No in vivo infection of triple immunosuppressed non-human primates after inoculation with high titers of porcine endogenous retroviruses

The prevention strategies of swine viruses related to xenotransplantation

Xenotransplantation is considered a solution for the shortage of organs, and pigs play an indispensable role as donors in xenotransplantation. The biosecurity of pigs, especially the zoonotic viruses carried by pigs, has attracted attention. This review introduces several viruses, including porcine endogenous retroviruses that are integrated into the pig genome in a DNA form, herpesviruses that have been proven to clearly affect recipient survival time in previous xenotransplant surgeries, the zoonotic hepatitis E virus, and the widely distributed porcine circoviruses. The detail virus information, such as structure, caused diseases, transmission pathways, and epidemiology was introduced in the current review. Diagnostic and control measures for these viruses, including detection sites and methods, vaccines, RNA interference, antiviral pigs, farm biosecurity, and drugs, are discussed. The challenges faced, including those posed by other viruses and newly emerged viruses, and the challenges brought by the modes of transmission of the viruses are also summarized.

Why was PERV not transmitted during preclinical and clinical xenotransplantation trials and after inoculation of animals?

Porcine endogenous retroviruses (PERVs) are present in the genome of all pigs, they infect certain human cells and therefore pose a special risk for xenotransplantation using pig cells, tissues and organs. Xenotransplantation is being developed in order to alleviate the reduced availability of human organs. Despite the fact that PERVs are able to infect certain human cells and cells from other species, transmission of PERVs has not been observed when animals (including non-human primates) were inoculated with PERV preparations or during preclinical xenotransplantations. The data indicate that PERVs were not transmitted because they were not released from the transplant or were inhibited by intracellular restriction factors and innate immunity in the recipient. In a single study in guinea pigs, a transient PERV infection and anti-PERV antibodies were described, indicating that in this case at least, the immune system may also have been involved.

[Renal transplantation in 2046: Future and perspectives]

OBJECTIVES

To report major findings that may build the future of kidney transplantation.

MATERIAL AND METHODS

Relevant publications were identified through Medline (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) database from 1960 to 2016 using the following keywords, in association, "bio-engineering; heterotransplantation; immunomodulation; kidney; regenerative medicine; xenotransplantation". Articles were selected according to methods, language of publication and relevance. A total of 5621 articles were identified including 2264 for xenotransplantation, 1058 for regenerative medicine and 2299 for immunomodulation; after careful selection, 86 publications were eligible for our review.

RESULTS

Despite genetic constructs, xenotransplantation faces the inevitable obstacle of species barrier. Uncertainty regarding xenograft acceptance by recipients as well as ethical considerations due to the debatable utilization of animal lives, are major limits for its future. Regenerative medicine and tridimensional bioprinting allow successful implantation of organs. Bioengineering, using decellularized tissue matrices or synthetic scaffold, seeded with pluripotent cells and assembled using bioreactors, provide exciting results but remain far for reconstituting renal complexity and vascular patency. Immune tolerance may be achieved through a tough initial T-cell depletion or a combined haplo-identical bone marrow transplant leading to lymphohematopoietic chimerism.

CONCLUSION

Current researches aim to increase the pool of organs available for transplantation (xenotransplants and bio-artificial kidneys) and to increase allograft survival through the induction of immune tolerance. Reported results suggest the onset of a thrilling new era for renal transplantation providing end-stage renal disease-patients with an improved survival and quality of life.

Virus safety of islet cell transplantation from transgenic pigs to marmosets

Transplantation of pig islet cells for the treatment of diabetes may be a more effective approach compared with the application of insulin. However, before introduction into the clinic, efficacy and safety of this treatment have to be shown. Non-human primate models may be used for this, despite the fact that they are characterised by several limitations. Here we investigate the prevalence of porcine endogenous retroviruses (PERVs), which are present in the genome of all pigs and which may infect human cells, as well as of porcine herpes viruses in donor pigs and their potential transmission to non-human primate recipients. Despite the fact that all three subtypes of PERV were present in all and porcine cytomegalovirus (PCMV) was found in some of the pigs, neither PERVs nor PCMV were found in the recipient animals under the experimental conditions applied. Porcine lymphotropic herpes viruses (PLHV) were not found in the donor pigs, hepatitis E virus (HEV) was not found in the recipients.

Immune modulation in xenotransplantation

The use of animals as donors of tissues and organs for xenotransplantations may help in meeting the increasing demand for organs for human transplantations. Clinical studies indicate that the domestic pig best satisfies the criteria of organ suitability for xenotransplantation. However, the considerable phylogenetic distance between humans and the pig causes tremendous immunological problems after transplantation, thus genetic modifications need to be introduced to the porcine genome, with the aim of reducing xenotransplant immunogenicity. Advances in genetic engineering have facilitated the incorporation of human genes regulating the complement into the porcine genome, knockout of the gene encoding the formation of the Gal antigen (α1,3-galactosyltransferase) or modification of surface proteins in donor cells. The next step is two-fold. Firstly, to inhibit processes of cell-mediated xenograft rejection, involving natural killer cells and macrophages. Secondly, to inhibit rejection caused by the incompatibility of proteins participating in the regulation of the coagulation system, which leads to a disruption of the equilibrium in pro- and anti-coagulant activity. Only a simultaneous incorporation of several gene constructs will make it possible to produce multitransgenic animals whose organs, when transplanted to human recipients, would be resistant to hyperacute and delayed xenograft rejection.

Comparison of porcine endogenous retroviruses infectious potential in supernatants of producer cells and in cocultures

BACKGROUND

Porcine endogenous retroviruses (PERV) pose a zoonotic risk potential in pig-to-human xenotransplantation given that PERV capacity to infect different human cell lines in vitro has been clearly shown in the past. However, PERV infectious potential for human peripheral blood mononuclear cells (huPBMC) has been also demonstrated, albeit with controversial results. As productive PERV infection of huPBMC involves immune suppression that may attract opportunistic pathogens as shown for other retroviruses, it is crucial to ascertain unequivocally huPBMC susceptibility for PERV. To address this question, we first investigated in vitro infectivity of PERV for huPBMC using supernatants containing highly infectious PERV-A/C. Second, huPBMC were cocultivated with PERV-A/C producer cells to come a step closer to the in vivo situation of xenotransplantation. In addition, cocultivation of huPBMC with porcine PBMC (poPBMC) isolated from German landrace pigs was performed to distinguish PERV replication competence when they were constitutively produced by immortalized cells or by primary poPBMC.

METHODS

Supernatants containing recombinant highly infectious PERV-A/C were used to infect PHA-activated huPBMC in the presence or absence of polybrene. Next, PERV-producing cell lines such as human 293/5° and primary mitogenically activated poPBMC of three German landrace pigs were cocultivated with huPBMC as well as with susceptible human and porcine cell lines as controls. PERV infection was monitored by using three test approaches. The presence of provirus DNA in putatively infected cells was detected via sensitive nested PCR. Viral expression was determined by screening for the activity of gammaretroviral reverse transcriptase (RT) in cell-free supernatants of infected cells. Virus release was monitored by counting the number of packaged RNA particles in supernatants via PERV-specific quantitative one-step real-time reverse transcriptase PCR.

RESULTS

Porcine endogenous retroviruses-A/C in supernatants of human producer 293/5° cells was not able to infect huPBMC. Neither RT activity nor PERV copies were detected. Even provirus could not be detected displaying the inability of PERV-A/C to induce a productive infection in huPBMC. In cocultivation experiments only non-productive infection of huPBMC with PERV derived from 293/5° cell line and from PHA-activated poPBMC was observed by detection of provirus DNA in infected cells.

CONCLUSION

Recombinant PERV-A/C in supernatants of producer cells failed to infect huPBMC, whereas coculture experiments with producer cell lines lead to non-productive infection of huPBMC. PERV in supernatants seem to have not sufficient infectious potential for huPBMC. However, extensive PERV exposure to huPBMC via cocultivation enabled at least virus cell entry as provirus was detected by nested PCR. Furthermore, results presented support previous data showing German landrace pigs as low producers with negligible infectious potential due to the absence of replication-competent PERV in the genome. The low PERV expression profile and the lack of significant replication competence of German landrace pigs raise hope for considering these animals as putative donor animals in future pig-to-human xenotransplantation. Nonetheless, data imply that PERV still represent a virological risk in the course of xenotransplantation, as the presence of PERV provirus in host cells may lead to a provirus integration resulting in insertional mutagenesis and chromosomal rearrangements.

No evidence of viral transmission following long-term implantation of agarose encapsulated porcine islets in diabetic dogs

We have previously described the use of a double coated agarose-agarose porcine islet macrobead for the treatment of type I diabetes mellitus. In the current study, the long-term viral safety of macrobead implantation into pancreatectomized diabetic dogs treated with pravastatin (n = 3) was assessed while 2 dogs served as nonimplanted controls. A more gradual return to preimplant insulin requirements occurred after a 2nd implant procedure (days 148, 189, and >652) when compared to a first macrobead implantation (days 9, 21, and 21) in all macrobead implanted animals. In all three implanted dogs, porcine C-peptide was detected in the blood for at least 10 days following the first implant and for at least 26 days following the second implant. C-peptide was also present in the peritoneal fluid of all three implanted dogs at 6 months after 2nd implant and in 2 of 3 dogs at necropsy. Prescreening results of islet macrobeads and culture media prior to transplantation were negative for 13 viruses. No evidence of PERV or other viral transmission was found throughout the study. This study demonstrates that the long-term (2.4 years) implantation of agarose-agarose encapsulated porcine islets is a safe procedure in a large animal model of type I diabetes mellitus.

The efficacy of an immunoisolating membrane system for islet xenotransplantation in minipigs

Developing a device that protects xenogeneic islets to allow treatment and potentially cure of diabetes in large mammals has been a major challenge in the past decade. Using xenogeneic islets for transplantation is required in light of donor shortage and the large number of diabetic patients that qualify for islet transplantation. Until now, however, host immunoreactivity against the xenogeneic graft has been a major drawback for the use of porcine islets. Our study demonstrates the applicability of a novel immunoprotective membrane that allows successful xenotransplantation of rat islets in diabetic minipigs without immunosuppressive therapy. Rat pancreatic islets were encapsulated in highly purified alginate and integrated into a plastic macrochamber covered by a poly-membrane for subcutaneous transplantation. Diabetic Sinclair pigs were transplanted and followed for up to 90 days. We demonstrated a persistent graft function and restoration of normoglycemia without the need for immunosuppressive therapy. This concept could potentially offer an attractive strategy for a more widespread islet replacement therapy that would restore endogenous insulin secretion in diabetic patients without the need for immunosuppressive drugs and may even open up an avenue for safe utilization of xenogeneic islet donors.

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.

Optimisation of expression and purification of the feline and primate foamy virus transmembrane envelope proteins using a 96 deep well screen

The production of recombinant transmembrane proteins is due to their biochemical properties often troublesome and time consuming. Here the prokaryotic expression and purification of the transmembrane envelope proteins of the feline and primate foamy viruses using a screening assay for optimisation of expression in 96 deep well plates is described. Testing simultaneously various bacterial strains, media, temperatures, inducer concentrations and different transformants, conditions for an about twentyfold increased production were quickly determined. These small scale test conditions could be easily scaled up, allowing purification of milligram amounts of recombinant protein. Proteins with a purity of about 95% were produced using a new purification protocol, they were characterised by gel filtration and circular dichroism and successfully applied in immunological assays screening for foamy virus infection and in immunisation studies. Compared to the previously described protocol (M. Mühle, A. Bleiholder, S. Kolb, J. Hübner, M. Löchelt, J. Denner, Immunological properties of the transmembrane envelope protein of the feline foamy virus and its use for serological screening, Virology 412 (2011) 333-340), proteins with similar characteristics but about thirtyfold increased yields were obtained. The screening and production method presented here can also be applied for the production of transmembrane envelope proteins of other retroviruses, including HIV-1.

Improvements in human sperm quality by long-term in vitro co-culture with isolated porcine Sertoli cells

BACKGROUND

Spermatogenesis is a complex process where spermatogonial germ cells become spermatozoa with the indispensable support of Sertoli cells (SCs), which provide 'ad hoc' structural and nutritional support. Unfortunately, for most sperm dysfunctions, no therapies are yet available except assisted reproductive technologies (ART) that are based on the use of different culture media to preserve sperm in vitro. However, sperm culture is only possible for short periods of time, since long-term culture would invariably and irreversibly damage the cells with negative impact on their fertilization potential.

METHODS

Fresh sperm cells (5 ml of 20 × 10(6)/ml) were co-cultured with SCs layers, derived from prepubertal pig testes or incubated in cell free SC medium or BWW (Biggers, Whitten and Whittingham) medium for 2, 4 or 7 days. Sperm viability, motility, mitochondrial status, DNA fragmentation, chromatin integrity, intracellular calcium and acrosome status were assessed after every co-culture or incubation time, but capacitation and induction of acrosome reaction (AR) with progesterone was only evaluated after 7 days.

RESULTS

SCs layers derived from prepubertal pig testes (co-culture of sperm and SC feeder, CCSCF) were able to preserve normal sperm viability, motility and normal mitochondrial function, after 7 days of culture; CCSCF did not induce AR or hyperactivation of spermatozoa, keeping the sperm in a quiescent state for 7 days of culture. Nevertheless, the sperm were readily able to initiate AR after stimulation with progesterone.

CONCLUSIONS

CCSCF maintained good sperm viability and motility for 7 days. This approach could improve retention of sperm viability and motility during ART procedures and maintain sperm viability, during transfer between two distant Centres, avoiding the need for cryopreservation.

Towards xenotransplantation of pig islets in the clinic

PURPOSE OF REVIEW

Porcine islet xenotransplantation into humans faces two major hurdles - safety issues related to xenosis and xenorejection of the transplants. The former has been overcome mainly by selection of a suitable disease-free source herd.

RECENT FINDINGS

Four strategies have been employed to date to overcome the rejection, all of which have shown some efficacy in animal models.

SUMMARY

Immune suppression, Sertoli cell co-transplantation and microencapsulation have been tried in type 1 diabetic humans with some clinical benefit derived reported from the latter two. Unaware hypoglycemia in particular seems amenable to the microencapsulation approach.

Current development of bioreactors for extracorporeal bioartificial liver (Review)

The research and development of extracorporeal bioartificial liver is gaining pace in recent years with the introduction of a myriad of optimally designed bioreactors with the ability to maintain long-term viability and liver-specific functions of hepatocytes. The design considerations for bioartificial liver are not trivial; it needs to consider factors such as the types of cell to be cultured in the bioreactor, the bioreactor configuration, the magnitude of fluid-induced shear stress, nutrients' supply, and wastes' removal, and other relevant issues before the bioreactor is ready for testing. This review discusses the exciting development of bioartificial liver devices, particularly the various types of cell used in current reactor designs, the state-of-the-art culturing and cryopreservation techniques, and the comparison among many today's bioreactor configurations. This review will also discuss in depth the importance of maintaining optimal mass transfer of nutrients and oxygen partial pressure in the bioreactor system. Finally, this review will discuss the commercially available bioreactors that are currently undergoing preclinical and clinical trials.

Absence of infection in pigs inoculated with high-titre recombinant PERV-A/C

Porcine endogenous retroviruses (PERVs) represent a risk for xenotransplantation using pig cells or organs since they are integrated in the genome of all pigs and infect human cells in vitro. Recombinants between PERV-A and PERV-C have been described in pigs in vivo and found de novo integrated in the genome of somatic cells, but not in the germ line. To study whether PERV-A/C can infect and have a pathogenic effect in normal pigs, German landrace pigs were inoculated with high-titre PERV-A/C. No provirus integration was found in blood cells or in various tissues, and no antibody production was observed, indicating the absence of infection.

Pig islet xenotransplantation acceptance in a Latin-American diabetic population

Progress in porcine islet xenotransplantation has been accompanied by studies on acceptance of this new procedure by patients, health professionals or the general public. Such studies have not been done in the Latin-American population. We conducted a questionnaire in 108 diabetes patients (insulin-dependent, n = 53; insulin-independent, n = 55) in a public hospital in Argentina. The questions addressed the general perception of the xenotransplant procedure and specific items related to the outcome (achieving insulin independence, improvement in metabolic control, delay in emergence of diabetic complications, need for repeat procedures, potential of transfer of infectious viruses, association with psychological problems, and anticipated success in relation to achieving a cure). Eighty-six (79%) of the patients accepted islet xenotransplantation; this incidence was not different for insulin-dependent or insulin-independent patients, patients with or without complications, or patients with good or poor metabolic control. Also, over 75% of patients accepted the procedure if this is only associated with a reduction in insulin requirement, if the procedure just delays but not prevents the onset of complications, or if the procedure needs to be performed every 6 months. Fifty-seven percent of patients indicated acceptance even if the potential transmission of a virus infection cannot be completely ruled out: this outcome was not affected by the outbreak of the H1N1 flu epidemic during the conduct of this study. Forty percent of patients indicated that living with porcine cells in their body could give psychological problems. We conclude that this population of Latin-American diabetic patients shows a high acceptance rate of a porcine islet xenotransplantation product.

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.

Company profile: Tissue regeneration for diabetes and neurological diseases at Living Cell Technologies

Living Cell Technologies’ (LCT’s) cell-based therapeutic for Type 1 diabetes, DIABECELL®, comprises encapsulated porcine insulin-producing cells. DIABECELL is presently in a Phase II clinical trial in New Zealand following positive early results. The cells are implanted into the abdomen to replace the patient’s pancreatic β-islet cells that have been lost as a result of autoimmune disease. LCT is also developing brain choroid plexus cells for the treatment of neurologic diseases. The aim is to enhance the brain’s natural repair mechanism by implanting cells releasing neurotrophins. Choroid plexus cell implants alleviate disease in animal models of Parkinson’s disease, Huntington’s disease and stroke. LCT encapsulates all cells in alginate, permitting implantation without using immunosuppressive drugs.