Feedback Supports Regenerative Proliferation of Epithelial Stem Cells in Bladder.” Nature, v.472 (2011).
Blood Adult Stem Cell: Current Research on Isolation or Production of Therapeutic Cells
Blood Adult Stem Cell: Current Research on Isolation or Production of Therapeutic Cells
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Blood Adult Stem Cell: Current Research on Isolation or Production of Therapeutic Cells
All adult stem cells—whether yielded from blood, bone marrow, or tissue—share multiple features that make them an interesting choice in the field of cell-based regeneration. Trials have shown that there is little risk associated with human therapeutic application. To demonstrate the essentiality of these cells in organisms with a prolonged life, the hematopoietic system of the human body is a good example. Highly specialized cells or mature blood cells are short-lived, such as red blood cells, which live for approximately 120 days and are then eliminated.
Billions of red blood cells circulate in our system and are destroyed every day; the blood cell source must be limitless to meet the demand, which can have the hematopoietic stem cells as the root. It produces more hematopoietic stem cells along with differentiated “progenitor cells,” which then further differentiate into all lineages of mature blood cells (white and red). Bone marrow serves as the major source of adult hematopoietic stem cells alongside the umbilical cord blood of newborns. Hematopoietic stem cells become permanently settled in bone marrow, but they can leave bone marrow for a short period and can be collected from peripheral blood.
For this mobilization of hematopoietic stem cells, leukocyte stimulating growth factors (cytokines) and granulocyte stimulating factors are applied. Hematopoietic stem cells can be collected via a process called aphresis, which targets specific white blood cells. The procedure is much less invasive for donors and is similar in quality to procedure for bone marrow-harvested stem cells. An important, recent clinical application of hematopoietic stem cells is transplantation of allogenic bone marrow for the treatment of leukemia.
Characteristics of Adult Stem Cells
Adult stem cells are partially committed to lineage, unlike embryonic stem cells, so they have the capacity to give rise to a particular germ layer. For example, post-transplant adult hematopoietic stem cells in the leukemia patient can repopulate the bone marrow for generating all blood cell lineages. The multipotent adult stem cell however cannot produce ectodermal or endodermal cell lineages. Unipotent stem cells have increased capacity of replication but they can only differentiate into a specific cell lineage. Adult stem cells have greater proliferation capacity and ability to repair or repopulate tissue in comparison to adult differentiated cells, although adult differentiated cells only give rise to cells of identical lineage.
Isolation and Application of Mesenchymal Stem Cells From Bone Marrow
Mesenchymal stem cells procured from human bone marrow (hBMSCs) have been studied broadly because of their comparatively easy collection and their differentiation potential to the adipogenic, osteogenic, and chondrogenic lineages and cells, including cardiomyocytes, hepatocytes, and neurons. Their self-renewal and multipotentiality has increased the potential use of this stem cell model as an intensified, self-renewing source in regenerative medicine and tissue engineering. In particular, the osteogenic potential of hBMSCs has been explored in depth in the evaluation of basic scaffolding structures involved in bone tissue engineering.
In addition, the isolation strategy based on their adherence to the culture substrates constitutes a simple strategy for eliminating non-mesenchymal lineages thereby reducing the virtual dependency on serious and complex methods of cell isolation, which essentially rely on the expression of clearly defined surface markers. A limited number of studies have also reported successful extraction of BMSCs from human femoral bone marrow. Most of these investigations with the femoral heads have essentially focused on isolating primary osteoblastic cells by generating explant cultures of trabecular bone or directly trypsinizing the trabecular bone. Schütze and collaborators (2007) demonstrated that the multipotent mesenchymal stem cells derived from the bone marrow can be isolated by processing the trabecular bone in the femoral heads following repeated and thorough washings to release these cells from the bone plugs. Pineda et al. modulated the protocol for the isolation of mesenchymal characteristic possessing cell population. The process involved trabecular bone disaggregation by mechanical means, which would ultimately lead to the release of cells from the femoral bone marrow. Others have gone on to improve on this method of isolation with regard to the efficiency of isolation, which was mainly brought about by the surface culture area reduction at the start of the primary culture. Moreover, the authors could establish the potential of the cells for osteogenesis, as upon osteogenic induction, the cells could cause matrix mineralization. The induction also resulted in the upregulation of the osteogenic marker gene expression.
Isolation of Marrow Stromal Cells From Murine Bone Marrow
As compared to the rat or human MSCs, it is a much harder task to isolate MSCs from the bone marrow and proceed for expansion in culture. The murine MSCs (mMSCs) are found to be contaminated with hematopoietic progenitor cells overgrowing in the culture medium when compared to the MSCs from rats or humans. One way to counter this problem could be the removal of hematopoietic precursors by immunodepletion. However, such immunodepletion leads to the accumulation of extracellular matrices in large amounts thereby yielding poor culture expansion. These limitations in the mMSCs’ features have restricted the testing of the cells in important genetic models, such as the transgenic mice. In a recent study, a new method for the isolation of murine MSCs was established wherein the mMSCs so isolated could be extensively expanded. In addition, the cells showed characteristics of multipotentiality and could differentiate into both mineralizing and adipocyte cells. The mMSCs isolated from the inbred mice strains shared the characteristics of rapid proliferation as represented by the single colony forming ability of the low density plated cells when the mMSCs showed a nearly sevenfold increase in growth rate. The cells also differed in their optimal growth requiring media content. The cells showed variation in the surface epitope profiles.
Adult Stem Cells in Vascular Regeneration
The development of adult stem cells for clinical application has undergone a paradigm shift compared to the rest of the stem cell therapeutic approaches. The adult stem cells are present in the circulation, bone marrow, or within specific tissue types as residents. Neovascularization therapies have included mainly circulating or bone marrow derived stem cell approaches. The application of adult stem cells in the vasculogenesis was set up with the discovery of a subpopulation of vasculogenic endothelial progenitor cells (EPCs) by Asahara in 1997. The idea has gone on to be used in recent clinical trials. The commonly used surface markers for EPC identification include the markers that are not endothelial lineage specific like CDR10 and CD133.
The standardization of EPC culturing, purifying, and harvesting are not yet fully elucidated. Thus, methodological variation compounds semantic confusion. The EPCs may be considered a mixed population of different lineage of progenitor cells. True endothelial progenitors constitute this population of cells that gets incorporated within the vascular network while the secretion of angiogenic cytokines makes up the contribution of the hematopoietic progenitors. The EPCs give rise to “late outgrowth” or “early outgrowth” colonies in cell culture. Cells originating from the early outgrowth colonies express hematopoietic lineage markers and are quite evidently not of endothelial origin. These cells are different from the late outgrowth cells morphologically. The late outgrowth cells are reminiscent of endothelial cells and grow in a cobblestone
