Xenotransplantation

Pre-clinical model of composite foetal pig pancreas fragment/renal xenotransplantation to treat renal failure and diabetes

 

BACKGROUND

Development of a limitless source of β cells for xenotransplantation into patients suffering type 1 diabetes and renal failure that can control their diabetes and provide normal renal function in one procedure would be a major achievement. For the islet tissue to survive transplantation, as an islet-kidney composite graft this would have significant advantages. It would simplify the surgical procedure; remove the complications caused by the exocrine pancreas whilst reversing diabetes and uraemia. It was our hypothesis that a composite foetal porcine pancreas fragment (FPPF)/renal graft could achieve these objectives in a large pre-clinical animal model as a means to establish whether this would be feasible before moving to the clinic.

METHODS

Inbred 'Westran' pig FPPF were transplanted under the kidney capsule of syngeneic Westran pig recipients without immunosuppression. Following maturation of the FPPF under the renal subcapsular space of this recipient, this kidney bearing the composite FPPF piggyback graft was removed and transplanted into another nephrectomized and pancreatectomized recipient to demonstrate function.

RESULTS

Under the kidney capsule of the first transplant group (n = 6), the FPPF-transplanted tissue developed and matured to form islet cell nests. These composite FPPF/renal grafts were then successfully removed and transplanted into the second functional assessment recipient group. This second group of six composite FPPF/renal-grafted pigs had normal renal function for more than 44 days and normal glucose homoeostasis without exogenous insulin as assessed by normal glucose tolerance tests, K values and normal glucagon secretion. Histological analysis showed despite the ischaemic insult during the composite kidney transplant procedure, there was appropriate development of islet-like structures up to and beyond 224 days after the original transplantation under the kidney capsule.

CONCLUSIONS

This study shows that the use of composite FPPF/renal grafts can cure both diabetes and renal failure with a single-transplant procedure. Using such composite grafts for xenotransplantation would simplify the surgical procedure and protect the islet graft from the immediate innate immune response.

Expression of human CD46 has no effect on porcine circovirus type 2 infection and shedding in the experimental pig model

Xenotransplantation of tissues from transgenic pigs with desired genetic modifications such as CD46 expression help minimize xenograft rejections. However, CD46 is a known receptor for some viruses. In this study, pigs transgenic for human CD46 (CD46-TG) and appropriate non-transgenic (non-TG) control pigs were utilized to determine possible differences in the level of replication and shedding of porcine circovirus type 2 (PCV2). Non-TG and CD46-TG were blocked by transgenic status and randomly divided into three groups: Non-TG negative controls (n = 3), non-TG-PCV2 (n = 10; PCV2a = 5, PCV2b = 5), and CD46-TG-PCV2 (n = 6; PCV2a = 3, PCV2b = 3). Blood, oral, nasal and fecal swabs were collected at regular intervals from the day of arrival until 70 days post inoculation (DPI). All samples were tested by quantitative real-time PCR for the presence of PCV2 DNA and serum was tested for presence of PCV2 antibodies by ELISA. Overall, the main effects "transgenic status" and "PCV2 subtype" had no influence on degree of PCV2 viremia and shedding or the anti-PCV2 humoral immune response in CD46-TG-PCV2 pigs compared to non-TG-PCV2 pigs. Differences in PCV2 concentrations between non-TG-PCV2 and CD46-TG-PCV2 pigs were minimal and limited to DPI 35 in sera, DPI 7 in fecal swabs and DPI 5 in nasal swabs when CD46-TG-PCV2 pigs had significantly higher concentrations of PCV2 DNA. At DPI 1, CD46-TG-PCV2 pigs had significantly lower concentrations of PCV2 DNA in oral swabs. Under the study conditions, the presence of human CD46 in transgenic pigs had no effect on PCV2 infection in otherwise healthy pigs capable of a normal immune response.

Somatic cell nuclear transfer in pigs: recent achievements and future possibilities

During the past 6 years, considerable advancement has been achieved in experimental embryology of pigs. This process was mainly generated by the rapidly increasing need for transgenic pigs for biomedical research purposes, both for future xenotransplantation to replace damaged human organs or tissues, and for creating authentic animal models for human diseases to study aetiology, pathogenesis and possible therapy. Theoretically, among various possibilities, an established somatic cell nuclear transfer system with genetically engineered donor cells seems to be an efficient and reliable approach to achieve this goal. However, as the result of unfortunate coincidence of known and unknown factors, porcine embryology had been a handicapped branch of reproductive research in domestic animals and a very intensive and focused research was required to eliminate or minimise this handicap. This review summarises recent achievements both in the background technologies (maturation, activation, embryo culture) and the actual performance of the nuclear replacement. Recent simplified methods for in vivo development after embryo transfer are also discussed. Finally, several fields of potential application for human medical purposes are discussed. The authors conclude that although in this early phase of research no direct evidence can be provided about the practical use of transgenic pigs produced by somatic cell nuclear transfer as organ donors or disease models, the future chances even in medium term are good, and at least proportional with the efforts and sums that are invested into this research area worldwide.

Evolution at the host-retrovirus interface

Retroviruses are unusual amongst animal viruses in their capacity to integrate into host genomes and be transmitted vertically to host progeny. Vertebrate genomes contain numerous and diverse retrovirus-derived sequences reflecting a long co-evolutionary history during which genome invasion has occurred repeatedly, with wide-ranging evolutionary consequences. Over the past 10 years, a detailed picture of retroviral diversity throughout vertebrate genomes has emerged, revealing striking and informative patterns that differ markedly across species. The power of these data to deliver far-reaching insights into the biology and evolution of retroviruses has been significantly advanced by recent studies identifying ongoing genome invasion in wild populations, and by the characterisation of conserved mechanisms of innate antiretroviral defence.

Attitude Toward Xenotransplantation in Kidney and Liver Patients on the Transplant Waiting List

INTRODUCTION

The deficit in transplant organs is encouraging research into stem cells and xenotransplantation. However, many studies have shown that using animals for human transplantation could be rejected by society. The objective here was to analyze the attitude of patients on the waiting list toward a possible transplant of an organ of animal origin.

MATERIALS AND METHODS

Patients on the waiting list for kidney and liver transplants including last year (n = 96) underwent a direct interview by an independent health professional from the transplant unit. Using a psychosocial survey, an evaluation was made of attitudes toward donation of organs of animal origin and its various options. Student t test and the chi-square test were used for analysis.

RESULTS

If results from xenotransplantation could be superimposed onto those of human transplantation, 71% would accept such an organ. In the case of the kidney, 83% would accept, 4% would not, and 13% have doubts; as opposed to 60%, 12%, and 28%, respectively, of liver cases (P < .05). Supposing that the results were worse than in human organs, only 26% would accept an animal organ. Thus, for kidney, 33% would accept it, 48% would not, and 20% would have doubts; and for liver, it would be 20%, 50%, and 30%, respectively. In a life-threatening situation 98% would accept an animal organ as a bridge of hope in the wait for a human organ. In addition, if the organ functioned correctly, 98% would keep the animal organ, thus avoiding an intervention to substitute a human organ.

CONCLUSION

If xenotransplantation became a clinical reality, acceptance of an animal organ by patients on the waiting list would be low, especially if the results could not be superimposed onto human ones. Only its use as a bridge until the arrival of a human organ would increase its acceptance.

Face value: challenges of transplant technology

What is the value of a human face? It is a vexing question with no simple answer. The question, however, is no longer fanciful given the trajectory of biomedical science that simultaneously captures our imagination and challenges our essence. Essential to each of us and to the whole of humanity, the face is primal in its individuated image and identity. It is intrinsically connected with us in a way that defied question—until now, given the highly anticipated next step in transplant science and technology, facial transplantation. This Article examines the value of the face in this context, along with a range of related issues.

The human face has rich significance. It is intrinsic and instrumental to the ontology of a person. A portal for emotions and expressions, the face reveals an inner-self essential to identity and is inscribed with an inherent dignity of human life.

Understanding of and attitudes to xenotransplantation: a survey among Italian university students

Xenotransplantation is currently at the experimental stages on animal models and many problems still have to be overcome in the biomedical, immunological and ethical fields. Moreover, people's attitudes to xenotransplantation vary: surveys among intensive-care staff have revealed negative opinions, while the general public and students seem to be more positive. Little is known about the influence of schooling and the choice of university faculty on attitudes to xenotransplantation. The aims of this study were: (i) to evaluate university students' attitudes to xenotransplantation; (ii) to investigate any socio-demographic, religious and educational determinants behind students' opinions on xenotransplantation. University undergraduates on five different courses were surveyed at Padua University. A 24-item questionnaire was distributed to students at the end of lectures and completed anonymously immediately after its distribution. No information was given to students beforehand.

STATISTICAL ANALYSIS

chi-squared, Pearson's test; P-values <0.05 were considered significant. A total of 585 of 602 (97.2%) students completed the questionnaire (132 males, 453 females, mean age 20.4, range 19 to 43 yr). They were on courses in Medicine (33.85%), Agriculture (5.98%), Veterinary Medicine (11.45%), Psychology (18.46%) and Educational Sciences (30.26%). As for their previous schooling, they came from classical or scientific high school (58.3%), technical college (14.7%), language college (6.3%), teacher training college (11.9%) or others (8.8%). Concerning their religious beliefs, 83% were Catholics, and 56.2% defined themselves as practising Catholics. Eighty-eight percentage of the students knew of the possibility of animal organs being transplanted into humans and 77.9% of them approved of this idea. When grouped according to gender and education, a higher proportion of students approving of xenotransplantation were male (P = 0.017) and had attended classical or scientific high school (P = 0.011). Disapproval for moral, ethical or religious reasons was higher among practising than among non-practising Catholics; the latter rejected xenotransplantation more for immunological and infectious reasons (P = 0.014). As for the type of university course, a higher proportion of students approving of xenotransplantation attended science courses (Veterinary Medicine, Agriculture and Medicine vs. Educational Sciences and Psychology) (P = 0.013). University students generally approved of xenotransplantation. Male gender and a high-school education were associated with a greater acceptance of xenotransplantation. Practising vs. non-practising Catholics reported significantly different reasons for any disapproval of xenotransplantation. The choice of a science rather than an arts faculty at university was more strongly associated with a positive opinion on xenotransplantation.

Application of reproductive biotechnology in animals: implications and potentials. Applications of reproductive cloning

The development of new methods of nuclear transfer in mammals is creating many new opportunities in research, medicine and agriculture. The method of cloning is repeatable and has been established in many laboratories worldwide. However, the present procedure is inefficient with fewer than 4% of embryos becoming viable offspring. A considerable improvement in efficiency is required before wide scale use for livestock improvement. The opportunity to introduce precise genetic changes to livestock is available for the first time through the use of gene targeting procedures in cultured cells that are used as nuclear donors. This has potential application in the production of organs for transplantation to humans, studies of human genetic disease and basic research in to the control of gene expression and function.

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.

The Leeuwenhoek Lecture 2001. Animal origins of human infectious disease

Since time immemorial animals have been a major source of human infectious disease. Certain infections like rabies are recognized as zoonoses caused in each case by direct animal-to-human transmission. Others like measles became independently sustained with the human population so that the causative virus has diverged from its animal progenitor. Recent examples of direct zoonoses are variant Creutzfeldt-Jakob disease arising from bovine spongiform encephalopathy, and the H5N1 avian influenza outbreak in Hong Kong. Epidemics of recent animal origin are the 1918-1919 influenza pandemic, and acquired immune deficiency syndrome caused by human immunodeficiency virus (HIV). Some retroviruses jump into and out of the chromosomal DNA of the host germline, so that they oscillate between being inherited Mendelian traits or infectious agents in different species. Will new procedures like animal-to-human transplants unleash further infections? Do microbes become more virulent upon cross-species transfer? Are animal microbes a threat as biological weapons? Will the vast reservoir of immunodeficient hosts due to the HIV pandemic provide conditions permissive for sporadic zoonoses to take off as human-to-human transmissible diseases? Do human infections now pose a threat to endangered primates? These questions are addressed in this lecture.

Recent strategies to overcome the hyperacute rejection in pig to human xenotransplantation

Due to the ever increasing shortage of suitable human donors, alternative strategies are sought to moderate the current discrepancy between the number of executable and required transplantations. Xenotransplantation (i.e., the transplantation of organs [tissues or cells] between different species) appears to be a reasonable solution. However, various problems (immunological, physiological, infectious-microbiological, ethical-juridicial) seem to be associated with xenotransplantation. One of the most formidable barriers to xenotransplantation is the phenomenon of hyperacute rejection that may lead to the destruction of the transplanted vascularized organ in a few minutes to hours. In the pathogenesis of hyperacute rejection, xenoreactive antibodies and the complement system appear to be of primary importance. Various methods can be applied to prevent hyperacute rejection; both the recipient and the donor can be treated. In this brief review, the author attempts to present a synopsis of the possible therapeutical interventions to prevent hyperacute rejection..

Viruses, cancer and AIDS

Patients with AIDS are at risk of lymphoma and Kaposi's sarcoma. These tumours are associated with the gamma herpesviruses, Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8), although a proportion of AIDS lymphomas lacks both viruses. EBV and HHV-8 are latent in the tumour cells, with genes that play a direct role in driving cell proliferation. Human immunodeficiency virus, in contrast, while being the greatest risk factor for lymphoma and Kaposi's sarcoma, acts indirectly, mainly by causing immune suppression, as immunosuppressed transplant patients are at risk for the same types of tumour.

Xenotransplantation: progress and promise

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Retroviruses: ancient and modern

Retroviruses are transmitted in two distinct ways: as infectious virions and as 'endogenous' proviral DNA integrated in the germ line of their hosts. Modern infectious viruses such as HIV recently infected mankind from simian hosts, whereas human endogenous retroviral genomes have been present throughout old world primate evolution. Recently we have characterised novel retroviruses in humans and pigs. Human retrovirus 5 (HRV-5) is detected as an exogenous genome in association with arthritis and systemic lupus erythematosus. Porcine endogenous retroviruses (PERV) are carried in swine DNA but can be activated to produce virions that are infectious for human cells, which has implications for xenotransplantation. A brief account of HRV-5 and PERV is given here.

The fourth barrier

At the entrance of a new era, clinical xenotransplantation is a valued and auspicious option in tackling the problem of donor shortage. Because of ethical and anatomical issues, domestic farm animals are considered the most favourable species for organ donation, but transplantation of their organs leads to a complex process of rejection. Mechanistically, three immunological barriers, namely hyperacute rejection, delayed xenograft rejection and a subsequent cellular rejection, are distinguished. A fifth (microbiological) barrier is also being recognised. This review focuses on problems regarding the fourth barrier, i.e. physiology, in possible clinical settings and their corresponding animal models. Besides anatomical differences and posture, biochemical differences may have a severe impact on recipient survival. Differences in blood components and electrolyte and other biochemical concentrations are easily detected throughout the species considered for xenotransplantation. Enzymes and hormones have complex routes of action, activation and inhibition, and their molecular differences can impede function. As infusion or medicine may correct certain imbalances in electrolytes and proteins, problems with complex interactions might be difficult to retrieve and solve. Experimentally, survival of discordant xenografts show promising results, but the first physiological problems have already been detected. So, based upon the few experimental data available and the comparison of veterinary physiology, one might expect differences between the organs grafted, regarding the possible occurrence of physiological problems. Moreover, precautions must be taken to extrapolate long-term survival, because of species specificity.