Liver allotransplantation after extracorporeal hepatic support with transgenic (hCD55/hCD59) porcine livers: clinical results and lack of pig-to-human transmission of the porcine endogenous retrovirus

Infection and clinical xenotransplantation: Guidance from the Infectious Disease Community of Practice of the American Society of Transplantation

This guidance was developed to summarize current approaches to the potential transmission of swine-derived organisms to xenograft recipients, health care providers, or the public in clinical xenotransplantation. Limited specific data are available on the zoonotic potential of pig pathogens. It is anticipated that the risk of zoonotic infection in xenograft recipients will be determined by organisms present in source animals and relate to the nature and intensity of the immunosuppression used to maintain xenograft function. Based on experience in allotransplantation and with preclinical models, viral infections are of greatest concern, including porcine cytomegalovirus, porcine lymphotropic herpesvirus, and porcine endogenous retroviruses. Sensitive and specific microbiological assays are required for routine microbiological surveillance of source animals and xenograft recipients. Archiving of blood samples from recipients, contacts, and hospital staff may provide a basis for microbiological investigations if infectious syndromes develop. Carefully implemented infection control practices are required to prevent zoonotic pathogen exposures by clinical care providers. Informed consent practices for recipients and their close contacts must convey the lack of specific data for infectious risk assessment. Available data suggest that infectious risks of xenotransplantation are manageable and that clinical trials can advance with carefully developed protocols for pretransplant assessment, syndrome evaluation, and microbiological monitoring.

The respective relevance of sensitization to alloantigens and xenoantigens in pig organ xenotransplantation

BACKGROUND

Antibody-mediated rejection is a major cause of graft injury and contributes to failure of pig xenografts in nonhuman primates (NHPs). Most 'natural' or elicited antibodies found in humans and NHPs are directed against pig glycan antigens, but antibodies binding to swine leukocyte antigens (SLA) have also been detected. Of clinical importance is (i) whether the presence of high levels of antibodies directed towards human leukocyte antigens (HLA) (i.e., high panel-reactive antibodies) would be detrimental to the outcome of a pig organ xenograft; and (ii) whether, in the event of sensitization to pig antigens, a subsequent allotransplant would be at increased risk of graft failure due to elicited anti-pig antibodies that cross-react with human HLA or other antigens.

SUMMARY

A literature review of pig-to-primate studies indicates that relatively few highly-HLA-sensitized humans have antibodies that cross-react with pigs, predicting that most would not be at increased risk of rejecting an organ xenograft. Furthermore, the existing evidence indicates that sensitization to pig antigens will probably not elicit increased alloantibody titers; if so, 'bridging' with a pig organ could be carried out without increased risk of subsequent antibody-mediated allograft failure.

KEY MESSAGE

These issues have important implications for the design and conduct of clinical xenotransplantation trials.

Genetic modifications designed for xenotransplantation attenuate sialoadhesin-dependent binding of human erythrocytes to porcine macrophages

The phenomenon of diminishing hematocrit after in vivo liver and lung xenotransplantation and during ex vivo liver xenoperfusion has largely been attributed to action by resident liver porcine macrophages, which bind and destroy human erythrocytes. Porcine sialoadhesin (siglec-1) was implicated previously in this interaction. This study examines the effect of porcine genetic modifications, including knockout of the CMAH gene responsible for expression of Neu5Gc sialic acid, on the adhesion of human red blood cells (RBCs) to porcine macrophages. Wild-type (WT) porcine macrophages and macrophages from several strains of genetically engineered pigs, including CMAH gene knockout and several human transgenes (TKO+hTg), were incubated with human RBCs and "rosettes" (≥3 erythrocytes bound to one macrophage) were quantified by microscopy. Our results show that TKO+hTg genetic modifications significantly reduced rosette formation. The monoclonal antibody 1F1, which blocks porcine sialoadhesin, significantly reduced rosette formation by WT and TKO+hTg macrophages compared with an isotype control antibody. Further, desialation of human RBCs with neuraminidase before addition to WT or TKO+hTg macrophages resulted in near-complete abrogation of rosette formation, to a level not significantly different from porcine RBC rosette formation on porcine macrophages. These observations are consistent with rosette formation being mediated by binding of sialic acid on human RBCs to sialoadhesin on porcine macrophages. In conclusion, the data predict that TKO+hTg genetic modifications, coupled with targeting of porcine sialoadhesin by the 1F1 mAb, will attenuate erythrocyte sequestration and anemia during ex vivo xenoperfusion and following in vivo liver, lung, and potentially other organ xenotransplantation.

Bridging to Allotransplantation-Is Pig Liver Xenotransplantation the Best Option?

In the past 20 y, the number of patients in the United States who died while waiting for a human donor liver totaled >52 000. The median national wait time for patients with acute liver failure and the most urgent liver transplant listing was 7 d in 2018. The need for a clinical "bridge" to allotransplantation is clear. Current options for supporting patients with acute liver failure include artificial liver support devices, extracorporeal liver perfusion, and hepatocyte transplantation, all of which have shown mixed results with regard to survival benefit and are largely experimental. Progress in the transplantation of genetically engineered pig liver grafts in nonhuman primates has grown steadily, with survival of the pig graft extended to almost 1 mo in 2017. Further advances may justify consideration of a pig liver transplant as a clinical bridge to allotransplantation. We provide a brief history of pig liver xenotransplantation, summarize the most recent progress in pig-to-nonhuman primate liver transplantation models, and suggest criteria that may be considered for patient selection for a clinical trial of bridging by genetically engineered pig liver xenotransplantation to liver allotransplantation.

Corneal xenotransplantation: Where are we standing?

The search for alternatives to allotransplants is driven by the shortage of corneal donors and is demanding because of the limitations of the alternatives. Indeed, current progress in genetically engineered (GE) pigs, the introduction of gene-editing technology by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9, and advanced immunosuppressants have made xenotransplantation a possible option for a human trial. Porcine corneal xenotransplantation is considered applicable because the eye is regarded as an immune-privileged site. Furthermore, recent non-human primate studies have shown long-term survival of porcine xenotransplants in keratoplasty. Herein, corneal immune privilege is briefly introduced, and xenogeneic reactions are compared with allogeneic reactions in corneal transplantation. This review describes the current knowledge on special issues of xenotransplantation, xenogeneic rejection mechanisms, current immunosuppressive regimens of corneal xenotransplantation, preclinical efficacy and safety data of corneal xenotransplantation, and updates of the regulatory framework to conduct a clinical trial on corneal xenotransplantation. We also discuss barriers that might prevent xenotransplantation from becoming common practice, such as ethical dilemmas, public concerns on xenotransplantation, and the possible risk of xenozoonosis. Given that the legal definition of decellularized porcine cornea (DPC) lies somewhere between a medical device and a xenotransplant, the preclinical efficacy and clinical trial data using DPC are included. The review finally provides perspectives on the current standpoint of corneal xenotransplantation in the fields of regenerative medicine.

Xenogeneic cross-circulation for extracorporeal recovery of injured human lungs

Patients awaiting lung transplantation face high wait-list mortality, as injury precludes the use of most donor lungs. Although ex vivo lung perfusion (EVLP) is able to recover marginal quality donor lungs, extension of normothermic support beyond 6 h has been challenging. Here we demonstrate that acutely injured human lungs declined for transplantation, including a lung that failed to recover on EVLP, can be recovered by cross-circulation of whole blood between explanted human lungs and a Yorkshire swine. This xenogeneic platform provided explanted human lungs a supportive, physiologic milieu and systemic regulation that resulted in functional and histological recovery after 24 h of normothermic support. Our findings suggest that cross-circulation can serve as a complementary approach to clinical EVLP to recover injured donor lungs that could not otherwise be utilized for transplantation, as well as a translational research platform for immunomodulation and advanced organ bioengineering.

Establishment of gene-edited pigs expressing human blood-coagulation factor VII and albumin for bioartificial liver use

BACKGROUND AND AIM

Bioartificial livers (BALs) are considered as a solution to bridge patients with acute liver failure to liver transplantation or to assist in spontaneous recovery for patients with end-stage liver disease. Pig is the best donor of hepatocytes for BALs in clinical trials, because metabolic and detoxification function of its liver are close to human. However, using pig hepatocytes for BALs remains controversial for safety concern owing to nonhuman proteins secretion. Herein, we attempt to establish modified pigs expressing humanized liver proteins, blood-coagulation factor VII (F7), and albumin (ALB). These pigs should also be porcine endogenous retrovirus subtype C (PERV-C) free so that their ability of transmitting PERV to human could be diminished seriously.

METHODS

We devised both homology-dependent and independent knock-in approaches to insert a fusion of hF7 and hALB gene downstream the site of pig endogenous F7 promoter in pig fetal fibroblasts negative for PERV-C. The modified pigs were then generated through somatic cell nuclear transfer.

RESULTS

We obtained 14 and 10 cloned pigs by homology-dependent and independent approaches, respectively. Among them, 19 cloned pigs were with expected gene modification and 13 are alive to date. These modified pigs can successfully express hF7 and hALB in the liver and serum, and the expressed hF7 exhibits normal coagulation activity.

CONCLUSIONS

The gene-edited pigs expressing hF7 and hALB in the liver were generated successfully. We anticipate that our pigs could provide an alternative cell source for BALs as a promising treatment for patients with acute liver failure.

Immortalization of porcine hepatocytes with a α-1,3-galactosyltransferase knockout background

BACKGROUND

In vivo pig liver xenotransplantation preclinical trials appear to have poor efficiency compared to heart or kidney xenotransplantation because of xenogeneic rejection, including coagulopathy, and particularly thrombocytopenia. In contrast, ex vivo pig liver (wild type) perfusion systems have been proven to be effective in "bridging" liver failure patients until subsequent liver allotransplantation, and transgenic (human CD55/CD59) modifications have even prolonged the duration of pig liver perfusion. Despite the fact that hepatocyte cell lines have also been proposed for extracorporeal blood circulation in conditions of acute liver failure, porcine hepatocyte cell lines, and the GalT-KO background in particular, have not been developed and applied in this field. Herein, we established immortalized wild-type and GalT-KO porcine hepatocyte cell lines, which can be used for artificial liver support systems, cell transplantation, and even in vitro studies of xenotransplantation.

METHODS

Primary hepatocytes extracted from GalT-KO and wild-type pigs were transfected with SV40 LT lentivirus to establish immortalized GalT-KO porcine hepatocytes (GalT-KO-hep) and wild-type porcine hepatocytes (WT). Hepatocyte biomarkers and function-related genes were assessed by immunofluorescence, periodic acid-Schiff staining, indocyanine green (ICG) uptake, biochemical analysis, ELISA, and RT-PCR. Furthermore, the tumorigenicity of immortalized cells was detected. In addition, a complement-dependent cytotoxicity (CDC) assay was performed with GalT-KO-hep and WT cells. Cell death and viability rates were assessed by flow cytometry and CCK-8 assay.

RESULTS

GalT-KO and wild-type porcine hepatocytes were successfully immortalized and maintained the characteristics of primary porcine hepatocytes, including albumin secretion, ICG uptake, urea and glycogen production, and expression of hepatocyte marker proteins and specific metabolic enzymes. GalT-KO-hep and WT cells were confirmed as having no tumorigenicity. In addition, GalT-KO-hep cells showed less apoptosis and more viability than WT cells when exposed to complement and xenogeneic serum.

CONCLUSIONS

Two types of immortalized cell lines of porcine hepatocytes with GalT-KO and wild-type backgrounds were successfully established. GalT-KO-hep cells exhibited higher viability and injury resistance against a xenogeneic immune response.

The role of industry in advancing xenotransplantation

PURPOSE OF REVIEW

Xenotransplantation offers the opportunity to alleviate the imbalance between the demand of patients with end stage organ failure and the supply of organs available for transplantation but remains aspirational. This review highlights how collaboration between academia and industry are essential for success.

RECENT FINDINGS

The science of xenotransplantation has accelerated in recent years with key discoveries in genetic engineering, enabling disruption of genes facilitating rejection, and transgenic expression of desired human genes. Combined with similar progress directed toward induction of transplant tolerance, the stage has been set for meaningful progress. These advances are reviewed in detail elsewhere in this volume and argue that the breakthroughs needed to deliver substantial cross-species organ survival have largely been achieved, heralding a liminal stage of human xenotransplantation. However, xenotransplantation as a meaningful therapy for medically refractory end organ failure will not be realized through scientific innovation alone. The advent of broadly available, therapeutic xenogeneic tissues requires extensive development and regulatory expertise; the biotechnology/pharmaceutical industry can provide extensive resources and expertise in those essential areas.

SUMMARY

Successful delivery of xenotransplantation as an available therapy for curing end stage organ failure is best accomplished through partnership and collaboration between academia and industry.

A review of pig liver xenotransplantation: Current problems and recent progress

Pig liver xenotransplantation appears to be more perplexing when compared to heart or kidney xenotransplantation, even though great progress has been achieved. The relevant molecular mechanisms involved in xenogeneic rejection, including coagulopathy, and particularly thrombocytopenia, are complex, and need to be systematically investigated. The deletion of expression of Gal antigens in the liver graft highlights the injurious impact of nonGal antigens, which continue to induce humoral rejection. Innate immunity, particularly mediated by macrophages and natural killer cells, interplays with inflammation and coagulation disorders. Kupffer cells and liver sinusoidal endothelial cells (LSECs) together mediate leukocyte, erythrocyte, and platelet sequestration and phagocytosis, which can be exacerbated by increased cytokine production, cell desialylation, and interspecies incompatibilities. The coagulation cascade is activated by release of tissue factor which can be dependent or independent of the xenoreactive immune response. Depletion of endothelial anticoagulants and anti-platelet capacity amplify coagulation activation, and interspecies incompatibilities of coagulation-regulatory proteins facilitate dysregulation. LSECs involved in platelet phagocytosis and transcytosis, coupled with hepatocyte-mediated degradation, are responsible for thrombocytopenia. Adaptive immunity could also be problematic in long-term liver graft survival. Currently, relevant evidence and study results of various genetic modifications to the pig donor need to be fully determined, with the aim of identifying the ideal transgene combination for pig liver xenotransplantation. We believe that clinical trials of pig liver xenotransplantation should initially be considered as a bridge to allotransplantation.

Is sensitization to pig antigens detrimental to subsequent allotransplantation?

An important question in xenotransplantation is whether an allotransplant can safely be carried out in a patient who has become sensitized to a pig xenograft. To answer this question, we have searched the literature. We primarily limited our review to the clinically relevant pig-to-non-human primate (NHP) model and found five studies that explored this topic. No NHP that had received a pig graft developed antibodies to alloantigens, and in vitro studies indicated no increased humoral and/or cellular alloreactivity. We carried out a small in vitro study ourselves that confirmed this conclusion. There have been three experiments in which patients undergoing dialysis were exposed to wild-type pig kidneys and three clinical studies related to bridging a patient in hepatic failure to liver allotransplantation. Despite the development of anti-pig antibodies, all subsequent organ (kidney or liver) allografts were successful (except possibly in one case). In addition, pig fetal islets were transplanted into patients with kidney allografts; there was no increase in panel-reactive alloantibodies and the kidney grafts continued to function satisfactorily. In conclusion, the limited data suggest that, after sensitization to pig antigens, there is no evidence of antibody-mediated or accelerated cellular rejection of a subsequent allograft.

N-glycolylneuraminic acid knockout reduces erythrocyte sequestration and thromboxane elaboration in an ex vivo pig-to-human xenoperfusion model

BACKGROUND

Wild-type pigs express several carbohydrate moieties on their cell surfaces that differ from those expressed by humans. This difference in profile leads to pig tissue cell recognition of human blood cells causing sequestration, in addition to antibody-mediated xenograft injury. One such carbohydrate is N-glycolylneuraminic acid (Neu5Gc), a sialic acid molecule synthesized in pigs but not in humans. Here, we evaluate livers with and without Neu5Gc in an ex vivo liver xeno perfusion model.

METHODS

Livers from pigs with an α1,3-galactosyl transferase gene knockout (GalTKO) and transgenic for human membrane cofactor (hCD46) with (n = 5) or without (n = 7) an additional Neu5Gc gene knock out (Neu5GcKO) were perfused ex vivo with heparinized whole human blood. A drug regimen consisting of a histamine inhibitor, thromboxane synthase inhibitor, and a murine anti-human GPIb-blocking antibody fragment was given to half of the experiments in each group.

RESULTS

Liver function tests (AST and ALT) were not significantly different between livers with and without the Neu5GcKO. GalTKO.hCD46.Neu5GcKO livers had less erythrocyte sequestration as evidenced by a higher mean hematocrit over time compared to GalTKO.hCD46 livers (P = .0003). The addition of Neu5GcKO did not ameliorate profound thrombocytopenia seen within the first 15 minutes of perfusion. TXB2 was significantly less with the added drug regimen (P = .006) or the presence of Neu5GcKO (P = .017).

CONCLUSIONS

The lack of Neu5Gc expression attenuated erythrocyte loss but did not prevent profound early onset thrombocytopenia or platelet activation, although TXB2 levels were decreased in the presence of Neu5GcKO.

Pig Liver Xenotransplantation: A Review of Progress Toward the Clinic

Experience with clinical liver xenotransplantation has largely involved the transplantation of livers from nonhuman primates. Experience with pig livers has been scarce. This brief review will be restricted to assessing the potential therapeutic impact of pig liver xenotransplantation in acute liver failure and the remaining barriers that currently do not justify clinical trials. A relatively new surgical technique of heterotopic pig liver xenotransplantation is described that might play a role in bridging a patient with acute liver failure until either the native liver recovers or a suitable liver allograft is obtained. Other topics discussed include the possible mechanisms for the development of the thrombocytopenis that rapidly occurs after pig liver xenotransplantation in a primate, the impact of pig complement on graft injury, the potential infectious risks, and potential physiologic incompatibilities between pig and human. There is cautious optimism that all of these problems can be overcome by judicious genetic manipulation of the pig. If liver graft survival could be achieved in the absence of thrombocytopenia or rejection for a period of even a few days, there may be a role for pig liver transplantation as a bridge to allotransplantation in carefully selected patients.

Long-term safety from transmission of porcine endogenous retrovirus after pig-to-non-human primate corneal transplantation

BACKGROUND

The risk of xenozoonosis mainly by porcine endogenous retrovirus (PERV) has been considered as one of the main hurdles in xenotransplantation and therefore should be elucidated prior to the clinical use of porcine corneal grafts. Accordingly, an investigation was performed to analyze the infectivity of PERVs from porcine keratocytes to human cells, and the long-term risk of transmission of PERVs was determined using pig-to-non-human primate (NHP) corneal transplantation models.

METHODS

The infectivity of PERVs from the SNU miniature pig keratocytes was investigated by coculture with a human embryonic kidney cell line. Twenty-two rhesus macaques underwent xenocorneal transplantation as follows: (i) group 1 (n=4): anterior lamellar keratoplasty (LKP) with freshly preserved porcine corneas, (ii) group 2 (n=5): anterior LKP with decellularized porcine corneas followed by penetrating keratoplasty (PKP) with allografts, (iii) group 3 (n=3): PKP under steroid-based immunosuppression, (iv) group 4 (n=4): PKP under anti-CD154 antibody-based immunosuppression, (v) group 5 (n=4): deep anterior LKP with freshly preserved porcine corneas under anti-CD40 antibody-based immunosuppression, and (vi) group 6 (n=2): PKP under anti-CD40 antibody-based immunosuppression. Postoperative blood samples were serially collected, and tissue samples were obtained from thirteen different organs at the end of each experiment. The existence of PERV DNA and RNA was investigated using PCR and RT-PCR.

RESULTS

Using two independent in vitro infectivity tests, neither PERV pol nor pig mitochondrial cytochrome oxidase II was detected after 41 and 92 days of coculture, respectively. After xenocorneal transplantation, a total of 257 serial peripheral blood mononuclear cell samples, 34 serial plasma samples, and 282 tissue samples were obtained from the NHP recipients up to 1176 days post-transplantation. No PERV transmission was evident in any samples.

CONCLUSIONS

Within the limits of this study, there is no evidence to support any risk of PERV transmission from porcine corneal tissues to NHP recipients, despite the existence of PERV-expressing cells in porcine corneas.

Recent investigations into pig antigen and anti-pig antibody expression

Genetic engineering of donor pigs to eliminate expression of the dominant xenogeneic antigen galactose α1,3 galactose (Gal) has created a sea change in the immunobiology of xenograft rejection. Antibody mediated xenograft rejection of GGTA-1 α-galactosyltransferase (GTKO) deficient organs is now directed to a combination of non-Gal pig protein and carbohydrate antigens. Glycan analysis of GTKO tissues identified no new neo-antigens but detected high levels of N-acetylneuraminic acid (Neu5Gc) modified glycoproteins and glycolipids. Humans produce anti-Neu5Gc antibody and in very limited clinical studies sometimes show an induced anti-Neu5Gc antibody response after challenge with pig tissue. The pathogenicity of anti-Neu5Gc antibody in xenotransplantation is not clear however as non-human transplant models, critical for modelling anti-Gal immunity, do not produce anti-Neu5Gc antibody. Antibody induced after xenotransplantation in non-human primates is directed to an array of pig endothelial cells proteins and to a glycan produced by the pig B4GALNT2 gene. We anticipate that immune suppression will significantly affect the T-cell dependent and independent specificity of an induced antibody response and that donor pigs deficient in synthesis of multiple xenogeneic glycans will be important to future studies.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Current progress in xenotransplantation and organ bioengineering

Organ transplantation represents a unique method of treatment to cure people with end-stage organ failure. Since the first successful organ transplant in 1954, the field of transplantation has made great strides forward. However, despite the ability to transform and save lives, transplant surgery is still faced with a fundamental problem the number of people requiring organ transplants is simply higher than the number of organs available. To put this in stark perspective, because of this critical organ shortage 18 people every day in the United States alone die on a transplant waiting list (U.S. Department of Health & Human Services, http://organdonor.gov/about/data.html). To address this problem, attempts have been made to increase the organ supply through xenotransplantation and more recently, bioengineering. Here we trace the development of both fields, discuss their current status and highlight limitations going forward. Ultimately, lessons learned in each field may prove widely applicable and lead to the successful development of xenografts, bioengineered constructs, and bioengineered xeno-organs, thereby increasing the supply of organs for transplantation.

Artificial liver

Artificial liver generally is classified as either inert or cell-based, although only the latter is a true artificial liver. Despite some major achievements and investment, no device is currently available; devices have either not been tested rigorously, or have failed to meet expectations in clinical trials. A successful device will provide the appropriate level of liver function, but it also must be applied in the appropriate clinical setting. An extracorporeal device may be capable of supporting a failing liver, but it will not correct portal hypertension. The future of this field depends on both the technical aspects of the device(s) and their application to the appropriate clinical situation.

Lack of cross-sensitization between α-1,3-galactosyltransferase knockout porcine and allogeneic skin grafts permits serial grafting

BACKGROUND

The current standard of care for burns requiring operative treatment consists of early burn excision and autologous split-thickness skin grafting. However, in large burns, sufficient donor sites may not be available to achieve total coverage, necessitating temporary coverage with allogeneic human cadaver skin grafts or synthetic skin substitutes. A previous study from this laboratory demonstrated that skin grafts from alpha-1,3 galactosyltransferase knockout (GalT-KO) miniature swine enjoyed survival comparable to that of allogeneic skin grafts in baboons.

METHODS

In the present study, we have evaluated the immune response against sequential GalT-KO and allogeneic skin grafts to determine whether such serial grafts could extend the period of temporary wound coverage before definitive grafting with autologous skin.

RESULTS

We report that rejection of primary GalT-KO skin grafts led to an anti-xenogeneic humoral response with no evidence for sensitization to alloantigens nor acceleration of rejection of allogeneic skin grafts. Similarly, presensitization with allogeneic skin did not lead to accelerated rejection of xenogeneic skin.

CONCLUSIONS

These data suggest that GalT-KO skin grafts could provide an early first-line treatment in the management of severe burns that would not preclude subsequent use of allografts, and that serial grafting of GalT-KO skin and allogeneic skin could potentially be used to provide an extended period of temporary burn wound coverage.

Proteomic analysis of domestic pig pancreas during development using two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry

Pig pancreas may be a therapeutic resource for human diabetic patients. However, this potential is hindered by a lack of knowledge of the molecular events of pig pancreas development. In this study, the embryonic day 60, neonate and 6-month protein profiles of pig pancreas were ascertained at using two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization-time of flight mass spectrometry. Twenty four proteins were differentially expressed during pig pancreas development. Among them, 12 spots increased and 7 spots decreased according to development. The expression of 5 protein were highest at birth. Expression of digestive enzymes including trypsin, pancreatic triacylglycerol lipase and pancreatic alpha-amylase was elevated in adults, whereas chymotrypsins were highly expressed in neonates. Proteins that were abundantly expressed during gestation were alpha-1-antitrypsin, alpha-fetoprotein and transferrins. Taken together, we found out that several proteins were significantly up- or down- regulated from pig pancreas based on developmental stage. This study will provide basis for understanding development of pig pancreas.

Long-term IgG response to porcine Neu5Gc antigens without transmission of PERV in burn patients treated with porcine skin xenografts

Acellular materials of xenogenic origin are used worldwide as xenografts, and phase I trials of viable pig pancreatic islets are currently being performed. However, limited information is available on transmission of porcine endogenous retrovirus (PERV) after xenotransplantation and on the long-term immune response of recipients to xenoantigens. We analyzed the blood of burn patients who had received living pig-skin dressings for up to 8 wk for the presence of PERV as well as for the level and nature of their long term (maximum, 34 y) immune response against pig Ags. Although no evidence of PERV genomic material or anti-PERV Ab response was found, we observed a moderate increase in anti-αGal Abs and a high and sustained anti-non-αGal IgG response in those patients. Abs against the nonhuman sialic acid Neu5Gc constituted the anti-non-αGal response with the recognition pattern on a sialoglycan array differing from that of burn patients treated without pig skin. These data suggest that anti-Neu5Gc Abs represent a barrier for long-term acceptance of porcine xenografts. Because anti-Neu5Gc Abs can promote chronic inflammation, the long-term safety of living and acellular pig tissue implants in recipients warrants further evaluation.

Infection barriers to successful xenotransplantation focusing on porcine endogenous retroviruses

Xenotransplantation may be a solution to overcome the shortage of organs for the treatment of patients with organ failure, but it may be associated with the transmission of porcine microorganisms and the development of xenozoonoses. Whereas most microorganisms may be eliminated by pathogen-free breeding of the donor animals, porcine endogenous retroviruses (PERVs) cannot be eliminated, since these are integrated into the genomes of all pigs. Human-tropic PERV-A and -B are present in all pigs and are able to infect human cells. Infection of ecotropic PERV-C is limited to pig cells. PERVs may adapt to host cells by varying the number of LTR-binding transcription factor binding sites. Like all retroviruses, they may induce tumors and/or immunodeficiencies. To date, all experimental, preclinical, and clinical xenotransplantations using pig cells, tissues, and organs have not shown transmission of PERV. Highly sensitive and specific methods have been developed to analyze the PERV status of donor pigs and to monitor recipients for PERV infection. Strategies have been developed to prevent PERV transmission, including selection of PERV-C-negative, low-producer pigs, generation of an effective vaccine, selection of effective antiretrovirals, and generation of animals transgenic for a PERV-specific short hairpin RNA inhibiting PERV expression by RNA interference.

Gal/non-Gal antigens in pig tissues and human non-Gal antibodies in the GalT-KO era

Our knowledge regarding Gal and non-Gal antigens in GalT-KO pig tissues can be summarized as α3Galactosyl-tranferase gene knock out eliminates the Galα3Galβ4GlcNAc-R antigen expression in pig tissues as well as anti-Gal antibody binding. Other Galα-terminating saccharides (e.g. iGb3 glycolipids and Galα2 determinants) may be present but have not been documented. α3Galactosyl-tranferase gene knock out slightly changes the carbohydrate antigen expression but no "new" antigens recognized by the human immune system have been found. Non-Gal antigens are both of protein and carbohydrate nature but their exact chemical structures are poorly defined. Regarding human non-Gal antibodies our knowledge is as Non-Gal antibodies exist naturally and increase in humans/non-human primate (NHP) receiving WT or GalT-KO pig grafts. Non-Gal antibodies with new antigen epitope recognition can be induced in humans/NHP after challenge by WT or GalT-KO pig grafts. Non-Gal antibodies react with both carbohydrates and proteins. Part of the protein reactivity is directed to glycoprotein carbohydrates chains. Non-Gal antibodies reacting with neuraminic acid terminated saccharides (both N-Acetyl and N-Glycoloyl variants) are present in humans/NHP. Anti-neuraminic acid antibodies are increased, as well as induced, after grafting pig organs into humans/NHP. Non-Gal antibodies does not cause hyperacute xenorejection but can be cytotoxic and cause xenoorgan damage. If humans sensitized to HLA antigens are at a higher risk of rejecting pig xenograft compared with non-sensitized individuals is not fully clarified. Clinical trials are needed to evaluate the relevance of non-Gal antigens/antibodies and for the xenofield to advance.

Extracorporeal liver perfusion system for artificial liver support across a membrane

BACKGROUND

An extracorporeal porcine liver perfusion (ECPLP) system circumvents the limitations of hepatocyte based bio-artificial liver, but its clinical application has been limited so far due to the potential risk of transmission of porcine endogenous retroviruses. The aim of this study was to develop an ECPLP model that can provide artificial hepatic support across a semi-permeable membrane, which has the potential to block porcine viruses due to its pore size.

MATERIALS AND METHODS

Livers from white landrace pigs were perfused with normothermic oxygenated blood using Medtronic BP560 centrifugal pump (Medtronic, Inc., Minneapolis. MN). This ECPLP system was used to support a "surrogate" patient across the filter Evaclio-EC4A. Function of liver was measured by indocyanine green retention at 15 min (ICGR15). Clearance of galactose, ammonia, and para-aminobenzoic acid infused into the "surrogate" patient circulation was calculated to assess liver support across the membrane. The study was designed as test (n = 15) versus control (n = 5), with control experiments having no liver in the circuit.

RESULTS

For the test experiments, we perfused 15 livers with mean hepatic artery pressure of 87 mm Hg and flows of 1.2 L/min. ICGR15 in test experiments was 11%. Ammonia clearance was 945 mg/min/kg, galactose metabolic rate was 111.7 mg/min/Kg, and the hippurate ratio was 91% in the test. In contrast, the control experiments did not show any significant change in the concentration of any of these compounds.

CONCLUSION

Our ECPLP model was able to provide hepatic support in an experimental setting across a hollow fiber filter. Further work on an anhepatic animal is needed prior to application in human trials.

Ex-vivo normothermic liver perfusion: an update

PURPOSE OF REVIEW

There is increasing disparity between the supply of acceptable donor organs and the number of potential transplant recipients. The shortage of organs for transplantation demands optimal utilization of a wider spectrum of donor organs, including nonheart-beating and other extended criteria donors. In the case of the liver, a substantial number of organs are discarded because of a risk of primary nonfunction.

RECENT FINDINGS

For many years hypothermic preservation has been the universal standard for organ preservation. Although limited in terms of the duration of preservation it has had the major advantages of simplicity, portability and affordability. Organ preservation by normothermic machine perfusion has repeatedly proven superiority over static cold storage in experimental settings. However, it is complex and costly and its place in clinical transplantation has not yet been established. In liver preservation normothermic perfusion provides the potential: (a) to preserve extended criteria grafts for long periods; (b) to assess the viability of these grafts during perfusion; and (c) to improve the condition of the grafts.

SUMMARY

Avoidance of cold ischaemic preservation damage and repair of injury sustained during warm ischaemia and organ procurement would potentially allow many livers from extended criteria donors to be transplanted reliably. The current challenges are, first to confirm the feasibility of the normothermic machine perfusion methodology in human livers and, second, to develop and introduce a functional device into the clinical arena.

Liver support systems today

A májelégtelenség – akár korábbi májbetegség fennállása nélkül alakult ki (akut májelégtelenség), akár krónikus májbetegség akut dekompenzációja („akut a krónikuson” májelégtelenség) következménye – magas halálozással jár. A végállapotú májbetegségek következtében kialakult májelégtelenség egyetlen kuratív megoldása ma a májtranszplantáció. Ennek fő gátját a rendelkezésre álló donorszervek hiánya képezi, emiatt sok, várólistán szereplő beteg exitál. A transzplantáció korlátai tették szükségessé olyan májtámogató rendszerek kifejlesztését, amelyek alkalmasak a beteg életben tartására a szervátültetésig vagy a máj regenerációjáig. A korai próbálkozások (hemodialízis, hemoperfúzió, cseretranszfúzió, kereszthemodialízis, keresztkeringés, plazmaferézis stb.) elégtelennek bizonyultak. Napjainkban a májpótló kezelésnek két fő iránya alakult ki: a sejtalapú, úgynevezett bioarteficiális és a nem sejtalapú, úgynevezett arteficiális rendszerek. A bioarteficiális rendszerek élő állati májsejteket vagy emberi májtumorsejteket tartalmaznak. Jellegzetességük, hogy a beteg vérét vagy szeparált plazmáját a májsejteket tartalmazó bioreaktoron áramoltatják át. Elviekben a májműködést ezek a metodikák modellezik a legtökéletesebben, mert a máj szintetizáló- és detoxikálófunkcióját egyaránt pótolják. Jelenlegi formájukban azonban még távol állnak az ideális megoldástól, alkalmazásuk számos immunológiai, infektológiai, onkológiai és financiális problémát vet fel, ezért egyelőre csak kísérleti célra állnak rendelkezésre. Az arteficiális rendszerek a klinikum számára már elérhetőek, bár széles körben még nem terjedtek el. Csak a máj detoxikálófunkcióját pótolják, a szintetikus funkció részben a hiányzó anyagok (plazmaproteinek, alvadási faktorok) szubsztitúciójával pótolható. Idetartozik a hemodiabszorpció, amely az Amerikai Egyesült Államokban terjedt el (liver dialysis unit), valamint a főleg Európában használatos albumindialízis és a legújabban kifejlesztett frakcionált plazmaszeparáció és -adszorpció (FPSA). Az albumindialízis egyszerű módszere a „single pass albumin dialysis” (SPAD), ennek továbbfejlesztett változata a „molecular adsorbent recirculating system” (MARS). Az FPSA high-flux hemodialízissel kiegészített változata a Prometheus-rendszer. Bár a felsorolt módszerek hatásosságát számos kísérleti és klinikai tanulmány támasztja alá, a konzervatív kezeléssel szemben a túlélésre kifejtett előnyös hatásuk bizonyítására még nagy esetszámot felölelő, randomizált, kontrollált vizsgálatok elvégzésére van szükség.

Pig liver xenotransplantation as a bridge to allotransplantation: which patients might benefit?

Acute liver failure is a potentially devastating clinical syndrome that, without liver transplantation (Tx), is associated with high mortality. Rapid deterioration in clinical status and a shortage of deceased human organs prohibits liver Tx in many patients. Bridging to liver Tx has been attempted by various approaches, for example, bioartificial liver support, extracorporeal pig liver perfusion, and hepatocyte Tx, but none of these approaches has convincingly improved patient survival. The orthotopic Tx of a genetically engineered pig liver could theoretically provide successful bridging. Immediate availability, perfect metabolic condition, adequate size-match and hepatocyte mass, and freedom from potentially pathogenic microorganisms could be assured. The advantages and disadvantages of bridging by pig liver Tx compared with other approaches are discussed. The selection of patients for an initial clinical trial of pig liver Tx would be similar to that of various prior trials in patients experiencing rapid and severe deterioration in liver function. The ability to give truly informed consent for a pig bridging procedure at the time of listing for liver Tx renders the patient with acute-on-chronic liver failure or primary allograft failure is a preferable candidate for this procedure than a patient who is admitted urgently with acute (fulminant) liver failure in whom consent may not be possible. Although several barriers to successful pig organ xenoTx remain, for example, coagulation dysfunction between pig and primate, if these can be resolved by further genetic engineering of the organ-source pigs, a pig liver may prove life saving to patients dying rapidly of liver failure.

No in vivo infection of triple immunosuppressed non-human primates after inoculation with high titers of porcine endogenous retroviruses

Porcine endogenous retroviruses (PERVs) released from pig tissue can infect selected human cells in vitro and therefore represent a safety risk for xenotransplantation using pig cells, tissues, or organs. Although PERVs infect cells of numerous species in vitro, attempts to establish reliable animal models failed until now. Absence of PERV transmission has been shown in first experimental and clinical xenotransplantations; however, these trials suffered from the absence of long-term exposure (transplant survival) and profound immunosuppression.

METHODS

We conducted infectivity studies in rhesus monkeys, pig-tailed monkeys, and baboons under chronic immunosuppression with cyclosporine A, methylprednisolone, and the rapamycin derivative. These species were selected because they are close to the human species and PERVs can be transmitted in vitro to cells of these species. In addition, the animals received twice, a C1 esterase inhibitor to block complement activation before inoculation of PERV. In order to overcome the complications of microchimerism, animals were inoculated with high titers of cell-free PERV. In addition, to enable transmission via cell-cell contact, some animals also received virus-producing cells. For inoculation the primate cell-adapted strain PERV/5 degrees was used which is characterized by a high infectious titer. Produced on human cells, this virus does not express alpha 1,3 Gal epitopes, does not contain porcine antigens on the viral surface and is therefore less immunogenic in non-human primates compared with pig cell-derived virus. Finally, we present evidence that PERV/5 degrees productively infects cells from baboons and rhesus monkeys.

RESULTS

In a follow-up period of 11 months, no antibody production against PERV and no integration of proviral DNA in blood cells was observed. Furthermore, no PERV sequences were detected in the DNA of different organs taken after necropsy.

CONCLUSION

These results indicate that in a primate model, in the presence of chronic immunosuppression, neither the inoculation of cell-free nor cell-associated PERV using a virus already adapted to primate cells results in an infection; this is despite the fact that peripheral blood mononuclear cells of the same animals are infectible in vitro.

Experimental multivisceral xenotransplantation

BACKGROUND

Organ shortage impairs the proposition of multivisceral transplantation to treat multiple organ failure. Interspecies (xeno) transplantation is a valid solution for organ shortage; however, suitable models of this advance are lacking. We describe an effective model of multivisceral xenotransplantation to study hyperacute rejection.

METHODS

Under general anesthesia, we in block recovered the distal esophagus, stomach, small bowel, colon, liver, pancreas, spleen, and kidneys from donors and implanted heterotopically in the lower abdomen of recipients. Animals were divided into four groups: I-canine donor, swine recipient (n = 6); II - swine donor, canine recipient (n = 5); III-canine donor, canine recipient (n = 4); and IV-swine donor, swine recipient (n = 5). Groups I and II comprised experimental (xenotransplantation) and III and IV control groups (allotransplantation). During the experiment, we appraised recipient evolution and graft modification by sequential biopsy up to 3 h. At this time, we killed animals for autopsy (experimental end point).

RESULTS

We accomplished all experiments successfully. Every grafts attained customary appearance and convenient urine output immediately after unclamp. Around 15 min after reperfusion, xenografts achieved signs of progressive hyperacute rejection and absence of urine output. At the end of experiments we observed moderate to severe hyperacute rejection at small bowel, colon, mesenteric lymph node, liver, spleen, pancreas, and kidney, while stomach and esophagus achieved mild lesions. In contrast, allograft achieved normal or minimum ischemia/reperfusion injury and constant urine output.

CONCLUSION

The present procedure assembles a simple and effective model to study multivisceral xenotransplantation and may ultimately spread researches toward hyperacute rejection.

Identification of two distinct structural regions in a human porcine endogenous retrovirus receptor, HuPAR2, contributing to function for viral entry

BACKGROUND

Of the three subclasses of Porcine Endogenous Retrovirus (PERV), PERV-A is able to infect human cells via one of two receptors, HuPAR1 or HuPAR2. Characterizing the structure-function relationships of the two HuPAR receptors in PERV-A binding and entry is important in understanding receptor-mediated gammaretroviral entry and contributes to evaluating the risk of zoonosis in xenotransplantation.

RESULTS

Chimeras of the non-permissive murine PAR and the permissive HuPAR2, which scanned the entire molecule, revealed that the first 135 amino acids of HuPAR2 are critical for PERV-A entry. Within this critical region, eighteen single residue differences exist. Site-directed mutagenesis used to map single residues confirmed the previously identified L109 as a binding and infectivity determinant. In addition, we identified seven residues contributing to the efficiency of PERV-A entry without affecting envelope binding, located in multiple predicted structural motifs (intracellular, extracellular and transmembrane). We also show that expression of HuPAR2 in a non-permissive cell line results in an average 11-fold higher infectivity titer for PERV-A compared to equal expression of HuPAR1, although PERV-A envelope binding is similar. Chimeras between HuPAR-1 and -2 revealed that the region spanning amino acids 152-285 is responsible for the increase of HuPAR2. Fine mapping of this region revealed that the increased receptor function required the full sequence rather than one or more specific residues.

CONCLUSION

HuPAR2 has two distinct structural regions. In one region, a single residue determines binding; however, in both regions, multiple residues influence receptor function for PERV-A entry.

APOBEC3 proteins and porcine endogenous retroviruses

Xenotransplantation of porcine cells, tissues, and organs offers a solution to overcome the shortage of human donor materials. In addition to the immunological and physiological barriers, the existence of numerous porcine microorganisms including viruses poses a risk for xenozoonosis. Three classes of functional gamma-type porcine endogenous retroviruses (PERV) have been identified, whereby functional polytropic PERV-A and PERV-B infect human embryonic kidney (HEK 293) and other cell lines in vitro. In the course of risk assessment for xenotransplantation the capacity of human cells to counteract PERV infections should be analyzed. Primates and other mammals display different means of protection against viral infections. APOBEC3 proteins which are cytidine deaminases and a part of the intrinsic immunity mediate potent activity against a wide range of retroviruses including murine leukemia viruses (MLV). As PERV and MLV belong to the same genus, we raised the question as to whether PERV is affected by APOBEC3 proteins. Initial data indicate that human and porcine cytidine deaminases inhibit PERV replication, thereby possibly reducing the risk for infection of human cells by PERV as a consequence of pig-to-human xenotransplantation.

Liver xenografts for the treatment of acute liver failure: clinical and experimental experience and remaining immunologic barriers

A critical element restricting the application of liver transplantation is the shortage of human deceased donor organs. Xenotransplantation using pig organs might be a solution to this shortage. Although the problems that still require resolution include the immunologic barrier, the potential risk of transferring infectious agents with the transplanted organ, and uncertainty about whether the transplanted organ will function satisfactorily in the human environment, recent progress in the genetic manipulation of pigs has led to the prospect that clinical xenografting, at least as a bridge to allotransplantation, may be possible in the foreseeable future. Experience with clinical auxiliary and orthotopic liver xenotransplantation and experimental liver xenotransplantation in nonhuman primate and other large animal models is reviewed, and the remaining immunologic problems are discussed. Evidence suggests that, in patients with hepatic failure, the pig liver may be less susceptible to antibody-mediated injury than other pig organs, such as the heart or kidney. Pig Kupffer cells and other macrophages will recognize and phagocytose primate red blood cells, but this problem should be overcome by pretransplant depletion of macrophages from the organ-source pig. From the evidence currently available, it does not seem unduly optimistic to anticipate that a liver from an alpha1,3-galactosyltransferase gene-knockout pig would survive at least long enough to function as a successful bridge to allotransplantation.

No evidence of PERV infection in healthcare workers exposed to transgenic porcine liver extracorporeal support

BACKGROUND

Clinical xenotransplantation holds great promise by providing one solution to the shortage of human organs for transplantation, while also posing a potential public health threat by facilitating transmission of infectious disease from source animals to humans. One potential vector for infectious disease transmission is healthcare workers (HCW) who are involved in administering xenotransplantation procedures.

METHODS

In this study, we studied 49 healthcare workers involved in the care of two subjects who participated in a study of porcine liver perfusion as treatment of fulminant hepatic failure. We looked for serologic and virologic evidence of transmission of porcine endogenous retrovirus, and found that HCW had no evidence of infection.

CONCLUSIONS

Results of our survey demonstrate that application of standard precautions may be sufficient to prevent transmission of porcine endogenous retrovirus, an agent of concern in ex vivo xenotransplantation products.

Artificial and bioartificial liver support: A review of perfusion treatment for hepatic failure patients

Liver transplantation and blood purification therapy, including plasmapheresis, hemodiafiltration, and bioartificial liver support, are the available treatments for patients with severe hepatic failure. Bioartificial liver support, in which living liver tissue is used to support hepatic function, has been anticipated as an effective treatment for hepatic failure. The two mainstream systems developed for bioartificial liver support are extracorporeal whole liver perfusion (ECLP) and bioreactor systems. Comparing various types of bioartificial liver in view of function, safety, and operability, we concluded that the best efficacy can be provided by the ECLP system. Moreover, in our subsequent experiments comparing ECLP and apheresis therapy, ECLP offers more ammonia metabolism than HD and HF. In addition, ECLP can compensate amino acid imbalance and can secret bile. A controversial point with ECLP is the procedure is labor intensive, resulting in high costs. However, ECLP has the potential to reduce elevated serum ammonia levels of hepatic coma patients in a short duration. When these problems are solved, bioartificial liver support, especially ECLP, can be adopted as an option in ordinary clinical therapy to treat patients with hepatic failure.

Physiological incompatibilities of porcine hepatocytes for clinical liver support

In fulminant hepatic failure, the use of bioartificial liver support (BAL) with porcine hepatocytes is the subject of a current and controversial debate.1 Specifically, the issue of cross-species physiological incompatibilities has not been addressed so far. We therefore investigated the effects of species-specific cytokines in single and cocultures on hepatocyte function. Hepatocyte cultures were isolated from human resection specimens and from Landrace pigs. Single and cocultures were exposed to porcine and human interleukin (IL)-6 or tumor necrosis factor (TNF)-alpha. Changes in expression of C-reactive protein (CRP), albumin, CCAAT enhancer binding protein (C/EBP)-alpha and C/EBP-beta and metabolic competence of cultured cells was studied by measuring testosterone metabolite production. After human or porcine IL-6 dosing, CRP was induced up to 100-fold in human hepatocyte cultures, while porcine hepatocytes responded marginally (2- to 5-fold). Treatment with human or porcine IL-6 or TNF-alpha resulted in reduced albumin production, albeit at different levels when human and porcine hepatocytes were compared (P = 0.001). Unlike human, porcine hepatocytes produced less of 6alpha-hydroxytestosterone (6alpha-HT) (P < 0.001) and 7alpha-HT (P < 0.001) after human or porcine IL-6 dosing and treatment with species-specific TNF-alpha induced (human hepatocytes) or decreased (porcine hepatocytes) 6beta-HT production (P = 0.021). In coculture with free exchange of metabolites, porcine hepatocytes produced less 6alpha-HT (P = 0.048) and 16alpha-HT (P = 0.033), whereas after treatment with human IL-6 reduced CRP gene and protein expression was observed with human hepatocytes (P = 0.013). In conclusion, species-specific responses of hepatocytes to cytokines and interactions with xenobiotic metabolites may limit the clinical effectiveness of porcine hepatocytes in BAL.

Uncoupling the systemic circulation and the Ex Vivo circuit during experimental isolated liver perfusion

Performing an ex vivo liver perfusion as a transient liver support requires perfusing the liver with a flow of 1 ml/min per kg of liver, which could reach 25% of the cardiac output when a human liver is used. This high flow could be detrimental in patients with acute liver failure. Therefore, in an ischemic-induced liver failure pig model, we developed a circuit allowing low flows going out of and into the systemic circulation, whereas the flow going through the ex vivo liver is maintained at a high value. This was obtained by uncoupling the ex vivo circuit from the systemic circulation. Ex vivo liver perfusion was performed in a closed circuit with a flow averaging 1 ml/min per kg of ex vivo liver (700 to 800 ml/min, according to the weight of the livers we used). It was linked to the systemic circulation with input and output flows equal to that used during hemodialysis (200 ml/min). Compared with previously reported direct circuits, this perfusion system was well tolerated from a circulatory point of view. After the induction of ischemic liver failure, the ex vivo liver perfusion led to an increase in urea, branched amino acids to aromatic amino acid ratio, and fractional clearance of indocyanine green and galactose and to a decrease in ammonia and lactic acid. This system allowed the ex vivo liver to keep its clearing properties despite a low extracorporeal flow. It represents an extracorporeal circuit that could be used in place of the direct extracorporeal high-flow liver perfusion.

Animal organs for human transplantation: how close are we?

Solid organ transplantation has been, by most measures, a phenomenal success. Nonetheless, the field is plagued by extreme shortages of available organs from a very limited number of donors. One potential solution to this organ availability crisis is the use of animals as organ donors for humans (xenotransplantation). Though the concept remains theoretical, significant advances are being made in the field of genetics and in our understanding of the immunological barriers to xenotransplantation. With these advances also comes increased knowledge about the potential risks of xenotransplants, especially disease transmission. The eventual clinical application of animal-to-human transplants will require a careful, balanced appraisal of these issues.

Development and perspectives of perfusion treatment for liver failure

To treat patients with severe liver failure, liver transplantation and blood purification therapy, including plasmapheresis, hemodiafiltration, and bioartificial liver support, are available. The two mainstream systems developed for bioartificial liver support are extracorporeal whole liver perfusion (ECLP) and the bioreactor system (BIS). We developed a method of cross-plasma perfusion, in which plasma is exchanged between the blood circuit of the patient and that of a hepatic functioning unit, through which immunologically free whole human blood is perfused. From the aspects of efficacy and epidemic safety, the best system of bioartificial liver support for clinical use is considered to be ECLP in cross-plasma perfusion. In opposition, a social antagonist for zoonosis has consistently been raised, with controversy surrounding the use of xenogeneic organs for human treatment, which might be final obstacle. It is possible that the combination therapy of hemodiafiltration and the administration of human serum albumin and anticoagulant factors, which minimizes the economic and medical resource costs through the development of transgenic livestock that secrete human pharmaceuticals systemically, will become a more desirable and practical treatment for patients with severe liver failure.

Liver support systems: promise and reality

Effective liver support is needed for a variety of indications. A large number of both biological (containing hepatocytes) and non-biological extracorporeal liver support systems have been described in the literature over the last 50 years. Despite this, there is a paucity of good quality randomized control data examining the effectiveness of these therapies in human liver failure. In this review article, we examine the available data, with particular emphasis on the current front runners, the MARS and HepatAssist systems. Other problems associated with the development of these liver support systems are also discussed. Although promising in animal studies, we conclude that the use of these technologies is not supported currently by a sufficient evidence base to recommend them for routine clinical use and that a lack of understanding about the critical functions required of a liver support system is retarding a more rational approach to the design of these systems.

Pseudotyping of porcine endogenous retrovirus by xenotropic murine leukemia virus in a pig islet xenotransplantation model

The potential of porcine endogenous retrovirus (PERV) as a human pathogen, particularly as a public health risk, is a major concern for xenotransplantation. In vitroPERV transmission to human cells is well established. Evidence from human/pig hematopoietic chimeras in immunodeficient mice suggests PERV transmission from pig to human cells in vivo. However, recently Yang et al. demonstrated in such a model that PERV-C, a nonhuman-tropic class, could be transmitted via pseudotyping by xenotropic murine leukemia virus (X-MLV). We developed a mouse pig islet xenotransplant model, where pig and human cells are located in physically separate compartments, to directly assess PERV transmission from a functional pig xenograft. X-MLV efficiently pseudotypes all three classes of PERV, including PERV-A and -B that are known to productively infect human cell lines and PERV-C that is normally not infectious for human cells. Pseudotyping also extends PERV's natural tropism to nonpermissive, nonhuman primate cells. X-MLV is activated locally by the surgical procedure involved in the tissue transplants. Thus, the presence and activation of endogenous X-MLV in immunodeficient mice limits the clinical significance of previous reports of in vivo PERV transmission from pig tissues to human cells.

Xenotransplantation: an update on recent progress and future perspectives

Currently, the number of patients awaiting transplantation is continuously increasing, and shortage of available deceased organ donors is the major limitation for organ and cell allotransplantation. Research to develop alternative sources of tissues is ongoing and xenogeneic organs or cells represent an attractive solution. This review focuses on recent progress achieved in this field, including the development of newly genetically modified animal donors and new immunosuppressive approaches. As xenotransplantation is moving closer to clinical application, future perspectives must establish guidelines to ensure that future clinical trials are carried out ethically and safely.