Liver transplantation. Living donor, hepatocyte, and xenotransplantation

Cell transplantation-based regenerative medicine in liver diseases

This review aims to evaluate the current preclinical state of liver bioengineering, the clinical context for liver cell therapies, the cell sources, the delivery routes, and the results of clinical trials for end-stage liver disease. Different clinical settings, such as inborn errors of metabolism, acute liver failure, chronic liver disease, liver cirrhosis, and acute-on-chronic liver failure, as well as multiple cellular sources were analyzed; namely, hepatocytes, hepatic progenitor cells, biliary tree stem/progenitor cells, mesenchymal stromal cells, and macrophages. The highly heterogeneous clinical scenario of liver disease and the availability of multiple cellular sources endowed with different biological properties make this a multidisciplinary translational research challenge. Data on each individual liver disease and more accurate endpoints are urgently needed, together with a characterization of the regenerative pathways leading to potential therapeutic benefit. Here, we critically review these topics and identify related research needs and perspectives in preclinical and clinical settings.

Cell therapy for advanced liver diseases: Repair or rebuild

Advanced liver disease presents a significant worldwide health and economic burden and accounts for 3.5% of global mortality. When liver disease progresses to organ failure the only effective treatment is liver transplantation, which necessitates lifelong immunosuppression and carries associated risks. Furthermore, the shortage of suitable donor organs means patients may die waiting for a suitable transplant organ. Cell therapies have made their way from animal studies to a small number of early clinical trials. Herein, we review the current state of cell therapies for liver disease and the mechanisms underpinning their actions (to repair liver tissue or rebuild functional parenchyma). We also discuss cellular therapies that are on the clinical horizon and challenges that must be overcome before routine clinical use is a possibility.

Intraoperative Continuous Renal Replacement Therapy During Liver Transplantation: A Meta-Analysis

Continuous renal replacement therapy (CRRT) is frequently used to treat recipients with renal failure before or after liver transplantation (LT), though evidence supporting its use during surgery remains unclear. Therefore, we conducted a quantitative meta-analysis to evaluate the effect of intraoperative continuous renal replacement therapy (IORRT) in recipients with pretransplant severe renal dysfunction. We searched PubMed, Embase, and the Cochrane database for trials focusing on LT recipients supported with or without IORRT. Outcomes assessed were mortality, preoperative characteristics, intraoperative data, and predefined postoperative outcomes. Seven trials with 1051 recipients were eligible. Preoperatively, the IORRT group recipients had higher Model for End-Stage Liver Disease scores (weighted mean difference [WMD], 6.19; 95% confidence interval [CI], 2.51-9.87), Charlson scores (WMD, 0.45; 95% CI, 0.09-0.80), acute liver failure (odds ratio [OR], 1.82; 95% CI, 1.27-2.61), serum creatinine (WMD, 71.33 μmol/L; 95% CI, 1.98-140.69 μmol/L), total bilirubin level (WMD, 5.05 μmol/L; 95% CI, 1.75-8.35 μmol/L), intensive care unit admission (OR, 3.53; 95% CI, 1.23-10.13), vasoactive therapy (OR, 3.80; 95% CI, 2.64-5.46), ventilator care (OR, 2.52; 95% CI, 1.18-5.35), and renal replacement therapy (RRT) (OR, 29.37; 95% CI, 7.66-112.54) compared with control patients. IORRT patients also required more intraoperative blood product transfusion and had more post-LT RRT (OR, 25.67; 95% CI, 4.92-133.85). However, there were no significant differences in short-term mortality (OR, 2.12; 95% CI, 0.82-5.44) between the groups. In addition, worse longterm mortality was seen in the IORRT group. In conclusion, IORRT is feasible and safe and may help sicker recipients tolerate the LT procedure to achieve short-term clinical outcomes comparable with less ill patients without IORRT. More high-quality evidence is needed to verify our conclusion in the future.

Clinical application of hepatocyte transplantation: current status, applicability, limitations, and future outlook

Introduction: Hepatocyte transplantation (HT) is a promising alternative to liver transplantation for the treatment of liver-based metabolic diseases and acute liver failure (ALF). However, shortage of good-quality liver tissues, early cell loss post-infusion, reduced cell engraftment and function restricts clinical application.Areas covered: A comprehensive literature search was performed to cover pre-clinical and clinical HT studies. The review discusses the latest developments to address HT limitations: cell sources from marginal/suboptimal donors to neonatal livers, differentiating pluripotent stem cells into hepatocyte-like cells, in vitro expansion, prevention of immune response to transplanted cells by encapsulation or using innate immunity-inhibiting agents, and enhancing engraftment through partial hepatectomy or irradiation.Expert opinion: To date, published data are highly encouraging specially the alginate-encapsulated hepatocyte treatment of children with ALF. Hepatocyte functions can be further improved through co-culturing with mesenchymal stromal cells. Moreover, ex-vivo genetic correction will enable the use of autologous cells in future personalized medicine.

Tracking of Primary Human Hepatocytes with Clinical MRI: Initial Results with Tat-Peptide Modified Superparamagnetic Iron Oxide Particles

The transplantation of primary human hepatocytes is a promising approach in the treatment of specific liver diseases. However, little is known about the fate of the cells following application. Magnetic resonance imaging (MRI) could enable real-time tracking and long-term detection of transplanted hepatocytes. The use of superparamagnetic iron oxide particles as cellular contrast agents should allow for the non-invasive detection of labelled cells on high-resolution magnetic resonance images. Experiments were performed on primary human hepatocytes to transfer the method of detecting labelled cells via clinical MRI into human hepatocyte transplantation. For labelling, Tat-peptide modified nano-sized superparamagnetic MagForce particles were used. Cells were investigated via a clinical MR scanner at 3.0 Tesla and the particle uptake within single hepatocytes was estimated using microscopic examinations. The labelled primary human hepatocytes were clearly detectable by MRI, proving the feasibility of this new concept. Therefore, this method is a useful tool to investigate the effects of human hepatocyte transplantation and to improve safety aspects of this method.

Hepatocyte Transplantation in Special Populations: Clinical Use in Children

Orthotopic liver transplantation remains the only proven cure for end-stage liver failure. Despite significant advances in the field, the clinical demand for donor organs far outweighs the supply. Hepatocyte transplantation has been proposed as an alternative approach to whole liver transplant in select diseases. Several international centers have reported experimental trials of human hepatocyte transplantation in acute liver failure and liver-based metabolic disorders. This chapter provides an introduction to hepatocyte transplantation from both a technical and clinical perspective. We will also focus on the special needs of pediatric patients, since historically the majority of clinical hepatocyte transplants have involved infants and children.

Phases I-II Matched Case-Control Study of Human Fetal Liver Cell Transplantation for Treatment of Chronic Liver Disease

Fetal hepatocytes have a high regenerative capacity. The aim of the study was to assess treatment safety and clinical efficacy of human fetal liver cell transplantation through splenic artery infusion. Patients with endstage chronic liver disease on the waiting list for liver transplantation were enrolled. A retrospectively selected contemporary matched-pair group served as control. Nonsorted raw fetal liver cell preparations were isolated from therapeutically aborted fetuses. The end points of the study were safety and improvement of the Model for End-Stage Liver Disease (MELD) and Child-Pugh scores. Nine patients received a total of 13 intrasplenic infusions and were compared with 16 patients on standard therapy. There were no side effects related to the infusion procedure. At the end of follow-up, the MELD score (mean ± SD) in the treatment group remained stable from baseline (16.0 ± 2.9) to the last observation (15.7 ± 3.8), while it increased in the control group from 15.3 ± 2.5 to 19 ± 5.7 ( p = 0.0437). The Child-Pugh score (mean ± SD) dropped from 10.1 ± 1.5 to 9.1 ± 1.4 in the treatment group and increased from 10.0 ± 1.2 to 11.1 ± 1.6 in the control group ( p = 0.0076). All treated patients with history of recurrent portosystemic encephalopathy (PSE) had no further episodes during 1-year follow-up. No improvement was observed in the control group patients with PSE at study inclusion. Treatment was considered a failure in six of the nine patients (three deaths not liver related, one liver transplant, two MELD score increases) compared with 14 of the 16 patients in the control group (six deaths, five of which were caused by liver failure, four liver transplants, and four MELD score increases). Intrasplenic fetal liver cell infusion is a safe and well-tolerated procedure in patients with end-stage chronic liver disease. A positive effect on clinical scores and on encephalopathy emerged from this preliminary study.

How regenerative medicine and tissue engineering may complement the available armamentarium in gastroenterology?

The increasing shortage of donors and the adverse effects of immunosuppression have restricted the impact of solid organ transplantation. Despite the initial promising developments in xenotransplantation, roadblocks still need to be overcome and this form of organ support remains a long way from clinical practice. While hepatocyte transplantation may be effectively correct metabolic defects, it is far less effective in restoring liver function than liver transplantation. Tissue engineering, using extracellular matrix scaffolds with an intact but decellularized vascular network that is repopulated with autologous or allogeneic stem cells and/or adult cells, holds great promise for the treatment of failure of organs within gastrointestinal tract, such as end-stage liver disease, pancreatic insufficiency, bowel failure and type 1 diabetes. Particularly in the liver field, where there is a significant mortality of patients awaiting transplant, human bioengineering may offer a source of readily available organs for transplantation. The use of autologous cells will mitigate the need for long term immunosuppression thus removing a major hurdle in transplantation.

Hepatocyte transplantation

Hepatocyte transplantation (HTx) has been developed for use in liver-based metabolic disorders and in acute liver failure. Worldwide, there are around 80 patients that have been transplanted with hepatocytes. Almost all reported studies prove feasibility and safety of the procedure with short- to medium-term success. Availability of good quality hepatocytes (HCs) is the main limiting factor, and therefore alternative sources of cells such as stem cells are being investigated. Other limiting factors include cell engraftment, survival, and function of transplanted cells. It remains to be seen if progress in HTx research can overcome these hurdles leading to the wider use of the technique as an alternative to liver transplantation in the future.

Anti-fibrogenic strategies and the regression of fibrosis

Liver fibrosis is an outcome of many chronic diseases, and often results in cirrhosis, liver failure, and portal hypertension. Liver transplantation is the only treatment available for patients with advanced stage of fibrosis. Therefore, alternative methods are required to develop new strategies for anti-fibrotic therapy. Available treatments are designed to substitute for liver transplantation or bridge the patients, they include inhibitors of fibrogenic cytokines such as TGF-β1 and EGF, inhibitors of rennin angiotensin system, and blockers of TLR4 signalling. Development of liver fibrosis is orchestrated by many cell types. However, activated myofibroblasts remain the primary target for anti-fibrotic therapy. Hepatic stellate cells and portal fibroblasts are considered to play a major role in development of liver fibrosis. Here we discuss the origin of activated myofibroblasts and different aspects of their activation, differentiation and potential inactivation during regression of liver fibrosis.

Monitoring of Liver Cell Transplantation in a Preclinical Swine Model Using Magnetic Resonance Imaging

Liver cell transplantation (LCT) is a promising treatment approach for certain liver diseases, but clinical implementation requires methods for noninvasive follow-up. Labeling with superparamagnetic iron oxide particles can enable the detection of cells with magnetic resonance imaging (MRI). We investigated the feasibility of monitoring transplanted liver cells by MRI in a preclinical swine model and used this approach to evaluate different routes for cell application. Liver cells were isolated from landrace piglets and labeled with micron-sized iron oxide particles (MPIO) in adhesion. Labeled cells (n = 10), native cells (n = 3), or pure particles (n = 4) were transplanted to minipigs via intraportal infusion into the liver, direct injection into the splenic parenchyma, or intra-arterial infusion to the spleen. Recipients were investigated by repeated 3.0 Tesla MRI and computed tomography angiography up to 8 weeks after transplantation. Labeling with MPIO, which are known to have a strong effect on the magnetic field, enabled noninvasive detection of cell aggregates by MRI. Following intraportal application, which is commonly applied for clinical LCT, MRI was able to visualize the microembolization of transplanted cells in the liver that were not detected by conventional imaging modalities. Cells directly injected into the spleen were retained, whereas cell infusions intra-arterially into the spleen led to translocation and engraftment of transplanted cells in the liver, with significantly fewer microembolisms compared to intraportal application. These findings demonstrate that MRI can be a valuable tool for noninvasive elucidation of cellular processes of LCT and-if clinically applicable MPIO are available-for monitoring of LCT under clinical conditions. Moreover, the results clarify mechanisms relevant for clinical practice of LCT, suggesting that the intra-arterial route to the spleen deserves further evaluation.

Barriers to the successful treatment of liver disease by hepatocyte transplantation

Management of patients with hepatic failure and liver-based metabolic disorders is complex and expensive. Hepatic failure results in impaired coagulation, altered consciousness and cerebral function, a heightened risk of multiple organ system failure, and sepsis [1]. Such manifold problems are only treatable today and for the foreseeable future by transplantation. In fact, whole or auxiliary partial liver transplantation is often the only available treatment option for severe, even if transient, hepatic failure. Patients with life-threatening liver-based metabolic disorders similarly require organ transplantation even though their metabolic diseases are typically the result of a single enzyme deficiency, and the liver otherwise functions normally. For all of the benefits it may confer, liver transplantation is not an ideal therapy, even for severe hepatic failure. More than 17,000 patients currently await liver transplantation in the United States, a number that seriously underestimates the number of patients that need treatment [2], as it has been estimated that more than a million patients could benefit from transplantation [3]. Unfortunately, use of whole liver transplantation to treat these disorders is limited by a severe shortage of donors and by the risks to the recipient associated with major surgery [4].

Recent advances in liver stem cell therapy

PURPOSE OF REVIEW

Patients with liver cirrhosis often require liver transplantation, which remains the only effective treatment of the end-stage cirrhosis. Here we briefly summarize the current concepts in treatment of liver diseases based on the transplantation of intrahepatic liver cells, capable of repopulating the injured liver. These cells include hepatocytes, oval cells (bipotential intrahepatic progenitor cells), bone marrow hematopoietic and mesenchymal stem cells, and induced pluripotent stem (iPS) cells.

RECENT FINDINGS

Although liver transplantation remains the only conventional treatment, liver cell transplantation is an experimental procedure which has been successfully used in clinical trials in patients with acute liver failure, chronic liver disease with end-stage cirrhosis. Extraordinary progress has been made in the field of hepatic progenitors and iPS. Liver precursor cells (oval cells) are recognized as bipotential precursor cells in the damaged liver. They can rapidly proliferate, change their cellular composition, and differentiate into hepatocytes and cholangiocytes to compensate for the cellular loss and maintain liver homeostasis in animal models of liver injury. Similarly, iPS are somatic cells obtained from patients and differentiated into hepatocytes in vitro. Future studies of iPS are designed to develop of specific conditions to expand and in vitro differentiate somatic cells into functionally mature liver cells.

SUMMARY

The current review defines and discusses different populations of hepatic cells which can be potentially used for liver cell transplantation to advance the therapy of hepatic cirrhosis.

[Hepatic cell transplantation: a new therapy in liver diseases]

Liver transplantation has been remarkably effective in the treatment in patients with end-stage liver disease. However, disparity between solid-organ supply and increased demand is the greatest limitation, resulting in longer waiting times and increase in mortality of transplant recipients. This situation creates the need to seek alternatives to orthotopic liver transplantation.Hepatocyte transplantation or liver cell transplantation has been proposed as the best method to support patients. The procedure consists of transplanting individual cells to a recipient organ in sufficient quantity to survive and restore the function. The capacity of hepatic regeneration is the biological basis of hepatocyte transplantation. This therapeutic option is an experimental procedure in some patients with inborn errors of metabolism, fulminant hepatic failure and acute and chronic liver failure, as a bridge to orthotopic liver transplantation. In the Hospital La Fe of Valencia, we performed the first hepatocyte transplantation in Spain creating a new research work on transplant program.

Herpes simplex virus sepsis and acute liver failure

Acute liver failure is a life threatening disease mostly triggered by drug-induced or toxic liver damage or viral hepatitis. Herpes Simplex virus (HSV) hepatitis is rare and accounts for only 1% of all acute liver failures. The importance of HSV-induced acute liver failure is based on its extremely severe clinical course with lethality rates of almost 75%. HSV hepatitis is just one of several clinical manifestations of HSV sepsis leading more frequently to encephalitis, pneumonia and esophagitis. Local herpes infection or recurrence of dermal lesions (herpes labialis, herpes genitalis), however, is common and account for the high prevalence of HSV-1 or HSV-2 infection in adults. Another rare entity is visual dissemination, which mostly affects immunocompromised patients. Compromised cellular immunity is a major risk factor for HSV sepsis because of either primary infection or reactivation of occult chronic HSV infection. Delayed diagnosis without antiviral therapy significantly contributes to the unfavorable outcome. Typically, anicteric hepatitis is seen in patients with HSV hepatitis. Because of its low incidence, however, and the lack of dermal manifestations, HSV hepatitis is rarely considered in the context of acute liver failure. In addition, diagnostic tests might not always be available. Therefore, it is a generally accepted consensus to begin antiviral therapy pre-emptively with acyclovir in cases of acute liver failure of unknown origin, in which high urgency (HU) liver transplantation remains the only therapeutical option. Even in the case of early specific therapy, sepsis may prevail and the indication for HU transplantation must be evaluated carefully. The outcome after liver transplantation for HSV-induced liver failure with reported survival rates of more than 40% is good. Because of the risk of recurrence, lifelong prophylaxis with acyclovir is recommended.

Stem cells for liver repopulation

PURPOSE OF REVIEW

The capacity of the liver to regenerate and maintain a constant size despite injury is unique. However, the exact mechanisms are not completely clear. Cell transplantation has been proposed as an alternative treatment of liver diseases. Recent progress has been reported on the generation of stem/progenitor cells that may differentiate toward the hepatic lineage. However, it is currently difficult to determine which of the stem/progenitor cell populations are the best for therapy of a given disease.

RECENT FINDINGS

The limited access to donor human hepatocytes has led to a great interest in the generation of hepatocyte-like cells. Several potential cell sources have been identified. However, general standardization of the methods to evaluate these cells is particularly important for the promise of stem/progenitor-derived hepatocyte-based therapies. Moreover, innovations aimed at improving hepatocyte delivery, survival, and engraftment have recently opened the field of organ engineering that may improve liver repopulation.

SUMMARY

Here we review current evidence reported from the perspective of potential clinical applications of different hepatic cell sources with repopulation capacities and the future perspectives and tools that can facilitate the translation of laboratory work into clinical success.

Human hepatocyte transplantation: state of the art

Hepatocyte transplantation is making its transition from bench to bedside for liver-based metabolic disorders and acute liver failure. Over eighty patients have now been transplanted world wide and the safety of the procedure together with medium-term success has been established. A major limiting factor in the field is the availability of good quality cells as hepatocytes are derived from grafts that are deemed unsuitable for transplantation. Alternative sources of cell, including stem cells may provide a sustainable equivalent to primary hepatocytes. There is also a need to develop techniques that will improve the engraftment, survival and function of transplanted hepatocytes. Such developments may allow hepatocyte transplantation to become an accepted and practical alternative to liver transplantation in the near future.

Cell transplantation in the treatment of liver diseases

The liver performs multiple functions that are essential for life, the most crucial being its role in the body metabolism. Impairment of this function, because of liver insufficiency, can be partially restored by medical management but OLT remains the ultimate therapeutic treatment. Because not always indicated or available, other alternatives are proposed such as LCT. Compared to OLT, this procedure is less invasive, less expensive, and fully reversible. More than 50 patients have thus far benefited of this technique and are reviewed here. Indications were multiple including inborn errors of metabolism, FHF, acute on chronic diseases, and decompensated end-stage cirrhosis. Documented results were encouraging, especially for metabolic disorders, with medium-term efficacy up to two yr. Related complications were exceptional. On this basis, LCT has entered its phase of clinical application and current indications and protocols are detailed. Ongoing lines of research are discussed, including cell quality, stem cell field, and rejection prevention. Further improvement of the procedure is therefore expected and should lead to broader applications of LCT.

External-beam radiotherapy as preparative regimen for hepatocyte transplantation after partial hepatectomy

PURPOSE

The transplantation of donor hepatocytes is considered a promising option to correct chronic liver failure through repopulation of the diseased organ. This study describes a novel selective external-beam irradiation technique as a preparative regimen for hepatocyte transplantation.

METHODS AND MATERIALS

Livers of dipeptidylpeptidase IV (DPPIV)-deficient rats were preconditioned with external-beam single-dose irradiation (25 Gy) delivered to two thirds of the liver. Four days later, a one-third partial hepatectomy (PH) was performed to resect the untreated liver section, and 15 million wild-type (DPPIV+) hepatocytes were transplanted via the spleen into the recipient livers. The degree of donor-cell integration and growth was studied 8 h, 3 days, and 5 and 12 weeks after transplantation.

RESULTS

Transplanted hepatocytes integrated rapidly into the irradiated liver and proliferated as clusters, finally repopulating the host liver to approximately 20% hepatocyte mass. After 12 weeks, donor cells and their numerous descendents were fully integrated and expressed functional markers to the same extent as host hepatocytes.

CONCLUSIONS

We demonstrate that external-beam liver irradiation is sufficient to achieve partial repopulation of the host liver after hepatocyte transplantation, under the additional stimulus of one-third PH. The method described has potentially good prospects for its application in a clinically viable form of treatment.

Factors that identify survival after liver retransplantation for allograft failure caused by recurrent hepatitis C infection

Hepatitis C virus (HCV) is becoming the most common indication for liver retransplantation (ReLTx). This study was a retrospective review of the medical records of liver transplant patients at our institution to determine factors that would identify the best candidates for ReLTx resulting from allograft failure because of HCV recurrence. The patients were divided into 2 groups on the basis of indication for initial liver transplant. Group 1 included ReLTx patients whose initial indication for LTx was HCV. Group 2 included patients who received ReLTx who did not have a history of HCV. We defined chronic allograft dysfunction (AD) as patients with persistent jaundice (> 30 days) beginning 6 months after primary liver transplant in the absence of other reasons. HCV was the primary indication for initial orthotopic liver transplantation (OLT) in 491/1114 patients (44%) from July 1996 to February 2004. The number of patients with AD undergoing ReLTx in Groups 1 and 2 was 22 and 12, respectively. The overall patient and allograft survival at 1 year was 50% and 75% in Groups 1 and 2, respectively (P = .04). The rates of primary nonfunction and technical problems after ReLTx were not different between the groups. However, the incidence of recurrent AD was higher in Group 1 at 32% versus 17% in Group 2 (P = .04). Important factors that predicted a successful ReLTx included physical condition at the time of ReLTx (P = .002) and Child-Turcotte-Pugh score (P = .008). In conclusion, HCV is associated with an increased incidence of chronic graft destruction with a negative effect on long-term results after ReLTx. The optimum candidate for ReLTx is a patient who can maintain normal physical activity. As the allograft shortage continues, the optimal use of cadaveric livers continues to be of primary importance. The use of deceased donor livers in patients with allograft failure caused by HCV remains a highly controversial issue.

Two-stage total hepatectomy and liver transplantation for acute deterioration of chronic liver disease: a new bridge to transplantation

Two-stage total hepatectomy and liver transplantation has been reported for acute liver disease such as fulminant hepatic failure, primary graft failure, severe hepatic trauma, and spontaneous hepatic rupture secondary to hemolysis, elevated liver function tests, low platelets syndrome, and preeclampsia. This is the first report of patients with cirrhosis to undergo a 2-stage total hepatectomy and liver transplantation. From 1984 to 2002, our institution performed 2008 orthotopic liver transplantations. We identified 4 patients with chronic liver disease who underwent a 2-stage hepatectomy and liver transplantation. This is a retrospective review of these 4 patients and a review of the literature on this procedure. All 4 patients were young men with an age range of 29-31 years and had underlying cirrhosis as well as a previous transjugular intrahepatic portosystemic shunt (TIPS)procedure. Acute decompensation fulfilling Ringes' criteria for toxic liver syndrome secondary to an upper gastrointestinal bleed occurred in all patients. The approximate average time between hepatectomy and liver transplantation was 20 hours (range: 8-42 hours). In all cases, the explanted liver showed histological changes of acute hepatic necrosis within the background of cirrhosis. After hepatectomy, vasopressor requirements were well documented in 2 patients. For 1 patient, there was a clear improvement in their hemodynamic status. The mean hospital stay of the 4 patients was 63 days. All patients were discharged from the hospital and are alive and well with adequate liver function at 6 to 37 months follow-up. Two-stage total hepatectomy and liver transplantation may be a life-saving procedure in highly selected cirrhotic patients with acute hepatic decompensation and multiorgan dysfunction.

Stem cell therapy of the liver--fusion or fiction?

Various stem cell populations have been described in distinct models of liver regeneration. This review provides an overview of these different stem cell populations aimed at unifying diverse views of liver stem cell biology. Embryonic stem cells, hemopoietic stem cells, mesenchymal stem cells, liver-derived hepatic stem cells, bone marrow-derived hepatic stem cells, and mature hepatocytes (as cells with stemlike properties) are considered separately. In so doing, we seek to clarify the nomenclature of putative liver stem cell types. Experiments that address the question of cellular fusion versus transdifferentiation as explanations for observed liver regeneration are highlighted. This review concludes with a series of open questions that should be addressed in the context of clinical liver disease before attempts at human therapeutic interventions.

Fulminant hepatic failure and liver transplantation: experience of Virgen de la Arrixaca Hospital

INTRODUCTION

For patients with fulminant hepatic failure who show a poor evolution despite medical treatment, liver transplantation is an option, with survival rates of greater than 50%. The ideal time to perform the transplant is controversial, as it must not be done too soon (when the liver disease is still reversible) or too late (when the patient is in an irreversible clinical situation).

PATIENTS AND METHODS

Retrospective review of the clinical histories of 34 patients admitted to our hospital with a diagnosis of fulminant hepatic failure included 26 who underwent transplantation. The most frequent cause was viral (n=10, 38%); with no etiology established in 11 cases (42%). Thirteen patients had preoperative complications, the most frequent being renal insufficiency. As for degree of AB0/DR compatibility, 13 cases were identical (40%), 17 compatible (51%), and the other three incompatible (9%).

RESULTS

Thirty-three transplants were performed in 26 patients: four were retransplants due to chronic rejection, two for primary graft failure, and one for hyperacute rejection. The overall mortality rate was 46% (12 patients). The most frequent cause of death was infection (50%). The overall actuarial survival rate was 68% at 1 year, 63% at 3 years, and 59% at 5 years. The factors associated with a poor prognosis were renal and respiratory insufficiency, a grade D electroencephalogram, and encephalopathy grades III and IV, the last being the only prognostic factor identified in the multivariate analysis. The prognostic factors for mortality were a grade D electroencephalogram, encephalopathy grades III and IV and respiratory insufficiency, the last being the only prognostic factor identified in the multivariate analysis.

CONCLUSION

Good results of transplantation for the management of fulminant hepatic failure depends on optimal selection of transplant candidates, which means identifying them early, reducing the waiting time, and excluding factors associated with a poor prognosis.

[Fulminant hepatic failure and liver transplantation. Experience of the Hospital Virgen de la Arrixaca]

INTRODUCTION

Medical treatment for fulminat hepatic failure seeks spontaneous recovery of the liver function, but the results are very discouraging (50-80% mortality). Liver transplantation is an option in patients with a poor evolution despite medical treatment, with survival rates of > 50%. The ideal moment for performing the transplant is controversial, as it should not be done too soon, when the liver disease is still reversible, or tool late, when the patient is in an irreversible clinical situation.

PATIENTS AND METHOD

A retrospective review was made of the clinical histories of 34 patients admitted to our hospital with a diagnosis of fulminant hepatic failure, of whom 26 underwent transplantation. The most frequent cause was viral, with 10 cases (38%); no aetiology at all could be established in 11 cases (42%). Thirteen patients had preoperative complications, the most frequent being renal insufficiency. As for degree of ABO/DR compatibility, 13 cases were identical (40%), 17 compatible (51%) and the other 3 incompatible (9%).

RESULTS

Thirty-three transplants were performed in 26 patients: 4 were retransplants due to chronic rejection, 2 for primary graft failure and 1 for hyperacute rejection. The overall mortality rate was 46% (12 patients), the most frequent cause of death being infection (50%). The overall actuarial survival rate was 68% at 1 year, 63% at 3 years and 59% at 5 years. The factors of poor prognosis were renal and respiratory insufficiency, a grade D electroencephalogram, and encephalopathy grades III and IV, the latter being the only prognostic factor identified in the multivariate analysis. The prognostic factors for mortality were a grade D electroencephalogram, encephalopathy grades III and IV and respiratory insufficiency, the latter being the only prognostic factor identified in the multivariate analysis.

CONCLUSIONS

The achievement of good results with the use of transplantation in the management of fulminant hepatic failure depends on an optimum selection of transplant candidates, which means identifying them early, i.e. early indication for transplant, reduction in mean waiting time and exclusion of factors of poor prognosis.

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Extracorporeal support of the failing liver

Successes in machine-based extracorporeal support for different organ functions stimulated research in the field of liver support approximately 50 years ago. Initial failure to improve outcome using detoxification methods like dialysis, blood and plasma exchange, or plasmapheresis over sorbents fueled interest in biologic liver support concepts using bioreactors or combined methods. New device configurations, technical improvement of existing detoxification methods, and the refinement in cell culture techniques led to a boost in research on biologic and nonbiologic approaches. Currently, many systems are in the preclinical phase or have entered clinical studies. A number of completed clinical trials have reported a favorable therapeutic impact of the most advanced solutions on the course and outcome of liver failure. Often, findings must be reconfirmed. However, current knowledge suggests that extracorporeal liver support can successfully stabilize liver function, improve the clinical condition of patients, and considerably improve survival in certain subgroups of patients with fulminant hepatic failure and acute decompensation of chronic hepatic failure. Although the initial focus of liver support methods was bridging to liver transplantation, bridging to recovery of organ function and treatment of intractable pruritus are now valuable indications.

Prospects for the temporary treatment of acute liver failure

At present, the most successful treatment of acute liver failure is orthotopic liver transplantation, with survival rates ranging from 70% to 85%. However, mortality rates for liver failure remain high because of the shortage of available donor organs. Therefore, there has been renewed interest in temporary treatment methods for patients with acute liver failure to either allow liver regeneration or await liver transplantation. It is thought that the function of the liver can only be replaced with the biological substrate, e.g. liver cells or a whole liver specimen, which requires the availability of liver tissue from xenogeneic or human sources. In this review, existing temporary liver support techniques are summarized and the potential hazards are described. These include the immunological implications of these techniques, e.g. the host versus graft reaction, which may influence the effectivity of the support system, and in the long run may sensitize the patient to subsequent allogeneic transplantation. The graft versus host reaction is also considered. At present, one of the major concerns is the threat of pig-to-human transmission of activated endogenous retrovirus present in the pig genome. An overview is given of literature concerning the transmission of retrovirus particles in vitro and in vivo. Finally, new solutions for the development of ex vivo systems for temporary treatment of patients with acute liver failure are discussed. These include the use of new immortalized human cell lines and human fetal hepatocytes, and the possibility of isolating, expanding and genetically manipulating stem cells in order to have stable differentiated and committed cells.

Acute liver failure

Acute liver failure (ALF) is defined as hepatic encephalopathy complicating acute liver injury. The most common etiologies are acute viral hepatitis A and B, medication overdose (e.g., acetaminophen), idiosyncratic drug reactions, ingestion of other toxins (e.g., amanita mushroom poisoning), and metabolic disorders (e.g., Reye's syndrome). Despite advances in intensive care management, mortality continues to be high (40-80%) and is partly related to ALF's complications, such as cerebral edema, sepsis, hypoglycemia, gastrointestinal bleeding, and acute renal failure. Several prognostic models have been developed to determine which patients will spontaneously recover. Treatment is directed at early recognition of the complications and general supportive measures. The only proven therapy for those who are unlikely to recover is liver transplantation. Therefore, recognition of ALF is paramount, and urgent referral to a transplant center is critical to assess transplantation status.