Transmission of porcine endogenous retrovirus in xenotransplantation / 器官移植

Organ transplantation is the most effective treatment for various types of end-stage diseases. To resolve the problem of donor shortage in organ transplantation, the possibility of xenotransplantation has been gradually explored by surgeons. Pig is one of the common donor sources for xenotransplantation. As a bridge between two species, the viruses carried by pig organs may be transmitted between species and cause the risk of zoonosis. Porcine endogenous retrovirus (PERV) is integrated into the genome, which is a category of retrovirus featuring cross-species transmission. In this article, the influencing factors of transmission characteristics of PERV, the transmission risk of PERV and its recombinant virus, and the detection and transmission risk assessment of PERV in xenotransplantation test were reviewed, aiming to provide reference for alleviating severe shortage of donor organs and driving the advancement of xenotransplantation technologies.

Preliminary report of preclinical trial of multi-genome engineering pig-to-macaque heart, liver and kidney transplantation / 器官移植

Objective To investigate the application prospect of the most extensive genome engineering pig internationally in preclinical xenotransplantation. Methods Porcine endogenous retrovirus (PERV) knockout combined with 3 major heterologous antigen gene knockouts and 9 humanized genes for inhibition of complement activation, regulation of coagulation disorders, anti-inflammatory and anti-phagocytosis were transferred into a pig (PERV-KO/3-KO/9-TG) as a donor, and the heart, liver and kidney were obtained and transplanted to 3 Rhesus macaque recipients respectively to establish a preclinical research model of pig-to-Rhesus macaque xenotransplantation. The functional status of xenografts after blood flow reconstruction was observed and the survival of recipients was summarized. The hemodynamics of xenografts were monitored. The change of hematological indexes of each recipient was compared. The histopathological manifestation of xenografts was observed. Results After the blood flow was reconstructed, all xenografts showed ruddy color, soft texture and good perfusion. The transplant heart, liver and kidney showed full arterial and venous blood flow and good perfusion at 1 d after operation. The postoperative survival time of heart, liver, and kidney transplant recipients was 7, 26, and 1 d, respectively. The levels of creatine kinase, creatine kinase isoenzyme, and lactate dehydrogenase increased in heart transplant recipient at 1 d after operation, and gradually recovered to near normal levels at 6 d after operation. All indexes increased sharply at 7 d after operation. The level of aspartate aminotransferase increased in liver transplant recipients at 2 d after operation, and the alanine aminotransferase basically returned to normal at 10 d after operation, but the total bilirubin continued to increase. Both aspartate aminotransferase and alanine aminotransferase increased at 12 d after operation, and reached a peak at 15 d after operation. The kidney transplant recipient developed mild proteinuria at 1 d after operation, and died of sudden severe arrhythmia. Histopathology showed that the tissue structure of cardiac and renal xenografts was close to normal, and liver xenografts presented with patchy necrosis, the liver tissue structure was disordered, accompanied by inflammatory damage, interstitial hemorrhage and thrombotic microangiopathy. Conclusions PERV-KO/3-KO/9-TG pig shows advantages in overcoming hyperacute rejection, mitigating humoral rejection and coagulation dysregulation. However, whether it can be used as potential donor for clinical xenotransplantation needs further evaluation.

Regulation of porcine endogenous retrovirus by dual LTR1+2 (Long Terminal Region) miRNA in primary porcine kidney cells

Porcine endogenous retroviruses (PERVs) integrate into germline DNA as proviral genome that enables vertical transmission from parents to their offspring. The provirus usually survives as part of the host genome rather than as an infectious agent, but may become pathogenic if it crosses species barriers. Therefore, replication-competent PERV should be controlled through selective breeding or knockout technologies. Two microRNAs (miRNAs), dual LTR1 and LTR2, were selected to inhibit the expression of PERV in primary porcine kidney cells. The inhibition efficiency of the miRNAs was compared based on their inhibition of different PERV regions, specifically long terminal repeats (LTRs), gag, pol, and env. Gene expression was quantified using real-time polymerase chain reaction and the C-type reverse transcriptase (RT) activity was determined. The messenger RNA (mRNA) expression of the PERV LTR and env regions was determined in HeLa cells co-cultured with primary porcine kidney cells. The mRNA expression of the LTR, gag, pol, and env regions of PERV was dramatically inhibited by dual miRNA from 24 to 144 h after transfection, with the highest inhibition observed for the LTR and pol regions at 120 h. Additionally, the RT activity of PERV in the co-culture experiment of porcine and human cells was reduced by 84.4% at the sixth passage. The dual LTR 1+2 miRNA efficiently silences PERV in primary porcine kidney cells.

Analysis of env Subtypes of Porcine Endogenous Retrovirus in SNU Miniature Pigs

All xenografts from pigs impose infection risk by porcine endogenous retrovirus (PERV). The purpose of this study was to investigate the env constructs with the comparison of the ratio of the competent form to the defective one of env in subtypes, PERV-A, PERV-B and PERV-C in different pig breeds. The results of PCR amplification of env represented that all env subtypes had more than two defective forms which cannot bind to host cells due to the absence of binding regions of env in miniature pigs, SNU and PWG, and farm pig breeds, Duroc, Yorkshire and Landrace. In addition, comparing the full sequences with the defective ones in three subtypes demonstrated that the present percentages of env sequences in defective PERV-A, PERV-B and PERV-C were approximately 50%, 38~45% and 4~11%, respectively, in SNU and PWG pigs whereas PERV-A and PERV-B occupied around 40 to 60% but PERV-C was not detected in farm pigs. Quantitative real-time PCR assays with primers and probes targeted to proline-rich region (PRR) of each env subtype were done to measure the copy numbers of each env subtype. When the reference was set with copy number of PERV-A, the ratio of those of PERV-B and PERV-C to the reference were 1.5 to 6.0 folds high in SNU and PWG pigs while 1.0 or less in farm pigs. These contradictory results of PERV-C constructs and copy numbers in SNU pigs suggests that many truncated or short defective sequences of PERV-C might be present in them.

Transmission of zoonoses in xenotransplantation: Porcine endogenous retroviruses from an immunological and molecular point of view.

Background and Objectives: Pigs offer an unlimited source of xenografts for humans. The use of transplants from animal origin offers a potential solution to the limited supply of human organs and tissues. However, like many other mammalian species, pigs harbor porcine endogenous retrovirus (PERV), which are encoded in their genomic DNA and are assumed to have been integrated into the porcine germ line more than 7.6 × 106 years ago and showing that the age correlates with the time of separation between pigs and peccaries 7.4 × 106 years ago. The ability of the PERV to infect human cells in vitro has heightened safety concerns regarding the transmission of PERV to pig xenograft recipients. In this study, we detected PERV-AC recombinant virus in porcine genomic DNA that may have resulted from exogenous viral recombination. Infectious risk in xenotransplantation will be defined by the activity of PERV loci in vivo. We identified unique Haemophilus aegyptius III HaeIII gag restriction fragment length polymorphism (RFLP) profiles resulting from single nucleotide polymorphisms; these were found only in animals that produced human tropic PERV. Materials and Methods: Porcine tissues were analyzed using validated assays specific for PERV: polymerase chain reaction (PCR) (for PERV DNA), RT-PCR (for PERV RNA), cell culture, RFLP analysis, and sequence analysis. Conclusions and Interpretation : These findings have demonstrated that the presence of both DNA and RNA forms of porcine endogenous retrovirus in porcine tissues needs to be carefully considered when the infectious disease potential of xenotransplantation is being assessed.

The factors influencing the transfer of porcine endogenous retroviruses across the membrane in bioartificial livers / 中华肝胆外科杂志

ObjectiveTo identify the factors influencing the transfer of porcine endogenous retroviruses across the membrane of a new bioartificial liver (BAL),which is a necessary caution to consider for BALs carrying porcine hepatocytes.MethodsA novel porcine BAL composed of two circuits was constructed using a plasma filter with membrane pore size of 500 nm and a plasma component separator with membrane pore sizes 10 nm,20 nm,30 nm,and 35 nm.Co-cultured cells of porcine hepatocytes and mesenchymal stem cells or single porcine hepatocytes were incubated in the bioreactors.The BAL was continuously worked for 72 hours during which the supernatant was collected from the internal and external circuits every 12 hours.PERV RNA,reverse transcriptase (RT) activity,and in vitro infectivity from the supernatant were detected.ResultsIn the plasma filter group,the PERV RNAlevels were the same in both circuits,suggesting little to no effect of the plasma filter on the PERV RNA's crossing.With plasma component separators,PERV RNA was found in the external circuits at different times without positive RT activity and HEK293 cell infection,but its level was reduced significantly.The larger the membrane pore size was,the earlier and the more RNA was detected.ConclusionsThe membrane pore size,the treatment time and the viral level in the internal circuit are contributing factors influencing the transfer of PERV RNA across the membrane in a BAL.

Detection of Human Cytomegalovirus (HCMV) and Porcine Endogenous Retrovirus (PERV) with One Step Extraction Method / 감염과화학요법

BACKGROUND: Xenotransplantation is thought to be one of the alternative methods to overcome the shortage of human organs for transplantation. Recipients should be immunosuppressed for graft survival, and thus, there is a need for developing diagnostic modality that can detect diverse infections originating from animals and recipients rapidly, in the early stage, and with high sensitivity using small volume of samples. This study was carried out to develop a fast, simple, and robust technique for the preparation of HCMV DNA and PERV RNA using small volume of samples. MATERIALS AND METHODS: Nucleic acids were extracted from serially diluted samples with one step extraction method as well as with Qiagen kit. The presence of genomic DNA of human cytomegalovirus (HCMV) and porcine endogenous retrovirus (PERV) was detected by PCR and specific primer set, respectively. RNA of HCMV and PERV was extracted and then detected by RT-PCR and specific primer set, respectively. For absolute quantification of HCMV, standard curve was established by real time PCR. RESULTS: HCMV DNA and PERV RNA were prepared from culture supernatant and cells for PCR or RT-PCR with one step extraction method. It was possible to extract both the DNA and RNA from the samples in about 20 minutes with one step extraction method in a single tube. HCMV and PERV could also be detected by PCR and one step extraction method, respectively. It was also good with small quantity samples. CONCLUSIONS: One step extraction method is simpler and faster method than other extraction methods when there are two types of DNA and RNA viruses in one sample. From these results, we could see that the one step extraction method could be very useful in detecting HCMV and PERV rapidly from the pig cells or organ transplanted recipients with a small amount of sample.

No Evidence of the Productive Replication of Porcine Endogenous Retrovirus (PERV) from SNU Miniature Pigs in Human Cell Line / 감염과화학요법

BACKGROUND: The presence of porcine endogenous retrovirus (PERV) has been considered as one of the main hurdles to transplant pig's organs or tissues to human beings. There has been no report that PERV infection is associated with human diseases. Because pigs have their own characteristics of PERV according to pig strain, it is necessary to analyze the infectivity of PERV from SNU miniature pig to human cells for future utilization as a transplantation donor. MATERIALS AND METHODS: Human cell lines were infected with culture supernatant from porcine cell line or immunomodulator-stimulated peripheral blood mononuclear cells (PBMC) of SNU miniature pigs. They were also co-cultured with PBMC or islet cells of SNU miniature pigs. The presence of PERV genes and general pig marker gene in cells was determined by nested PCR with primer set for PERV pol and pig mitochondrial cytochrome oxidase II (COII), respectively. RESULTS: Infection test with the culture supernatant from PBMC of SNU miniature pigs showed that PERV pol but not COII was detected only in a few cases, but there was no uniform infection pattern in scope of stimulators and cell types. PERV pol was not demonstrated in co-cultures of human cell line with PBMC or islet cells from SNU miniature pigs after 80 days of co-cultures. CONCLUSIONS: In vitro infectivity test suggests that PERV from SNU miniature pig might not replicate productively in human cell lines although it could infect human cells and integrate into chromosome.

Analysis of the differential expression of Stathmin in HEK293 cells infected with human-tropic porcine endogenous retrovirus / 中华微生物学和免疫学杂志

Objective To analyze the differential expression of Stathmin in human cells infected with human-tropic porcine endogenous retrovirus(PERV)and to explore the potential molecular effect of human-tropic PERV on human cells.Methods HEK293 cells were infected with the human-tropic PERV infectious molecular clone.PCR,real-time RT-PCR and immunofluorescence analysis were applied to confirm that HEK293 cells were infected.Then real-time RT-PCR and Western blot were carried out to analyze the differential expression of Stathmin at the mRNA level and protein level,respectively.Results HEK293 cells were infected by human-tropic PERV.Real-time RT-PCR and Western blot analysis showed that Stathmin was up-regulated in HEK293 cells infected with PERV compared with the control cells.Conclusion Stathmin was up-regulated in HEK293 cells infected with human-tropic PERV.These studies will be helpful for revealing the interaction of PERV and human cells,and for understanding the molecular effect of humantropic PERV on human cells.In addition,it suggested that PERV infection may infect cell growth and physiological functions,even be pathogenic.These will help to clarify the biologic characteristics of PERV and evaluate the safety of PERV in pig to human xenotransplantation.

Characterization of Clones of Human Cell Line Infected with Porcine Endogenous Retrovirus (PERV) from Porcine Cell Line, PK-15 / 감염과화학요법

BACKGROUND: Porcine endogenous retroviruses (PERVs) form part of the chromosomes of all pigs. Since they can be produced as infectious virion and infect human cells, safety issues on PERVs infection to human are still controversial and is one of main hurdles of xenotransplantation using pig cells or organs. It has been reported that the established porcine cell line, PK-15, produces PERVs and can infect the human cell lines. Therefore, clonal analysis on human cell line infected with PERV is a prerequisite to characterize the infectivity to human cells and to investigate the harmfulness of PERVs to human. MATERIALS AND METHODS: For the characterization of PERV that originates from porcine cell line, PK-15, full length PERV cloning from genomic DNA of PK-15 was performed and partial sequences of both ends were achieved. Cell clones from human cell line, 293, persistently infected with PERVs from PK-15 were established by the method of limiting dilution. Nested PCR and direct sequencing of PCR products in each clone were carried out so as to confirm the PERV genomes in each clone. The growth rate of each clone was checked using cell counting and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, the infectivity by reverse transcriptase (RT) assay, and genetic analysis by karyotyping. RESULTS: A total of 12 genomic PERV clones could be retrieved; 1 with full length, 4 with defective forms, and others with irrelevant sequences. Intact PERV was thought to be able to infect 293 and the PERV-infected cell clones were selected by limiting dilution. PCR results confirmed that nine cell clones were infected with PERV, and sequence alignment data on PCR products of pol region from PK-15 and human cell clones with PERV showed very similar results. Cell counting and MTT assay for growth kinetics of each clone indicated that two clones showed reduced growth rate. However, it was difficult to verify the effect of PERV infection on the cell growth because of the presence of many genetic alterations in 293 parental cells. No RT activities were detected in the culture supernatant from PERV-infected 293 cell clones. CONCLUSION: The sequences of PERVs were detected in human cell clones after PERV infection, but PERV virions could not be detected from the culture supernatant by RT assay.

Characterization of Clones of Human Cell Line Infected with Porcine Endogenous Retrovirus (PERV) from Porcine Cell Line, PK-15 / 감염과화학요법

BACKGROUND: Porcine endogenous retroviruses (PERVs) form part of the chromosomes of all pigs. Since they can be produced as infectious virion and infect human cells, safety issues on PERVs infection to human are still controversial and is one of main hurdles of xenotransplantation using pig cells or organs. It has been reported that the established porcine cell line, PK-15, produces PERVs and can infect the human cell lines. Therefore, clonal analysis on human cell line infected with PERV is a prerequisite to characterize the infectivity to human cells and to investigate the harmfulness of PERVs to human. MATERIALS AND METHODS: For the characterization of PERV that originates from porcine cell line, PK-15, full length PERV cloning from genomic DNA of PK-15 was performed and partial sequences of both ends were achieved. Cell clones from human cell line, 293, persistently infected with PERVs from PK-15 were established by the method of limiting dilution. Nested PCR and direct sequencing of PCR products in each clone were carried out so as to confirm the PERV genomes in each clone. The growth rate of each clone was checked using cell counting and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, the infectivity by reverse transcriptase (RT) assay, and genetic analysis by karyotyping. RESULTS: A total of 12 genomic PERV clones could be retrieved; 1 with full length, 4 with defective forms, and others with irrelevant sequences. Intact PERV was thought to be able to infect 293 and the PERV-infected cell clones were selected by limiting dilution. PCR results confirmed that nine cell clones were infected with PERV, and sequence alignment data on PCR products of pol region from PK-15 and human cell clones with PERV showed very similar results. Cell counting and MTT assay for growth kinetics of each clone indicated that two clones showed reduced growth rate. However, it was difficult to verify the effect of PERV infection on the cell growth because of the presence of many genetic alterations in 293 parental cells. No RT activities were detected in the culture supernatant from PERV-infected 293 cell clones. CONCLUSION: The sequences of PERVs were detected in human cell clones after PERV infection, but PERV virions could not be detected from the culture supernatant by RT assay.

Cultivation and identification of porcine skin fibroblasts / 第三军医大学学报

Objectives To establish an ideal cellular model for the study of infection of porcine endogenous retrovirus in intro and in vivo and to lay the foundation for evaluating the biological safety of xenotransplantation. Methods Porcine skin fibroblasts were cultured by tissue pieces, cold trypsin, and heat trypsin, respectively. The merit and defect of these methods were analyzed. Results Porcine skin fibroblast line was established and the tissue piece method was superior to trypsin methods. Conclusion Culture of porcine skin fibroblasts with tissue pieces is superior to trypsin method, with the characteristics of low cost and easy operation. The established porcine skin fibroblast cell line supplies an ideal cell model for the study of infection of porcine endogenous retrovirus in vitro and in vivo, provides a new method for the evaluation of biological safety of xenotransplantation, and plays an important role in the skin culture model of production of cloned animals.

Polymerase Chain Reaction Detection for Porcine Endogenous Retrovirus in 4 Pig Cell Lines / 中国兽医学报

Porcine endogenous retroviruses (PERV) can infect human cell in vitro, which raised widely concerns re-garding the transmission of PERV to xenograft recipients. It's essential to establish a method for detection of PERV.3 pairs of primers were synthesized according to the sequence of gag, pol and env gene of PERV. Polymerase chainreaction (PCR) and reverse transcription PCR (RT-PCR) assays were performed for detection of PERV provirusDNA and PERV specific mRNA. The results showed that provirus DNA and mRNA of PERV existed and expressedin all 4 tested cell lines. The sizes of amplified fragments are identical with the predicted. These methods may be suit-able for monitoring PERV in other cells or tissue.