This little piggy went to market: the xenotransplantation and xenozoonose debate

Isolation of an Ecotropic Porcine Endogenous Retrovirus PERV-C from a Yucatan SLAD/D Inbred Miniature Swine

Xenotransplantation may compensate the limited number of human allografts for transplantation using pigs as organ donors. Porcine endogenous retroviruses inherit infectious potential if pig cells, tissues, or organs were transplanted to immunosuppressed human recipients. Particularly, ecotropic PERV-C that could recombine with PERV-A to highly replication-competent human-tropic PERV-A/C should be excluded from pig breeds designed for xenotransplantation. Because of their low proviral background, SLAD/D (SLA, swine leukocyte antigen) haplotype pigs are potential candidates as organ donors as they do not bear replication-competent PERV-A and -B, even if they carry PERV-C. In this work, we characterized their PERV-C background isolating a full-length PERV-C proviral clone number 561 from a SLAD/D haplotype pig genome displayed in a bacteriophage lambda library. The provirus truncated in env due to cloning in lambda was complemented by PCR, and the recombinants were functionally characterized, confirming an increased infectivity in vitro compared to other PERV-C. Recombinant clone PERV-C(561) was chromosomally mapped by its 5'-proviral flanking sequences. Full-length PCR using 5'-and 3'-flanking primers specific to the PERV-C(561) locus verified that this specific SLAD/D haplotype pig harbors at least one full-length PERV-C provirus. The chromosomal location is different from that of the previously described PERV-C(1312) provirus, which was derived from the porcine cell-line MAX-T. The sequence data presented here provide further knowledge about PERV-C infectivity and contribute to targeted knockout in order to generate PERV-C-free founder animals. IMPORTANCE Yucatan SLAD/D haplotype miniature swine are candidates as organ donors for xenotransplantation. A full-length replication-competent PERV-C provirus was characterized. The provirus was chromosomally mapped in the pig genome. In vitro, the virus showed increased infectivity compared to other functional PERV-C isolates. Data may be used for targeted knockout to generate PERV-C free founder animals.

Ethical considerations in tissue engineering research: Case studies in translation

Tissue engineering research is a complex process that requires investigators to focus on the relationship between their research and anticipated gains in both knowledge and treatment improvements. The ethical considerations arising from tissue engineering research are similarly complex when addressing the translational progression from bench to bedside, and investigators in the field of tissue engineering act as moral agents at each step of their research along the translational pathway, from early benchwork and preclinical studies to clinical research. This review highlights the ethical considerations and challenges at each stage of research, by comparing issues surrounding two translational tissue engineering technologies: the bioartificial pancreas and a tissue engineered skeletal muscle construct. We present relevant ethical issues and questions to consider at each step along the translational pathway, from the basic science bench to preclinical research to first-in-human clinical trials. Topics at the bench level include maintaining data integrity, appropriate reporting and dissemination of results, and ensuring that studies are designed to yield results suitable for advancing research. Topics in preclinical research include the principle of "modest translational distance" and appropriate animal models. Topics in clinical research include key issues that arise in early-stage clinical trials, including selection of patient-subjects, disclosure of uncertainty, and defining success. The comparison of these two technologies and their ethical issues brings to light many challenges for translational tissue engineering research and provides guidance for investigators engaged in development of any tissue engineering technology.

Reflections on the ethics of biomaterials science

The subject of biomaterials science concerns artificial materials used in medical devices to repair or reconstruct natural human tissue damaged by disease or trauma. It embraces the emerging field of tissue engineering, where artificial materials are used as scaffolds to provide the architecture for replacement organs. As such, the field raises numerous ethical issues, which are reviewed in this paper. These include the use of animal models, the testing materials and devices in patients, and what may be viewed as potential abuses, where augmentation and repair are carried out for cosmetic as opposed to clinical reasons. The paper gives detailed consideration of the recent problems of metal-on-metal hip replacements as an exemplar of some of the key ethical issues that arise in this field.

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.

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.

Should we add "xeno" to "transplantation"?

Proponents of xenotransplantation hope that it will provide organs to fill the gap between the demand for and supply of organs for transplant. The scientific obstacles to transplanting animal organs into humans are daunting, as are the moral, political, and policy issues. Among them are concerns about animal rights and welfare, patient acceptance and informed consent, and broader public health issues, such as the cost-efficient deployment of scarce resources and the risk of disease in third parties. The latter is, in my view, the most immediately urgent issue. Pigs, the current animal of choice, carry many bacterial and viral pathogens, and it is currently impossible to assess the risk of disease to human populations. Because of this risk, a moratorium on xenotransplantation is necessary to protect public health; it is also questionable whether the technology, if successful, would be the most cost-effective way to promote health.

Engineering blood: synthetic substitutes from fluorinated compounds

Concerns about blood safety and the logistical problems associated with conventional transfusion have fuelled the search for effective alternatives (so-called blood substitutes). Such materials include hemoglobin derivatives and those based on synthetic, highly fluorinated, inert organic compounds called perfluorochemicals (PFCs). PFCs dissolve large volumes of oxygen and other gases, are unreactive in the body, and are excreted primarily as a vapor by exhalation. Liquid PFCs are immiscible with blood and other body fluids, but can be injected safely into the bloodstream as submicron emulsions. Emulsified PFCs have been evaluated in clinical trials as temporary, intravascular tissue-oxygenating fluids. One such emulsion, a commercial perflubron-based, phospholipid-stabilized formulation, is in advanced clinical trials as an alternative to transfusing donated (allogeneic) blood during surgery. Basic and clinical studies have shown that this emulsion can adequately maintain tissue oxygenation during acute blood loss with no abnormal hemodynamic changes. The use of PFC emulsions as an efficacious, short-term transfusion alternative underpins the longer term objective of producing a totally synthetic, bioengineered blood substitute.

Stem cell policies in the United States and in Germany

The article compares policymaking in the field of human embryonic stem cell research in the United States and Germany. Although experimental research with human stem cells is controversial in both countries, restrictions on research are much more strict in Germany than in the United States. In order to explain the contrast between the United States and Germany in dealing with human embryonic stem cell research and to predict possible future developments, we need to look carefully at a number of important differences in the interpretations and discourses of embryonic stem cell research and their consequences for the strategies of institutions and actors in the political-regulatory realm.

Xenografts: are the risks so great that we should not proceed?

Animal organs could save patients needing transplants, but further research is necessary to resolve remaining problems with organ rejection. Furthermore, xenotransplantation risks transmitting animal pathogens to patients and to the general population. It would be unethical to proceed with clinical trials before principles and procedures for dealing with this risk are in place.

Report of the Xenotransplantation Advisory Committee of the International Society for Heart and Lung Transplantation: the present status of xenotransplantation and its potential role in the treatment of end-stage cardiac and pulmonary diseases

An urgent and steadily increasing need exists world-wide for a greater supply of donor thoracic organs. Xenotransplantation offers the possibility of an unlimited supply of hearts and lungs that could be available electively when required. However, anti-body- mediated mechanisms cause the rejection of pig organs transplanted into non-human primates, and these mechanisms provide major immunologic barriers that have not yet been overcome. Having reviewed the literature on xenotransplantation, we present a number of conclusions on its present status with regard to thoracic organs, and we make a number of recommendations relating to eventual clinical trials. Although pig hearts have functioned in heterotopic sites in non-human primates for periods of several weeks, median survival of orthotopically transplanted hearts is currently ,1 month. No transplanted pig lung has functioned for even 24 hours. Current experimental results indicate that a clinical trial would be premature. A potential risk exists, hitherto undetermined, of transferring infectious organisms along with the donor pig organ to the recipient, and possibly to other members of the community. A clinical trial of xeno-transplantation should not be undertaken until experts in microbiology and the relevant regulatory authorities consider this risk to be minimal. A clinical trial should be considered when approximately 60% survival of life-supporting pig organs in non-human primates has been achieved for a minimum of 3 months, with at least 10 animals surviving for this minimum period. Furthermore, evidence should suggest that longer survival (.6 months) can be achieved. These results should be achieved in the absence of life-threatening complications caused by the immunosuppressive regimen used. The relationship between the presence of anti-HLA antibody and anti-pig antibody and their cross-reactivity, and the outcome of pig-organ xenotransplantation in recipients previously sensitized to HLA antigens require further investigation. We recommend that the patients who initially enter into a clinical trial of cardiac xenotransplantation be unacceptable for allotransplantation, or acceptable for allotransplantation but unlikely to survive until a human cadaveric organ becomes available, and in whom mechanical assist-device bridging is not possible. National bodies that have wide-reaching government-backed control over all aspects of the trials should regulate the initial clinical trial and all subsequent clinical xenotransplantation procedures for the foreseeable future. We recommend coordination and monitoring of these trials through an international body, such as the International Society for Heart and Lung Transplantation, and setting up a registry to record and widely disperse the results of these trials. Xenotransplantation has the potential to solve the problem of donor-organ supply, and therefore research in this field should be actively encouraged and supported.