Homeostasis of adult stem cells and carcinogenesis

Treatment of malignant tumors using radiotherapy, chemotherapy, immunosuppressive drugs required to recover bone marrow transplant by the donor bone marrow or purified adult stem cells. During the next 1-15 years of follow up of these patients compared with healthy individuals of the same age increases the risk of multiple malignancies. It used to be attributed to the influence of therapeutic effects. However, it is revealed that some of the cells and the stroma of the secondary tumors are composed of descendants of transplanted stem cells. This indicates the important role of stem cells in tumor growth. This is also evidenced by numerous studies showing that adult stem cells from both mice and humans multiplied in vitro, after transplantation into the body give the sarcoma, cancer foci and other types of malignant growth. In this, malignant growth is most intense in the presence of focal chronic inflammation. No less than the experimental data, including those obtained in humans suggest that the transplanted stem cells actively colonize stroma of tumor tissue, stimulating the growth of the tumor and its metastasis. The human condition of survival is the presence of rigid homeostatic control mechanisms of low numbers of stem cells in the body and the limit their division, even in areas of regeneration. After the transplantation of stem cells their number in the bloodstream and, consequently, in the pathological foci of regeneration, increases in many dozens of times--this level can not be achieved by the organism itself. This leads to a sharp increase in the rate of regeneration of tissues, which creates conditions for amplification of malignant growth.     

Human mesenchymal stem cells engraft and demonstrate site-specific differentiation after in utero transplantation in sheep

Mesenchymal stem cells are multipotent cells that can be isolated from adult bone marrow and can be induced in vitro and in vivo to differentiate into a variety of mesenchymal tissues, including bone, cartilage, tendon, fat, bone marrow stroma, and muscle. Despite their potential clinical utility for cellular and gene therapy, the fate of mesenchymal stem cells after systemic administration is mostly unknown. To address this, we transplanted a well-characterized human mesenchymal stem cell population into fetal sheep early in gestation, before and after the expected development of immunologic competence. In this xenogeneic system, human mesenchymal stem cells engrafted and persisted in multiple tissues for as long as 13 months after transplantation. Transplanted human cells underwent site-specific differentiation into chondrocytes, adipocytes, myocytes and cardiomyocytes, bone marrow stromal cells and thymic stroma. Unexpectedly, there was long-term engraftment even when cells were transplanted after the expected development of immunocompetence. Thus, mesenchymal stem cells maintain their multipotential capacity after transplantation, and seem to have unique immunologic characteristics that allow persistence in a xenogeneic environment. Our data support the possibility of the transplantability of mesenchymal stem cells and their potential utility in tissue engineering, and cellular and gene therapy applications.     

Mobilization‐based transplantation of young‐donor hematopoietic stem cells extends lifespan in mice

Mammalian aging is associated with reduced tissue regeneration and loss of physiological integrity. With age, stem cells diminish in their ability to regenerate adult tissues, likely contributing to age‐related morbidity. Thus, we replaced aged hematopoietic stem cells (HSCs) with young‐donor HSCs using a novel mobilization‐enabled hematopoietic stem cell transplantation (HSCT) technology as an alternative to the highly toxic conditioning regimens used in conventional HSCT. Using this approach, we are the first to report an increase in median lifespan (12%) and a decrease in overall mortality hazard (HR: 0.42, CI: 0.273–0.638) in aged mice following transplantation of young‐donor HSCs. The increase in longevity was accompanied by reductions of frailty measures and increases in food intake and body weight of aged recipients. Young‐donor HSCs not only preserved youthful function within the aged bone marrow stroma, but also at least partially ameliorated dysfunctional hematopoietic phenotypes of aged recipients. This compelling evidence that mammalian health and lifespan can be extended through stem cell therapy adds a new category to the very limited list of successful anti‐aging/life‐extending interventions. Our findings have implications for further development of stem cell therapies for increasing health and lifespan.     

Components of the hematopoietic compartments in tumor stroma and tumor-bearing mice

Solid tumors are composed of cancerous cells and non-cancerous stroma. A better understanding of the tumor stroma could lead to new therapeutic applications. However, the exact compositions and functions of the tumor stroma are still largely unknown. Here, using a Lewis lung carcinoma implantation mouse model, we examined the hematopoietic compartments in tumor stroma and tumor-bearing mice. Different lineages of differentiated hematopoietic cells existed in tumor stroma with the percentage of myeloid cells increasing and the percentage of lymphoid and erythroid cells decreasing over time. Using bone marrow reconstitution analysis, we showed that the tumor stroma also contained functional hematopoietic stem cells. All hematopoietic cells in the tumor stroma originated from bone marrow. In the bone marrow and peripheral blood of tumor-bearing mice, myeloid populations increased and lymphoid and erythroid populations decreased and numbers of hematopoietic stem cells markedly increased with time. To investigate the function of hematopoietic cells in tumor stroma, we co-implanted various types of hematopoietic cells with cancer cells. We found that total hematopoietic cells in the tumor stroma promoted tumor development. Furthermore, the growth of the primary implanted Lewis lung carcinomas and their metastasis were significantly decreased in mice reconstituted with IGF type I receptor-deficient hematopoietic stem cells, indicating that IGF signaling in the hematopoietic tumor stroma supports tumor outgrowth. These results reveal that hematopoietic cells in the tumor stroma regulate tumor development and that tumor progression significantly alters the host hematopoietic compartment.     

Impact of parathyroid hormone on bone marrow-derived stem cell mobilization and migration

Parathyroid hormone (PTH) is well-known as the principal regulator of calcium homeostasis in the human body and controls bone metabolism via actions on the survival and activation of osteoblasts. The intermittent administration of PTH has been shown to stimulate bone production in mice and men and therefore PTH administration has been recently approved for the treatment of osteoporosis. Besides to its physiological role in bone remodelling PTH has been demonstrated to influence and expand the bone marrow stem cell niche where hematopoietic stem cells, capable of both self-renewal and differentiation, reside. Moreover, intermittent PTH treatment is capable to induce mobilization of progenitor cells from the bone marrow into the bloodstream. This novel function of PTH on modulating the activity of the stem cell niche in the bone marrow as well as on mobilization and regeneration of bone marrow-derived stem cells offers new therapeutic options in bone marrow and stem cell transplantation as well as in the field of ischemic disorders.     

Adult mesenchymal stem cells and cell-based tissue engineering

The identification of multipotential mesenchymal stem cells (MSCs) derived from adult human tissues, including bone marrow stroma and a number of connective tissues, has provided exciting prospects for cell-based tissue engineering and regeneration. This review focuses on the biology of MSCs, including their differentiation potentials in vitro and in vivo, and the application of MSCs in tissue engineering. Our current understanding of MSCs lags behind that of other stem cell types, such as hematopoietic stem cells. Future research should aim to define the cellular and molecular fingerprints of MSCs and elucidate their endogenous role(s) in normal and abnormal tissue functions.     

脐带血移植的应用进展及脐带血库建设

脐带血(umbilical cord blood)作为公认的造血干细胞重要来源之一,已经被广泛地用于治疗儿童和成人的良恶性血液系统疾病以及中枢神经系统疾病、实体瘤、缺血性下肢血管病和组织再生等。相对于骨髓移植和外周血来源的造血干细胞移植,脐带血移植(UCBT)在细胞收集使用、干细胞增殖能力以及移植物抗宿主反应等方面都具有明显的优势。目前的数据显示,因为HLA配型等原因而无法进行骨髓移植的患者应该尽早进行UCBT。此外,UCBT的增多促进了脐带血库的快速建设。本文针对UCBT和脐带血库的最新进展进行了综述。     

Adult stem cells: seing is not being

Recent unexpected observations in adult rodents that stem/progenitor cells located in the bone marrow, but also in other tissues, could, after their transplantation to an irradiated host contribute to the regeneration of damaged organs such as brain, liver, pancreas or muscle, have raised much hope for future therapeutic applications. These data have also initially been interpreted as a proof of a possible transdifferentiation or plasticity of adult stem cells located in these tissues. Additional experiments rigorously analyzed have tempered initial enthusiasm, by showing that if marrow cells do migrate in damaged muscles and liver, their contribution to organ repair is low, and in some cases, explained by cell fusion. Nevertheless, among bone marrow cells, two categories of stem cells now emerge that have a potentially tremendous interest in cell therapy, if we succeed in understanding how to purify, amplify and differentiate these more efficiently and reproducibly.     

Endothelial progenitor cells for postnatal vasculogenesis

In the past decade, researchers have defined committed stem or progenitor cells from various tissues, including bone marrow, peripheral blood, brain, liver, and reproductive organs, in both adult animals and humans. Whereas most cells in adult organs are composed of differentiated cells, which express a variety of specific phenotypic genes adapted to each organ's environment, quiescent stem or progenitor cells are maintained locally or in the systemic circulation and are activated by environmental stimuli for physiological and pathological tissue regeneration. Recently, endothelial progenitor cells (EPCs) were isolated from peripheral blood CD34, Flk-1, or AC133 antigen-positive cells, which are considered to include a hematopoietic stem cell population, and were shown to be incorporated into foci of neovascularization. This finding, that circulating EPCs may home to sites of neovascularization and differentiate into endothelial cells in situ, is consistent with "vasculogenesis," a critical paradigm for embryonic neovascularization, and suggests that vasculogenesis and angiogenesis may constitute complementary mechanisms for postnatal neovascularization. Previous reports demonstrating therapeutic potential of EPC transplantation in animal models of hindlimb and myocardial ischemia opened the way to the clinical application of cell therapy: the replacement of diseased or degenerating cell populations, tissues, and organs. In this review, we summarize biological features of EPCs and speculate on the utility of EPCs for vascular and general medicine. cell transplantation; ischemia; neovascularization; stem cell     

Application of hypothermia to autologous stem cell purging

Autologous stem cell transplantation is used widely after high-dose chemotherapy for treating hematological and other malignancies. Bone marrow harvested for autologous bone marrow transplantation may contain residual malignant cells even when the cancer is judged to be in remission. Attempts to purge marrow of its putative residual malignant cells may delay hemopoietic reconstitution and are of uncertain efficacy. In this report, we demonstrate the possibility of applying hypothermia to autologous stem cell purging. Using clonogenic assay, we compared the surviving fraction of human leukemia (HL60, K562) and human small cell lung cancer (H69) cell lines with that of normal human bone marrow CFU-GM and BFU-E cells after incubation at 4 +/- 0.1 degrees C for 24 and 48 h. Hypothermia decreased the surviving fraction of HL60, H69, and K562 cells. In contrast, the surviving fractions of stem cells were not affected by the temperature shift. The surviving fraction of HL60 cells at 4 degrees C cooling was significantly lower than that at 22 degrees C cooling. These findings suggest that in vitro hypothermia may selectively purge residual malignant cells in stored remission bone marrow and may be applicable before autologous bone marrow transplantation. In addition, the method is very simple and cost effective.     

Adult mesenchymal stem cells and cell-based tissue engineering

The identification of multipotential mesenchymal stem cells (MSCs) derived from adult human tissues, including bone marrow stroma and a number of connective tissues, has provided exciting prospects for cell-based tissue engineering and regeneration. This review focuses on the biology of MSCs, including their differentiation potentials in vitro and in vivo, and the application of MSCs in tissue engineering. Our current understanding of MSCs lags behind that of other stem cell types, such as hematopoietic stem cells. Future research should aim to define the cellular and molecular fingerprints of MSCs and elucidate their endogenous role(s) in normal and abnormal tissue functions.     

胎肝造血干细胞的移植特性

胚胎发育中,肝脏是一个重要的造血器官。近年来胎肝移植的临床应用重新引起了人们的关注。本文应用染色体的 C-带染色法研究了小鼠骨髓和胎肝造血干细胞在照射受体小鼠中的增殖能力与相互间的竞争作用。实验结果表明胎肝造血干细胞在成年骨髓中的植入率比较同样条件下的成年骨髓造血干细胞低,但胎肝造血干细胞比较成年骨髓造血干细胞具有更强的自我更新或增殖能力。在同种胎肝造血干细胞移植中,为了降低同种移植抗力,提高移植的胎肝造血干细胞在受体中的耐受性,移植前对受体作适当的免疫抑制处理是必要的。因此,克服个体发育屏障和移植免疫屏障是提高同种胎肝造血干细胞移植效果中两个重要的研究课题。     

Modelling of ex vivo expansion/maintenance of hematopoietic stem cells

In this study, we described the modelling of the expansion/maintenance of human hematopoietic stem/progenitor cells from adult human bone marrow. CD 34(+)-enriched cell populations from bone marrow were cultured in the presence and absence of human stroma in serum-free media containing bFGF, SCF, LIF and Flt-3 ligand for several days. The cells in the culture were analysed for expansion and phenotype by flow cytometry. Although significant expansion of bone marrow cultures occurred in the presence and absence of human stroma, the results of expansion were effectively better in the presence of a stromal layer. In both situations the phenotypic analysis demonstrated a great expansion of CD 34(+)38(-) cells. The differentiative potential of bone marrow CD 34(+) cells co-cultured with human stroma was primarily shifted towards the myeloid lineage with the presence of CD 15 and CD 33.     

Contribution of hematopoietic stem cells to skeletal muscle

Cells from adult bone marrow participate in the regeneration of damaged skeletal myofibers. However, the relationship of these cells with the various hematopoietic and nonhematopoietic cell types found in bone marrow is still unclear. Here we show that the progeny of a single cell can both reconstitute the hematopoietic system and contribute to muscle regeneration. Integration of bone marrow cells into myofibers occurs spontaneously at low frequency and increases with muscle damage. Thus, classically defined single hematopoietic stem cells can give rise to both blood and muscle.     

成体干细胞的生物学特点及应用前景

成体干细胞存在于人和哺乳动物组织中,具有自我更新和一定的分化潜能,现已从骨髓,软骨,血液,神经,肌肉,脂肪,皮肤,角膜缘,肝脏,胰腺等许多组织中获得成体干细胞,发现部分组织成体干细胞具有多向分化潜能,成体干细胞的研究在再生医学中有十分广阔的应用前景。     

Laminin expression during bone marrow mononuclear cell transplantation in hepatectomized rats

The adult bone marrow retains two populations of stem cells with emerging importance for the treatment of diverse liver diseases: hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs). However, the mechanisms that control liver regeneration after bone marrow cell transplantation are still controversial. Liver regeneration after partial hepatectomy is a complex process that requires the proliferation of all hepatic cells. Growth factors, cytokines and extracellular matrix molecules are key elements in this process. Laminins are a family of extracellular matrix proteins with adhesive and chemotactic functions, expressed in the portal and centrolobular veins of the normal liver. The aim of this study was to investigate laminin expression during liver regeneration induced by partial hepatectomy followed by bone marrow mononuclear cell (BMMNC) transplantation. Rat BMMNCs were isolated by Ficoll-gradient centrifugation, stained with DAPI and injected into recently hepatectomyzed rats via the portal vein. Liver sections obtained 15 min, 1 day and 3 days after the surgery were immunolabeled with anti-rat CD34 and/or laminin primary antibodies and observed under a laser scanning confocal microscope. Results showed that 15 min after partial hepatectomy, a transplanted CD34+ HSC was found in contact with laminin, which was localized in the portal and centrolobular veins of rat livers. Furthermore, 1 and 3 days after hepatectomy, transplanted BMMNCs were found in the hepatic sinusoids expressing laminin. These results strongly suggest that laminin might be an important extracellular matrix component for bone marrow cell attachment and migration in the injured liver.     

Stromal fibroblasts activated by tumor cells promote angiogenesis in mouse gastric cancer

Myofibroblasts, also known as activated fibroblasts, constitute an important niche for tumor development through the promotion of angiogenesis. However, the mechanism of stromal fibroblast activation in tumor tissues has not been fully understood. A gastric cancer mouse model (Gan mice) was recently constructed by simultaneous activation of prostaglandin (PG) E2 and Wnt signaling in the gastric mucosa. Because both the PGE2 and Wnt pathways play a role in human gastric tumorigenesis, the Gan mouse model therefore recapitulates the molecular etiology of human gastric cancer. Microvessel density increased significantly in Gan mouse tumors. Moreover, the expression of vascular endothelial growth factor A (VEGFA) was predominantly induced in the stromal cells of gastric tumors. Immunohistochemistry suggested that VEGFA-expressing cells in the stroma were alpha-smooth muscle actin-positive myofibroblasts. Bone marrow transplantation experiments indicated that a subset of gastric myofibroblasts is derived from bone marrow. Importantly, the alpha-smooth muscle actin index in cultured fibroblasts increased significantly when stimulated with the conditioned medium of Gan mouse tumor cells, indicating that gastric tumor cells activate stromal fibroblasts. Furthermore, conditioned medium of Gan mouse tumor cells induced VEGFA expression both in embryonic and gastric fibroblasts, which further accelerated the tube formation of human umbilical vein endothelial cells in vitro. Notably, stimulation of fibroblasts with PGE2 and/or Wnt1 did not induce VEGFA expression, thus suggesting that factors secondarily induced by PGE2 and Wnt signaling in the tumor cells are responsible for activation of stromal fibroblasts. Such tumor cell-derived factors may therefore be an effective target for chemoprevention against gastric cancer.