 |
 Page 2 |
- Identification of functional endothelial progenitor cells suitable for the treatment of ischemic tissue using human umbilical cord blood. Nagano M, Yamashita T, Hamada H, Ohneda K, Kimura K, Nakagawa T, Shibuya M, Yoshikawa H, Ohneda O. Blood. 2007;110:151-160.
Neovascularization in adults is recognized in the process of angiogenesis involving the recruitment of pre-existing endothelial cells in ischemic tissues. Recent studies suggest that BM-derived endothelial progenitor cells (EPCs) also play an essential role in the process of vasculogenesis. EPCs derived from PB, UCB and BM have been shown to be involved in neovascularization during vascular injury, ischemia and tumor growth. So far, the clinical applications for EPC transfusion are limited because of the small number of available cells. UCB has an advantage over PB and BM as a source of EPCs because of its accessibility and higher EPC content.
Umbilical cord blood (UCB) has been used as a potential source of various kinds of stem cells, including hematopoietic stem cells, mesenchymal stem cells, and endothelial progenitor cells (EPCs), for a variety of cell therapies. Recently, EPCs were introduced for restoring vascularization in ischemic tissues. An appropriate procedure for isolating EPCs from UCB is a key issue for improving therapeutic efficacy and eliminating the unexpected expansion of nonessential cells.
The authors report a novel method for isolating EPCs from UCB by a combination of negative immunoselection and cell culture techniques. In addition, EPCs were divided into 2 subpopulations according to the aldehyde dehydrogenase (ALDH) activity. EPCs with low ALDH activity (Alde-Low) possess a greater ability to proliferate and migrate compared to those with high ALDH activity (Alde-High). Moreover, hypoxia-inducible factor proteins are up-regulated and VEGF, CXCR4, and GLUT-1 mRNAs are increased in Alde-Low EPCs under hypoxic conditions, while the response was not significant in Alde-High EPCs. In fact, the introduction of Alde-Low EPCs significantly reduced tissue damage in ischemia in a mouse flap model. Thus, the introduction of Alde-Low EPCs may be a potential strategy for inducing rapid neovascularization and subsequent regeneration of ischemic tissues.
- Therapeutic potential of human umbilical cord-derived stem cells in ischemic diseases. Wu KH, Zhou B, Mo XM, Cui B, Yu CT, Lu SH, Han ZC, Liu YL. Transplant Proc. 2007;39:1620-1622.
The aim of this study was to investigate the therapeutic potential of human umbilical cord-derived stem (UCDS) cells in ischemic diseases. The UCDS cells were characterized by flow cytometry and differentiation into osteogenic and adipogenic cells. Unilateral hind limb ischemia was surgically induced by femoral artery ligation in nude mice. The animals were intramuscularly injected with 10(6) UCDS cells or control phosphate-buffered saline. Blood perfusion of ischemic limbs was detected by laser Doppler perfusion imaging. Transplantation of UCDS cells to the ischemic limbs of nude mice significantly improved the blood flow to the affected limbs. Thus, transplantation of UCDS cells may potentially be a promising treatment for human ischemic diseases.
- Identification of stem cells from human umbilical cord blood with embryonic and hematopoietic characteristics. Zhao Y, Wang H, Mazzone T. Exp Cell Res. 2006;312:2454-2464.
Embryonic stem (ES) cells display two unique properties: self-renewal and pluripotentiality for differentiation. Stem-cell based therapy, therefore, has significant potential to cure important and common human diseases. However, a major limitation for stem cell based therapy has been identification of a suitable source of stem cells.
In this report, the authors report that they have identified a novel type of stem cell from umbilical cord blood, designated cord blood-stem cells (CB-SC). CB-SC displayed important ES cell characteristics including expression of ES-cell-specific molecular markers including transcription factors OCT-4 and Nanog, along with stage-specific embryonic antigen (SSEA)-3 and SSEA-4. CB-SC also expressed hematopoietic cell antigens including CD9, CD45 and CD117, but were negative for CD34. CB-SC displayed very low immunogenicity as indicated by expression of a very low level of major histocompatibility complex (MHC) antigens and failure to stimulate the proliferation of allogeneic lymphocytes. CB-SC can also give rise to cells with characteristics of three embryonic layers: e.g., mesoderm (endothelial-like cells), ectoderm (neuronal-like cells) and endoderm (insulin-producing cells).
The authors indicate that the most important property of CB-SC is their ability to produce a therapeutic glycemic effect in an STZ mouse model of diabetes. Accumulating evidence suggests that insulin-producing cells derived from stem cells can normalize blood glucose in diabetic animal models. However, in previous reports, these cells were derived from ES cells and fetal tissues, raising ethical concerns for theirs clinical application. The widespread availability of human cord blood underlines the potential usefulness of CB-SC for clinical therapeutics.
- Identification of very small embryonic like (VSEL) stem cells in bone marrow. Kucia M, Wysoczynski M, Ratajczak J, Ratajczak MZ. Cell Tissue Res. 2008;331:125-134.
Bone marrow (BM) develops in mammals by the end of the second/beginning of the third trimester of gestation and becomes a major hematopoietic organ in postnatal life. The alpha-chemokine stromal derived factor-1 (SDF-1) to CXCR4 axis plays a major role in BM colonization by stem cells. By the end of the second trimester of gestation, BM becomes colonized by hematopoietic stem cells (HSC), which are chemo-attracted from the fetal liver in a CXCR4-SDF-1-dependent manner. Whereas CXCR4 is expressed on HSC, SDF-1 is secreted by BM stroma and osteoblasts that line BM cavities. Mounting evidence indicates that BM also contains rare CXCR4(+) pluripotent stem cells (PSC).
The investigators in this group have identified a population of CXCR4(+) very small embryonic like stem cells in murine BM and human cord blood. They hypothesize that these cells are deposited during development in BM as a mobile pool of circulating PSC that play a pivotal role in postnatal tissue turnover, both of non-hematopoietic and hematopoietic tissues.
- An in vivo evidence that murine very small embryonic like (VSEL) stem cells are mobilized into peripheral blood after acute myocardial infarction (AMI) and contribute to myocardiac regeneration. Zuba-Surma EK, Kucia M, Guo Y, Dawn B, Bolli R, Ratajczak MZ. Blood 2007;110;1079A (Abstract)
The authors identified a population of SSEA-1+/Oct-4+/Sca-1+/lin-/CD45- pluripotent, very small embryonic-like stem cells (VSEL) in adult murine bone marrow. They found that VSEL possess the ability to differentiate in vitro into all three germ layers including cardiac lineage. However, the input of these cells in regeneration of injured tissues including infarcted myocardium was uncertain. The aim of this study was to establish if VSEL are mobilized into peripheral blood after acute myocardial infarction (AMI) and could play a potential role in myocardiac regeneration.
In vitro data indicated that VSEL were mobilized in mice that had undergone a 30-min coronary occlusion followed by reperfusion. VSEL were detectable in PB on low level under baseline conditions but increased significantly after AMI, peaking at 48h post AMI both in younger and older mice.
The authors also investigated regenerative potential of VSEL injected into infracted myocardium in vivo. Mice underwent a 30-minute coronary occlusion followed by reperfusion and, 48h later, received intramyocardial injection of vehicle, freshly sorted VSEL, or VSEL pre-differentiated in cardiomyogenic medium. At 35 days of follow up, the heart function was investigated by echocardiography. Mice in the group receiving VSEL pre-differentiated in cardiomyogenic medium exhibited improved function of infarcted left ventricle showing higher LV ejection fraction. Other parameters including infarct wall thickening fraction and end-diastolic volume also indicated improvement of heart function. Thus, VSEL are not only mobilized from the bone marrow into the peripheral blood after AMI, but also participate in regenerative processes of infracted myocardium.
- Embryonic-like stem cells from umbilical cord blood and potential for neural modeling. McGuckin C, Forraz N, Baradez MO, Basford C, Dickinson AM, Navran S, Hartgerink JD. Acta Neurobiol Exp. 2006;66:321-329.
The authors point out that umbilical cord blood (UCB) is a valuable source of stem cells in terms of access and supply. They state that they have proved that cells exist in UCB that have multi-tissue differentiation capability. To do this, they optimized a series of stringent and rapid cell separation methods whereby sequential immunomagnetic removal of mature cells in UCB combined to standardized subculture protocols reproducibly revealed immature stem cell groups with embryonic characteristics. They call these cells cord blood derived embryonic-like stem cells (CBE’s) since they were found to reproducibly express markers contiguous with embryonic stem cells. They have also repeated the work on frozen cord blood units thus removing the doubt that such cells could be produced from currently cryopreserved CB units worldwide. The authors suggest that their methods developing CBE’s may now enable preliminary expansion of the primitive CBE stem cells prior to differentiation into neural progenitors and differentiated tissues.
In summary, cord blood has a long history of successful transplantation for hematological and immune system diseases and now with the multipotentiality confirmed in vitro to produce tissues from all three human germ layers, ectodermal, endodermal and mesodermal, demonstrates that it has viability for the regenerative medicine arena.
- Concise review: recent advances on the significance of stem cells in tissue regeneration and cancer therapies. Mimeault M, Batra SK. Stem Cells. 2006;24:2319-45.
The title is misleading because this is an extensive review (26 pages) which must be read in the original because it is too comprehensive to be well summarized here so that only an outline can be provided.
There is great interest in the biology of adult stem cells because of their capacity to self-renew and their high plasticity. These traits enable adult stem cells to produce diverse mature cell progenitors that actively participate in the maintenance of homeostatic processes by replenishing the cells that repopulate the tissues/organs during a lifespan and regenerate damaged tissues during injury. In general, embryonic, fetal, and adult stem cells show several common functional properties including their high self-renewal capacity and potential to generate differentiated cell progenitors of different lineages under simplified culture conditions in vitro and after transplantation in the host in vivo. This suggests that they may contribute to the regeneration of damaged tissues. Therefore, the use of stem cells and their progenitors is a promising strategy in cellular and genetic therapies for multiple degenerative disorders, as well as adjuvant immunotherapy for diverse aggressive cancer types. Parkinson and Alzheimer diseases, muscular degenerative disorders, chronic liver and heart failures, and type 1 and 2 diabetes, as well as skin, eye, kidney, and hematopoietic disorders could be treated by the stem cell-based therapies.
The authors list possible therapeutic applications of embryonic, umbilical cord blood and adult stem cell progenitors in a detailed table. The authors then report the structural and functional features of embryonic, umbilical cord and adult stem cells and their niches, as well as the procedures that are used for their differentiation into particular cell lineages in vitro and in vivo. A detailed description is provided of embryonic stem cells, amniotic epithelial cells, fetal stem cells, umbilical cord stem cells, and adult stem cells. Next the authors discuss adult stem cells of endodermal origin (pulmonary epithelial stem cells, GI tract stem cells and urogenital stem cells), and then review adult stem cells of mesodermal origin (hematopoietic stem cells, stromal stem cells, cardiac stem cells) and stem cells of ectodermal origin (neural stem cells, skin stem cells, ocular stem cells).
The possibility of using stem cells and their more differentiated progenitors to treat numerous degenerative disorders has stimulated great interest in developing safe transplantable sources of stem cells that are unable to form teratomas but are able to repopulate damaged tissues. The authors report the recent advances on the more promising stem cell-based strategies that have been developed for the treatment of numerous degenerative disorders and aggressive cancer types. This discussion includes a review of regenerative medicine in pancreatic diseases, CNS disorders and diseases, Parkinson and Alzheimer disease, spinal cord injuries, ocular disorders, and blood and immune system disorders. Finally, the role of stem cells in cancer therapies is discussed including the use of high-dose cancer therapy plus HSCs.
The authors conclude with a hopeful note suggesting that future works should establish molecular changes occurring in adult stem cells and their progenitors during tissue repair and etiopathogenesis. Hence, these further studies could lead to the development of more effective treatments for numerous genetic and degenerative disorders by cell replacement. Moreover, the identification of specific markers and targeting distinct tumorigenic cascades in cancer progenitor cells should also contribute to developing novel early detection methods and combination therapies for diverse aggressive and lethal cancers derived from the malignant transformation of adult stem cells.
- Clinical trials with adult stem/progenitor cells for tissue repair: let's not overlook some essential precautions. Prockop DJ, Olson SD. Blood. 2007;109:3147-51.
This is a thoughtful “Perspective” discussing the current wave of enthusiasm for clinical trials in which adult stem/progenitor cells are used to repair tissues. In theory, adult stem/progenitor cells may provide a therapy for an almost unlimited number of serious and currently untreatable diseases. In the wave of enthusiasm, however, several essential precautions are not being fully addressed.
As with most dramatically new therapies, the data from basic studies and from animal models are never as conclusive as one would like. The best one can say is that the data are encouraging enough to justify carefully controlled trials in patients in whom the risks can be fully justified.
Currently, the largest number of clinical trials is in patients with heart disease. Here, a confusing variety of cells and strategies for different syndromes have been tested and are outlined in an extensive table in the publication. Most of the trials using bone marrow cells have reported improvements in cardiac function. However, the number of patients enrolled in well-controlled trials is still limited.
Potential dangers of such trials are indicated: One such danger is that the clinical trials will be performed without appropriate controls or without well-defined end points. This danger seems particularly apparent in trials concerning acute myocardial infarction in which there is great variability in the size and location of the lesions, the outcomes are difficult to predict, and different parameters have been used to assess heart function.
Ironically, a second potential risk arises from the striking ability of stem/progenitor cells to enhance repair of tissues and to suppress immune reactions: several reports demonstrated that multipotent mesenchymal stem cells (MSCs) will enhance the growth of cancers in mice. Therefore, there is a risk that administering MSCs or similar cells will enhance the growth of a previously undetected cancer in a patient. Also, stem/progenitor cells that are extensively expanded in culture may themselves generate tumors in patients.
A further danger is posed by cells that are injected in high concentrations into tissues. Such cells can form aggregates with the potential to differentiate their own microenvironment to form nodules of bone or other undesirable structures.
Finally, researchers currently face the danger of generating a great deal of confusion by clinical trials in which the cells used are not adequately characterized. Certainly, researchers will all be sorry if clinical trials with adult stem/progenitor cells do not incorporate some of the simple and essential precautions that can prematurely close down new therapies.
- Differentiation of umbilical cord blood-derived multilineage progenitor cells into respiratory epithelial cells. Berger MJ, Adams SD, Tigges BM, Sprague SL, Wang XJ, Collins DP, McKenna DH. Cytotherapy. 2006; 8:480-487.
The authors report differentiation of human UCB-derived multipotent stem cells, termed multilineage progenitor cells (MLPC), into respiratory epithelial cells (i. e. type II alveolar cells).
Using a cell separation medium (PrepaCyte-MLPC; BioE Inc. ) and plastic adherence, MLPC were isolated from four of 16 UCB units and expanded. Cultures were grown to 80% confluence in mesenchymal stromal cell growth medium (MSCGM; Cambrex BioScience) prior to addition of small airway growth medium (SAGM; Cambrex BioScience), an airway maintenance medium. Following a 3-8-day culture, cells were characterized by light microscopy, transmission electron microscopy, immunofluorescence and reverse transcriptase (RT)-PCR.
MLPC were successfully differentiated into type II alveolar cells (four of four mixed lines; two of two clonal lines). Differentiated cells were characterized by epithelioid morphology with lamellar bodies. Both immunofluorescence and RT-PCR confirmed the presence of surfactant protein C, a protein highly specific for type II cells.
The authors state that, to the best of their knowledge, this is the first time human non-embryonic multipotent stem cells have been differentiated into type II alveolar cells. Further studies to evaluate the possibilities for both research and therapeutic applications are necessary.
- Characterizing donor-derived cells in nonhematopoietic tissue. Ramakrishnan A, Shi D, Torok-Storb B. Biol Blood Marrow Transplant. 2006; 12:990-992.
The concept that adult stem cells harvested from marrow may differentiate into both hematopoietic and nonhematopoietic tissues is appealing and, if true, would have significant therapeutic potential. Numerous reports documenting adult stem cell plasticity have been published in the last decade, in which authors reported differentiation of bone marrow stem cells into muscle, nerve, liver, lung and intestinal epithelium. The data in these reports were obtained primarily from sex-mismatched transplantation studies in which immunohistochemistry (IHC) for tissue-specific antigens was combined with fluorescence in situ hypridization (FISH) for sex chromatin to identify donor-derived cells in nonhematopoietic tissues. However, the validity of these findings has remained controversial.
The authors sought to address this controversy and, to that end, obtained liver and intestinal tissue from a female patient at day 109 after allogeneic stem cell transplantation from a male donor. They prepared slides and on the same sections combined IHC for the CD45 antigen to distinguish cells from the hematopoietic lineage and FISH for X and Y chromatin to distinguish between donor and host. Under high power, 200 nuclei were counted; the donor chromatin signal was, with few exceptions, always associated with CD45. Similar findings were obtained in the tissues of 2 other females who had also undergone sex-mismatched transplantation. The only exceptions were a few cells detected in liver sections that were CD45-negative and contained 2 X chromosomes and 1 Y chromosome, suggesting full fusion.
These observations, together with previous studies in which the authors found no evidence of donor-derived stroma in patients at 0.15-27 years post-allogeneic transplantation, call into question the concept of a totipotent marrow stem cell.
Future studies designed to address this topic should include IHC for CD45 to definitively determine whether a donor signal is associated with a cell derived from the hematopoietic lineage.
- The Politics and Promise of Stem-Cell Research. Schwartz, RS. N Engl J Med 2006 355: 1189-1191.
In this Perspective on stem cell research, the author who is a deputy editor of the New Eng J Med, points out that the notion that adult stem cells have the same developmental potential as embryonic stem cells, let alone "more promise" is dubious. He also derides some information available on the internet regarding cures of diseases with adult stem cells as "pure hokum." He further insists that anecdotal reports, such as that of a wheel-chair bound patient with multiple sclerosis who received cord blood stem cells and recovered her ability to walk within minutes, are lures used to trap hapless patients into a treatment that has no merit whatsoever. (Also see in News & Issues: "Stem cell treatment warning" and "Patients warned over dangers of untested stem-cell wonder cures".)
Experiments to establish the existence of a pluripotent stem cell in adults are crucial but, currently, there is no clinical evidence of such cells. There had been no prospective trial to test the proposition that adult hematopoietic stem cells can improve the function of a tissue other than bone marrow. However, in the September 21, 2006 issue of the New Eng J Med, three important articles correct this deficiency.
The authors of these three articles merit high praise for carrying out very difficult studies in humans with myocardial infarction. However, the studies are open to two important criticisms: the injected cells were not always rigorously purified hematopoietic stem cells, and they provide no evidence that the injected hematopoietic cells actually settled in the heart and became cardiac myocytes.
Overall, the results of the three studies of a combined total of 376 patients do not promote the use of intracoronary infusions of autologous bone marrow to improve ventricular function. Lunde et al (citation 23) found no significant differences between the control and bone marrow-treated groups in left ventricular function or infarct size; Schächinger et al. (citation 24) and Assmus et al. (citation 25) found small, significant but clinically uncertain improvements in ventricular function in the bone marrow-treated groups.
These three clinical trials will probably not stop the clinical exploitation of patients with promises that bone marrow (or cord blood) can cure almost any chronic disease. It is important to play down promises to the public that the work will produce anything of clinical value in the foreseeable future. We simply don’t know how an embryonic stem cell will behave in a human, and we don’t know whether human marrow contains a pluripotent stem cell that can transdifferentiate. Equally important, we don’t yet know whether research on embryonic stem cells will teach us how to revise the differentiation program of a tissue-specific stem cell, thereby circumventing the need for embryonic cells.
The author makes it abundantly clear that he feels that the delay of medical advances by theological disputes is not in the best interests of the sick and disabled.
