MESENCHYMAL STEM CELLS

Over the last decade, cellular therapy has developed quickly at the level of in vitro and in vivo preclinical research and in clinical trials. Thus, one of the types of adult stem cells that have provided a great amount of interest in the field of regenerative medicine due to their unique biological properties is Mesenchymal stem cells (MSCs).
 Mesenchymal stem cells (MSCs) are known to be multipotent stromal cells that can differentiate into a variety of cell types which include osteoblasts (bone cells), chondrocytes (cartilage cells), myocytes (muscle cells) and adipocytes (fat cells which give rise to marrow adipose tissue). Furthermore, MSCs are responsible for tissue repair, growth, wound healing and cell substitution resulting from physiological or pathological causes; they have various therapeutic applications such as in the treatment of central nervous system afflictions like spinal cord lesions (1). Similarly, they are characterized by an extensive capacity for self-renewal, proliferation, potential to differentiate into multiple lineages and their immune-modulatory role on various cells.
Mesenchymal stem cells have the ability to expand in many folds in culture while retaining their growth and multilineage potential. Also, they can be identified by the expression of many molecules including CD105 (SH2) CD73 and CD34, CD45.  Thus, these properties of MSCs make these cells potentially ideal candidates for tissue technology.
In addition, it has been discovered that MSCs, when transplanted systemically, have the ability to transport to sites of physical harm or damage in animals, suggesting that MSCs have migratory capacity. This migration property of MSCs is important in regenerative medicine, where various injection routes are utilized depending on the damaged tissue or organ.
The first source of Mesenchymal stem cells was in the bone marrow and considered to be the gold standard for clinical research, although various other sources have being discovered which include: Adipose tissue, Dental pulp, Mobilised Peripheral blood, Amniotic fluid, Joint synovium, synovial fluid, Endosteum, Periosteum, Menstrual blood and birth-derived tissues.
Cohnheim (German Biologist) hypothesized in the late nineteenth century that fibroblastic cells derived from bone marrow were involved in wound healing throughout the body, while in 1970, Alexander Friedenstein described a population of plastic-adherent cells that emerged from long-term cultures of bone marrow and other blood-forming organs, and he showed to have colony forming capacity and osteogenic differentiation characteristics in vitro as well as in vivo upon re-transplantation.
Arnold Caplan (1991),  coined the term “mesenchymal stem cell and stated that the cells as multipotent mesenchymal cell populations which can differentiate into several tissue types, and demonstrated roles for MSCs in the regeneration of bone, cartilage or ligaments in animal and clinical studies. However, the first clinical trials of MSCs were completed in 1995 when a group of 15 patients were injected with cultured MSCs to test the safety of the treatment.
According to International Society for Cellular Therapy, the proposed minimum criteria to define MSCs include the following:
 (a) The cells should exhibits plastic adherence
(b) The cell should possess specific set of cell surface markers, i.e. cluster of differentiation (CD) 73, D90, CD105 and lack expression of CD14, CD34, CD45 and human leucocyte antigen-DR (HLA-DR).
(c) The cells should have the ability to differentiate in vitro into adipocyte, chondrocyte and osteoblast.
Thus, these characteristics are valid for all MSCs, although few differences exist in MSCs isolated from various tissue origins.
Mesenchymal stem/stromal cells (MSCs) can be isolated from neonatal tissues, most of which are discarded after birth, including placental tissues, fetal membranes, umbilical cord, and amniotic fluid. Placenta is an ideal starting material for the large-scale manufacture of multiple cell doses of allogeneic MSC. The placenta is a fetomaternal organ from which either fetal or maternal tissue can be isolated.
MSC derived from placenta have long-term proliferation and immunomodulatory capacity, superior to bone marrow-derived MSC. The placenta is a fetomaternal organ consisting of both fetal and maternal tissue, and thus MSC of fetal or maternal origin can be, theoretically isolated.  Thus, neonatal tissues are easily available and they have biological advantages in comparison to adult sources that make them a useful source for stem cells including MSCs. They appear to be more primitive and have greater multipotentiality than their adult counterparts.
 Clinical Application
Ø  MSCs have been widely used to treat immune-based disorders, such as Crohn’s disease, rheumatoid arthritis, diabetes, and multiple sclerosis.
Ø  MSCs have been widely used as a treatment for numerous orthopedic diseases, including bone defects, osteoarthritis (OA), femoral head necrosis, degenerative disc, spinal cord injury, knee varus, osteogenesis imperfecta, and other systemic bone diseases.
Ø  MSCs are promising cell source for treatment of autoimmune, degenerative and inflammatory diseases due to the homing ability, multilineage potential, secretion of anti-inflammatory molecules and immunoregulatory effects.
Ø  MSCs play a key role in the maintenance of bone marrow homeostasis and regulate the maturation of both hematopoietic and non-hematopoietic cells.
Ø  MSCs have been shown to be powerful tools in gene therapies, and can be effectively transduced with viral vectors containing a therapeutic gene, as well as with cDNA for specific proteins, expression of which is desired in a patient.
Ø  It has been proved that MSCs can differentiate into insulin producing cells and have the capacity to regulate the immunomodulatory effects 
REFERENCES

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2.     Friedenstein AJ, Piatetzky II S, Petrakova KV. Osteogenesis in transplants of bone marrow cells. J Embryol Exp Morphol. 1966;16:381–90

3.     Friedenstein AJ, Chailakhyan RK, Latsinik NV, Panasyuk AF, Keiliss-Borok IV. Stromal cells responsible for transferring the microenvironment of the hemopoietic tissues. Cloning in vitro and retransplantation in vivo. Transplantation. 1974;17:331–40.

4.     Pittenger MF, Mackay AM, Beck SC, Jaiswal RK, Douglas R, Mosca JD, et al. Multilineage potential of adult human mesenchymal stem cells. Science. 1999;284:143–7.

5.     Caplan AI, Dennis JE. Mesenchymal stem cells as trophic mediators. J Cell Biochem. 2006;98:1076–84.

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