الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Stem cells are unspecialized cells that can self-renew indefinitely and can also differentiate into more mature cells with specialized functions. Generally Stem cells are considered to exhibit four major properties: (1) capacity for self - maintenance (2) multipotency (capable
of producing progeny in at least two lineages); (3) functional, long term tissue reconstitution; and (4) serial transplantability.
Stem cells can be classified into four broad types according
to their potency:(1) Totipotent stem cells, (2) Pluripotent stem cells, (3) Multipotent stem cells and (4) Unipotent stem cells. And can be classified into four broad types based on their origin: (1) stem cells from embryos; (2) stem cells from the fetus; (3) stem cells from the infant or umbilical cord; and (4) stem cells from the adult. Each of
these can be grouped into subtypes .
Different Liver stem / progenitor cell candidates are present but the commonest stem cells transplanted in liver diseases are Bone Marrow - Stem Cells , Hepatic Stem Cells and Fetal Stem Cells.
At present, there are 3 generally used routes for stem cell transplantation: the portal vein, splenic vein, and peritoneal cavity, But the spleen is considered an adequate site for hepatocyte transplantation, particularly in cirrhotic patients, Other sites for infusion are the pancreas and the pulmonary parenchyma .
Liver cell transplantation is carried out by means of a 3 - step method: isolation of hepatocytes from donor liver, then preparing a cell suspension for infusion and, finally, hepatocytes are implanted into the recipient, It is essential to be able to cryopreserve and store cells with good thawed cell function. These include pretreatment of cells, freezing solution, cryoprotectants and freezing - thawing
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protocols, so unlike whole organs, hepatocytes can be cryopreserved and stored in cell banks, offering the advantage of immediate availability in emergencies to replace the liver cells functionally and restore their metabolic function even for a specified period of time.
To date, liver stem cell transplantation still cannot replace liver transplantation although successful outcomes have been achieved for some liver diseases; For acute and chronic liver diseases, although the results of cell transplantation therapies with human clinical trials are some what promising, they are not yet definitive; it can only stimulate liver regeneration or temporary improve liver functions to serve as a bridge until liver transplantation can be performed with the purpose to reduce the risk related to liver transplantation in patients with clinical complications. In this situation, the complete benefit of hepatocyte transplantation into the liver without restoring the normal liver architecture may be questionable. Hepatocyte transplantation to treat metabolic deficiencies has shown promising early improvement in liver function This includes a number of genetic diseases that produce liver disease such as Wilson‟s disease (copper accumulation), Crigler - Najjar syndrome (lack bilirubin conjugation activity) and tyrosinaemia, and cases where there is extrahepatic expression of the disease, e.g. Factor IX deficiency; however, long-term success has not been achieved and limited by incomplete and time limited metabolic control.
Egyptian trials were done for stem cell transplantation in liver diseases,the results revealed beneficial effect on synthetic functions of the liver and possibly improve survival and quality of life of patients with end stage liver disease .
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There are complications and challenges of stem cell transplantation including hepatic , pulmonary , renal complications , immune system and graft rejection complications , gastrointestinal complications after stem cell transplantation ,There is possibilities of infection, ocular complications , also neurologic ,cardiac, endocrine , skeletal disorders as osteoporosis, thrombotic complication ,carcinogenesis and ectopic tissues formation in arteries.
Ethical issues as how to apply the studies conducted on animals on the human body, stem cell availability, potential rejection, possibilities of infection , renal impairment , carcinogenesis, and limited understanding of the totipotent capabilities of embryonic stem cells are the limitations that prevent their use for restoration of liver function. This cell therapy field cannot expect to succeed without taking every precaution for patient safety. This possess several challenges for genomic and epigenomic assessment of stem cells.
Despite liver stem cell transplantation is a promising method in treatment of liver diseases it remains an alternative experimental treatment to bridge patients to orthotopic transplantation or auxiliary partial orthotopic liver transplantation (APOLT) with the purpose to reduce the risk frelated to liver transplantation in patients with clinical complications.