hematopoiesis.

Bone marrow microenvironment in myelomagenesis: its potential role in early diagnosis

Multiple myeloma (MM) is the second most common hematological malignancy, with an overall survival of 4-6 years. It is always preceded by a premalignant stage called monoclonal gammopathy of unknown significance (MGUS). Importantly, at this time we lack reliable predictors to determine who will progress from MGUS to MM, and who will remain stable. The bone marrow microenvironment plays a key role in myelomagenesis (growth, survival and migration of malignant plasma cells). In the present review, we summarize and discuss our current understanding of the bone marrow microenvironment and its compartments in relation to myelomagenesis. Although it remains to be proven, we believe that an improved characterization of the cellular constituents, the extracellular matrix components and the soluble factors of the bone marrow could open up novel avenues to better understand underlying mechanisms of the transformation from MGUS to MM. Ultimately, this will lead to the development of early treatment of high-risk precursor disease aimed to delay/prevent MM.

Bone marrow stromal cells from multiple myeloma patients uniquely induce bortezomib resistant NF-kappaB activity in myeloma cells

Background

Components of the microenvironment such as bone marrow stromal cells (BMSCs) are well known to support multiple myeloma (MM) disease progression and resistance to chemotherapy including the proteasome inhibitor bortezomib. However, functional distinctions between BMSCs in MM patients and those in disease-free marrow are not completely understood. We and other investigators have recently reported that NF-κB activity in primary MM cells is largely resistant to the proteasome inhibitor bortezomib, and that further enhancement of NF-κB by BMSCs is similarly resistant to bortezomib and may mediate resistance to this therapy. The mediating factor(s) of this bortezomib-resistant NF-κB activity is induced by BMSCs is not currently understood.

Results

Here we report that BMSCs specifically derived from MM patients are capable of further activating bortezomib-resistant NF-κB activity in MM cells. This induced activity is mediated by soluble proteinaceous factors secreted by MM BMSCs. Among the multiple factors evaluated, interleukin-8 was secreted by BMSCs from MM patients at significantly higher levels compared to those from non-MM sources, and we found that IL-8 contributes to BMSC-induced NF-κB activity.

Conclusions

BMSCs from MM patients uniquely enhance constitutive NF-κB activity in MM cells via a proteinaceous secreted factor in part in conjunction with IL-8. Since NF-κB is known to potentiate MM cell survival and confer resistance to drugs including bortezomib, further identification of the NF-κB activating factors produced specifically by MM-derived BMSCs may provide a novel biomarker and/or drug target for the treatment of this commonly fatal disease.

Osteoblastogenesis and tumor growth in myeloma

Myeloma is associated with suppression of osteoblastogenesis, consequentially resulting in increased osteoclast activity and induction of typical osteolytic bone disease. The molecular mechanisms by which myeloma cells suppress osteoblastogenesis and the consequences of increased osteoblast activity on myeloma cell growth have been partially delineated only recently. Reduced osteoblastogenesis is a consequence of abnormal properties and impaired osteogenic potential of osteoprogenitor cells from myeloma patients and is also the result of production of multiple osteoblastogenesis inhibitors by myeloma cells and by microenvironmental cells within the myelomatous bone. Nevertheless, novel osteoblast-activating agents (e.g. proteasome inhibitor bortezomib) are capable of inducing bone formation in myeloma animal models and clinically. These agents induce increased osteoblast activity, often coupled with a concomitant reduction in osteoclastogenesis, that is strongly associated with reduced myeloma tumor burden. In vitro, osteoblasts, in contrast to osteoclasts, attenuate the growth of myeloma cells from a large subset of patients; potential molecular mechanisms are discussed. These studies suggest that myeloma cells suppress osteoblastogenesis to their advantage and that increased osteoblast activity is a promising approach to treat myeloma bone disease and simultaneously control myeloma development and progression.

The clonogenic potential of hematopoietic stem cells and mesenchymal stromal cells in various hematologic diseases: a pilot study

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) are the most popular cells used in regenerative medicine and biotechnology. The clonogenic potential of these cells is defined by colony-forming unit-fibroblasts (CFU-F). It is well known that there is an interaction between hematopoietic cells and stromal cells in disease formation pathogenesis. Therefore we hypothesized that there should be a quantitative and qualitative relationship between MSC colonies (CFU-F) and hematopoietic stem cell colonies (colony-forming unit-granulocyte-macrophages; CFU-GM) among patients with and without hematologic diseases.

METHODS

Forty-two patients were included in this study. Patients were divided into three groups: group A, patients with hematologic malignancies (n =20); group B, patients with bone marrow (BM) failure (n =11); group C, patients without hematologic diseases (n =11). BM aspirates were plated in different densities for CFU-F culture. The plating density was the same for CFU-GM culture.

RESULTS

CFU-GM colonies grew in 90% of group A cells and all of group B and C cells (P= 0.0001). CFU-F colonies became visible on the ninth day of plating in group A and on the eight day in groups B and C. There was no statistically significant difference between the groups for the duration of CFU-F colony formation (P= 0.12). There were differences in the morphology of the colonies among the groups.

CONCLUSIONS

This is the first study that has compared the clonogenic potential of stromal cells and hematopoietic stem cells in the same subjects with and without hematologic diseases. No correlation was shown between the clonogenic potential of stromal cells and hematopoietic cells.

Advances in the understanding of myeloma bone disease and tumour growth

Advances in multiple myeloma support the notion that the associated bone disease, characterized by increased osteoclastogenesis and suppressed osteoblastogenesis, is both a consequence and necessity of tumour progression. Osteoblastogenesis is suppressed by secreted inhibitors and dysregulation of cell-surface 'coupling' factors on osteogenic cells. Osteoclastogenesis is increased as a consequence of osteoblast deactivation and of production of osteoclast-activating factors. Osteoclasts express soluble and cell-surface factors that stimulate myeloma growth, while osteoblasts produce bone-building factors that restrain growth of myeloma cells that are dependent on the microenvironment; detailed molecular mechanisms are discussed. Experimental and clinical findings indicate that pharmacological and experimental osteoblast-activating agents that effectively promote bone formation also reduce growth of myeloma cells within bone, seemingly by simultaneously stimulating osteoblastogenesis and restraining osteoclastogenesis. Unravelling mechanisms of myeloma bone disease expands horizons for developing novel interventions and also facilitates better understanding of the association between induction of osteolysis and disease progression.

Regulation of stemness and stem cell niche of mesenchymal stem cells: implications in tumorigenesis and metastasis

Human mesenchymal stem cells (MSCs) derived from adult tissues have been considered a candidate cell type for cell-based tissue engineering and regenerative medicine. These multipotent cells have the ability to differentiate along several mesenchymal lineages and possibly along non-mesenchymal lineages. MSCs possess considerable immunosuppressive properties that can influence the surrounding tissue positively during regeneration, but perhaps negatively towards the pathogenesis of cancer and metastasis. The balance between the naïve stem state and differentiation is highly dependent on the stem cell niche. Identification of stem cell niche components has helped to elucidate the mechanisms of stem cell maintenance and differentiation. Ultimately, the fate of stem cells is dictated by their microenvironment. In this review, we describe the identification and characterization of bone marrow-derived MSCs, the properties of the bone marrow stem cell niche, and the possibility and likelihood of MSC involvement in cancer progression and metastasis.

Distinct transcriptional profiles characterize bone microenvironment mesenchymal cells rather than osteoblasts in relationship with multiple myeloma bone disease

OBJECTIVE

Multiple myeloma (MM) is characterized by a high incidence of osteolytic bone lesions, which have been previously correlated with the gene expression profiles of MM cells. The aim of this study was to investigate the transcriptional patterns of cells in the bone microenvironment and their relationships with the presence of osteolysis in MM patients.

MATERIALS AND METHODS

Both mesenchymal (MSC) and osteoblastic (OB) cells were isolated directly from bone biopsies of MM patients and controls to perform gene expression profiling by microarrays and real-time polymerase chain reaction on selected bone-related genes.

RESULTS

We identified a series of upregulated and downregulated genes that were differentially expressed in the MSC cells of osteolytic and nonosteolytic patients. Comparison of the osteolytic and nonosteolytic samples also showed that the MSC cells and OB had distinct transcriptional patterns. No significantly modulated genes were found in the OBs of the osteolytic and nonosteolytic patients.

CONCLUSIONS

Our data suggest that the gene expression profiles of cells of the bone microenvironment are different in MM patients and controls, and that MSC cells, but not OBs, have a distinct transcriptional pattern associated with the occurrence of bone lesions in MM patients. These data support the idea that alterations in MSC cells may be involved in MM bone disease.

Vascular endothelial growth factor (VEGF) as a key therapeutic trophic factor in bone marrow mesenchymal stem cell-mediated cardiac repair

We recently demonstrated a novel effective therapeutic regimen for treating hamster heart failure based on injection of bone marrow mesenchymal stem cells (MSCs) or MSC-conditioned medium into the skeletal muscle. The work highlights an important cardiac repair mechanism mediated by the myriad of trophic factors derived from the injected MSCs and local musculature that can be explored for non-invasive stem cell therapy. While this therapeutic regimen provides the ultimate proof that MSC-based cardiac repair is mediated by the trophic actions independent of MSC differentiation or stemness, the trophic factors responsible for cardiac regeneration after MSC therapy remain largely undefined. Toward this aim, we took advantage of the finding that human and porcine MSCs exhibit species-related differences in expression of trophic factors. We demonstrate that human MSCs when compared to porcine MSCs express and secrete 5-fold less vascular endothelial growth factor (VEGF) in conditioned medium (40+/-5 and 225+/-17 pg/ml VEGF, respectively). This deficit in VEGF output was associated with compromised cardiac therapeutic efficacy of human MSC-conditioned medium. Over-expression of VEGF in human MSCs however completely restored the therapeutic potency of the conditioned medium. This finding indicates VEGF as a key therapeutic trophic factor in MSC-mediated myocardial regeneration, and demonstrates the feasibility of human MSC therapy using trophic factor-based cell-free strategies, which can eliminate the concern of potential stem cell transformation.

The ephrinB2/EphB4 axis is dysregulated in osteoprogenitors from myeloma patients and its activation affects myeloma bone disease and tumor growth

Myeloma bone disease is caused by uncoupling of osteoclastic bone resorption and osteoblastic bone formation. Bidirectional signaling between the cell-surface ligand ephrinB2 and its receptor, EphB4, is involved in the coupling of osteoblastogenesis and osteoclastogenesis and in angiogenesis. EphrinB2 and EphB4 expression in mesenchymal stem cells (MSCs) from myeloma patients and in bone cells in myelomatous bones was lower than in healthy counterparts. Wnt3a induced up-regulation of EphB4 in patient MSCs. Myeloma cells reduced expression of these genes in MSCs, whereas in vivo myeloma cell-conditioned media reduced EphB4 expression in bone. In osteoclast precursors, EphB4-Fc induced ephrinB2 phosphorylation with subsequent inhibition of NFATc1 and differentiation. In MSCs, EphB4-Fc did not induce ephrinB2 phosphorylation, whereas ephrinB2-Fc induced EphB4 phosphorylation and osteogenic differentiation. EphB4-Fc treatment of myelomatous SCID-hu mice inhibited myeloma growth, osteoclastosis, and angiogenesis and stimulated osteoblastogenesis and bone formation, whereas ephrinB2-Fc stimulated angiogenesis, osteoblastogenesis, and bone formation but had no effect on osteoclastogenesis and myeloma growth. These chimeric proteins had similar effects on normal bone. Myeloma cells expressed low to undetectable ephrinB2 and EphB4 and did not respond to the chimeric proteins. The ephrinB2/EphB4 axis is dysregulated in MM, and its activation by EphB4-Fc inhibits myeloma growth and bone disease.

Muscular dystrophy therapy by nonautologous mesenchymal stem cells: muscle regeneration without immunosuppression and inflammation

BACKGROUND

The use of nonautologous stem cells isolated from healthy donors for stem-cell therapy is an attractive approach, because the stem cells can be culture expanded in advance, thoroughly tested, and formulated into off-the-shelf medicine. However, human leukocyte antigen compatibility and related immunosuppressive protocols can compromise therapeutic efficacy and cause unwanted side effects.

METHODS

Mesenchymal stem cells (MSCs) have been postulated to possess unique immune regulatory function. We explored the immunomodulatory property of human and porcine MSCs for the treatment of delta-sarcoglycan-deficient dystrophic hamster muscle without immunosuppression. Circulating and tissue markers of inflammation were analyzed. Muscle regeneration and stem-cell fate were characterized.

RESULTS

Total white blood cell counts and leukocyte-distribution profiles were similar among the saline- and MSC-injected dystrophic hamsters 1 month posttreatment. Circulating levels of immunoglobulin A, vascular cell adhesion molecule-1, myeloperoxidase, and major cytokines involved in inflammatory response were not elevated by MSCs, nor were expression of the leukocyte common antigen CD45 and the cytokine transcriptional activator NF-kappaB in the injected muscle. Treated muscles exhibited increased cell-cycle activity and attenuated oxidative stress. Injected MSCs were found to be trapped in the musculature, contribute to both preexisting and new muscle fibers, and mediates capillary formation.

CONCLUSIONS

Intramuscular injection of nonautologous MSCs can be safely used for the treatment of dystrophic muscle in immunocompetent hosts without inflaming the host immune system.

A comparison of cytokine production in 2-dimensional and 3-dimensional cultures of bone marrow stromal cells of multiple myeloma patients in response to RPMI8226 myeloma cells

We examined cytokine production by bone marrow stromal cells (BMSCs) of patients with multiple myeloma (MM) in response to contact with myeloma RPMI8226 cells in standard 2-dimensional (2D) cultures and in 3-dimensional (3D) cultures on a gelatine sponge scaffold. It was detected that BMSCs in the 3D cultures produced more IL-11 and HGF and less IL-10 than in the 2D cultures. Moreover, RPMI8226 cells after contact with BMSCs in 3D cultures produced more sIL-6R than in the classic 2D cultures. We concluded that 3D cultures of BMSCs with myeloma cells offered a promising model for in vitro examination of interactions between myeloma cells and the bone marrow stroma and for examination of potent antimyeloma agents.

Mesenchymal stem cells from multiple myeloma patients display distinct genomic profile as compared with those from normal donors

It is an open question whether in multiple myeloma (MM) bone marrow stromal cells contain genomic alterations, which may contribute to the pathogenesis of the disease. We conducted an array-based comparative genomic hybridization (array-CGH) analysis to compare the extent of unbalanced genomic alterations in mesenchymal stem cells from 21 myeloma patients (MM-MSCs) and 12 normal donors (ND-MSCs) after in vitro culture expansion. Whereas ND-MSCs were devoid of genomic imbalances, several non-recurrent chromosomal gains and losses (>1 Mb size) were detected in MM-MSCs. Using real-time reverse transcription PCR, we found correlative deregulated expression for five genes encoded in regions for which genomic imbalances were detected using array-CGH. In addition, only MM-MSCs showed a specific pattern of 'hot-spot' regions with discrete (<1 Mb) genomic alterations, some of which were confirmed using fluorescence in situ hybridization (FISH). Within MM-MSC samples, unsupervised cluster analysis did not correlate with particular clinicobiological features of MM patients. We also explored whether cytogenetic abnormalities present in myelomatous plasma cells (PCs) were shared by matching MSCs from the same patients using FISH. All MM-MSCs were cytogenetically normal for the tested genomic alterations. Therefore we cannot support a common progenitor for myeloma PCs and MSCs.

Abnormal cytokine production by bone marrow stromal cells of multiple myeloma patients in response to RPMI8226 myeloma cells

INTRODUCTION

Recent studies indicate that bone marrow stromal cells (BMSCs) derived from patients with multiple myeloma (MM) differ from those of healthy donors in their expression of extracellular matrix compounds and in cytokine production. It is not known whether these abnormalities are primary or are acquired by BMSCs on contact with MM cells.

MATERIALS AND METHODS

Interleukin (IL)-6, IL-11, IL-10, and tumor necrosis factor (TNF)-alpha production by CD166+ mesenchymal BMSCs and the CD38+/CD138+ RPMI8226 myeloma cell line cultivated in vitro in monocultures or co-cultivated under cell-to-cell contact or non-contact conditions in the presence of a tissue culture insert were measured. Intracellular cytokines were measured by flow cytometry analysis as the percentage of cytokine-producing cells or by mean fluorescence intensity as the level of cytokine expression in cells. Additionally, ELISA was used to measure IL-6, soluble IL-6 receptor (sIL-6R), IL-11, IL-10, TNF-alpha, B-cell-activating factor of the TNF family (BAFF), hepatocyte growth factor (HGF), and osteopontin (OPN) production in the supernatants of the cultures and co-cultures.

RESULTS

A higher ability of the BMSCs of MM patients than in controls was detected to produce IL-6, IL-10, TNF-alpha, OPN, and especially HGF and BAFF in response to the RPMI8226 cells. Moreover, the BMSCs of the MM patients significantly enhanced the production of sIL-6R by the RPMI8226 cells.

DISCUSSION

Cytokines over-expressed by BMSCs of MM patients can function as growth factors for myeloma cells (IL-6, IL-10, HGF), migration stimulatory factors for tumor plasma cells (TNF-alpha, HGF), adhesion stimulatory factors (HGF, BAFF and OPN), stimulators of osteoclastogenesis (IL-6, TNF-alpha), and angiogenic factors (TNF-alpha). The results of this experiment strongly suggest that the BMSCs from MM patients differed in spontaneous and myeloma cell-induced production of cytokines, especially of HGF and BAFF, and these abnormalities were both primary and acquired by the BMSCs on contact with the MM cells. This in turn suggests the presence of an undefined, autocrine stimulation pathway resulting in a prolonged production of cytokines even in long-term cultures in vitro and in vivo. These abnormalities might provide optimal conditions for the proliferation and differentiation of residual tumor cells or their precursors in the affected bone marrow.

Elevated tumor necrosis factor-alpha suppresses TAZ expression and impairs osteogenic potential of Flk-1+ mesenchymal stem cells in patients with multiple myeloma

One of the clinical features of multiple myeloma (MM) is the occurrence of skeletal events, which are characterized by increased bone resorption and decreased bone formation. In contrast to enhanced osteoclastogenesis, little is known about the mechanism of impaired bone formation in MM. Because TAZ, a Runx2/Cbfa1 transcriptional co-activator, has recently been shown to modulate mesenchymal stem cell (MSC) differentiation in favor of osteoblast differentiation, we investigated whether the regulation of TAZ expression played a role in the decreased bone formation of MM. We isolated and purified Flk-1(+)CD31(-)CD34(-) cells with MSC characters from bone marrow (BM) of myeloma patients and healthy donors. We found the osteogenic potential of the MSCs from myeloma patients decreased significantly, and TAZ expression of these cells was lower than that of healthy donors. Human myeloma cell lines (HMCLs) and CD138(+) myeloma cells (MCs) from myeloma patients inhibited osteogenesis of the MSCs from healthy volunteers, which were accompanied by a reduced TAZ expression and elevated TNF-alpha concentration in the supernatant of co-culture systems. The repressed osteogenesis and TAZ expression were both partially restored by neutralization of TNF-alpha. Thus, the decreased osteogenic potential of MSCs of myeloma patients was in part due to TNF-alpha suppressed TAZ expression.

Down-regulation of MHC II in mesenchymal stem cells at high IFN-gamma can be partly explained by cytoplasmic retention of CIITA

Mesenchymal stem cells (MSCs) are located in postnatal bone marrow, show plasticity, are linked to various bone marrow disorders, exhibit phagocytosis, exert Ag-presenting properties (APC), and are immune suppressive. Unlike professional APCs, MSCs respond bimodally to IFN-gamma in MHC-II expression, with expression at 10 U/ml and baseline, and down-regulation at 100 U/ml. The effects at high IFN-gamma could not be explained by down-regulation of its receptor, IFN-gammaRI. In this study, we report on the mechanisms by which IFN-gamma regulates MHC-II expression in MSCs. Gel shift assay and Western blot analyses showed dose-dependent increases in activated STAT-1, indicating responsiveness by IFN-gammaRI. Western blots showed decreased intracellular MHC-II, which could not be explained by decreased transcription of the master regulator CIITA, based on RT-PCR and in situ immunofluorescence. Reporter gene assays with PIII and PIV CIITA promoters indicate constitutive expression of PIII in MSCs and a switch to PIV by IFN-gamma, indicating the presence of factors for effect promoter responses. We explained decreased MHC-II at the level of transcription because CIITA protein was observed in the cytosol and not in nuclei at high IFN-gamma level. The proline/serine/threonine region of CIITA showed significant decrease in phosphorylation at high IFN-gamma levels. An understanding of the bimodal effects could provide insights on bone marrow homeostasis, which could be extrapolated to MSC dysfunction in hematological disorders.

Mesenchymal stem cell abnormalities in patients with multiple myeloma

Osteolytic bone lesions are common in patients with multiple myeloma (MM), a clonal plasma cell disorder, and result from increased osteoclastic bone resorption and decreased osteoblastic bone formation. Because mesenchymal stem cells (MSCs) are committed towards cells of the osteoblast lineage, we compared the in vitro characteristics of MSCs from the bone marrow of 18 MM patients (MM-MSCs) and eight normal donors (ND-MSCs). MM-MSCs displayed deficient growth that could be explained in part by the reduced expression of several growth factor receptors on the surface of MM-MSCs compared with ND-MSCs. Receptor downregulation was observed on RT-PCR analysis. A major finding was an approximately fivefold higher expression of osteoblast inhibitor DKK1 at transcript and protein levels in MM-MSCs than ND-MSCs. These data suggest that defective osteoblast function in patients with advanced MM may be related not only to factors released by tumor myeloma cells but also to MSC abnormalities.

Bone marrow mesenchymal stem cells are abnormal in multiple myeloma

Recent literature suggested that cells of the microenvironment of tumors could be abnormal as well. To address this hypothesis in multiple myeloma (MM), we studied bone marrow mesenchymal stem cells (BMMSCs), the only long-lived cells of the bone marrow microenvironment, by gene expression profiling and phenotypic and functional studies in three groups of individuals: patients with MM, patients with monoclonal gamopathy of undefined significance (MGUS) and healthy age-matched subjects. Gene expression profile independently classified the BMMSCs of these individuals in a normal and in an MM group. MGUS BMMSCs were interspersed between these two groups. Among the 145 distinct genes differentially expressed in MM and normal BMMSCs, 46% may account for a tumor-microenvironment cross-talk. Known soluble factors implicated in MM pathophysiologic features (i.e. IL (interleukin)-6, DKK1) were revealed and new ones were found which are involved in angiogenesis, osteogenic differentiation or tumor growth. In particular, GDF15 was found to induce dose-dependent growth of MOLP-6, a stromal cell-dependent myeloma cell line. Functionally, MM BMMSCs induced an overgrowth of MOLP-6, and their capacity to differentiate into an osteoblastic lineage was impaired. Thus, MM BMMSCs are abnormal and could create a very efficient niche to support the survival and proliferation of the myeloma cells.

Phenotypic and functional characterization of bone marrow mesenchymal stem cells derived from patients with multiple myeloma

Multiple myeloma (MM) is a B-cell neoplasia caused by the proliferation of clonal plasma cells, primarily in the bone marrow (BM). The role of the BM microenvironment in the pathogenesis of the disease has been demonstrated, especially for the survival and growth of the myeloma plasma cells. Functional characterization of the major component of the BM microenvironment, namely the recently characterized mesenchymal stem cells (MSCs), was never performed in MM. Based on a series of 61 consecutive patients, we evaluated the ability of MSCs derived from myeloma patients to differentiate into adipocytes and osteocytes, inhibit T-cell functions, and support normal hematopoiesis. MSCs phenotypic characterization and quantification of interleukin-6 (IL-6) secretion were also performed. As compared to normal MSCs, MSCs from MM patients exhibited normal phenotype, differentiation capacity and long-term hematopoietic support, but showed reduced efficiency to inhibit T-cell proliferation and produced abnormally high amounts of IL-6. Importantly, these characteristics were observed in the absence of any detectable tumor plasma cell. Chromosomal analysis revealed that MM patients MSCs were devoid of chromosomal clonal markers identified in plasma cells. MM MSCs present abnormal features that may participate in the pathogenesis of MM.

In vitro functional defects of bone marrow-derived CD34+ progenitors from newly diagnosed mature B-cell malignancies with bone marrow tumor involvement

OBJECTIVE

We hypothesized that the presence of tumor cells in bone marrow (BM) could alter hematopoietic progenitor cell functions. Therefore, we evaluated phenotypic and in vitro functional properties of BM-derived CD34+ progenitors issued from untreated and newly diagnosed patients presenting a mature B-lymphoproliferative disorder (LPD) involving the BM (Inv+).

PATIENTS AND METHODS

In vitro proliferation and differentiation capacities of primitive and committed progenitors were evaluated by cobblestone area-forming cell (CAFC) and colony-forming cell (CFC) assays, and ex vivo cell expansion. Migratory capacities of CD34+ cells were explored by chemotaxis assays using a CXCL12alpha gradient.

RESULTS

Our results showed that CD34+ cells from Inv+ patients overexpressed CD117 and had a significant decrease of week-3 and -6 CAFC, and CFC frequencies, compared to cells obtained from healthy volunteers and LPD patients without BM involvement (Inv-). In addition, progenitors from Inv+ patients maintained a significantly decreased CFC capacity after ex vivo cell expansion, compared to healthy volunteers. However, the former cells held their migratory capacity in response to CXCL12alpha.

CONCLUSION

Functional defects of primitive and committed CD34+ progenitors detected among LPD patients with BM tumor involvement suggest either that tumor cells may induced bystander effects on progenitors or that "unusual" CD34+ cells may exist in the BM that could belong to the proliferating tumor tissue.

Mesenchymal stem cells in myelodysplastic syndromes: phenotypic and cytogenetic characterization

Bone marrow-derived mesenchymal stem cells (MSC) have been defined as primitive, undifferentiated cells, capable of self-renewal and with the ability to give rise to different cell lineages, including adipocytes, osteocytes, fibroblasts, chondrocytes, and myoblasts. MSC are key components of the hematopoietic microenvironment. Several studies, including some from our own group, suggest that important quantitative and functional alterations are present in the stroma of patients with myelodysplasia (MDS). However, in most of such studies the stroma has been analyzed as a complex network of different cell types and molecules, thus it has been difficult to identify and characterize the cell(s) type(s) that is (are) altered in MDS. In the present study, we have focused on the biological characterization of MSC from MDS. As a first approach, we have quantified their numbers in bone marrow, and have worked on their phenotypic (morphology and immunophenotype) and cytogenetic properties. MSC were obtained by a negative selection procedure and cultured in a MSC liquid culture medium. In terms of morphology, as well as the expression of certain cell markers, no differences were observed between MSC from MDS patients and those derived from normal marrow. In both cases, MSC expressed CD29, CD90, CD105 and Prolyl-4-hydroxylase; in contrast, they did not express CD14, CD34, CD68, or alkaline phosphatase. Interestingly, in five out of nine MDS patients, MSC developed in culture showed cytogenetic abnormalities, usually involving the loss of chromosomal material. All those five cases also showed cytogenetic abnormalities in their hematopoietic cells. Interestingly, in some cases there was a complete lack of overlap between the karyotypes of hematopoietic cells and MSC. To the best of our knowledge, the present study is the first in which a pure population of MSC from MDS patients is analyzed in terms of their whole karyotype and demonstrates that in a significant proportion of patients, MSC are cytogenetically abnormal. Although the reason of this is still unclear, such alterations may have an impact on the physiology of these cells. Further studies are needed to assess the functional integrity of MDS-derived MSC.

Cancer and the microenvironment: myeloma-osteoclast interactions as a model

We have investigated the interaction between tumor cells and specific cells in their microenvironment using myeloma as a model. The role of myeloma-induced osteoclastogenesis in the disease was studied ex vivo. Myeloma plasma cells freshly purified from patients' bone marrow attracted committed osteoclast (OC) precursors (n = 9; P < 0.01) and in 22 experiments directly induced their differentiation to multinucleated, bone-resorbing OCs (P < 0.00002) in a receptor activator of nuclear factor-kappaB ligand-mediated mechanism that was inhibited by the receptor activator of nuclear factor-kappaB (RANK-Fc) in 13 experiments by 71 +/- 12% (P < 0.008). In contrast, myeloma cells did not induce differentiation of peripheral blood mononuclear cells. Myeloma plasma cells cocultured with OCs retained their viability and proliferative activity for >13 weeks. After 14 days in coculture, the plasma cells from 29 patients had higher viability (P < 2 x 10(-6)), fewer apoptotic cells (P < 4 x 10(-15)), and a higher bromodeoxyuridine labeling index (P < 0.0006) than controls. Physical contact between OCs and myeloma cells was required for these effects to take place. No differences were observed between OCs from healthy donors and those from myeloma patients. Blocking interleukin 6 activity, while reducing survival of myeloma cells, had no effect on their proliferative activity. These results support data obtained from animal models and clinical observations on the essential role of the microenvironment in tumor sustenance and progression.

Hypoxia promotes murine bone-marrow-derived stromal cell migration and tube formation

Recent evidence indicates that bone-marrow-derived stromal cells (MSCs) have a histology coherent with endothelial cells that may enable them to contribute to tumor angiogenesis through yet undefined mechanisms. In this work, we investigated the angiogenic properties of murine MSCs involved in extracellular matrix degradation and in neovascularization that could take place in a hypoxic environment such as that encountered in tumor masses. MSCs were cultured in normoxia (95% air and 5% CO(2)) or in hypoxia (1% oxygen, 5% CO(2), and 94% nitrogen). We found that hypoxic culture conditions rapidly induced MSC migration and three-dimensional capillary-like structure formation on Matrigel. In vitro, MSC migration was induced by growth-factor- and cytokine-enriched conditioned media isolated from U-87 glioma cells as well as from MSCs cultured in hypoxic conditions, suggesting both paracrine and autocrine regulatory mechanisms. Although greater vascular endothelial growth factor levels were secreted by MSCs in hypoxic conditions, this growth factor alone could not explain their greater migration. Interestingly, matrix metalloproteinase (MMP)-2 mRNA expression and protein secretion were downregulated, while those of membrane-type (MT)1-MMP were strongly induced by hypoxia. Functional inhibition of MT1-MMP by a blocking antibody strongly suppressed MSC ability to migrate and generate capillary-like structures. Collectively, these data suggest that MSCs may have the capacity to participate in tumor angiogenesis through regulation of their angiogenic properties under an atmosphere of low oxygen that closely approximates the tumor microenvironment.

Environmental guidance of normal and tumor cell plasticity: epithelial mesenchymal transitions as a paradigm

Epithelial mesenchymal transitions are a remarkable example of cellular plasticity. These transitions are the hallmark of embryo development, are pivotal in cancer progression, and seem to occur infrequently in adult organisms. The reduced incidence of transitions in the adult could result from restrictive functions of the microenvironment that stabilizes adult cell phenotypes and prevents plastic behavior. Multipotential progenitor cells exhibiting a mesenchymal phenotype have been derived from various adult tissues. The ability of these cells to differentiate into all germ layer cell types, raises the question as to whether mesenchymal epithelial transitions occur in the adult organism more frequently than presently appreciated. A series of cytokines are known to promote the transitions between epithelium and mesenchyme. Moreover, several transcription factors and other intracellular regulator molecules have been conclusively shown to mediate these transitions. However, the exact molecular basis of these transitions is yet to be resolved. The identification of the restrictive mechanisms that prevent cellular transitions in adult organisms, which seem to be unleashed in cancerous tissues, may lead to the development of tools for therapeutic tissue repair and effective tumor suppression.

Vascular progenitors derived from murine bone marrow stromal cells are regulated by fibroblast growth factor and are avidly recruited by vascularizing tumors

Bone marrow-derived stromal cells (BMSC) possess a population of vascular progenitor cells that enable them to acquire a histology and immunophenotype coherent with endothelial cells (EC). Recent evidence indicates that a hypoxic environment such as that encountered in tumor masses regulates BMSC angiogenic properties by pathways that remain to be defined. It is also unclear as to what extent these marrow-derived precursor cells could contribute to the growth of endothelium-lined vessels at the vicinity of tumor masses. In this study, we found that BMSC exhibited the ability to generate three-dimensional capillary-like networks on Matrigel, and that this property was up-regulated by growth factors-enriched conditioned media isolated from several tumor-derived cell lines. In particular, basic fibroblast growth factor, a key mediator of angiogenesis, was found to be the most potent growth factor for inducing BMSC proliferation, migration, and tubulogenesis. The setup of a new two-dimensional in vitro co-culture assay further showed that BMSC were massively recruited when cultured in the presence of either cancerous or differentiated EC lines. In vivo, subcutaneous co-injection of BMSC with U-87 glioma cells in nude mice resulted in the formation of highly vascularized tumors, where BMSC differentiated into CD31-positive cells and localized at the lumen of vascular structures. Our data suggest that BMSC could be recruited at the sites of active tumor neovascularization through paracrine regulation of their angiogenic properties. These observations may have crucial implications in the development of novel therapies using BMSC engineered to secrete anti-cancerous agents and to antagonize tumor progression.

Gene profiling of a myeloma cell line reveals similarities and unique signatures among IL-6 response, N-ras-activating mutations, and coculture with bone marrow stromal cells

ANBL-6, a myeloma cell line, proliferates in response to interleukin 6 (IL-6) stimulation, coculture with bone marrow stromal cells, and when harboring a constitutively active mutant N-ras gene. Eighteen samples, including 4 IL-6-treated, 3 mutant N-ras-transfected, 3 normal stroma-stimulated, 2 multiple myeloma (MM) stroma-stimulated, and 6 untreated controls were profiled using microarrays interrogating 12 626 genes. Global hierarchical clustering analysis distinguished at least 6 unique expression signatures. Notably, the different stimuli altered distinct functional gene programs. Class comparison analysis (P =.001) revealed 138 genes (54% involved in cell cycle) that distinguished IL-6-stimulated versus nontreated samples. Eighty-seven genes distinguished stroma-stimulated versus IL-6-treated samples (22% encoded for extracellular matrix [ECM] proteins). A total of 130 genes distinguished N-ras transfectants versus IL-6-treated samples (26% involved in metabolism). A total of 157 genes, 20% of these involved in signaling, distinguished N-ras from stroma-interacting samples. All 3 stimuli shared 347 genes, mostly of metabolic function. Genes that distinguished MM1 from MM4 clinical groups were induced at least by one treatment. Notably, only 3 genes (ETV5, DUSP6, and KIAA0735) are uniquely induced in mutant ras-containing cells. We have demonstrated gene expression patterns in myeloma cells that distinguish an intrinsic genetic transformation event and patterns derived from both soluble factors and cell contacts in the bone marrow microenvironment.

Hyaluronan, a major non-protein glycosaminoglycan component of the extracellular matrix in human bone marrow, mediates dexamethasone resistance in multiple myeloma

Originating from a post-switch memory B cell or plasma cell compartment in peripheral lymphoid tissues, malignant multiple myeloma (MM) cells accumulate in the bone marrow of patients with MM. In this favourable microenvironment, their growth and survival are dependent upon both soluble factors and physical cell-to-cell and cell-to-extracellular-matrix contacts. In this study, hyaluronan (HA), a major non-protein glycosaminoglycan component of the extracellular matrix in mammalian bone marrow, acted as a survival factor against dexamethasone (Dex)-induced apoptosis in MM cell lines. These effects were mediated through an interleukin 6 (IL-6) autocrine pathway, involving signal transducers and activators of transcription-3 phosphorylation on IL-6-dependent XG-1 and XG-6 cell lines. HA promoted accumulation of IL-6 in the culture medium without affecting IL-6 gene expression, suggesting that HA protects, stabilizes and concentrates IL-6 close to its site of secretion, thus favouring its autocrine activity. In contrast, in the IL-6-independent RPMI8226 cell line, HA survival effect was mediated through a gp80-IL-6 receptor-independent pathway, resulting in the upregulation of Bcl-2 anti-apoptotic protein expression and nuclear factor-kappaB activation. Taken together, these data suggest that HA antagonizes Dex-induced apoptosis of MM cells by favouring the autocrine activity of different cytokines or growth factors. As HA is a major component of the bone marrow extracellular matrix, these findings support the idea that HA could play a major role in the survival of MM cells in vivo, and could explain why MM cells accumulate in the bone marrow of patients with MM and escape conventional chemotherapy.

Characterization of hyaluronan synthase expression and hyaluronan synthesis in bone marrow mesenchymal progenitor cells: predominant expression of HAS1 mRNA and up-regulated hyaluronan synthesis in bone marrow cells derived from multiple myeloma patients

Hyaluronan (HA) is suggested to play a role in the pathophysiology of multiple myeloma. To further investigate the role of HA in this disease, we examined hyaluronan synthase (Has) gene expression and HA production in bone marrow mesenchymal progenitor cells (bmMPCs) derived from multiple myeloma patients. The relative abundance of mRNA for each HAS gene was determined using competitive reverse transcription-polymerase chain reaction (cRT-PCR), whereas HA production was detected by fluorophore-assisted carbohydrate electrophoresis (FACE). We determined the basal expression of Has isoforms in myeloma bmMPCs and then compared this expression with expression in healthy donor bmMPCs. Of the 3 Has isoforms, Has1 mRNA was expressed predominantly in myeloma bmMPCs, with expression 7.6-fold greater than Has2. Compared with normal bmMPCs, Has1 mRNA expression was 20-fold greater in myeloma bmMPCs. Normal bmMPCs predominantly expressed Has2 mRNA (8.2-fold greater than myeloma bmMPCs). Upon coculture of myeloma bmMPCs with plasma cells, Has1 transcript was strongly attenuated. FACE results show that myeloma bmMPCs synthesize 5.7-fold more HA than those from healthy donors. These data suggest that myeloma bmMPCs could be an important component of the myeloma pathophysiology in vivo by their increased expression of extracellular matrix (ECM) components relevant to plasma cell growth and survival.

The endogenous granulocyte colony-stimulating factor response following autologous peripheral blood stem cell transplantation is impaired in patients with myeloma

Granulocyte colony-stimulating factor (G-CSF) levels were studied in 23 patients (10 myeloma, 13 relapsed Hodgkin's disease, non-Hodgkin's lymphoma or germ cell tumours), post autologous peripheral blood stem cell transplantation (PBSCT). The two groups had similar previous chemotherapy and numbers of CD34+ cells transplanted. All patients received G-CSF by injection starting 8 d post transplantation. Twenty out of 23 patients showed raised endogenous levels of G-CSF before cytokine administration. Myeloma patients showed significantly lower levels of endogenous G-CSF than the other patients (0.767 versus 3.262 ng/ml, P < 0.05). Further rises in G-CSF levels were seen following the administration of exogenous G-CSF which then fell, despite ongoing administration of G-CSF, as neutrophil recovery occurred.