Advance in bone marrow derived cell therapy:CD31-expressing cells as next generation cardiovascular cell therapy

In the recent past,bone marrow(BM)-derived cells have been used to regenerate damaged cardiovascular tissues post myocardial infarction (MI).Recent clinical trials have shown controversial results in recovering damaged cardiac tissue. New progress has shown that the underlying mechanisms of cell-based therapy relies more heavily on humoral and paracrine effects rather than on new tissue generation.However,studies have also reported the potential of new endothelial cell generation from BM cells.Thus,efforts have been made to identify cells having higher humoral or therapeutic effects as well as their surface markers.Specifically, BM-derived CD31~+ cells were isolated by a surface marker and demonstrated high angio-vasculogenic effects. I will present recent advances in the therapeutic use of BM-derived cells and the usefulness of CD31~+ cells as a next generation cell therapy.     

Are bone marrow stem cells plastic or heterogenous--that is the question

The concept that bone marrow (BM) may contain heterogeneous populations of stem cells was surprisingly not taken carefully enough into consideration in several recently reported experiments demonstrating so-called plasticity or trans-dedifferentiation of hematopoietic stem cells (HSC). These studies, without including proper controls to exclude this possibility, often lead to wrong interpretations. Accumulated evidence suggests that in addition to hematopoietic stem cells (HSC), bone marrow (BM) also harbors versatile subpopulations of tissue-committed stem cells (TCSC) and perhaps even more primitive pluripotent stem cells (PSC), and that these rare cells accumulate in bone marrow during ontogenesis, and being a mobile population of cells are released from BM into peripheral blood after tissue injury to regenerate damaged organs. Thus, the presence of TCSC/PSC in BM tissue should be considered before experimental evidence is interpreted simply as trans-dedifferentiation/plasticity of HSC. In this review, we will discuss this alternative explanation of plasticity of HSC, providing data from others and our laboratory that supports the concept that BM-derived stem cells are heterogeneous.     

Plasticity of marrow-derived stem cells

Bone marrow (BM) contains hematopoietic stem cells (HSCs), which differentiate into every type of mature blood cell; endothelial cell progenitors; and marrow stromal cells, also called mesenchymal stem cells (MSCs), which can differentiate into mature cells of multiple mesenchymal tissues including fat, bone, and cartilage. Recent findings indicate that adult BM also contains cells that can differentiate into additional mature, nonhematopoietic cells of multiple tissues including epithelial cells of the liver, kidney, lung, skin, gastrointestinal (GI) tract, and myocytes of heart and skeletal muscle. Experimental results obtained in vitro and in vivo are the subject of this review. The emphasis is on how these experiments were performed and under what conditions differentiation from bone marrow to epithelial and neural cells occurs. Questions arise regarding whether tissue injury is necessary for this differentiation and the mechanisms by which it occurs. We also consider which bone marrow subpopulations are capable of this differentiation. Only after we have a better understanding of the mechanisms involved and of the cells required for this differentiation will we be able to fully harness adult stem cell plasticity for clinical purposes.     

The role of bone marrow stem cells in liver regeneration

Hepatic oval cells involved in some forms of liver regeneration express many markers also found on hematopoietic stem cells (HSCs). In addition, multiple independent reports have demonstrated that bone marrow cells can give rise to several hepatic epithelial cell types, including oval cells, hepatocytes, and duct epithelium. These observations have resulted in the hypothesis that bone marrow resident stem cells, specifically HSCs, are an important source for liver epithelial cell replacement, particularly during chronic injury. The function of such stem cells in hepatic injury responses is the topic of this article. Taken together, the published data on the role of bone marrow stem cells in liver damage suggest that they do not play a significant physiological role in the replacement of epithelial cells in any known form of hepatic injury. Fully functional bone marrow-derived hepatocytes exist but are extremely rare and are generated by cell fusion, not stem cell differentiation. Nonetheless, bone marrow-derived cells may play important indirect roles in liver regeneration. First, they may serve as a source for the replacement of endothelial cells. Second, hematopoietic cells, including lymphocytes, neutrophils, macrophages, and platelets, may provide crucial factors required for efficient healing of damaged liver.     

Assessment of cystic fibrosis transmembrane conductance regulator (CFTR) activity in CFTR-null mice after bone marrow transplantation

Several studies have demonstrated that bone marrow (BM)-derived cells give rise to rare epithelial cells in the gastrointestinal (GI) and respiratory tracts after BM transplantation into myeloablated recipients. We investigate whether, after transplantation of cystic fibrosis transmembrane conductance regulator (CFTR)-positive BM-derived cells, BM-derived GI and airway epithelial cells can provide CFTR activity in the GI tract and nasal epithelium of recipient cystic fibrosis mice. CFTR-/- mice were transplanted with wild-type BM after receiving different doses of irradiation, and CFTR activity was assessed in vivo in individual mice over time by using rectal and nasal potential difference analyses and in vitro by Ussing chamber analysis. The data suggest that rare BM-derived epithelial cells in the GI and nasal epithelium detected in CFTR-/- transplanted mice provide a modest level of CFTR-dependent chloride secretion. Detection of CFTR mRNA and protein in tissues of transplanted CFTR-/- mice supports these data.     

Bone marrow-derived cells can acquire renal stem cells properties and ameliorate ischemia-reperfusion induced acute renal injury

ABSTRACT: BACKGROUND: Bone marrow (BM) stem cells have been reported to contribute to tissue repair after kidney injury model. However, there is no direct evidence so far that BM cells can trans-differentiate into renal stem cells. METHODS: To investigate whether BM stem cells contribute to repopulate the renal stem cell pool, we transplanted BM cells from transgenic mice, expressing enhanced green fluorescent protein (EGFP) into wild-type irradiated recipients. Following hematological reconstitution and ischemia-reperfusion (I/R), Sca-1 and c-Kit positive renal stem cells in kidney were evaluated by immunostaining and flow cytometry analysis. Moreover, granulocyte colony stimulating factor (G-CSF) was administrated to further explore if G-CSF can mobilize BM cells and enhance trans-differentiation efficiency of BM cells into renal stem cells. RESULTS: BM-derived cells can contribute to the Sca-1+ or c-Kit+ renal progenitor cells population, although most renal stem cells came from indigenous cells. Furthermore, G-CSF administration nearly doubled the frequency of Sca-1+ BM-derived renal stem cells and increased capillary density of I/R injured kidneys. CONCLUSIONS: These findings indicate that BM derived stem cells can give rise to cells that share properties of renal resident stem cell. Moreover, G-CSF mobilization can enhance this effect.     

Alveolar epithelial cells: differentiation and lung injury

Abstract:   Re-epithelialization of alveolar epithelial cells is one of the important repair processes in many types of lung injury. The major functions of alveolar type II cells are synthesis and secretion of surfactant, hyperplasia in reaction to alveolar epithelial injury, and serving as progenitor cells for alveolar type I cells. The authors have examined the effects of several soluble factors on cultured alveolar type II cells in vitro , and also examined the histopathology and gene expression of surfactant proteins in the rat lungs with LPS, bleomycin and/or treated with keratinocyte growth factor. The authors next examined the effects of bone marrow stromal cells (BMSC) implanted transvenously into bleomycin-induced lungs. The authors found that keratinocyte growth factor (KGF) is a strong growth factor for alveolar type II cells, and that KGF instillation prevents bleomycin-induced lung injury. Furthermore, the authors showed the possibility of differentiation of implanted BMSC into alveolar epithelial cells. KGF and BMSC may play an important role in maintaining the alveolar epithelium and repairing the damaged epithelium after injury, and may well provide potential therapeutic alternatives.     

Crosspresentation by nonhematopoietic and direct presentation by hematopoietic cells induce central tolerance to myelin basic protein

Central tolerance plays a critical role in eliminating self-reactive T cells specific for peripheral antigens. Here we show that central tolerance of MHC class I-restricted T cells specific for classic myelin basic protein (MBP), a component of the myelin sheath, is mediated by both bone marrow (BM)-derived and nonBM-derived cells. Unexpectedly, BM-derived cells induce tolerance directly by using classic MBP that they synthesize, whereas nonBM-derived cells mediate tolerance by crosspresenting classic MBP acquired from an exogenous source. Thus, tolerance to tissue-specific antigens can involve multiple cell types and mechanisms in the thymus, which may account for the limited spectrum of autoimmune syndromes observed when expression of tissue-specific antigens is impaired only in thymic epithelial cells.     

Bone marrow-derived cells and tumor growth: contribution of bone marrow-derived cells to tumor micro-environments with special focus on mesenchymal stem cells

Research has provided evidence that tumor growth depends on the interaction of tumor cells with stromal cells, as already suggested in 1889 by Paget. Experimental and clinical studies have revealed that tumor stromal cells can be derived from bone marrow (BM)-derived progenitor cells, such as mesenchymal stem cells (MSCs), which can be mobilized into the circulation and incorporate into tumor micro-environments. Many observations indicate that, in the tumor micro-environment, MSCs have several tumor growth promoting functions, including expression of growth factors, promotion of tumor vessel formation and creation of tumor stem cell niches. This review will discuss the currently known tumor growth promoting BM-derived cells and focus on the role of MSCs in modulating tumor micro-environments. In addition, we will discuss the potential of inhibiting BM-derived cells and their utilization as cellular vehicles for selective delivery of cancer therapeutics as additional strategies in the treatment of cancer.     

Increase of bone marrow-derived secretory lineage epithelial cells during regeneration in the human intestine

BACKGROUND & AIMS: We have previously reported that bone marrow (BM)-derived cells contribute to the regeneration of the human intestinal epithelium. To analyze further how these cells arise, proliferate, and differentiate as epithelial cells, histologic analysis was conducted using endoscopic specimens. METHODS: Thirty biopsy specimens from 14 female, sex-mismatched BM-transplantation recipients were examined. BM-derived cells were identified by fluorescent in situ hybridization (FISH) for the Y chromosome and immunohistochemistry. Multicolor FISH was used to exclude cell fusion. These cells were further analyzed for various differentiation or proliferation markers. RESULTS: No evidence of cell fusion was detected. BM-derived cells did not distribute within the crypt as stem cells and rarely expressed Musashi-1. However, BM-derived epithelial cells frequently expressed Ki-67, and some of these cells appeared as pairs of adjacent cells. These cells also expressed markers of all 4 lineages of terminally differentiated cells. During regeneration following graft-vs-host disease, the number of BM-derived cells was substantially increased within Ki-67-positive cells. Interestingly, the number of cells expressing markers for secretory lineage cells was significantly increased within BM-derived cells. This change was unique for BM-derived cells, resulting in a significantly increased proportion of BM-derived cells among secretory lineage cells. CONCLUSIONS: BM-derived epithelial cells arise via a mechanism other than cell fusion and rarely give rise to stem cells. However, a small proportion of these cells express proliferation markers, and a majority reside as terminally differentiated cells. During regeneration BM-derived cells increase as secretory lineage cells, thereby contributing to restore epithelial functions.     

Hematopoietic Progenitor Cells Residing in Muscle Engraft into Bone Marrow following Transplantation

Hematopoietic and mesenchymal stem cells can potentially be the same cell type or adhere simultaneously in both bone marrow (BM) and muscle. In this study, we asked whether murine BM-derived cells could be tracked in muscle tissue after BM transplantation and whether muscle-derived cells have hematopoietic potential. To answer the first question, we transplanted BM from male BALB/c mice into irradiated female recipients and analyzed for engraftment. We used quantitative polymerase chain reaction (PCR) and fluorescent in situ hybridization techniques for Y chromosome-specific gene probes. A high number of BM-derived cells were located in both the intravascular and extravascular spaces in muscle tissue after BM transplantation. To answer the second question, we analyzed colony-forming potential in vitro with soft-agar assays and the competitive engraftment potential in vivo of muscle-derived cells. Engraftment levels of male cell populations were tested by quantitative PCR. The long-term engraftment potential of muscle-derived cells was low compared with that of BM. We conclude that there is intensive cellular trafficking between BM and muscle tissue. The engraftment potential of muscle-derived stem cells into BM is low and corresponds to the low amounts of hematopoietic colony-forming cells found in muscle tissue.     

Transregulation of memory CD8 T-cell proliferation by IL-15Ralpha+ bone marrow-derived cells

Interleukin 15 (IL-15) and the IL-15 receptor alpha (IL-15Ralpha) chain are both required for the basal proliferation of memory CD8 T cells, but which cell types are required to express IL-15 or IL-15Ralpha to mediate this proliferation is not known. Using bone marrow (BM) chimeras, we showed that virus-specific CD8 memory T-cell proliferation was driven by IL-15 produced by either BM-derived or parenchymal cells. Experiments using mixed BM chimeras showed that IL-15Ralpha expression by memory CD8 T cells was not required for their division. In addition, wild-type memory CD8 T cells did not divide after transfer into IL-15Ralpha(-/-) mice. Further analyses demonstrated that IL-15Ralpha(+) BM-derived cells were crucial in driving memory CD8 T-cell division in the spleen while both parenchymal and BM-derived cells promoted memory cell division in the lung. Proliferation in response to soluble IL-15 in vivo required expression of IL-15Ralpha by opposing cells and IL-15Rbeta by CD8 memory cells, indicating that IL-15 interacted directly with the T cells. These results indicate that transpresentation of IL-15 by IL-15Ralpha on BM-derived cells mediates the basal proliferation of memory CD8 T cells.     

Stimulation of interleukin-6 production by endothelin in rat bone marrow-derived stromal cells

Endothelin (ET) produced by endothelial cells has recently been found to be a potent vasoconstricting hormone. In this report, ET is shown to be a potent stimulator of interleukin-6 (IL-6) production by rat bone marrow (BM)-derived stromal cells. It was also shown that ET increased the level of mRNA for IL-6 in these cells. The two types of ET receptor (R), ETAR and ETBR, were shown to be expressed on both BM-derived stromal cells in culture and ex vivo in BM tissue, suggesting that ET works as a physiologic stimulator of IL-6 production in the BM. It was shown that ETAR is coupled to phospholipase C activation, leading to the production of inositol 1,4,5-trisphosphate (IP3) and 1,2- diacylglycerol (DAG) as second messengers in BM-derived stromal cells. This was corroborated by data showing that IL-6 production in these cells was induced by combined stimulation with ionomycin and phorbol myristate acetate, thereby bypassing the effects of IP3 and DAG, respectively. This is the first report on the hormonal regulation of IL- 6 production by BM stromal cells, indicating that hematopoiesis is subject to endocrinologic regulation under physiologic conditions. ET has recently been reported to be produced by macrophages in response to bacterial lipopolysaccharide and human immunodeficiency virus-1 glycoprotein 120. These facts, taken together with our findings, raise the possibility that ET shares the same role of IL-1 as a local cytokine, mediating an intercellular signal between macrophages and BM stromal cells in response to bacterial or viral stimulation.     

Role of bone marrow-derived cells in colon cancer: lessons from mouse model studies

The role of the tumor stroma in carcinogenesis and cancer progression have been documented for a long time. However, the molecules and mechanisms involved have not been understood precisely. Recently, various mediators involved in the communication between the tumor epithelium and stroma and their roles have been revealed by utilizing new technology such as array analysis, laser capture sampling, and genetically altered mice. Moreover, accumulating evidence indicates that some cells in the tumor stroma are derived from the bone marrow (BM). While some of these BM-derived cells are well-known players in inflammation, as exemplified by macrophages, other types of BM-derived cells have been described only recently and are still poorly characterized. In this review, I focus on the latter class of BM-derived cells in colon carcinogenesis, with reference to similar cells in other types of cancer as well. Studies of these myeloid cells should help us understand the inflammation and immune response from a broader perspective as the body’s reaction to pathogenic insults.     

Bone marrow (BM) transplantation promotes beta-cell regeneration after acute injury through BM cell mobilization

There is controversy regarding the roles of bone marrow (BM)-derived cells in pancreatic beta-cell regeneration. To examine these roles in vivo, mice were treated with streptozotocin (STZ), followed by bone marrow transplantation (BMT; lethal irradiation and subsequent BM cell infusion) from green fluorescence protein transgenic mice. BMT improved STZ-induced hyperglycemia, nearly normalizing glucose levels, with partially restored pancreatic islet number and size, whereas simple BM cell infusion without preirradiation had no effects. In post-BMT mice, most islets were located near pancreatic ducts and substantial numbers of bromodeoxyuridine-positive cells were detected in islets and ducts. Importantly, green fluorescence protein-positive, i.e. BM-derived, cells were detected around islets and were CD45 positive but not insulin positive. Then to examine whether BM-derived cell mobilization contributes to this process, we used Nos3(-/-) mice as a model of impaired BM-derived cell mobilization. In streptozotocin-treated Nos3(-/-) mice, the effects of BMT on blood glucose, islet number, bromodeoxyuridine-positive cells in islets, and CD45-positive cells around islets were much smaller than those in streptozotocin-treated Nos3(+/+) controls. A series of BMT experiments using Nos3(+/+) and Nos3(-/-) mice showed hyperglycemia-improving effects of BMT to correlate inversely with the severity of myelosuppression and delay of peripheral white blood cell recovery. Thus, mobilization of BM-derived cells is critical for BMT-induced beta-cell regeneration after injury. The present results suggest that homing of donor BM-derived cells in BM and subsequent mobilization into the injured periphery are required for BMT-induced regeneration of recipient pancreatic beta-cells.