Defining appropriate health status and management programs for specific-pathogen-free swine for xenotransplantation

Early weaning completely eliminates porcine cytomegalovirus from a newly established pig donor facility for xenotransplantation

For clinical xenotransplantation, transplants must be free of porcine cytomegalovirus (PCMV). Piglets become infected primarily in the perinatal period by the mother sow. While individual donor animals can be protected from infection by isolation husbandry, success is not guaranteed and this strategy poses the risk of undetected infections and raises animal welfare questions. Here, we present the establishment of a completely PCMV-negative pig herd for breeding donor animals for xenotransplantation. Eleven pregnant DanAvl Basic hybrid sows were purchased from a designated pathogen-free (DPF), PCMV-positive colony and transferred to a new pig facility at the Centre for Innovative Medical Models (CiMM) 4 weeks prior to farrowing. At the age of 24 hours, piglets were early-weaned and transferred to a commercially available Rescue Deck system dedicated to motherless rearing of piglets. Sows were removed from the facility. The PCMV status of F1-generation animals was determined at regular intervals over a period of 14 months by a sensitive real-time PCR-based detection method testing blood, nasal swabs and cultured peripheral blood mononuclear cells (PBMCs). F1 sows were used as recipients of genetically modified embryos to generate a xenotransplant donor herd. Offspring were tested for PCMV accordingly. All offspring have remained PCMV negative over the whole observation period of 14 months. A completely PCMV-negative pig herd for xenotransplantation has thus been successfully established.

AN69 Hollow Fiber Membrane will Reduce but Not Abolish the Risk of Transmission of Porcine Endogenous Retroviruses

As the risk of porcine endogenous retrovirus (PERV) infection is a major obstacle to the xenotransplantation of porcine tissue, we investigated whether an AN69 hollow fibre membrane, used for islets of Langerhans transplantation, could prevent the transfer of PERVs and thus reduce the risk of PERV infection. PK15 cells were used as a PERV source. A specific and highly sensitive RCR was used for detection of a PERV provirus DNA (gag region) and a porcine mtDNA. Human U293 cells were incubated in vitro with encapsulated PK15 cells, concentrated encapsulated PK15 supernatant, or concentrated PK15 supernatant as a control. CD1 mice were implanted in vivo with encapsulated PK15 cells or injected with PK15 supernatant. We found no infection in human cells incubated with either encapsulated PK15 supernatant or in 10 out of 11 samples after coincubation with encapsulated PK15 cells. Infection of human cells was, however, detected in 1 out of 11 samples after coincubation with encapsulated PK15 cells. The presence of PERV provirus DNA and porcine mtDNA was detected in all the investigated tissues of the mice injected with PK15 supernatant and in various tissues of the mice implanted with encapsulated PK15 cells. Four weeks after the last injection of PK15 supernatant or a fiber explantation, no mouse showed any presence of PERV provirus DNA or porcine mtDNA. Our results demonstrate that AN69 hollow fiber membrane will reduce but not abolish the risk of PERV infection. Because the real risk of PERV infection still remains unknown, it is necessary to investigate further the real protection that could be provided by hollow fibers to ensure the safety of clinical xenotransplantation.

Impact of hypothermic preservation on tissue yield and viability in pig pancreata

INTRODUCTION

Chronic shortage of quality human cadaveric pancreata limits islet transplantation. Porcine islet xenotransplantation is being explored to increase the donor pool. For clinical-ready islets, centralized animal husbandry, Current Good Manufacturing Practice-regulated processing facilities, and organ transportation support are required. Amount of cold ischemia time (CIT) before isolation significantly affects transplantation. The goal of this study was to determine the maximum safe CIT of whole pancreata before islet isolation.

MATERIALS AND METHODS

Pancreata were rapidly removed from Yorkshire pigs (age, 14-22 days) and stored in modified University of Wisconsin solution or in EuroCollins solution at 4(°)C. Pancreata were processed with <1 hour CIT (control) or stored for 4 or 12 hours before isolation. Islet yield and percent purity and viability were determined after 7 days of in vitro tissue culture and maturation. Samples from nonprocessed pancreata were collected and snap-frozen in liquid nitrogen at 0, 3, 6, 9, 12, 15, and 24 hours of preservation, then analyzed for adenosine diphosphate/adenosine triphosphate ratio as a measure of tissue energetics.

RESULTS

Up to 12 hours in cold storage had no significant impact on overall islet yield after 7 days of in vitro culture compared with controls; islet yield at the end of the maturation process was 28,700 ± 500 islet equivalents per pancreas (mean ± SEM control yield, 30,300 ± 900 islet equivalents per pancreas); islet purity was 75 ± 5% compared with 74 ± 5% in controls. Islet viability was significantly reduced at 12 hours compared with controls (80 ± 6% vs 96 ± 5%; P < .05). The tissue adenosine diphosphate/adenosine triphosphate ratio was maintained within the first 6 hours (1.6 ± 0.1 to 1.8 ± 0.2; P = NS) but was markedly increased during the 24-hour study (3.3 ± 0.1 at 24 hours), indicating a progressive loss of adenosine triphosphate tissue stores.

CONCLUSIONS

Young pig pancreata can be hypothermically stored for up to 12 hours without affecting islet yield and purity; however, islet viability is reduced. These data highlight the need for uniform shipping parameters to standardize islet quality, ideally with CIT <6 hours.

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.

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.

Xenotransplantation: an overview of the field

Xenotransplantation, the transplantation of cells, tissues, or organs between different species, has the potential to overcome the current shortage of human organs and tissues for transplantation. In the last decade, the progress made in the field is remarkable, suggesting that clinical xenotransplantation procedures, particularly those involving cells, may become a reality in the not-too-distant future. However, several hurdles remain, mainly immunological barriers, physiological discrepancies, and safety issues, making xenotransplantion a complex and multidisciplinary discipline.

Atherosclerosis and thrombosis: insights from large animal models

Atherosclerosis and its thrombotic complications are responsible for remarkably high numbers of deaths. The combination of in vitro, ex vivo, and in vivo experimental approaches has largely contributed to a better understanding of the mechanisms underlying the atherothrombotic process. Indeed, different animal models have been implemented in atherosclerosis and thrombosis research in order to provide new insights into the mechanisms that have already been outlined in isolated cells and protein studies. Yet, although no model completely mimics the human pathology, large animal models have demonstrated better suitability for translation to humans. Indeed, direct translation from mice to humans should be taken with caution because of the well-reported species-related differences. This paper provides an overview of the available atherothrombotic-like animal models, with a particular focus on large animal models of thrombosis and atherosclerosis, and examines their applicability for translational research purposes as well as highlights species-related differences with humans.

Comparison of the age-related porcine endogenous retrovirus (PERV)expression using duplex RT-PCR

Porcine endogenous retroviruses (PERVs) are members of family Retroviridae, genus Gamma retrovirus, and transmitted by both horizontally and vertically like other endogenous retroviruses (ERVs). PERV was initially described in the 1970s having inserted its gene in the host genome of different pig breeds, and three classes, PERV-A, PERV-B, and PERV-C are known. The therapeutic use of living cells, tissues, and organs from animals called xenotransplantation might relieve the limited supply of allografts in the treatment of organ dysfunction. Because of ethical considerations, compatible organ sizes, and physiology, the pig has been regarded as an alternative source for xenotransplantation. Sensitive duplex reverse transcription-polymerase chain reaction protocols for simultaneously detecting PERV gag mRNA and porcine glyceraldehydes 3-phosphate dehydrogenase mRNA in one tube was established. To compare the age-related PERV expression patterns of the lung, liver, spleen, kidney, heart, and pancreas in commercial pigs, 20 pigs from four age groups (5 heads each in 10 days-, 40 days-, 70 days-, and 110 days-old, respectively) were used in this study. The expression patterns of PERV were statistically different among age groups in lung, liver, and kidney (ANOVA, p < 0.05). These data may support in the selection of appropriate donor pigs expressing low levels of PERV mRNA.

Can nutraceuticals affect the structure of intestinal mucosa? Qualitative and quantitative microanatomy in L-glutamine diet-supplemented weaning piglets

Weaning piglets were fed an L-glutamine-supplemented diet with the aim of monitoring the effects on gut mucosal turnover and barrier function, to elucidate the potential preventive or therapeutic roles of glutamine as a nutraceutical or 'functional food'. Sixteen female weaning piglets were divided into two groups, which were fed a control diet (Ctr group: n = 8) or a Ctr + 0.5% L-glutamine diet (G group: n = 8) for 28 days. In the ileum of group G piglets the villus height (V) and crypt depth (C) were increased, and the V:C ratio was decreased (p < 0.01). The PCNA and TUNEL immunoreactivities were also tested. The number of mitotic mucosal cells (M) was increased, and that of mucosal cells with apoptotic nuclei (A) decreased in such a way that the A:M index diminished (p < 0.01). The A:M index also decreased at the level of some components of the gut-associated lymphatic tissue (GALT), thus indicating a positive effect on the gut barrier function. This trial showed that L: -glutamine supplementation influenced some morphofunctional characteristics of piglet ileal mucosa. These data corroborate the nutraceutical role of glutamine as a trophic agent for mucosal repair, improvement of barrier function and gut adaptation in the swine per se and as an animal model.

Quarantine facilities and operations

This chapter focuses on quarantine requirements at animal facilities. The well-established quarantine measures for nonhuman primates and those that have re-emerged for rodents are very important. The increased use and exchange of genetically engineered mutant mice especially demands rodent quarantine capabilities for the majority of research institutions. Apart from species-specific housing requirements, it is important to consider pathogens to be contained in terms of the route of transmission, and degree of hazard to human and animal health. Animals obtained from commercial vendors, as opposed to other research institutions, may be less likely to harbor undesirable microorganisms, often allowing them to be exempt from a quarantine program. The ideal quarantine facility should be flexible enough to allow the use of multiple species, and take into account the number and frequency of shipments expected. The more shipments and different species involved, the more subdivided the facility should be, through the use of multiple rooms, cubicles, isolators, etc. At a minimum, ABSL2 design criteria should be used to enable the containment of pathogens at the room or cage level, while also preventing agent transmission via contaminated animal waste, fomites, and personnel.

Polyclonal antibody to porcine p53 protein: a new tool for studying the p53 pathway in a porcine model

Although the tumor suppressor protein p53 is important in the control of various cellular activities, the analysis of p53 in the porcine model has been hampered by a lack of a suitable antibody that is specific for porcine p53. Using a recombinant porcine p53, we generated a rabbit polyclonal antibody (designated SH0797) that is directed against porcine p53. The results of the study show that the antibody is capable of detecting recombinant p53 protein expressed in Escherichia coli, as well as FLAG-tagged p53 that is expressed in the transfected cells. This demonstrates that the antibody is specific for the porcine p53 protein. The antibody also showed the ability to immunoprecipitate p53 protein from extracts of porcine cells and to cross-react with human p53 protein. In addition, expression of porcine p53 could be induced readily in porcine cells and detected using this new tool. This antibody is a useful tool for use in studies of the cellular pathways that involve p53 in the porcine model.

Characteristics of primary and immortalized fibroblast cells derived from the miniature and domestic pigs

Background

The pig, Sus scrofa domestica includes both the miniature and commercial domestic breed. These animals have influenced the human life and economies and have been studied throughout history. Although the miniature breeds are more recent and have increasingly been used in a variety of biomedical studies, their cell lines have rarely been established. Therefore, we sought to establish primary and immortal cell lines derived from both the miniature and domestic pig to better enable insight into possible in vivo growth differences.

Results

The in vitro lifespan of primary domestic pig fibroblast (PF) and miniature pig fibroblast (MPF) cells using a standard 3T3 protocol was determined. Both of the primary PF and MPF cells were shown to have a two-step replicative senescence barrier. Primary MPF cells exhibited a relatively shorter lifespan and slower proliferation rate compared to those of primary PF cells. Beyond senescence barriers, lifespan-extended PF and MPF cells were eventually established and indicated spontaneous cellular immortalization. In contrast to the immortalized PF cells, immortal MPF cells showed a transformed phenotype and possessed more frequent chromosomal abnormalities and loss of p53 regulatory function. The lifespan of primary MPF and PF cells was extended by inactivation of the p53 function using transduction by SV40LT without any detectable senescent phenotype.

Conclusion

These results suggest that p53 signaling might be a major determinant for the replicative senescence in the MPF cells that have the shorter lifespan and slower growth rate compared to PF cells in vitro.

Preparation of swine for the laboratory

Swine are an important model in many areas of biomedical research. These animals have been used predominantly as preclinical models involving surgical and interventional protocols. The systems most commonly studied include cardiovascular, integumentary, digestive, and urological. Swine are intelligent social animals and require species-specific socialization and handling techniques. It is important to acclimate the animals to the facility and to personnel before they are placed on chronic protocols. Gentle handling techniques instead of forceful procedures are essential to their socialization. They require sturdy caging with specific construction standards, and toys for environmental enrichment. Because the species is covered by both the Animal Welfare Act and the US Department of Agriculture, interstate transport requires a health certificate with destination state-specific disease screening standards. This manuscript provides an overview of best practices that have been utilized in the authors' facility.

No evidence of in vitro and in vivo porcine endogenous retrovirus infection after plasmapheresis through the AMC-bioartificial liver

BACKGROUND

Currently a number of bioartificial livers (BAL) based on porcine liver cells have been developed as a treatment to bridge acute liver failure patients to orthotopic liver transplantation or liver regeneration. These xenotransplantation related treatments hold the risk of infection of treated patients by porcine endogenous retrovirus (PERV) released from the porcine cells, as in vitro infection experiments and transplantations in immunocompromised mice have shown that PERV is able to infect human cells. The Academic Medical Center (AMC)-BAL, unlike other BALs, is characterized by direct contact between porcine liver cells and human plasma, and might therefore be permissive for PERV transfer.

METHODS

Prior to a clinical phase I trial, human plasma perfused through the AMC-BAL was investigated for PERV DNA and RNA. Moreover productive infectivity was analyzed by exposing the plasma to HEK-293 cells that were subsequently tested for PERV DNA, PERV RNA and reverse transcriptase activity.

RESULTS

Although PERV DNA was detected in the perfused plasma, no productive infectivity was detected. Consequently fourteen patients were treated with the AMC-BAL and monitored for PERV transmission. Immediately after treatment the plasma of the patients was positive for PERV DNA, most probably due to porcine liver cell lysis. The PERV DNA was cleared within 2 weeks post-treatment and no PERV RNA was detected. No productive infectivity in human embryonic kidney (HEK)-293 cells exposed to plasma of treated patients was detectable.

CONCLUSION

To conclude, no release of infective PERV particles from the AMC-BAL was observed. Therefore we consider the AMC-BAL as safe, however careful surveillance of patients will be continued.

Xenotransplantation and pig endogenous retroviruses

Xenotransplantation, in particular transplantation of pig cells, tissues and organs into human patients, may alleviate the current shortage of suitable allografts available for human transplantation. This overview addresses the physiological, immunological and virological factors considered with regard to xenotransplantation. Among the issues reviewed are the merits of using pigs as xenograft source species, the compatibility of pig and human organ physiology and the immunological hindrances with regard to the various types of rejection and attempts at abrogating rejection. Advances in the prevention of pig organ rejection by creating genetically modified pigs that are more suited to the human microenvironment are also discussed. Finally, with regard to virology, possible zoonotic infections emanating from pigs are reviewed, with special emphasis on the pig endogenous retrovirus (PERV). An in depth account of PERV studies, comprising their discovery as well as recent knowledge of the virus, is given. To date, all retrospective studies on patients with pig xenografts have shown no evidence of PERV transmission, however, many factors make us interpret these results with caution. Although the lack of PERV infection in xenograft recipients up to now is encouraging, more basic research and controlled animal studies that mimic the pig to human xenotransplantation setting more closely are required for safety assessment.

Limiting potential infectious risks of transplanting insulin-producing pig cells into humans

AIMS

Prior to commencing a study of grafting foetal/neonatal pig islet-like cell clusters into type I diabetic human subjects, the microbiological risks of transplanting porcine pancreatic tissue were assessed.

METHODS

An exclusion list for screening donor animals and graft tissue in Australia was compiled following evaluation of the disease risks posed by 121 organisms, including 36 bacteria, 12 fungi, four mycoplasma, 31 parasites and 38 viruses. The list of evaluated agents was derived from the literature, interviews with veterinarians and physicians, and a survey of laboratories.

RESULTS

The exclusion list contains 35 organisms (including 20 bacteria, four fungi, one mycoplasma, one parasite and nine viruses) that are zoonotic, pathogens of immunocompromised hosts (including human allograft recipients), pathogens resistant to antibiotics or potentially able to recombine with the human genome. These 35 agents can be detected by culture (e.g., Actinomyces), serological testing (e.g., influenza viruses) or nucleic acid amplification (e.g., Mycobacteria).

CONCLUSIONS

It is recommended that: (i) source pigs designated for use in human xenotransplantation trials should be tested regularly for the 35 organisms; (ii) the mothers of donor foetal/neonatal pigs and, when possible, the foetal/ neonatal pigs themselves should be tested immediately prior to the grafting of tissue into humans; and (iii) the exclusion list be modified for designated source pig herds in countries other than Australia.

Porcine endogenous retroviruses (PERVs): generation of specific antibodies, development of an immunoperoxidase assay (IPA) and inhibition by AZT

Xenotransplantation may be associated with the risk of transmission of microorganisms. In particular, the porcine endogenous retroviruses (PERV) have raised concerns as in vitro experiments show susceptibility of human cells for PERV infection. However, it remains unclear whether PERVs are able to infect transplant recipients in vivo and whether they are pathogenic. It is therefore essential that the risks are evaluated and for this purpose specific and sensitive screening methods for PERVs have to be developed. We generated specific antibodies against all major structural proteins of PERV and developed several assays which allow antibodies against PERV to be detected as indirect evidence of infection. For direct detection of PERV production, reverse transcriptase (RT) assays were used. PCR methods were used to detect provirus integration and the presence of viral mRNA. Here we present an immunoperoxidase assay (IPA), which would allow the detection of viral proteins in infected cells as well as antibodies against PERV in the serum of an infected host. The specificity of the sera used in the assay was determined by several methods, including immunoelectron microscopy, and the sensitivity of the assay was compared with other methods. This IPA was used to detect PERV infection in in vitro experiments for evaluation of the virus host range, for titrating the virus and for testing anti-viral properties of AZT. Using this method it was shown that AZT inhibits replication of PERV. This IPA may be very useful for the surveillance of preclinical and clinical xenotransplantations.

Porcine endogenous retroviruses: in vitro host range and attempts to establish small animal models

Using transgenic pigs as the source of cells or organs for xenotransplantation is associated with the risk of porcine endogenous retrovirus (PERV) transmission. Multiple proviruses are integrated into the genome of all pigs, and virus particles, some of which are able to infect human cells, are released from normal pig cells. In order to evaluate the potential risk posed by the transmission of PERVs, in vitro infection studies were performed as a basis for small animal as well as non-human primate models. In vitro infectivity was demonstrated for permanent cell lines and primary cells from a wide range of species. Productive infection was shown using reverse transcriptase (RT) assays and RT-PCR for mink, feline and human kidney cell lines, primary rhesus peripheral blood mononuclear cells (PBMCs), and baboon spleen cells and PBMCs as well as for different human lymphoid and monocyte cell lines and PBMCs. In an attempt to establish a small animal model, naive guinea pigs, non-immunosuppressed rats, rats immunosuppressed by cyclosporin-A and immunosuppressed rats treated with cobra venom factor were inoculated with PERVs produced from porcine kidney PK-15 cells, infected human 293 kidney cells and mitogen-stimulated porcine PBMCs. Animals were also inoculated with PERV-producing PK-15 and 293 cells. No antibodies against PERV and no provirus integration were observed in any of the treated animals. This suggests that productive infection of these animals did not occur in this experimental setting.

Porcine endogenous retroviruses inhibit human immune cell function: risk for xenotransplantation?

Transgenic pigs are currently the most favored potential source of organs for xenotransplantation. Like all mammalian species they all harbor endogenous retroviruses in their genome. These porcine endogenous retroviruses (PERVs) are produced from several primary cells and cell lines and are able to infect human cells. Here we demonstrate that different pig strains and different animals of one strain differ in their ability to produce PERVs from normal blood cells. We report that purified PERV particles show a protein pattern typical for type C retroviruses and are antigenically related to mammalian leukemia viruses. Like most retroviruses, purified PERVs and peptides derived from the highly conserved immunosuppressive domain of their transmembrane envelope protein inhibit human immune cell functions. This indicates that high titer replication of PERVs in the transplant recipient could therefore lead to an immunodeficiency disease.