Prevalence of porcine endogenous retrovirus in domestic pigs in Japan and its potential infection in dogs xenotransplanted with porcine pancreatic islet cells

Promoter activity analysis and methylation characterization of LTR elements of PERVs in NIH miniature pig

The potential risk of porcine endogenous retrovirus (PERV) transmission is an important issue in xenotransplantation (pig-to-human transplantation). Long terminal repeats (LTRs) in PERV elements show promoter activity that could affect neighboring functional genes. The methylation status and promoter activities of 3 LTR structures (PERV-LTR1, LTR2, and LTR3 elements) belonging to the PERV-A family were examined using luciferase reporter genes in human liver cell lines (HepG2 and Hep3B). The PERV LTR3 element exhibited hypomethylation and stronger promoter activity than the other LTR elements in human liver cells. We also performed comparative sequences analysis of the PERV LTR elements by using bioinformatics tools. Our findings showed that several transcription factors such as Nkx2-2 and Elk-1 positively influenced the high transcriptional activity of the PERV LTR3 element.

Suboptimal porcine endogenous retrovirus infection in non-human primate cells: implication for preclinical xenotransplantation

Background

Porcine endogenous retrovirus (PERV) poses a potential risk of zoonotic infection in xenotransplantation. Preclinical transplantation trials using non-human primates (NHP) as recipients of porcine xenografts present the opportunity to assess the zoonosis risk in vivo. However, PERV poorly infects NHP cells for unclear reasons and therefore NHP may represent a suboptimal animal model to assess the risk of PERV zoonoses. We investigated the mechanism responsible for the low efficiency of PERV-A infection in NHP cells.

Principal Findings

Two steps, cell entry and exit, were inefficient for the replication of high-titer, human-tropic A/C recombinant PERV. A restriction factor, tetherin, is likely to be responsible for the block to matured virion release, supported by the correlation between the levels of inhibition and tetherin expression. In rhesus macaque, cynomolgus macaque and baboon the main receptor for PERV entry, PERV-A receptor 1 (PAR-1), was found to be genetically deficient: PAR-1 genes in these species encode serine at amino acid 109 in place of the leucine in human PAR-1. This genetic defect inevitably impacts in vivo sensitivity to PERV infection of these species. In contrast, African green monkey (AGM) PAR-1 is functional, but PERV infection is still poor. Although the mechanism is unclear, tunicamycin treatment, which removes N-glycosylated sugar chains, increases PERV infection, suggesting a possible role for the glycosylation of the receptors.

Conclusions

Since cynomolgus macaque and baboon, species often used in pig-to-NHP xenotransplantation experiments, have a defective PAR-1, they hardly represent an ideal animal model to assess the risk of PERV transmission in xenotransplantation. Alternatively, NHP species, like AGM, whose both PARs are functional may represent a better model than baboon and cynomolgus macaque for PERV zoonosis in vivo studies.

Investigation of porcine endogenous retrovirus in the conservation population of Ningxiang pig

Porcine endogenous retrovirus (PERV) varies between pig breeds. Screening and analysis of PERV in putative pig breeds may provide basic parameters to evaluate the biological safety of xenotransplantation from pigs to humans. In this study, PERV was investigated among the conservation population of the Ningxiang pig. The result revealed that the genotype of PERV distribution was subtype A, 100%; subtype B, 100%; and subtype C, 100%. The env sequences of PERV-A and -B showed 11 clones detected by KpnI and MboI digestion, indicating that there existed multiple variants of PERV-A and -B in the Ningxiang pig. Reverse transcriptase polymerase chain reaction results showed that PERV had transcriptional activity in these individuals. In addition, PERV A/C recombinant was detected in most individuals of Ningxiang pig. Because PERV A/C recombinants increase the potential infectious risk, the breed may not be a proper donor for xenotransplantation.

Prevalence of porcine endogenous retroviruses in domestic, minature, and genetically modified pigs in Japan

The present study examined the prevalence of porcine endogenous retroviruses (PERV) in pigs available in Japan using polymerase chain reaction (PCR) with primers specific for PERV-A, PERV-B, and PERV-C and for the full-length 5' to 3' long terminal repeat and using PCR-Southern blotting with env A-, env B-, env C-, and pol/pro-specific probes. All 376 pigs tested--Berkshire (B), Landrace (L), Duroc (D), Large White (W), miniature, and genetically modified triple-cross breed (LWD)--harbored both PERV-A and PERV-B genes. However, the prevalence of PERV-C differed among pigs: LWD, miniature, B, D, W, and L pigs were 100% (36/36), 83% (5/6), 68% (129/191), 52% (26/50), 21% (9/43), and 16% (8/50), respectively. These results show that W and L pigs may be preferable as xenotransplantation donors, because they may not produce human-tropic replication-competent hybrids of PERV-A and PERV-C.

Multilayer nanoencapsulation. New approach for immune protection of human pancreatic islets

Immune protection of artificial tissue by means of pancreatic islet microencapsulation is a very ambitious new approach to avoid life-long immune suppression. But the success in the utilization of the alginate-beads with incorporated islets is unfortunately limited. Some of the problems cannot be solved by a two-component system, so polymer encapsulation of the microbeads was tested to improve the properties. In the present paper a pure nanoencapsulation multilayer approach was tested in order to reduce the size of the capsule and possibly apply in the future a multilayer capsule with individual properties in each layer or region of the capsule. Different polycations were attached in a self-assembly process. The advantage in using the surface charge of islets as binding site for the polyions is the guarantee of complete coverage after the second layer. Release of insulin was determined to characterize the function of the islets after encapsulation as well as the permeability of the capsule. Fluorescence microscopy was used to visualize the polyelectrolyte layers. Finally by means of an immune assay, the protection capability of the capsule was proved. In these first measurements the encapsulation with a multilayer nanocapsule was shown to be a possible alternative to the more space-consuming and random islet-trapping microencapsulation.

Functional Assessment of Microencapsulated Porcine Islets With Agarose Polystyrene Sulfonic Acid In Vitro and in Xenotransplantation

We evaluated the functional efficacy of microencapsulated porcine islet xenografts transplanted into nonobese diabetic (NOD) mice. Islets were isolated from the pancreata of CSK miniature swine by manual collagenase digestion and Ficoll purification. Purified porcine islets were immediately encapsulated into microbeads of agarose polystyrene sulfonic acid (Ag-PSSa). They remained morphologically intact by dithizone staining after 7 days in culture. Insulin secretion from encapsulated islets was determined in response to glucose challenge during perifusion. When encapsulated islets were exposed to 200 mg/dL glucose, within 5 minutes, insulin release became 5-fold greater than that at 80 mg/dL. However, a second phase insulin secretion appeared in response to 250 mg/dL glucose challenge. In xenotransplantation, microencapsulated porcine islets (1000 to 1800 MC islets) were transplanted into the peritoneal cavity of diabetic NOD mice (n = 4) without immunosuppression. The survival times after the onset of diabetes were observed after both MC islets transplanted NOD mice and nontransplanted NOD mice (n = 4). MC islets transplant recipients had significantly (P < .05) longer survival (47.5 +/- 18.6; mean +/- SD) than nontransplanted NOD mice (21.0 +/- 9.31), although random blood glucose levels were not normalized.

Diabetes mellitus: rational basis, clinical approach and future therapy

Clinical islet transplantation has recently received a strong impulse from the results obtained with the introduction of the Edomonton group. However, islet transplantation is at present a minimally invasive procedure and offers for the future the unique possibility of being performed under donor-specific tolerant conditions because islets may potentially be engineered in vitro. In addition, various approaches such as in vitro islet expansion, or xenogenic islets could make the availability of donor tissues unlimited. Recent advances in tissue engineering (technology) and cell biology may allow for the development of novel strategies for the treatment and cure of type I diabetes. In particular, it is now possible to envisage restoration of insulin secretion by cell-replacement therapy. And it will be necessary to ensure that implanted beta-cells are protected in some way from recognition by the immune system (a bio-artificial endocrine pancreas).