Mesenchymal stem cells inhibit proliferation and apoptosis of tumor cells: impact on in vivo tumor growth

Amniotic membrane-derived cells inhibit proliferation of cancer cell lines by inducing cell cycle arrest

Cells derived from the amniotic foetal membrane of human term placenta have drawn particular attention mainly for their plasticity and immunological properties, which render them interesting for stem-cell research and cell-based therapeutic applications. In particular, we have previously demonstrated that amniotic mesenchymal tissue cells (AMTC) inhibit lymphocyte proliferation in vitro and suppress the generation and maturation of monocyte-derived dendritic cells. Here, we show that AMTC also significantly reduce the proliferation of cancer cell lines of haematopoietic and non-haematopoietic origin, in both cell–cell contact and transwell co-cultures, therefore suggesting the involvement of yet-unknown inhibitory soluble factor(s) in this ‘cell growth restraint’. Importantly, we provide evidence that the anti-proliferative effect of AMTC is associated with induction of cell cycle arrest in G0/G1 phase. Gene expression analyses demonstrate that AMTC can down-regulate cancer cells' mRNA expression of genes associated with cell cycle progression, such as cyclins (cyclin D2, cyclin E1, cyclin H) and cyclin-dependent kinase (CDK4, CDK6 and CDK2), whilst they up-regulate cell cycle negative regulator such as p15 and p21, consistent with a block in G0/G1 phase with no progression to S phase. Taken together, these findings warrant further studies to investigate the applicability of these cells for controlling cancer cell proliferation in vivo.

Antitumor effect of embryonic stem cells in a non-small cell lung cancer model: antitumor factors and immune responses

Research in recent years has revealed that embryonic stem cells (ESCs) could generate obvious antitumor effects in both vitro and vivo. In vitro, ESCs could secrete soluble factors that are capable of blocking cancer cells proliferation, moreover, embryonic microenvironments could effectively inhibit tumorigenesis and metastasis; while in vivo, administration of ESCs in tumor-bearing mice could generate significant antitumor effects by indirectly activating the antitumor immune system. In this study, non-small cell lung cancer cells (Lewis Lung Carcinoma cells, LLCs) and ESCs were co-injected together into mice, after that subcutaneous tumor growth was monitored, cellular and humoral immune responses were detected, and different control groups were set to compare the results in different conditions. Our results suggested that compared to be injected alone, ESCs co-injected with cancer cells could inhibit cancer cell growth more efficiently in vivo, with more CD8+ lymphocytes generated in both peripheral circulation and spleen, and with higher serum anticancer cytokine level (interleukin (IL)-2 and interferon (IFN)-γ). We conclude that the boosted antitumor effects induced by ESCs and cancer cells co-injection may be both the effects of antitumor factors secreted by ESCs and immune responses induced by ESCs in vivo.

Immune privilege of stem cells

Immune privilege provides protection to vital tissues or cells of the body when foreign antigens are introduced into these sites. The modern concept of relative immune privilege applies to a variety of tissues and anatomical structures, including the hair follicles and mucosal surfaces. Even sites of chronic inflammation and developing tumors may acquire immune privilege by recruiting immunoregulatory effector cells. Adult stem cells are no exception. For their importance and vitality, many adult stem cell populations are believed to be immune privileged. A preimplantation-stage embryo that derives from a totipotent stem cell (i.e., a fertilized oocyte) must be protected from maternal allo-rejection for successful implantation and development to occur. Embryonic stem cells, laboratory-derived cell lines of preimplantation blastocyst-origin, may, therefore, retain some of the immunological properties of the developing embryo. However, embryonic stem cells and their differentiated tissue derivatives transplanted into a recipient do not necessarily have an ability to subvert immune responses to the extent required to exploit their pluripotency for regenerative medicine. In this review, an extended definition of immune privilege is developed and the capacity of adult and embryonic stem cells to display both relative and acquired immune privilege is discussed. Furthermore, we explore how these intrinsic properties of stem cells may one day be harnessed for therapeutic gain.

Human versus porcine mesenchymal stromal cells: phenotype, differentiation potential, immunomodulation and cardiac improvement after transplantation

Although mesenchymal stromal cells (MSCs) have been applied clinically to treat cardiac diseases, it is unclear how and to which extent transplanted MSCs exert their beneficial effects. To address these questions, pre-clinical MSC administrations are needed for which pigs appear to be the species of choice. This requires the use of porcine cells to prevent immune rejection. However, it is currently unknown to what extent porcine MSCs (pMSCs) resemble human MSCs (hMSCs). Aim of this study was to compare MSC from porcine bone marrow (BM) with human cells for phenotype, multi-lineage differentiation potential, immune-modulatory capacity and the effect on cardiac function after transplantation in a mouse model of myocardial infarction. Flow cytometric analysis revealed that pMSC expressed surface antigens also found on hMSC, including CD90, MSCA-1 (TNAP/W8B2 antigen), CD44, CD29 and SLA class I. Clonogenic outgrowth was significantly enriched following selection of CD271+ cells from BM of human and pig (129 ± 29 and 1961 ± 485 fold, respectively). hMSC and pMSC differentiated comparably into the adipogenic, osteogenic or chondrogenic lineages, although pMSC formed fat much faster than hMSC. Immuno-modulation, an important feature of hMSC, was clearly demonstrated for pMSC when co-cultured with porcine peripheral blood cells stimulated with PMA and pIL-2. Finally, pMSC transplantation after myocardial infarction attenuated adverse remodelling to a similar extent as hMSC when compared to control saline injection. These findings demonstrate that pMSCs have comparable characteristics and functionality with hMSCs, making reliable extrapolation of pre-clinical pMSC studies into a clinical setting very well possible.

Microvesicles derived from human bone marrow mesenchymal stem cells inhibit tumor growth

Mesenchymal stem cells (MSCs) have opposite effects on tumor growth, being able either to favor angiogenesis and tumor initiation or to inhibit progression of established tumors. Factors produced by MSCs within the tumor microenvironment may be relevant for their biological effects. Recent studies demonstrated that microvesicles (MVs) are an integral component of inter-cellular communication within the tumor microenvironment. In the present study, we evaluated whether MVs derived from human bone marrow MSCs may stimulate or inhibit in vitro and in vivo growth of HepG2 hepatoma, Kaposi's sarcoma, and Skov-3 ovarian tumor cell lines. We found that MVs inhibited cell cycle progression in all cell lines and induced apoptosis in HepG2 and Kaposi's cells and necrosis in Skov-3. The observed activation of negative regulators of cell cycle may explain these biological effects. In vivo intra-tumor administration of MVs in established tumors generated by subcutaneous injection of these cell lines in SCID mice significantly inhibited tumor growth. In conclusion, MVs from human MSCs inhibited in vitro cell growth and survival of different tumor cell lines and in vivo progression of established tumors.

Advances in stem cell therapy for spinal cord injury

Spinal cord injury (SCI) is a devastating condition producing great personal and societal costs and for which there is no effective treatment. Stem cell transplantation is a promising therapeutic strategy, though much preclinical and clinical research work remains. Here, we briefly describe SCI epidemiology, pathophysiology, and experimental and clinical stem cell strategies. Research in stem cell biology and cell reprogramming is rapidly advancing, with the hope of moving stem cell therapy closer to helping people with SCI. We examine issues important for clinical translation and provide a commentary on recent developments, including termination of the first human embryonic stem cell transplantation trial in human SCI.

Close interactions between mesenchymal stem cells and neuroblastoma cell lines lead to tumor growth inhibition

Mesenchymal stem cells (MSCs) have attracted much interest in oncology since they exhibit marked tropism for the tumor microenvironment and support or suppress malignant cell growth depending on the tumor model tested. The aim of this study was to investigate the role of MSCs in the control of the growth of neuroblastoma (NB), which is the second most common solid tumor in children. In vivo experiments showed that systemically administered MSCs, under our experimental conditions, did not home to tumor sites and did not affect tumor growth or survival. However, MSCs injected intratumorally in an established subcutaneous NB model reduced tumor growth through inhibition of proliferation and induction of apoptosis of NB cells and prolonged the survival of hMSC-treated mice. The need for contact between MSCs and NB cells was further supported by in vitro experiments. In particular, MSCs were found to be attracted by NB cells, and to affect NB cell proliferation with different results depending on the cell line tested. Moreover, NB cells, after pre-incubation with hMSCs, acquired a more invasive behavior towards CXCL12 and the bone marrow, i.e., the primary site of NB metastases. In conclusion, this study demonstrates that functional cross-talk between MSCs and NB cell lines used in our experiments can occur only within short range interaction. Thus, this report does not support the clinical use of MSCs as vehicles for selective delivery of antitumor drugs at the NB site unless chemotherapy and/or radiotherapy create suitable local conditions for MSCs recruitment.

Immune protection function of multipotent mesenchymal stromal cells: role of transforming growth factor-β1

The immunosuppressive functions of multipotent mesenchymal stromal cells (MSCs) may give cancer cells a survival advantage. This study tests the hypothesis that MSCs protect leukemia cells from immune clearance. Our results demonstrate that MSCs are capable of inhibiting peripheral blood mononuclear cells (PBMNCs) proliferation and their migration toward leukemic cells by the reduction of CCL5 and CXCL12. In addition, we find that MSCs can inhibit the cytolytic functions of NK-cells and CTLs. TGF-β1 secreted by MSCs is responsible for impaired CTLs and NK function by down-modulating surface NKG2D expression. These inhibitory functions of MSCs have negative effects on the CTLs or NK-mediated graft-versus-leukemia (GVL), particularly in the allogeneic hematopoietic stem cells transplantation setting.

MSC and Tumors: Homing, Differentiation, and Secretion Influence Therapeutic Potential

: Mesenchymal stromal/stem cells (MSC) are adult multipotent progenitors with fibroblast-like morphology able to differentiate into adipocytic, osteogenic, chondrogenic, and myogenic lineages. Due to these properties, MSC have been studied and introduced as therapeutics in regenerative medicine. Preliminary studies have also shown a possible involvement of MSC as precursors of cellular elements within tumor microenvironments, in particular tumor-associated fibroblasts (TAF). Among a number of different possible origins, TAF may originate from a pool of circulating progenitors from bone marrow or adipose tissue-derived MSC. There is growing evidence to corroborate that cells immunophenotypically defined as MSC are able to reside as TAF influencing the tumor microenvironment in a potentially bi-phasic and obscure manner: either promoting or inhibiting growth depending on tumor context and MSC sources. Here we focus on relationships between the tumor microenvironment, cancer cells, and MSC, analyzing their diverse ability to influence neoplastic development. Associated activities include MSC homing driven by the secretion of various mediators, differentiation towards TAF phenotypes, and reciprocal interactions with the tumor cells. These are reviewed here with the aim of understanding the biological functions of MSC that can be exploited for innovative cancer therapy.

Isolation and characterisation of mesenchymal stem cells derived from human placenta tissue

AIM

To explore the feasibility of placenta tissue as a reliable and efficient source for generating mesenchymal stem cells (MSC).

METHODS

MSC were generated from human placenta tissue by enzymatic digestion and mechanical dissociation. The placenta MSC (PLC-MSC) were characterized for expression of cell surface markers, embryonic stem cell (ECS) gene expression and their differentiation ability into adipocytes and osteocytes. The immunosuppressive properties of PLC-MSC on resting and phytohemagglutinin (PHA) stimulated allogenic T cells were assessed by means of cell proliferation via incorporation of tritium thymidine ((3)H-TdR).

RESULTS

The generated PLC-MSC appeared as spindle-shaped cells, expressed common MSC surface markers and ESC transcriptional factors. They also differentiated into adipogenic and osteogenic lineages when induced. However, continuous cultivation up to passage 15 caused changes in morphological appearance and cellular senescence, although the stem cell nature of their protein expression was unchanged. In terms of their immunosuppressive properties, PLC-MSC were unable to stimulate resting T cell proliferation; they inhibited the PHA stimulated T cells in a dose dependent manner through cell to cell contact. In our study, MSC generated from human placenta exhibited similar mesenchymal cell surface markers; MSC-like gene expression pattern and MSC-like differentiation potential were comparable to other sources of MSC.

CONCLUSION

We suggest that placenta tissues can serve as an alternative source of MSC for future experimental and clinical studies.

Growth Inhibitory Effect of Palatine Tonsil-derived Mesenchymal Stem Cells on Head and Neck Squamous Cell Carcinoma Cells

Objectives

Mesenchymal stem cells (MSCs) play an important role in the development and growth of tumor cells. However, the effect of human MSCs on the growth of human tumors is not well understood. The purpose of this study is to confirm the growth effect of palatine tonsil-derived MSCs (TD-MSCs) on head and neck squamous cell carcinoma (HNSCC) cell lines and to elucidate the mechanism of their action.

Methods

TD-MSCs were isolated from patient with chronic tonsillitis and tonsillar hypertrophy. Two human HNSCC cell lines (PNUH-12 and SNU-899) were studied and cocultured with isolated palatine tonsil-derived MSC. The growth inhibitory effect of MSCs on HNSCC cell lines was tested through methylthiazolyldiphenyl-tetrazolium (MTT) assay. The apoptosis induction effect of MSCs on cell lines was assessed with flow cytometry and reverse transcriptase (RT)-PCR.

Results

Palatine tonsil-derived MSCs exhibited a growth inhibitory effect on both cell lines. Cell cycle analysis showed an accumulation of tumor cells predominantly in G0/G1 phase with an increase in concentration of TD-MSCs, which was confirmed by increased mRNA expression of cell cycle negative regulator p21. Apoptosis of tumor cells increased significantly as concentration of cocultured TD-MSCs increased. Additionally, mRNA expression of caspase 3 was upregulated with increased concentration of TD-MSCs.

Conclusion

TD-MSCs have a potential growth inhibitory effect on HNSCC cell lines in vitro by inducing apoptotic cell death and G1 phase arrest of cell lines.

Human mesenchymal stem cells protect neutrophils from serum-deprived cell death

We have previously shown that human MSC (mesenchymal stem cells) inhibit the proliferation of most of the immune cells. However, there are innate immune cells such as neutrophils and other PMN (polymorphonuclear) cells that do not require an extensive proliferation prior to their effector function. In this study, the effect of MSC on neutrophils in the presence of complete and serum-deprived culture media was investigated. In the presence of MSC, the viability of neutrophils increase as measured in 24 h of incubation at various supplementation of serum concentration. We have utilized Annexin V and PI (propidium iodide) staining to confirm whether the enhancement of neutrophil's viability is due to a reduction in PCD (programmed cell death). MSC significantly rescue neutrophils from apoptosis at 1, 5 and 10% of FBS (fetal bovine serum) supplementation. The fractions of viable and dead cells were increased and decreased respectively in the presence of MSC. Our results indicate MSC rescue neutrophils from nutrient- or serum-deprived cell death. However, whether this effect is exerted through a specific signalling pathway or confining neutrophils in resting state by MSC requires further investigation.

Bone marrow-derived mesenchymal stromal cells are attracted by multiple myeloma cell-produced chemokine CCL25 and favor myeloma cell growth in vitro and in vivo

Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells that are predominantly localized in the bone marrow (BM). Mesenchymal stromal cells (MSCs) give rise to most BM stromal cells that interact with MM cells. However, the direct involvement of MSCs in the pathophysiology of MM has not been well addressed. In this study, in vitro and in vivo migration assays revealed that MSCs have tropism toward MM cells, and CCL25 was identified as a major MM cell-produced chemoattractant for MSCs. By coculture experiments, we found that MSCs favor the proliferation of stroma-dependent MM cells through soluble factors and cell to cell contact, which was confirmed by intrafemoral coengraftment experiments. We also demonstrated that MSCs protected MM cells against spontaneous and Bortezomib-induced apoptosis. The tumor-promoting effect of MSCs correlated with their capacity to enhance AKT and ERK activities in MM cells, accompanied with increased expression of CyclinD2, CDK4, and Bcl-XL and decreased cleaved caspase-3 and poly(ADP-ribose) polymerase expression. In turn, MM cells upregulated interleukin-6 (IL-6), IL-10, insulin growth factor-1, vascular endothelial growth factor, and dickkopf homolog 1 expression in MSCs. Finally, infusion of in vitro-expanded murine MSCs in 5T33MM mice resulted in a significantly shorter survival. MSC infusion is a promising way to support hematopoietic recovery and to control graft versus host disease in patients after allogeneic hematopoietic stem cell transplantation. However, our data suggest that MSC-based cytotherapy has a potential risk for MM disease progression or relapse and should be considered with caution in MM patients.

The role of mesenchymal stem cells in anti-cancer drug resistance and tumour progression

It is becoming increasingly clear that the tumour microenvironment has a very important role in tumour progression and drug resistance. Many different cell types within the tumour stroma have an effect on tumour progression either in a positive or in a negative way. Mesenchymal stem cells (MSCs) are a distinct population of cells that have been linked with tumour growth. Mesenchymal stem cells can home to tumours where they modulate the immune system and facilitate tumour growth, angiogenesis and metastasis. Recent studies have shown that MSCs also have an important role in the resistance to various anti-cancer drugs. This mini-review provides an overview of the functional properties of MSCs in tumour progression and drug resistance.

Mesenchymal stem cell signaling in cancer progression

Mesenchymal (multipotent) stem/stromal cells (MSCs) may affect cancer progression through a number of secreted factors triggering activation of various cell signaling pathways. Depending on receptor status, phosphatase and tensin homolog (PTEN) status, or Wnt activation in the cancer cells, the signals may either result in increased growth and metastasis or lead to inhibition of growth with increased cell death. Thus, MSCs can play a dual role in cancer progression depending on the cellular context wherein they reside. The phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway has a central role in regulating tumor growth, and several MSC secreted factors stimulate activation of this pathway. A comprehensive understanding of the signals regulating MSC-tumor cross-talk is highly important for the development of MSCs as potential therapeutic vehicles. Thus, the presented review focuses on factors released by MSCs and on the dual role they may have on various stages of tumorigenesis.

Hepatic carcinoma-associated fibroblasts promote an adaptative response in colorectal cancer cells that inhibit proliferation and apoptosis: nonresistant cells die by nonapoptotic cell death

Carcinoma-associated fibroblasts (CAFs) are important contributors of microenvironment in determining the tumor's fate. This study aimed to compare the influence of liver microenvironment and primary tumor microenvironment on the behavior of colorectal carcinoma. Conditioned medium (CM) from normal colonic fibroblasts (NCFs), CAFs from primary tumor (CAF-PT) or liver metastasis (CAF-LM) were obtained. We performed functional assays to test the influence of each CM on colorectal cell lines. Microarray and gene set enrichment analysis (GSEA) were performed in DLD1 cells cultured in matched CM. In DLD1 cells, CAF-LM CM compared with CAF-PT CM and NCF led to a more aggressive phenotype, induced the features of an epithelial-to-mesenchymal transition more efficiently, and stimulated migration and invasion to a greater extent. Sustained stimulation with CAF-LM CM evoked a transient G(2)/M cell cycle arrest accompanied by a reduction of apoptosis, inhibition of proliferation, and decreased viability of SW1116, SW620, SW480, DLD1, HT-29, and Caco-2 cells and provoked nonapoptotic cell death in those cells carrying KRAS mutations. Cells resistant to CAF-LM CM completely changed their morphology in an extracellular signal-regulated protein kinase-dependent process and depicted an increased stemness capacity alongside the Wnt pathway stimulation. The transcriptomic profile of DLD1 cells treated with CAF-LM CM was associated with Wnt and mitogen-activated protein kinase pathways activation in GSEA. Therefore, the liver microenvironment induces more efficiently the aggressiveness of colorectal cancer cells than other matched microenvironments do but secondarily evokes cell death. Resistant cells displayed higher stemness capacity.

Therapeutic potential of intravenously administered human mesenchymal stromal cells

Mesenchymal stem cells (MSC) represent a stem and progenitor cell population that has been shown to promote tissue recovery in pre-clinical and clinical studies. The study of MSC migration following systemic infusion of exogenous MSC is difficult. The challenges facing these efforts are due to a number of factors, including defining culture conditions for MSC, the phenotype of cultured MSC, the differences observed between cultured MSC and freshly isolated MSC. However, even if, MSC populations consist of a mixture of stem and more committed multipotent progenitors, it remains probable that these cell populations are still useful in the clinic as discussed in this review.

Expansion of Mesenchymal Stem/Stromal cells under xenogenic-free culture conditions

Mesenchymal Stem/Stromal cells (MSCs) are increasingly applied in cell-based regenerative medicine. To yield clinically relevant cell doses, ex vivo expansion of MSCs is required to be compliant with good manufacturing practice (GMP) guidelines. A lack of standardization and harmonization seems to hamper rapid progress in the translational phase. Most protocols still use fetal bovine serum (FBS) to expand MSCs. However, the high lot-to-lot variability, risk of contamination and immunization call for xenogenic-free culture conditions. Chemically defined media are the ultimate achievement in terms of standardization. These media, however, need to maintain all key cellular and therapy-relevant features of MSCs. Because of the numerous constituents of FBS, the development of such chemically defined media with an optimal composition of the few essential factors is only beginning. Meanwhile, various human blood-derived components are under investigation, including human plasma, human serum, human umbilical cord blood serum and human platelet derivatives such as platelet lysate.

Mesenchymal stem cells and glioma cells form a structural as well as a functional syncytium in vitro

The interaction of human mesenchymal stem cells (hMSCs) and tumor cells has been investigated in various contexts. HMSCs are considered as cellular treatment vectors based on their capacity to migrate towards a malignant lesion. However, concerns about unpredictable behavior of transplanted hMSCs are accumulating. In malignant gliomas, the recruitment mechanism is driven by glioma-secreted factors which lead to accumulation of both, tissue specific stem cells as well as bone marrow derived hMSCs within the tumor. The aim of the present work was to study specific cellular interactions between hMSCs and glioma cells in vitro. We show, that glioma cells as well as hMSCs differentially express connexins, and that they interact via gap-junctional coupling. Besides this so-called functional syncytium formation, we also provide evidence of cell fusion events (structural syncytium). These complex cellular interactions led to an enhanced migration and altered proliferation of both, tumor and mesenchymal stem cell types in vitro. The presented work shows that glioma cells display signs of functional as well as structural syncytium formation with hMSCs in vitro. The described cellular phenomena provide new insight into the complexity of interaction patterns between tumor cells and host cells. Based on these findings, further studies are warranted to define the impact of a functional or structural syncytium formation on malignant tumors and cell based therapies in vivo.

Anti-tumor effects of canine adipose tissue-derived mesenchymal stromal cell-based interferon-β gene therapy and cisplatin in a mouse melanoma model

BACKGROUND AIMS

Adipose tissue (AT)-derived mesenchymal stromal cells (MSC) (AT-MSC) represent a novel tool for delivering therapeutic genes to tumor cells. Interferon (IFN)-β is a cytokine with pleiotropic cellular functions, including anti-proliferative, immunomodulatory and anti-angiogenic activities. The purpose of this study was to engineer canine AT-MSC (cAT-MSC) producing IFN-β and to evaluate the anti-tumor effect of cAT-MSC-IFN-β combined with cisplatin in mouse melanoma model.

METHODS

cAT-MSC engineered to express mouse IFN-β were generated using a lentiviral vector (cAT-MSC-IFN-β) and the secreted IFN-β-induced inhibition of tumor cell growth and apoptosis on B16F10 cells was investigated in vitro prior to in vivo studies. Melanoma-bearing mouse was developed by injecting B16F10 cells subcutaneously into 6-week-old C57BL/6 mice. After 14 days, cisplatin (10 mg/kg) was injected intratumorally, and 3 days later the engineered cAT-MSC were injected subcutaneously every 3 days to death. Tumor volume and survival times were measured.

RESULTS

The combination treatment of cAT-MSC-IFN-β with cisplatin was more effective in inhibiting the growth of melanoma and resulted in significantly extended survival time than both an unengineered cAT-MSC-cisplatin combination group and a cisplatin-alone group. Interestingly, subcutaneously injected cAT-MSC-IFN-β were migrated to tumor sites.

CONCLUSIONS

Our data suggest that canine AT-MSC could serve as a powerful cell-based delivery vehicle for releasing therapeutic proteins to tumor lesions. Maximal anti-tumor effects were seen when this therapy was combined with a DNA-damaging chemotherapeutic agent. This study demonstrates the possible applicability of AT-MSC-mediated IFN-β in treating canine and human cancer patients.

Mesenchymal Stem Cell-mediated delivery of the sodium iodide symporter supports radionuclide imaging and treatment of breast cancer

Mesenchymal Stem Cells (MSCs) migrate specifically to tumors in vivo, and coupled with their capacity to bypass immune surveillance, are attractive vehicles for tumor-targeted delivery of therapeutic agents. This study aimed to introduce MSC-mediated expression of the sodium iodide symporter (NIS) for imaging and therapy of breast cancer. Tumor bearing animals received an intravenous or intratumoral injection of NIS expressing MSCs (MSC-NIS), followed by (99m) Technetium pertechnetate imaging 3-14 days later using a BazookaSPECT γ-camera. Tissue was harvested for analysis of human NIS (hNIS) expression by relative quantitative-polymerase chain reaction. Therapy animals received an i.p. injection of (131) I or saline 14 days after injection of MSC-NIS, and tumor volume was monitored for 8 weeks. After injection of MSC-NIS, BazookaSPECT imaging revealed an image of animal intestines and chest area at day 3, along with a visible weak tumor image. By day 14, the tumor was visible with a significant reduction in radionuclide accumulation in nontarget tissue observed. hNIS gene expression was detected in the intestines, heart, lungs, and tumors at early time points but later depleted in nontarget tissues and persisted at the tumor site. Based on imaging/biodistribution data, animals received a therapeutic dose of (131) I 14 days after MSC-NIS injection. This resulted in a significant reduction in tumor growth (mean ± SEM, 236 ± 62 mm(3) vs. 665 ± 204 mm(3) in controls). The ability to track MSC migration and transgene expression noninvasively in real time before therapy is a major advantage to this strategy. This promising data supports the feasibility of this approach as a novel therapy for breast cancer.

Human ovarian carcinoma–associated mesenchymal stem cells regulate cancer stem cells and tumorigenesis via altered BMP production

Accumulating evidence suggests that mesenchymal stem cells (MSCs) are recruited to the tumor microenvironment; however, controversy exists regarding their role in solid tumors. In this study, we identified and confirmed the presence of carcinoma-associated MSCs (CA-MSCs) in the majority of human ovarian tumor samples that we analyzed. These CA-MSCs had a normal morphologic appearance, a normal karyotype, and were nontumorigenic. CA-MSCs were multipotent with capacity for differentiating into adipose, cartilage, and bone. When combined with tumor cells in vivo, CA-MSCs promoted tumor growth more effectively than did control MSCs. In vitro and in vivo studies suggested that CA-MSCs promoted tumor growth by increasing the number of cancer stem cells. Although CA-MSCs expressed traditional MSCs markers, they had an expression profile distinct from that of MSCs from healthy individuals, including increased expression of BMP2, BMP4, and BMP6. Importantly, BMP2 treatment in vitro mimicked the effects of CA-MSCs on cancer stem cells, while inhibiting BMP signaling in vitro and in vivo partly abrogated MSC-promoted tumor growth. Taken together, our data suggest that MSCs in the ovarian tumor microenvironment have an expression profile that promotes tumorigenesis and that BMP inhibition may be an effective therapeutic approach for ovarian cancer.

Modeling sarcomagenesis using multipotent mesenchymal stem cells

Because of their unique properties, multipotent mesenchymal stem cells (MSCs) represent one of the most promising adult stem cells being used worldwide in a wide array of clinical applications. Overall, compelling evidence supports the long-term safety of ex vivo expanded human MSCs, which do not seem to transform spontaneously. However, experimental data reveal a link between MSCs and cancer, and MSCs have been reported to inhibit or promote tumor growth depending on yet undefined conditions. Interestingly, solid evidence based on transgenic mice and genetic intervention of MSCs has placed these cells as the most likely cell of origin for certain sarcomas. This research area is being increasingly explored to develop accurate MSC-based models of sarcomagenesis, which will be undoubtedly valuable in providing a better understanding about the etiology and pathogenesis of mesenchymal cancer, eventually leading to the development of more specific therapies directed against the sarcoma-initiating cell. Unfortunately, still little is known about the mechanisms underlying MSC transformation and further studies are required to develop bona fide sarcoma models based on human MSCs. Here, we comprehensively review the existing MSC-based models of sarcoma and discuss the most common mechanisms leading to tumoral transformation of MSCs and sarcomagenesis.

Concise review: Mesenchymal stem cell tumor-homing: detection methods in disease model systems

Despite the decline in U.S. cancer incidence and mortality rates, cancer remains the number one cause of death for people under the age of 85 and one in four people in the U.S. will die of cancer, mainly because of metastasis. Recently, interest in mesenchymal stem cell (MSC) tumor-homing has led to inquires into: (a) why MSCs home to tumors, (b) what the inherent protumor and antitumor consequences are, and (c) how to best capitalize on MSC tumor-homing for cell-based diagnostics and therapy. Here, these questions are reviewed and method for addressing them using animal models and tracking methodologies (or, synonymously, detection methodologies) are discussed. First, MSCs in a regenerative and tumor-homing context are reviewed, followed by MSC delivery and genetic labeling methods for tissue model systems. Finally, the use of the nonoptical methods, magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography, along with optical methods, fluorescence imaging and bioluminescent imaging, are reviewed related to tracking MSCs within disease model settings. The benefits and drawbacks of each detection method in animal models is reviewed along with the utility of each for therapeutic use.

Mesenchymal stem cells: angels or demons?

Mesenchymal stem cells (MSCs) have been used in cell-based therapy in various disease conditions such as graft-versus-host and heart diseases, osteogenesis imperfecta, and spinal cord injuries, and the results have been encouraging. However, as MSC therapy gains popularity among practitioners and researchers, there have been reports on the adverse effects of MSCs especially in the context of tumour modulation and malignant transformation. These cells have been found to enhance tumour growth and metastasis in some studies and have been related to anticancer-drug resistance in other instances. In addition, various studies have also reported spontaneous malignant transformation of MSCs. The mechanism of the modulatory behaviour and the tumorigenic potential of MSCs, warrant urgent exploration, and the use of MSCs in patients with cancer awaits further evaluation. However, if MSCs truly play a role in tumour modulation, they can also be potential targets of cancer treatment.

Human mesenchymal stem cells play a dual role on tumor cell growth in vitro and in vivo

Nowadays, some evidences demonstrate that human mesenchymal stem cells (hMSCs) favor tumor growth; however, others show that hMSCs can suppress tumorigenesis and tumor growth. With the indeterminateness of the effect of hMSCs on tumors, we investigated the effect of hMSCs on lung cancer cell line A549 and esophageal cancer cell line Eca-109 in vitro and in vivo. Our results revealed that hMSCs inhibited the proliferation and invasion of A549 and Eca-109 cells, arrested tumor cells in the G1 phase of the cell cycle and induced the apoptosis of tumor cells in vitro by using a co-culture system and the hMSCs-conditioned medium. However, animal study showed that hMSCs enhanced tumor formation and growth in vivo. Western blotting and immunoprecipitation data showed that the expressions of proliferating cell nuclear antigen (PCNA), Cyclin E, phospho-retinoblastoma protein (pRb), B-cell lymphoma/leukemia-2 (Bcl-2), Bcl-xL, and matrix metalloproteinase 2 (MMP-2) were downregulated and the formation of Cyclin E-cyclin-dependent kinase 2 (CDK2) complexes was inhibited in the tumor cells treated with the hMSCs-conditioned medium. According to the observation of tumor mass and the result of microvessel density (MVD), we found that the promoting role of hMSCs on tumor growth was related with the increase of tumor vessel formation. Our present study suggests that hMSCs have a contradictory effect on tumor cell growth between in vitro and in vivo, and therefore, the exploitation of hMSCs in new therapeutic strategies should be cautious under the malignant conditions.

Hematopoietic stem cell niche is a potential therapeutic target for bone metastatic tumors

Despite significant improvements in therapy, the prognosis for cancer with bone metastasis is generally poor. Therefore, there is a great need for new therapeutic approaches for metastatic disease. It has been appreciated that tumor cells metastasize to bone using mechanisms similar to those of hematopoietic stem cells (HSC) homing to bone marrow (e.g., CXCL12/CXCR4). It was recently found that prostate cancer cells target the bone marrow microenvironment for HSCs, or the HSC niche, during metastasis. Of importance, these disseminated prostate cancer cells can be mobilized out of the niche with the use of HSC mobilizing agents. These findings suggest that the bone marrow HSC niche is a potential therapeutic target for metastatic disease. Therefore, a hypothesis worth considering is that agents that can disrupt the interactions between tumor cells and the HSC niche may be efficacious when used in conjunction with standard chemotherapeutic agents. Although further understanding of the tumor-niche interactions is needed, the concept of targeting the niche in conjunction with chemotherapy could open up new possibilities to eradicate incurable metastatic diseases.

Cell therapy of burns

Severe burns remain a life-threatening local and general inflammatory condition often with serious sequelae, despite remarkable progress in their treatment over the past three decades. Cultured epidermal autografts, the first and still most up-to-date cell therapy for burns, plays a key role in that progress, but drawbacks to this need to be reduced by using cultured dermal-epidermal substitutes. This review focuses on what could be, in our view, the next major breakthrough in cell therapy of burns - use of mesenchymal stromal cells (MSCs). After summarizing current knowledge, including our own clinical experience with MSCs in the pioneering field of cell therapy of radiation-induced burns, we discuss the strong rationale supporting potential interest in MSCs in treatment of thermal burns, including limited but promising pre-clinical and clinical data in wound healing and acute inflammatory conditions other than burns. Practical options for future therapeutic applications of MSCs for burns treatment, are finally considered.

Mesenchymal stem cells isolated from human uterine cervix cancer tissues

In the present study, MSCs (mesenchymal stem cells) were successfully isolated and identified from hUCC (human uterine cervix cancer) tissues. The morphological appearance, immunophenotype, growth curve, cell cycle, cytogenetic features and differentiation potential of these cells were investigated. Results showed that cells isolated from the uterine cervix cancer tissues displayed fibroblast-like morphology and grew into colonies. Immunophenotyping by flow cytometry revealed that the isolated cells were positive for CD13, CD29, CD44, CD105 and HLA-I, while negative for CD10, CD14, CD31, CD34, CD38 and HLA-DR. The cells kept a normal karyotype by chromosome analysis. At the third passage, the percentages of cells in G0-/G1-, 2-/M- and S-phase were 84.94, 8.36 and 6.71%, respectively. Under appropriate induction conditions, these cells can differentiate into osteogenic, adipogenic cells and hepatocytes. Taken together, MSCs were confirmed to exist in hUCC tissues, which may provide a new target for clinical cancer therapy.

Malignant tumor formation after transplantation of short-term cultured bone marrow mesenchymal stem cells in experimental myocardial infarction and diabetic neuropathy

RATIONALE

Bone marrow (BM)-derived mesenchymal stem cells (MSCs) hold great promise for cardiovascular cell therapy owing to their multipotency and culture expandability.

OBJECTIVE

The aim of the study was to investigate whether MSCs can treat experimental acute myocardial infarction (MI) and diabetic neuropathy.

METHODS AND RESULTS

We isolated mononuclear cells from mouse BM and cultured MSCs in a conventional manner. Flow cytometry analyses of these cultured cells at passage 4 showed expression of typical MSC markers such as CD44 and CD29, but not hematopoietic markers such as c-kit, flk1, and CD34. To determine the therapeutic effects of MSCs, we injected MSCs into the peri-infarct area after ligation of the left anterior descending coronary arteries of mice and, as separate experiments, injected the same batch of MSCs into hindlimb muscles of mice with diabetic neuropathy. During the follow-up at 4 to 8 weeks after cell transplantation, growing tumors were observed in 30% of hearts in the MI model, and in 46% of hindlimbs in the diabetic neuropathy model. Histological examination of the tumors revealed hypercelluarity, pleomorphic nucleoli, cytological atypia and necrosis, and positive staining for α-smooth muscle actin, indicative of malignant sarcoma with myogenic differentiation. Chromosomal analysis of these MSCs showed multiple chromosomal aberrations including fusion, fragmentation, and ring formation.

CONCLUSIONS

Genetically unmodified MSCs can undergo chromosomal abnormalities even at early passages and form malignant tumors when transplanted in vivo. These results suggest that careful monitoring of chromosomal status is warranted when in vitro expanded MSCs are used for cell therapy such as for MI.

Mesenchymal stromal cells promote tumor growth through the enhancement of neovascularization

Mesenchymal stromal cells (MSCs), also called mesenchymal stem cells, migrate and function as stromal cells in tumor tissues. The effects of MSCs on tumor growth are controversial. In this study, we showed that MSCs increase proliferation of tumor cells in vitro and promote tumor growth in vivo. We also further analyzed the mechanisms that underlie these effects. For use in in vitro and in vivo experiments, we established a bone marrow-derived mesenchymal stromal cell line from cells isolated in C57BL/6 mice. Effects of murine MSCs on tumor cell proliferation in vitro were analyzed in a coculture model with B16-LacZ cells. Both coculture with MSCs and treatment with MSC-conditioned media led to enhanced growth of B16-LacZ cells, although the magnitude of growth stimulation in cocultured cells was greater than that of cells treated with conditioned media. Co-injection of B16-LacZ cells and MSCs into syngeneic mice led to increased tumor size compared with injection of B16-LacZ cells alone. Identical experiments using Lewis lung carcinoma (LLC) cells instead of B16-LacZ cells yielded similar results. Consistent with a role for neovascularization in MSC-mediated tumor growth, tumor vessel area was greater in tumors resulting from co-injection of B16-LacZ cells or LLCs with MSCs than in tumors induced by injection of cancer cells alone. Co-injected MSCs directly supported the tumor vasculature by localizing close to vascular walls and by expressing an endothelial marker. Furthermore, secretion of leukemia inhibitory factor, macrophage colony-stimulating factor, macrophage inflammatory protein-2 and vascular endothelial growth factor was increased in cocultures of MSCs and B16-LacZ cells compared with B16-LacZ cells alone. Together, these results indicate that MSCs promote tumor growth both in vitro and in vivo and suggest that tumor promotion in vivo may be attributable in part to enhanced angiogenesis.

Growth inhibition of colorectal carcinoma by lentiviral TRAIL-transgenic human mesenchymal stem cells requires their substantial intratumoral presence

Colorectal carcinoma (CRC) constitutes a common malignancy with limited therapeutic options in metastasized stages. Mesenchymal stem cells (MSC) home to tumours and may therefore serve as a novel therapeutic tool for intratumoral delivery of antineoplastic factors. Tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) which promises apoptosis induction preferentially in tumour cells represents such a factor. We generated TRAIL-MSC by transduction of human MSC with a third generation lentiviral vector system and analysed their characteristics and capacity to inhibit CRC growth. (1) TRAIL-MSC showed stable transgene expression with neither changes in the defining MSC characteristics nor signs of malignant transformation. (2) Upon direct in vitro coculture TRAIL-MSC induced apoptosis in TRAIL-sensitive CRC-cell lines (DLD-1 and HCT-15) but also in CRC-cell lines resistant to soluble TRAIL (HCT-8 and SW480). (3) In mixed subcutaneous (s.c.) xenografts TRAIL-MSC inhibited CRC-tumour growth presumably by apoptosis induction but a substantial proportion of TRAIL-MSC within the total tumour cell number was needed to yield such anti-tumour effect. (4) Systemic application of TRAIL-MSC had no effect on the growth of s.c. DLD-1 xenografts which appeared to be due to a pulmonary entrapment and low rate of tumour integration of TRAIL-MSC. Systemic TRAIL-MSC caused no toxicity in this model. (5) Wild-type MSC seemed to exert a tumour growth-supporting effect in mixed s.c. DLD-1 xenografts. These novel results support the idea that lentiviral TRAIL-transgenic human MSC may serve as vehicles for clinical tumour therapy but also highlight the need for further investigations to improve tumour integration of transgenic MSC and to clarify a potential tumour-supporting effect by MSC.

Mesenchymal stromal cells for graft-versus-host disease

Mesenchymal stromal cells (MSCs) have been shown to mediate immune responses in vitro and in vivo. These observations have led to clinical trials of MSC administration to ameliorate acute graft-versus-host disease (GVHD), the most serious complication arising after allogeneic hematopoietic cell transplantation. Clinical data suggest a benefit in approximately two-thirds of patients with steroid-resistant acute GVHD. Preliminary studies have been reported on the use of MSCs to treat de novo acute GVHD, for prophylaxis of the condition, and more recently, in the management of chronic GVHD. Although preclinical data inferred a possible role of MSCs in affecting GVHD mechanisms, more robust animal models became available only after numerous clinical trials with these cells had been undertaken. Further clinical trials, the development of more appropriate animal models and an effective means of tracking and imaging the introduced cells in real time in patients, are required to better define their role in this important area of medicine.

Inhibition of lung cancer cell proliferation mediated by human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are mostly studied for their potential clinical use. Recently, much attention in the field of cancer research has been paid to hMSCs. In this study, we investigated the influence of hMSCs on the proliferation of lung cancer cell lines SK-MES-1 and A549 in vitro and in vivo by using a co-culture system and the hMSCs-conditioned medium. Our results demonstrated that hMSCs could inhibit the proliferation of SK-MES-1 and A549 cells, and induce the apoptosis of tumor cells in vitro via some soluble factors. Animal study showed that these soluble factors from hMSCs could suppress tumorigenesis and tumor angiogenesis by treating preliminarily tumor cells with the hMSCs-conditioned medium. The downregulated expression of vascular endothelial growth factor in tumor cells might be the mechanism of interference in tumor angiogenesis, which was verified by western blot analysis and immunohistochemistry assay. Taken together, our results suggested that the hMSCs could inhibit tumor cell growth by secreting some soluble factors.

Bone marrow mesenchymal stem cells reduce the antitumor activity of cytokine-induced killer/natural killer cells in K562 NOD/SCID mice

Adoptive cellular immunotherapy is an important treatment to eliminate residual tumor cells after hematopoietic stem-cell transplantation. Bone marrow mesenchymal stem cells (MSC) have previously been shown to exert immunoregulation functions, including inhibition of proliferation and killing activities of T cells and natural killer (NK) cells in vitro and reduction of the graft-versus-host disease. MSC can survive in vivo for a long period of time, the influence of MSC on the antitumor activity of subsequently infused immune killer cells is not clear. The aim of this study was to investigate the influences of MSC infused via different paths and at different times on the antitumor activities of cytokine-induced killer (CIK)/NK cells derived from umbilical cord blood in K562 NOD/SCID mice. The potential interaction mechanisms of MSC and CIK/NK cells infused through different paths using different intervals in vivo were subsequently explored. The results show that the antitumor activities of CIK/NK cells was inhibited by MSC when injected via the same path (tail vein), and the suppressive effect of MSC on CIK/NK cells were less pronounced when they were injected separately through different paths. There were no effects of MSC on the antitumor activities of CIK/NK cells if the MSC and CIK/NK cells were injected with a 48-h interval. Moreover, the suppressive effect continuous, even if MSC were infused 48 h earlier than CIK/NK cells. It suggests that pre-injected MSC can reduce the antitumor activities of CIK/NK cells in vivo. The probable mechanisms are that MSC and CIK/NK cells might have a greater opportunity to meet and interact if they are injected simultaneously via the same path. The suppression of MSC on CIK/NK cells in vivo mainly takes place in the reticuloendothelial system, including the lung and the liver.

Human bone marrow stromal cells and skin fibroblasts inhibit natural killer cell proliferation and cytotoxic activity

Mesenchymal stromal cells (MSCs) are potent immunomodulators that have successfully been used to circumvent various types of inflammations, including steroid-resistant graft-versus-host disease. Although initially believed to be restricted to multipotent MSCs, this immunoregulatory function is shared with differentiated cells from the mesenchymal lineage such as skin fibroblasts (SFs). Mesenchymal cell-induced immunoregulation is so potent that it may allow the reactivation of dormant malignancies, a fact that would preclude using such cells as therapeutic agents. Because NK cells are pivotal effectors controlling tumor cell containment we investigated the effect of allogenic MSCs and SFs on NK cell function in vitro. When NK cells were incubated with IL-15 and MSCs or SFs for 6 days, their proliferation and cytotoxic activity were significantly decreased compared to NK cells cultured with IL-15 alone or with human venous endothelial cells. Cytotoxic activity inhibition reached 86% when assayed on MHC-I(+) allogenic primary hematopoietic blasts, and was associated with a significant decrease in cytolytic granule exocytosis and in perforin release. Stromal cell-mediated inhibition was effective only if cell-cell proximity was long lasting: when NK cells were activated with IL-15 in the absence of MSCs and assayed for cytotoxicity in their presence no inhibition occurred. MSC inhibition was ultimately mediated by a soluble factor generated upon incubation with NK cells activated by IL-15 or IL-2. The indoleamine 2,3 dioxygenase was activated in MSCs and SFs because L-kynurenine was detected in inhibitory supernatants, but its blockade did not restore NK cell functions. The profound inhibition of cytotoxic activity directed against allogenic hematopoietic blasts exerted by MSCs and SFs on NK cells may be a concern. Should this occur in vivo it may induce the inability of NK cells to control residual or dormant malignant diseases after infusion of therapeutic MSCs.

Mesenchymal stem cells enhance growth and metastasis of colon cancer

Recently, mesenchymal stem cells (MSCs) were reported to migrate to tumor stroma as well as injured tissue. We examined the role of human MSCs in tumor stroma using an orthotopic nude mice model of KM12SM colon cancer. In in vivo experiments, systemically injected MSCs migrated to the stroma of orthotopic colon tumors and metastatic liver tumors. Orthotopic transplantation of KM12SM cells mixed with MSCs resulted in greater tumor weight than did transplantation of KM12SM cells alone. The survival rate was significantly lower in the mixed-cell group, and liver metastasis was seen only in this group. Moreover, tumors resulting from transplantation of mixed cells had a significantly higher proliferating cell nuclear antigen labeling index, significantly greater microvessel area and significantly lower apoptotic index. Splenic injection of KM12SM cells mixed with MSCs, in comparison to splenic injection of KM12SM cells alone, resulted in a significantly greater number of liver metastases. MSCs incorporated into the stroma of primary and metastatic tumors expressed α-smooth muscle actin and platelet-derived growth factor receptor-β as carcinoma-associated fibroblast (CAF) markers. In in vitro experiments, KM12SM cells recruited MSCs, and MSCs stimulated migration and invasion of tumor cells through the release of soluble factors. Collectively, MSCs migrate and differentiate into CAFs in tumor stroma, and they promote growth and metastasis of colon cancer by enhancing angiogenesis, migration and invasion and by inhibiting apoptosis of tumor cells.

Mesenchymal stem cells and cancer: tumor-specific delivery vehicles or therapeutic targets?

Mesenchymal stem cells (MSCs) are a subset of nonhematopoietic multipotent cells found primarily within the bone marrow stroma. The ability of MSCs to specifically home to sites of tumors and their metastases, while escaping host immune surveillance, holds tremendous promise for tumor-targeted delivery of therapeutic agents. Concerns that MSCs may have an inherent capacity for transformation have led to a number of studies investigating their stability in vitro, as significant ex vivo expansion will be necessary to yield the number of cells required for therapeutic applications. MSCs have also been seen to influence the morphology and proliferation of cells within their vicinity through a combination of cell-to-cell interactions and the secretion of chemoattractant cytokines. Understanding interactions between MSCs and tumor cells is required to support realization of their clinical potential. This review discusses MSCs and cancer in terms of (1) potential for transformation and de novo tumor formation, (2) interactions with epithelial cancer cells in tumor establishment, and (3) potential role after engraftment at the site of an established tumor. Elucidation of any potential negative effect of MSCs in the tumor setting will support development of protocols to minimize these effects while taking full advantage of the remarkable tumor-homing capacity of these cells.

Late sarcoma development after curettage and bone grafting of benign bone tumors

BACKGROUND AND AIM

Rarely sarcomas develop in previous benign lesions, after a long term disease free interval. We report the experience on these rare cases observed at a single Institution.

PATIENTS AND METHODS

12 cases curetted and grafted, without radiotherapy developed sarcomas, between 1970 and 2005, 6.5-28 years from curettage (median 18, average 19). Age ranged from 13 to 55 years (median 30, average 32) at first diagnosis; tumors were located in the extremities (9 GCT, benign fibrous histiocytoma, ABC, and solitary bone cyst). Radiographic and clinic documentation, for the benign and malignant lesions, were available. Histology was available for 7 benign and all malignant lesions.

RESULTS

To fill cavities, autogenous bone was used in 4 cases, allograft in 2, allograft and tricalcium-phosphate/hydroxyapatite in 1, autogenous/allograft in 1, heterogenous in 1. For 3 cases the origin was not reported. Secondary sarcomas, all high grade, were 8 osteosarcoma, 3 malignant fibrous histiocytoma, and 1 fibrosarcoma.

CONCLUSIONS

Recurrences with progression from benign tumors are possible, but the very long intervals here reported suggest a different cancerogenesis for these sarcomas. This condition is extremely rare accounting for only 0.26% of all malignant bone sarcomas treated in the years 1970-2005 and represents only 8.76% of all secondary bone sarcomas treated in the same years. This incidence is the same as that of sarcomas arising on fibrous dysplasia, and is lower than those arising on bone infarcts or on Paget's disease. This possible event must be considered during follow-up of benign lesions.

Mesenchymal stem cells display hepato-protective activity in lymphoma bearing xenografts

A disseminated model of non-Hodgkin's lymphoma with prevalent liver metastasis was generated by intraperitoneal (i.p.) injection of EBV(+) B lymphoblastoid SKW6.4 in nude-SCID mice. The survival of SKW6.4 xenografts (median survival = 27 days) was significantly improved when hyaluronan scaffolds embedded with mesenchimal stem cells (MSC) were implanted in the abdominal area 4 days after SKW6.4 injection (median survival = 39.5 days). Mice implanted with MSC showed a significant improvement of hepatic functionality in lymphoma xenografts, as demonstrated by measurement of serum ALT/AST levels. Co-culture of MSC with lymphoma cells enhanced the release of hepatocyte growth factor (HGF) by MSC. These data suggest that hyaluronan-embedded MSC exert anti-lymphoma activity by ameliorating hepatic functionality.