World-wide, there are reports of more than 30 patients, including 10 children at King’s College Hospital London, who have been treated by HT, with the main cause to date being children with urea cycle defects. The number of cells transplanted usually represents approximately 5% of theoretical liver mass, and either fresh or cryopreserved cells have been used. However, cell function often declines after about 9 months, with the result that patients then undergo OLT. Problems with immunosuppression and rejection may be an important factor in this. Patients with acute liver failure (ALF) are another group in which HT has been used, where the aim is to maintain liver function as a bridge to OLT or until regeneration of the native liver occurs.
Isolation of hepatocytes from donor liver
Human hepatocytes are isolated from liver tissues rejected/unused for transplantation, including livers from non-heartbeating donors. A collagenase perfusion technique is used to digest donor liver tissue, and the cells are purified by centrifugation. Donor livers can be contaminated with microorganisms as a result of their coming from patients in the intensive care unit, but this is usually eliminated from the final cell product during processing. The addition of the antioxidant Nacetylcysteine to the perfusion solution, when isolating hepatocytes from fatty liver, gave significant improvement in cell viability and metabolic function. This is now used routinely for isolation of hepatocytes for clinical use. The quality of the isolated hepatocytes is assessed (cell number, viability, microbiology). Cells are either transplanted immediately after isolation, or cryopreserved and banked for future use..
Procedure - route and criteria
Patients receive immunosuppression, usually 10 mg/kg methylprednisolone, as an intravenous bolus with tacrolimus to maintain a 12-hr trough blood level of 10 g/L and a tapering oral dose of prednisolone (2 to 1 mg/kg/day) as given to patients undergoing OLT. Once injected into the liver, hepatocytes become wedged in sinusoids, causing portal hypertension and ischemia – reperfusion injury. Various approaches have been employed in animal models to improve hepatocyte engraftment, such as the use of hepatic sinusoidal vasodilators, disruption of the sinusoidal endothelium by specific drugs, such as cyclophosphamide and doxorubicin, and inhibition of macrophage function. It is difficult to detect cell rejection by the release of liver cytosolic enzymes. New sensitive (bio) markers of hepatocyte rejection after transplantation are needed.
Monitoring cell engraftment
Currently, once hepatocytes have been administered, it is difficult to determine their fate in the recipient liver. Methods to track the transplanted cells are needed; the outcome of HT is limited by the low efficiency of integration of transplanted cells into the host liver parenchyma. In inborn errors of metabolism, indirect evidence of engraftment after HT can be obtained from levels of metabolic products, but this may not provide reliable information about the location or number of functioning engrafted cells. Liver biopsies have the risk of procedurerelated morbidity and likelihood of sampling error. Methods to track the transplanted cells are needed.
New cell sources
One of the main obstacles to the wider clinical application of hepatocyte transplantation is the limited source, and often marginal quality of cells from donor livers. Liver stem and/or progenitor cells, bone-marrow-derived stem cells and embryonic stem cells are showing promising results for future use.
Advantages of HT
Hepatocyte Transplantation has a number of potential advantages compared with whole-organ transplantation. The procedure provides a less invasive surgical approach with lower risk of morbidity and mortality. One donor liver provides enough hepatocytes for several recipients, thus possibly improving the ratio of donor organs to patients on the waiting list. In contrast to whole organs, cells can be cryopreserved and stored until needed. Patients keep their own liver, allowing it to recover from acute liver failure or providing the necessary liver function in case the graft should fail.
The proof of principle for Hepatocyte Transplantation has been established, and the technique is currently being developed by a number of centres around the world.
Dr Rajeev Tomar is Medical Director of KCH Clinics Abu Dhabi, Head of Paediatrics, and Consultant Paediatrician and Paediatric Hepatologist at Kings College Hospital Clinics, Abu Dhabi. www.kchclinics.com
to Date – Hepatocyte Transplantation
Researchers discover new disease gene for severe paediatric heart disease
Cardiomyopathy, or a deterioration of the ability of the heart muscle to contract, generally leads to progressive heart failure. It is frequently inherited, and, because approximately 40% of children born with it are likely to die within fi ve years of diagnosis, being able to identify its genetic basis is particularly important. Now, an international team of researchers has identifi ed a new disease gene which is implicated in the development of severe paediatric cardiomyopathies. The gene is probably also involved in a milder, adult-onset form of the condition.
Presenting the results of the study to the annual conference of the European Society of Human Genetics in May, Johanna Herkert, MD, a clinical geneticist at the University Medical Centre of Groningen, The Netherlands, describes how analysis of the exomes (the parts of the genome that produce proteins) of children who were seriously ill with earlyonset cardiomyopathies led to the fi nding that a mutation in the gene alpha-kinase 3 (ALPK3) had been inherited from both their fathers and mothers. In cases where both parents carry the mutation, the risk of having a child with a severe cardiomyopathy is 25%. Since the child does not carry a normal copy of gene the condition will develop at an early age.
“However, several family members who carried only one mutated gene copy also developed cardiac disease, albeit at a later stage in life,” says Dr Herkert. “The identifi cation of these mutations enables us to provide genetic counselling, predictive testing of family members, and prenatal testing in future pregnancies. It also allows us to provide early treatment, and a potential target for drug development in the future.”
The researchers studied fi ve children with cardiomyopathy from three unrelated families of different ethnic backgrounds. The families had previously been screened for mutations in other cardiomyopathy-related genes. Four patients were diagnosed during foetal life, or within hours of birth, and the fi fth only developed symptoms at four years old. Three of the children died between 35 weeks of gestation and five days of birth; the other two were still alive at 11 years old, but showed signs of severe cardiomyopathy.
“We knew that mice without a functional ALPK3 gene displayed very similar cardiomyopathy related features to those observed in our paediatric patients,” says Dr Herkert, “but we did not quite know how dramatic its effect would be in humans. Our fi ndings show that we now should include this gene in routine diagnostic screening in order to be able to identify affected children and their family members at risk. This will also give us an insight into the prevalence of ALPK3-related cardiomyopathy in the general population.”
Although the possibility of treating an affected foetus in the womb is still a long way off, the gene could provide a drug development target for a medicine to be administered immediately after birth before the disease has a chance to develop further. Affected family members with only one ALPK3 mutation could also be treated later in life.
“We are currently studying the effect of the ALPK3 mutations on the production of the protein in heart muscle, but also in skeletal muscle, as ALPK3 gene mutations may result in skeletal muscle problems too. Moreover, a large genome study has shown a possible link between ALPK3 and cardiac hypertrophy, or thickening of the heart muscle. We would like to explore this fi nding further as it may well mean that ALPK3 is implicated in other heart diseases in the general population, and once again this could suggest new treatment possibilities.
“Better knowledge of the precise role of the gene in disease development, as well as the elucidation of the molecular pathways involved, should lead us towards improved clinical care from the point of view of screening and surveillance, and to targeted drug development,” Dr Herkert concludes.
Date of upload: 8th Jul 2016
Copyright © 2016 MiddleEastHealthMag.com. All Rights Reserved.