Transplantation of allogeneic hepatocytes without immunosuppression: Long-term survival

Hepatocyte Transplantation in Children

The liver has an important function in the human body and plays a crucial role in its metabolism. Orthotopic liver transplantation (OLT) is the gold standard treatment for patients presenting liver failure or end stage liver diseases, and is also applied for liver based intractable metabolic disorders. Due to organ shortage, invasive surgery and persistent mortality/morbidity, other treatments have to be explored. Amongst these, hepatocyte transplantation is an attractive alternative and has shown promising results in the treatment of miscellaneous metabolic disorders.

Engineered liver for transplantation

Orthotopic liver transplantation is the only definitive treatment for end stage liver failure and the shortage of donor organs severely limits the number of patients receiving transplants. Liver tissue engineering aims to address the donor liver shortage by creating functional tissue constructs to replace a damaged or failing liver. Despite decades of work, various bottoms-up, synthetic biomaterials approaches have failed to produce a functional construct suitable for transplantation. Recently, a new strategy has emerged using whole organ scaffolds as a vehicle for tissue engineering. This technique involves preparation of these organ scaffolds via perfusion decellularization with the resulting scaffold retaining the circulatory network of the native organ. This important phenomenon allows for the construct to be repopulated with cells and to be connected to the blood torrent upon transplantation. This opinion paper presents the current advances and discusses the challenges of creating fully functional transplantable liver grafts with this whole liver engineering approach.

Safety evaluation of stem cells used for clinical cell therapy in chronic liver diseases; with emphasize on biochemical markers

There are several issues to be considered to reduce the risk of rejection and minimize side effects associated with liver cell transplantation in chronic liver diseases. The source and the condition of stem cell proliferation and differentiation ex vivo and the transplantation protocols are important safety considerations for cell based therapy. The biochemical and molecular markers are important tools for safety evaluation of different processes of cell expansion and transplantation. Studies show that hepatocytes differentiated from adult and embryonic stem cells exhibit biochemical and metabolic properties resembling mature hepatocytes. Therefore these assays can help to assess the biological and metabolic performance of hepatocytes and progenitor stem cells. The assays also help in testing the contribution of transplanted hepatocytes in improving the repair and function of damaged liver in the recipient. Here we review the biochemical and metabolic markers, which are implicated in evaluation of safety issues of stem cells used for therapeutic purposes in chronic liver diseases and regeneration of damaged liver. We also highlight application of biochemical tests for assessment of liver cell transplantation.

Human hepatocyte transplantation

Over the last decade the interest in hepatocyte transplantation has been growing continuously and this treatment may represent an alternative clinical approach for patients with acute liver failure and life-threatening liver-based metabolic disorders. The technology also serves as the proof of concept and reference for future development in stem cell technology. This chapter reviews the field of hepatocyte transplantation from bench to bedside.

In vitro and in vivo bioluminescent quantification of viable stem cells in engineered constructs

Bioluminescent quantification of viable cells inside three-dimensional porous scaffolds was performed in vitro and in vivo. The assay quantified the bioluminescence of murine stem (C3H10T1/2) cells tagged with the luciferase gene reporter and distributed inside scaffolds of either soft, translucent, AN69 polymeric hydrogel or hard, opaque, coral ceramic materials. Quantitative evaluation of bioluminescence emitted from tagged cells adhering to these scaffolds was performed in situ using either cell lysates and a luminometer or intact cells and a bioluminescence imaging system. Despite attenuation of the signal when compared to cells alone, the bioluminescence correlated with the number of cells (up to 1.5 x 10(5)) present on each material scaffold tested, both in vitro and noninvasively in vivo (subcutaneous implants in the mouse model). The noninvasive bioluminescence measurement technique proved to be comparable to the cell-destructive bioluminescence measurement technique. Monitoring the kinetics of luciferase expression via bioluminescence enabled real-time assessment of cell survival and proliferation on the scaffolds tested over prolonged (up to 59 days) periods of time. This novel, sensitive, easy, fast-to-implement, quantitative bioluminescence assay has great, though untapped, potential for screening and determining noninvasively the presence of viable cells on biomaterial constructs in the tissue engineering and tissue regeneration fields.

Intramuscular transplantation of engineered hepatic tissue constructs corrects acute and chronic liver failure in mice

BACKGROUND & AIMS

Transplantation of isolated hepatocytes holds great promise as an alternative to whole organ liver transplantation. For treatment of liver failure, access to the portal circulation has significant risks and intrahepatic hepatocyte engraftment is poor. In advanced cirrhosis, transplantation into an extrahepatic site is necessary and intrasplenic engraftment is short-lived. Strategies that allow repeated extrahepatic infusion of hepatocytes could improve the efficacy and safety of hepatocyte transplantation for the treatment of liver failure.

METHODS

A non-immunogenic self-assembling peptide nanofiber (SAPNF) was developed as a three-dimensional scaffold and combined with growth factors derived from a conditionally immortalized human hepatocyte cell line to engineer a hepatic tissue graft that would allow hepatocyte engraftment outside the liver.

RESULTS

The hepatic tissue constructs maintained hepatocyte-specific gene expression and functionality in vitro. When transplanted into skeletal muscle as an extrahepatic site for engraftment, the engineered hepatic grafts provided life-saving support in models of acute, fulminant, and chronic liver failure that recapitulates these clinical diseases.

CONCLUSIONS

SAPNF-engineered hepatic constructs engrafted and functioned as hepatic tissues within the muscle to provide life-sustaining liver support. These engineered tissue constructs contained no animal products that would limit their development as a therapeutic approach.

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.

Improved survival of fulminant liver failure by transplantation of microencapsulated cryopreserved porcine hepatocytes in mice

The aim of this study was to establish hepatocyte isolation in pigs, and to evaluate function of isolated hepatocytes after encapsulation, cryopreservation, and transplantation (Tx) in a mouse model of fulminant liver failure (FLF). After isolation, porcine hepatocytes were microencapsulated with alginate-poly-L-Lysine-alginate membranes and cryopreserved. In vitro, albumin production of free and encapsulated hepatocytes were measured by enzyme linked-immunoadsorbent assay. In vivo, encapsulated hepatocytes were transplanted into different groups of mice with FLF and the following experimental groups were performed: group 1, Tx of empty capsules; group 2, Tx of free primary porcine hepatocytes; group 3, Tx of fresh encapsulated porcine hepatocytes; group 4, Tx of cryopreserved encapsulated porcine hepatocytes. In vitro, fresh or cryopreserved encapsulated porcine hepatocytes showed a continuous decreasing metabolic function over 1 week (albumin and urea synthesis, drug catabolism). In vivo, groups 1 and 2 showed similar survival (18% and 25%, respectively, p > 0.05). In groups 3 and 4, Tx of fresh or cryopreserved encapsulated porcine hepatocytes significantly increased survival rate to 75% and 68%, respectively (p < 0.05). Primary porcine hepatocytes maintained metabolic functions after encapsulation and cryopreservation. In mice with FLF, Tx of encapsulated xenogeneic hepatocytes significantly improved survival. These results indicate that porcine hepatocytes can successfully be isolated, encapsulated, stored using cryopreservation, and transplanted into xenogeneic recipients with liver failure and sustain liver metabolic functions.

Comparative analysis of preparation of human hepatocytes by the ethylenediamine tetraacetic acid and collagenase technique

PURPOSE

To compare the viability of human hepatocytes dissociated by the ethylenediaminetetraacetic acid and collagenase techniques.

METHODS

Hepatocytes were prepared by dissociation of liver fragments obtained from hepatectomies performed for therapeutic purposes at the Service of Digestive Tract Surgery, Federal University of Triângulo Mineiro.

RESULTS

During the first 4 days of the experiment, 70% of the cells presented birefringent membranes and were not stained with 2% erythrosine, and were therefore considered to be viable. During the first 3 days, hepatocyte viability was on average 71% in the EDTA group and 76% in the collagenase group, with no significant difference between groups. No significant difference was observed between groups at any time. The secretion of albumin by the cultured hepatocytes was preserved up to the seventh day. Mean albumin secretion during the first 3 days was 50 microg/ml in the two groups and a reduction of albumin production was observed from the fourth to the seventh day. Again, no significant difference was observed between groups at any time.

CONCLUSION

Cell viability and preservation of albumin secretion by hepatocytes are similar for the EDTA and collagenase techniques.

Coencapsulation of hepatocytes and bone marrow cells: In vitro and in vivo studies

Bioencapsulation of cells is one of the many areas of artificial cells being extensively investigated by centers around the world. This includes the bioencapsulation of hepatocytes. A number of methods have been developed to maintain the specific function and phenotype of the bioencapsulated hepatocytes for in vitro and in vivo applications. These include supplementation of factors in the culture medium; use of appropriate substrates and the co-cultivation of hepatocytes with other type of cells, the so called "feeder cells". These feeder cells can be of liver origin or non-liver origin. We have recently studied the role of bone marrow cells in the maintenance of hepatocytes viability and phenotype by using the coculture of hepatocytes with bone marrow cells (nucleated cells including stem cells), and the coencapsulation of hepatocytes with bone marrow stem cells. This way, the hepatocytes viability and specific function can be maintained significantly longer. In vivo studies of both syngeneic and xenogeneic transplantation show that the hepatocytes viability can be maintained longer when coencapsulated with bone marrow cells. Transplantation of coencapsulated hepatocytes and bone marrow cells enhances the ability of the hepatocytes in correcting congenital hyperbilirubinmia in Gunn rats. Both in vitro and in vivo studies show that bone marrow cells can enhance the viability and phenotype maintenance of hepatocytes. Thus, bone marrow cells play an important role as a new type of feeder cells for bioencapsulated hepatocytes for the cellular therapy of liver diseases.

Viabilidade do fígado bioartificial utilizando hepatócitos humanos imunoprotegidos por macroencapsulação

OBJETIVO: O transplante de hepatócitos xenogênicos encapsulados pode ser utilizado no futuro em situações como a insuficiência hepática fulminante. Porém, observa-se perda precoce da expressão de genes hepatocitários específicos em hepatócitos humanos. O objetivo deste estudo é avaliar a influência da resposta imunológica na perda da expressão genética hepatocitária de hepatócitos humanos encapsulados e transplantados em ratos. MÉTODO: Hepatócitos humanos foram isolados de fragmentos hepáticos, encapsulados em fibras e transplantados em ratos. Nos dias 3, 7 e 14 após o transplante as fibras foram coletadas e avaliadas a morfologia por microscopia óptica e eletrônica, e a expressão dos genes por biologia molecular. O ARNm da albumina humana foi quantificado por RT-PCR e Northern blot. A resposta imunológica contra os hepatócitos foi avaliada através do ADN hepatocitário na busca de apoptose do núcleo celular e pelo aumento da expressão do CMH de classe I. RESULTADOS: Os aspectos morfológicos dos hepatócitos mantiveram-se normais até o sétimo dia após o transplante. Não se observaram células envolvidas com resposta imunológica do receptor nas fibras. Os transcritos da albumina foram detectados até D-14. Entre os dias 3 e 7 estavam em 30% em relação ao dia 0. A análise do ADN mostrou bandas preservadas sem a presença de fenômenos de apoptose nos diferentes dias. Não ocorreu aumento da expressão do CMH de classe I. CONCLUSÕES: Hepatócitos humanos encapsulados e transplantados em ratos permanecem viáveis apesar da diminuição da expressão de determinados genes. Este fenômeno, não se deve à resposta imunológica do receptor, mas ao próprio processo de isolamento celular.

Survival and differentiation of porcine hepatocytes encapsulated by semiautomatic device and allotransplanted in large number without immunosuppression

BACKGROUND/AIMS

The aim of this study was to evaluate the survival and functions of porcine hepatocytes transplanted in large quantities in the peritoneal cavity of allogeneic animals following semiautomatic encapsulation.

METHODS

Isolated porcine hepatocytes and a polymer solution composed of AN69 were coextruded through a double lumen spinneret. Minitubes containing hepatocytes were transplanted in the peritoneal cavity of 12 pigs (4 x 10(9) cells/animal) in the absence of immunosuppressive therapy. Seven, 15, and 21 days after transplantation, minitubes was collected and processed for analyses. The morphology was examined under light and electron microscopy. Albumin synthesis was assessed by semi-quantitative reverse transcription-polymerase chain reaction. Cytochrome P450 3A (CYP3A) gene expression was analyzed by Western blot and by testosterone 6-beta-hydroxylation assay.

RESULTS

The device allowed to encapsulate 55 x 10(6) hepatocytes/min. Hepatocytes exhibited normal structural and ultrastructural features up to day 21. Albumin gene expression decreased progressively between days 0 and 21. The amount of CYP3A protein and 6-beta-hydroxylase activity were approximately 2-fold lower at days 7 and 15 than in freshly encapsulated hepatocytes, and further decreased thereafter.

CONCLUSIONS

The preservation of hepatocyte functions during 1-2 weeks is encouraging for potential short-term use of such bioartificial liver in future clinical application.

Survival and functions of encapsulated porcine hepatocytes after allotransplantation or xenotransplantation without immunosuppression

BACKGROUND

This study evaluated the survival and functions of encapsulated porcine hepatocytes after intraperitoneal allotransplantation and xenotransplantation without immunosuppression.

METHODS

Isolated porcine hepatocytes were encapsulated in AN 69 polymer capsules (45.10(6)/capsule) and transplanted intraperitoneally in 12 rats and 12 pigs. Fifteen, 30, and 60 days after transplantation, capsules were removed and the viability and morphology of explanted hepatocytes were examined under light and electronic microscopy. The potential to produce albumin was assessed by evaluating the level of albumin messenger RNA, using semiquantitative reverse transcription-polymerase chain reaction. 6beta-Hydroxylase activity was measured by high-performance liquid chromatography. In addition, cytochrome P450 3A proteins were detected by Western blot only in allogeneic hepatocytes.

RESULTS

Similar results were observed after allotransplantation and xenotransplantation. Histologic studies showed that hepatocytes were well-preserved and arranged in cords for up to 30 days. The expression of porcine albumin gene was maintained up to 15 days. 6beta-Hydroxylase activity was 2.5-fold lower at day 15 than in freshly encapsulated hepatocytes, which were not transplanted. In allogeneic hepatocytes, the expression of CYP 3A protein was detected up to 60 days after transplantation.

CONCLUSIONS

Encapsulated porcine hepatocytes remain viable and functional for at least 15 days after allotransplantation and xenotransplantation without immunosuppression. The demonstration of maintained hepatic functions in transplanted porcine hepatocytes up to 15 days is a first step toward application in the treatment of acute liver failure.

Semiautomatic macroencapsulation of large numbers of porcine hepatocytes by coextrusion with a solution of AN69 polymer

We have previously demonstrated that allogenic and xenogenic hepatocytes macroencapsulated manually in AN-69 polymer and transplanted intra-peritoneally in rats remained viable for several weeks. However, this manual technique is inadequate to encapsulate several billions of hepatocytes which would be required to correct hepatic failure in big animals or humans. In the present study, we developed an original semiautomatic device in which isolated pig hepatocytes and the polymer solution containing 6% poly(acrylonitrile-sodium methallylsulfonate), 91% dimethylsulfoxide and 3% 0.9% NaCl solution were coextruded through a double-lumen spinneret. The extruded minitube (inner diameter: 1.8 mm, wall thickness: 0.07-0.1 mm) containing the encapsulated hepatocytes fell and coiled up in a 0.9% NaCl solution at 4 degrees C and was cut down in 4 m units containing about 120 million hepatocytes. This process allowed to encapsulate 50 million hepatocytes by minute with a preserved immediate cell viability (92 +/- 5%). To test prolonged cell viability after coextrusion, the minitubes were implanted intraperitoneally in rats. Three and seven days after implantation, they were explanted and analyzed. Cells were viable and well-preserved. Therefore, the semiautomatic device appears able to efficiently macroencapsulate in a limited time several billions of porcine hepatocytes which remain viable after transplantation in xenogenic conditions.

Factors affecting hepatocyte viability and CYPIA1 activity during encapsulation

Hepatocytes encapsulated in alginate-poly-1-lysine-alginate (APA) are used in transplantation studies and in bioartificial liver support systems. Loss of cell viability in the process of APA encapsulation is usually 20-30% while the effect on cytochrome CYP450 activity is rarely reported. This work investigates the negative influences on hepatocyte viability and CYPIA1 activity during APA encapsulation, and reports methods to alleviate these influences by incorporating certain reagents into the encapsulation solution. The results show that loss of hepatocyte viability and CYPIA1 activity was caused almost entirely by extracellular calcium toxicity rather than by mechanical damage (p < 0.05). Use of 10 mM instead of 100 mM calcium chloride (CaCl2) in the encapsulation process improved CYPIA1 activity (p < 0.05), but did not improve hepatocyte viability (p > 0.05) or result in satisfactory microcapsules. Hepatocyte viability was 25% higher (p < 0.05) in CaCl2 than in calcium lactate (CaLa) when the cells were gelled by contact with these calcium solutions at room temperature (RT). Hepatocyte viability showed little improvement by processing at 4 degrees C than at RT in CaCl2 (p > 0.05) but was 23% higher at 4 degrees C than at RT in CaLa (p < 0.05). Calcium used in the process of encapsulation caused cell necrosis rather than apoptosis. Addition of Dulbecco's modified Eagle's medium (containing 10% foetal bovine serum) or 20 mM fructose to the calcium solution did not improve cell survival. However, nifedipine at a final concentration of 25 mM modestly improved hepatocyte survival in solution containing 100 mM CaCl2 (p = 0.003). Glutathione and taurine in certain concentrations showed protective effects against loss of CYPIA1 activity (p < 0.05 and <0.01 respectively). In conclusion, to optimise the use of calcium during the process of encapsulation, CaCl2 is preferred to CaLa and inclusion of nifedipine, glutathione or taurine in 100 mM CaCl2 solution is recommended.

Suppression of humoral immunization against encapsulated xenogeneic hepatocytes and prolongation of their function by 2-week cyclosporine treatment in the rat

BACKGROUND

Xenogeneic liver transplantation may induce immune reactions not only against the grafted liver but also against the proteins that it synthesizes. We investigated whether 2-week cyclosporine treatment could suppress immunization and improve graft function in a xenogeneic hepatocyte transplantation model.

METHODS

Free or encapsulated human hepatoma cells (HepG2) were cocultured for 28 days with splenocytes from Lewis rats or implanted for 60 days into the peritoneum of Lewis rats.

RESULTS

Anti-HepG2 and antialbumin antibodies were detected in the supernatants of rat splenocytes that were cocultured with HepG2 cells and in the serum of rats that had undergone transplantation with HepG2 cells. Cyclosporine suppressed this antibody production both in vitro and in vivo. Human alpha-GST blood levels, which reflect hepatocyte injury, were low in cyclosporine-treated animals but high when encapsulated HepG2 cells were transplanted without cyclosporine therapy. Western blots revealed human albumin from day 3 to day 60 in the serum of rats treated with cyclosporine, but not after day 30 in untreated rats.

CONCLUSIONS

Xenogeneic hepatocytes induce a humoral response that impairs their viability and function. A 2-week course of cyclosporine suppresses this immune response and improves graft function for up to 60 days.

Encapsulated xenogeneic hepatocytes remain functional after peritoneal implantation despite immunization of the host

BACKGROUND/AIMS

Xenogeneic hepatocytes encapsulated in semipermeable membranes could be used in the future for the treatment of acute liver failure and congenital liver defects. However, host immune response could affect the viability and function of transplanted cells. The purpose of this study was to investigate the immunological consequences of intraperitoneal implantation of encapsulated xenogeneic hepatocytes and their effects.

METHODS

Recipient Lewis rats received 2 x 10(7) human hepatocytes encapsulated in semipermeable hydrogel-based hollow fibers, 2 x 10(7) free human hepatocytes or 2 x 10(7) encapsulated Lewis rat hepatocytes. The presence of human albumin in rat sera was assessed by Western blot and the presence of anti-human hepatocytes and anti-human albumin antibodies by ELISA.

RESULTS

Anti-hepatocyte antibodies were detected on the 7th day, and their level increased progressively on days 21 and 28 in rats grafted with encapsulated or free human hepatocytes. Anti-albumin antibodies were detected on day 7 and increased progressively in rats grafted with encapsulated human hepatocytes, but were not detected in the other groups. No immune complexes or complement components of donor origin were detected by immunofluorescence in the recipients' tissues. Despite immunization of the host, encapsulated xenogeneic hepatocytes survived and produced albumin, whereas free hepatocytes had been lysed.

CONCLUSION

Transplantation of encapsulated xenogeneic hepatocytes resulted in immunization of the host with production of anti-hepatocyte and anti-albumin antibodies. However, hepatocytes could be efficiently protected by the membrane and remained viable and functional during the study.

Internal bioartificial liver with xenogeneic hepatocytes prevents death from acute liver failure: an experimental study

OBJECTIVE

To demonstrate that a bioartificial liver, using allogeneic or xenogeneic hepatocytes protected from rejection by a semipermeable membrane, could prevent death from acute liver failure.

SUMMARY BACKGROUND DATA

An implantable bioartificial liver using isolated hepatocytes could be an alternative to orthotopic liver transplantation to treat patients with acute liver failure. It could serve either as a bridge until liver transplantation or as the main treatment until recovery of the native liver. However, allogeneic or xenogeneic hepatocytes that could be used in clinical applications are spontaneously rejected.

METHODS

Acute liver failure was induced in rats by 95% liver resection. Twenty-five million hepatocytes harvested in rats (allogeneic) or guinea pigs (xenogeneic) were encapsulated in a semipermeable membrane to protect them from rejection. The hollow fibers containing hepatocytes were transplanted into the peritoneum of recipient rats. Survival rates were compared between rats transplanted or not with hepatocytes.

RESULTS

In groups not transplanted with viable hepatocytes, 73% to 93% of rats died after 95% liver resection. The mortality rate was reduced to 39% in rats transplanted with allogeneic hepatocytes and 36% in rats transplanted with xenogeneic hepatocytes. The bioartificial liver could be removed 1 month after transplantation, when regeneration of the native liver was complete. Allogeneic and xenogeneic hepatocytes remained viable.

CONCLUSIONS

The implantable bioartificial liver was able to prevent death in this model of acute liver failure. This could be an important step toward clinical application of the method.

[Intraperitoneal transplantation of isolated hepatocytes of the pig: the implantable bioartificial liver]

The general aim is to prepare a bioartificial liver to treat acute hepatic failure using allo- and xenogeneic hepatocytes, immunoprotected by macroencapsulation and transplanted into the peritoneal cavity. The goal of this study was to prepare a large amount of isolated porcine hepatocytes, to encapsulate them within biocompatible membranes for transplant in allo- and xenogeneic combinations and to examine the viability and functionality of the cells 6 weeks later. Hepatocyte isolation was performed in 12 kg pigs (n = 15) by dissociation of the liver with collagenase D (1 g) without oxygenation. Encapsulation of the hepatocyte suspension (10(7)/mL) was performed in hydrogel membranes AN69; hollow fibers (2 m x 0.8 mm) and flaskes (1.8 cm), and transplanted to Yucatan pigs (n = 4) and Lewis rats (n = 12). Six weeks later, they were removed to study the cell viability by histological examination, and the production of albumin by immunonephelometry. The rate of isolated hepatocytes was 38 +/- 5 x 10(9)/mL by liver of pig and the mean viability was 93 +/- 2%. Six weeks after transplantation, hepatocytes were viable, organized in lobules, and showed conserved albumin production. The same results were observed for allogenic and xenogeneic combinations. In conclusion, this method of liver dissociation allowed for preparation of a large amount of isolated hepatocytes from a single pig liver, theoretically sufficient to treat a patient with acute liver failure. Hydrogel membranes were well tolerated and allowed immunoprotection without immunosuppression. Transplanted hepatocytes remained functional. This work is an important step in progress toward clinical application.

Non-autologous transplantation with immuno-isolation in large animals--a review

Transplantation has become a successful method for the management of functional failure of a variety of tissues or organs. However, the majority of clinical transplantations use non-autologous allogeneic donor tissue implanted from one human to another. In order to prevent rejection of the allogeneic tissue, methods to overcome the immune barrier are necessary. Although prevention of organ rejection is currently achieved with pharmacological immune suppression, the undesirable side effects of this method have incited interest in novel methods to overcome the immune barrier. One such novel method of preventing immune reaction is immuno-isolation, in which the non-autologous tissues are physically isolated from the host tissues by placement in devices with perm-selective membranes. The membranes of these devices allow release of the therapeutic product required from the transplanted tissues, as well as diffusion of nutrients and waste necessary for survival of the non-autologous tissues. The membranes also prevent host immune mediators from contacting the non-autologous cells, thus preventing immune rejection. This technology has been tested for efficacy in large animal models, and is currently in the process of clinical trials in humans. This review will discuss the progress made in using immuno-isolation of non-autologous tissues in large animals. Immuno-isolation can be subdivided into two major areas of interest based on whether the non-autologous tissue used in the immuno-isolation device is genetically altered (gene therapy) or not. Studies using non-genetically altered non-autologous cells for immune-isolation have been dominated by the use of pancreatic islet cells for the treatment of diabetes. This work has been tested in large animal models of diabetes, including canine and primate model animals, and human clinical trials are underway. As well, there has also been work on treatment of neurological disorders such as Parkinson's disease or chronic pain using non-autologous immuno-isolated adrenal chromaffin cells or dopaminergic PC12 cells in large animals such as sheep and primates. This work will be reviewed in detail as to the types of disorders, immuno-isolation devices used and the type of large animals involved. Immune-isolation for gene therapy is a more recently developed field of research. In this case, the non-autologous cells used are first genetically altered to secrete a recombinant therapeutic product before placement in the immune-isolation devices. Genetic engineering of the non-autologous cells is beneficial, as it allows the use of a cell type that tolerates well the environment of the immune-isolation device, while still delivering the therapeutic product of interest. This form of gene therapy has been tested in our laboratory for delivery of marker products such as human growth hormone to canines. As several large animal models of human genetic disorders are available, such as canines affected with hemophilia or the lysosomal storage disease mucopolysaccharidosis, testing the efficacy of immuno-isolation for gene therapy in large animal models is an important prelude to human clinical trials. This review will discuss the topics outlined above, as well as some further considerations of the usefulness of large animal models in studying immune-isolation for non-autologous transplantation. Large animals may be more appropriate model organisms than rodents in which to study immune-isolation, as issues such as biocompatibility and immune response in a larger animal can be addressed. As well, large animal studies of immune isolation may provide data that are more relevant than rodent studies to the eventual application to human clinical trials.

Evidence for survival and metabolic activity of encapsulated xenogeneic hepatocytes transplanted without immunosuppression in Gunn rats

BACKGROUND

Hepatocyte transplantation could be an alternative to whole organ transplantation to correct enzymatic disorders. To this end, it would be of major importance to use xenogeneic cells without immunosuppression. The aim of this study was to investigate the survival and metabolic activity of encapsulated xenogeneic hepatocytes in the absence of immunosuppression. For this purpose, we used Gunn rats genetically incapable of bilirubin conjugation.

METHODS

Xenogeneic (from guinea pigs) and allogeneic (from Lewis rats) hepatocytes (2x10(7)) were isolated, macroencapsulated in hydrogel hollow fibers made with an acrylonitrile-sodium methallyl-sulfonate copolymer, and transplanted into the peritoneum of Gunn rats without any immunosuppression. Plasma bilirubin levels were evaluated weekly. Bilirubin conjugates in bile and cell morphology were studied after 5 and 12 weeks, respectively.

RESULTS

In Gunn rats transplanted with xenogeneic hepatocytes, a significant decrease in the serum bilirubin level was observed between 3 and 9 weeks after transplantation when compared with controls transplanted with empty hollow fibers: it fell to 62% of the initial level at weeks 5-7 (P < 0.01). A comparable result was observed in Gunn rats transplanted with encapsulated allogeneic cells. Bilirubin conjugates were observed in bile samples of rats transplanted with encapsulated hepatocytes. After explantation, hollow fibers appeared intact with minimal fibrosis. Cell viability and hepatocyte morphology were preserved.

CONCLUSIONS

These results indicate that macroencapsulated xenogeneic hepatocytes can survive and remain functional for more than 2 months when transplanted in vivo in the absence of any immunosuppression.