Pig-to-non-human primate heart transplantation: The final step toward clinical xenotransplantation?

BACKGROUND: The demand for donated human hearts far exceeds the number available. Xenotransplantation of genetically modified porcine organs provides an alternative. In 2000, an Advisory Board of the International Society for Heart and Lung Transplantation set the benchmark for commencing clinical cardiac xenotransplantation as consistent 60% survival of non-human primates after life-supporting porcine heart transplantations. Recently, we reported the stepwise optimization of pig-to-baboon orthotopic cardiac xenotransplantation finally resulting in consistent success, with 4 recipients surviving 90 (n = 2), 182, and 195 days. Here, we report on 4 additional recipients, supporting the efficacy of our procedure. RESULTS: The first 2 additional recipients succumbed to porcine cytomegalovirus (PCMV) infections on Days 15 and 27, respectively. In 2 further experiments, PCMV infections were successfully avoided, and 3-months survival was achieved. Throughout all the long-term experiments, heart, liver, and renal functions remained within normal ranges. Post-mortem cardiac diameters were slightly increased when compared with that at the time of transplantation but with no detrimental effect. There were no signs of thrombotic microangiopathy. The current regimen enabled the prolonged survival and function of orthotopic cardiac xenografts in altogether 6 of 8 baboons, of which 4 were now added. These results exceed the threshold set by the Advisory Board of the International Society for Heart and Lung Transplantation. CONCLUSIONS: The results of our current and previous experimental cardiac xenotransplantations together fulfill for the first time the pre-clinical efficacy suggestions. PCMV-positive donor animals must be avoided.

Large Animal Models of Diabetes.

Safe and reliable large animal diabetes models are a key prerequisite for advanced preclinical studies on diabetes. Chemical induction is the standard model of diabetes in rodents but is often critiqued in higher animals due to reduced efficacy, relevant side effects, and inadequate mortality rate. In this chapter, we aim to describe both pharmacological and surgical approaches for reproducible and safe diabetes models in minipigs and primates. In addition, genetically modified pig models for diabetes research are described.

Author Correction: Consistent success in life-supporting porcine cardiac xenotransplantation.

In this Letter, Mayuko Kurome and Valeri Zakhartchenko have been added to the author list (affiliated with Institute of Molecular Animal Breeding and Biotechnology, Gene Center, LMU Munich, Munich, Germany). The author list and 'Author contributions' section have been corrected online; see accompanying Amendment.

Seroprevalence of viral infections in captive rhesus and cynomolgus macaques.

Macaques serve as important animal models for biomedical research. Viral infection of macaques can compromise animal health as well as the results of biomedical research, and infected animals constitute an occupational health risk. Therefore, monitoring macaque colonies for viral infection is an important task. We used a commercial chip-based assay to analyze sera of 231 macaques for the presence of antibody responses against nine animal and human viruses. We report high seroprevalence of cytomegalovirus (CMV), lymphocryptovirus (LCV), rhesus rhadinovirus (RRV) and simian foamy virus (SFV) antibodies in all age groups. In contrast, antibodies against simian retrovirus type D (SRV/D) and simian T cell leukemia virus (STLV) were detected only in 5 % and 10 % of animals, respectively, and were only found in adult or aged animals. Moreover, none of the animals had antibodies against herpes B virus (BV), in keeping with the results of in-house tests previously used for screening. Finally, an increased seroprevalence of measles virus antibodies in animals with extensive exposure to multiple humans for extended periods of time was observed. However, most of these animals were obtained from external sources, and a lack of information on the measles antibody status of the animals at the time of arrival precluded drawing reliable conclusions from the data. In sum, we show, that in the colony studied, CMV, LCV, RRV and SFV infection was ubiquitous and likely acquired early in life while SRV/D and STLV infection was rare and likely acquired during adulthood.

Consistent success in life-supporting porcine cardiac xenotransplantation.

Heart transplantation is the only cure for patients with terminal cardiac failure, but the supply of allogeneic donor organs falls far short of the clinical need1-3. Xenotransplantation of genetically modified pig hearts has been discussed as a potential alternative4. Genetically multi-modified pig hearts that lack galactose-α1,3-galactose epitopes (α1,3-galactosyltransferase knockout) and express a human membrane cofactor protein (CD46) and human thrombomodulin have survived for up to 945 days after heterotopic abdominal transplantation in baboons5. This model demonstrated long-term acceptance of discordant xenografts with safe immunosuppression but did not predict their life-supporting function. Despite 25 years of extensive research, the maximum survival of a baboon after heart replacement with a porcine xenograft was only 57 days and this was achieved, to our knowledge, only once6. Here we show that α1,3-galactosyltransferase-knockout pig hearts that express human CD46 and thrombomodulin require non-ischaemic preservation with continuous perfusion and control of post-transplantation growth to ensure long-term orthotopic function of the xenograft in baboons, the most stringent preclinical xenotransplantation model. Consistent life-supporting function of xenografted hearts for up to 195 days is a milestone on the way to clinical cardiac xenotransplantation7.

Favorable outcome of experimental islet xenotransplantation without immunosuppression in a nonhuman primate model of diabetes.

Transplantation of pancreatic islets for treating type 1 diabetes is restricted to patients with critical metabolic lability resulting from the need for immunosuppression and the shortage of donor organs. To overcome these barriers, we developed a strategy to macroencapsulate islets from different sources that allow their survival and function without immunosuppression. Here we report successful and safe transplantation of porcine islets with a bioartificial pancreas device in diabetic primates without any immune suppression. This strategy should lead to pioneering clinical trials with xenotransplantation for treatment of diabetes and, thereby, represents a previously unidentified approach to efficient cell replacement for a broad spectrum of endocrine disorders and other organ dysfunctions.

Characterization of the 10q26-orthologue in rhesus monkeys corroborates a functional connection between ARMS2 and HTRA1.

Age-related macular degeneration, which is the leading cause of blindness in industrialized countries, is a multifactorial, degenerative disorder of the macula with strong heritability. For age-related macular degeneration in humans, the genes ARMS2 and HTRA1 in the region 10q26 are both promising candidates for being involved in pathogenesis. However, the associated variants are located in a region of strong linkage disequilibrium and so far, the identification of the causative gene in humans was not yet possible. This dilemma might be solved using an appropriate model organism. Rhesus monkeys suffer from drusen, a major hallmark of age-related macular degeneration, and the drusen-phenotype shares susceptibility factors with human macular degeneration. Thus, the rhesus monkey represents a natural animal model to uncover genetic factors leading to macular degeneration. Moreover, the existence of genetically homogenous cohorts offers an excellent opportunity to determine risk factors. However, the 10q26-orthologue genomic region in rhesus monkeys is not characterized in detail so far. Therefore, the aim of this study is to analyze the rhesus linkage disequilibrium structure and to investigate whether variants in ARMS2 or HTRA1 are associated with the drusen-phenotype as well. We sequenced parts of a 20 kb region around ARMS2 and HTRA1 in a genetically homogeneous cohort of 91 rhesus monkeys descending from the CPRC rhesus cohort on Cayo Santiago and currently housed in the German Primate Centre in Göttingen. Within this group, ophthalmoscopic examinations revealed a naturally high drusen prevalence of about 47% in monkeys >5 years. We detected 56 genetic variants within and around ARMS2 and HTRA1 and, as one deviates from Hardy-Weinberg-Equilibrium, 55 polymorphisms were used to generate a linkage disequilibrium-Plot and to perform association studies. We observed strong linkage disequilibrium between the markers and were able to define two haplotype blocks. One of these blocks spanned the whole ARMS2 locus and the 5' part of HTRA1 - almost perfectly resembling the situation found in humans. Tests for association revealed a variant in the promoter region of HTRA1 and two variants in the 5'-UTR of ARMS2 to be associated with drusen. The strong linkage disequilibrium inhibits - as in humans - a determination of the risk gene using statistical methods only. However, the conserved linkage disequilibrium structure in humans and macaques goes in line with the recently emerged dual causality model proposing that ARMS2 and HTRA1 are functionally connected and that both genes contribute to the disease pathology. Moreover, the characterization of the 10q26-orthologue genomic region of the rhesus monkey provides a basis for now needed functional investigations in a well-characterized model organism.