[show abstract][hide abstract] ABSTRACT: Gammaretroviral and lentiviral vectors have been used successfully in several clinical gene therapy trials, although powerful enhancer elements have caused insertional mutagenesis and clonal dysregulation. Self-inactivating vectors with internal heterologous regulatory elements have been developed as potentially safer and more effective alternatives. Lentiviral vectors containing a ubiquitous chromatin opening element from the human HNRPA2B1-CBX3 locus (A2UCOE), which allows position-independent, long-term transgene expression, are particularly promising. In a recently described assay, aberrantly spliced mRNA transcripts initiated in the vector A2UCOE sequence were found to lead to upregulation of growth hormone receptor gene (Ghr) expression in transduced murine Bcl-15 cells. Aberrant hybrid mRNA species formed between A2UCOE and a number of other cellular genes were also detected in transduced human PLB-985 myelomonocytic cells. Modification of the A2UCOE by mutation or deletion of recognized and potential cryptic splice donor sites was able to abrogate these splicing events and hybrid mRNA formation in Bcl-15 cells. This modification did not compromise A2UCOE regulatory activity in terms of resistance to CpG methylation and gene silencing in murine P19 embryonic carcinoma cells. These refined A2UCOE regulatory elements are likely to improve intrinsic biosafety and may be particularly useful for a number of clinical applications where robust gene expression is desirable.
Journal of Virology 06/2012; 86(17):9088-95. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Some gene therapy strategies are compromised by the levels of gene expression required for therapeutic benefit, and also by the breadth of cell types that require correction. We designed a lentiviral vector system in which a transgene is under the transcriptional control of the short form of constitutively acting elongation factor 1α promoter (EFS) combined with essential elements of the locus control region of the β-globin gene (β-LCR). We show that the β-LCR can upregulate EFS activity specifically in erythroid cells but does not alter EFS activity in myeloid or lymphoid cells. Experiments using the green fluorescent protein (GFP) reporter or the human adenosine deaminase (ADA) gene demonstrate 3-7 times upregulation in vitro but >20 times erythroid-specific upregulation in vivo, the effects of which were sustained for 1 year. The addition of the β-LCR did not alter the mutagenic potential of the vector in in vitro mutagenesis (IM) assays although microarray analysis showed that the β-LCR upregulates ~9% of neighboring genes. This vector design therefore combines the benefits of multilineage gene expression with high-level erythroid expression, and has considerable potential for correction of multisystem diseases including certain lysosomal storage diseases through a hematopoietic stem cell (HSC) gene therapy approach.
[show abstract][hide abstract] ABSTRACT: Xenotransplantation carries the potential risk of the transmission of infection with the cells or tissues of the graft. The degree of risk is unknown in the absence of clinical trials. The clinical application of xenotransplantation has important implications for infectious disease surveillance, both at the national and international levels. Preclinical data indicate that infectious disease events associated with clinical xenotransplantation from swine, should they occur, will be rare; data in human trials are limited but have demonstrated no transmission of porcine microorganisms including porcine endogenous retrovirus. Xenotransplantation will necessitate the development of surveillance programs to detect known infectious agents and, potentially, previously unknown or unexpected pathogens. The development of surveillance and safety programs for clinical trials in xenotransplantation is guided by a "Precautionary Principle," with the deployment of appropriate screening procedures and assays for source animals and xenograft recipients even in the absence of data suggesting infectious risk. All assays require training, standardization and validation, and sharing of laboratory methods and expertise to optimize the quality of the surveillance and diagnostic testing. Investigation of suspected xenogeneic infection events (xenosis, xenozoonosis) should be performed in collaboration with an expert data safety review panel and the appropriate public health and competent authorities. It should be considered an obligation of performance of xenotransplantation trials to report outcomes, including any infectious disease transmissions, in the scientific literature. Repositories of samples from source animals and from recipients prior to, and following xenograft transplantation are essential to the investigation of possible infectious disease events. Concerns over any potential hazards associated with xenotransplantation may overshadow potential benefits. Careful microbiological screening of source animals used as xenotransplant donors may enhance the safety of transplantation beyond that of allotransplant procedures. Xenogeneic tissues may be relatively resistant to infection by some human pathogens. Moreover, xenotransplantation may be made available at the time when patients require organ replacement on a clinical basis. Insights gained in studies of the microbiology and immunology of xenotransplantation will benefit transplant recipients in the future. This document summarizes approaches to disease surveillance in individual recipients of nonhuman tissues.
[show abstract][hide abstract] ABSTRACT: Lentiviral vectors (LV) are promising vaccines because they transduce dendritic cells (DC) in vivo. To translate LV vaccines into clinical trials, bulk production will be necessary. The present study aimed to find a suitable envelope for LV vaccine production from stable packaging cells because the commonly used vesicular stomatitis virus envelope (VSV-G) is cytotoxic.
The envelope from Ross river virus (RRV) was selected. It can infect mouse and human cells, allowing testing in animals before clinical translation. We used VSV-G for comparison. Vectors produced with each envelope were titred on human 293T cells and mouse 3T3 cells.
RRV-pseudotyped LV (RRV-LV) infected mouse myeloid DC in culture and immunized mice. An approximately 50-fold higher dose of RRV-LV than VSV-G-LV was required to generate a similar T cell response. The RRV-LV could also be used to infect human mDC and to prime a human T cell immune response.
RRV envelope is a suitable candidate to be used for the construction of an LV producer cell line. LV vaccines with RRV envelope can be tested in mice and in human immune cell cultures. The higher dose of RRV-LV required for vaccine efficacy compared to VSV-G-LV will partly be offset by ease of production.
The Journal of Gene Medicine 03/2011; 13(3):181-7. · 2.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: Insertional mutagenesis by viral vectors is a problem in gene therapy. We recently reported that lentiviral vectors with an intact HIV long terminal repeat (LTR) caused insertional gene activation by transcripts from the 5' LTR splicing to an adjacent gene. Here we demonstrate that the level of transcription from the 5' LTR, and also insertional gene activation, is dependent on the internal promoter in the vector. We also show that there are more transcripts originating from the 5' LTR than from, or reading through, the 3' LTR. This study will allow the design of safer lentiviral vectors for applications in which an intact HIV LTR is required.
Journal of Virology 02/2010; 84(9):4856-9. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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.
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.
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.
PLoS ONE 01/2010; 5(10):e13203. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The risk of transmission of porcine endogenous retrovirus (PERV) is one of the major safety issues in xenotransplantation. Human tetherin, recently described as an antiviral protein able to inhibit the release of enveloped viruses, and its porcine homologue were shown to inhibit PERV release from producer cells, establishing themselves as candidate molecules to suppress PERV production in porcine xenografts by animal engineering.
Journal of Virology 12/2009; 84(5):2618-22. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Tetherin is an IFN-inducible restriction factor that inhibits HIV-1 particle release in the absence of the HIV-1 countermeasure, viral protein U (Vpu). Although ubiquitous in HIV-1 and simian immunodeficiency viruses from chimpanzees, greater spot nosed monkeys, mustached monkeys, and Mona monkeys, other primate lentiviruses do not encode a Vpu protein. Here we demonstrate that SIV from Tantalus monkeys (SIVtan) encodes an envelope glycoprotein (SIVtan Env) able to counteract tetherin from Tantalus monkeys, rhesus monkeys, sooty mangabeys, and humans, but not from pigs. We show that sensitivity to Vpu but not SIVtan Env can be transferred with the human tetherin transmembrane region. We also identify a mutation in the tetherin extracellular domain, which almost completely abolishes sensitivity of human tetherin to SIVtan Env without compromising antiviral activity or sensitivity to Vpu. SIVtan Env expression results in a reduction of surface tetherin, as well as reduction in tetherin co-localization with mature surface-associated virus. Immuno-electron microscopy reveals co-localization of SIVtan Env with tetherin in intracellular tubulo-vesicular structures, suggesting that tetherin is sequestered away from budding virions at the cell surface. Along with HIV-1 Vpu and SIV Nef, envelope glycoprotein is the third and most broadly active lentiviral-encoded tetherin countermeasure to be described. Our observations emphasize the importance of tetherin in protecting mammals against viral infection and suggest that HIV-1 Vpu inhibitors may select active envelope mutants.
Proceedings of the National Academy of Sciences 10/2009; 106(49):20889-94. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Potential transmission of zoonotic porcine viruses is a major safety issue in xenotransplantation. This review will first summarize recent studies involving transmission and control of the major concern, porcine endogenous retrovirus (PERV). Second, the potential for zoonotic transfer and safety measures required against other viruses of concern will be discussed.
As studies on PERV genomics continue, distribution of PERV, particularly porcine endogenous retrovirus-C in individual pigs in relation to their ability to transmit PERV in vitro, is becoming clearer. However, further study is required to establish pig lines devoid of problematic copies of PERV. As an extra level of safety, several strategies have been sought, with some success, to reduce PERV infectivity and be used to produce transgenic, PERV-suppressed pigs. Porcine herpesviruses, hepatitis E virus, arenaviruses and an Anellovirus, Torque teno virus, have been highlighted as other viruses of potential risk.
Xenotransplantation is a unique situation in which pathogen monitoring may be required to be more comprehensive than that required for specific pathogen-free sources. With evidence of transmission of novel viruses via allotransplantation, significant attention should be paid to emerging and as yet unknown viruses.
Current opinion in organ transplantation 05/2009; 14(2):175-9. · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: The potential risk of cross-species transmission of porcine endogenous retroviruses (PERV) to humans has slowed the development of xenotransplantation, using pigs as organ donors. Here, we show that PERVs are insensitive to restriction by divergent TRIM5alpha molecules despite the fact that they strongly restrict a variety of divergent lentiviruses. We also show that the human PERV A/C recombinant clone 14/220 reverse transcribes with increased efficiency in human cells, leading to significantly higher infectivity. We conclude that xenotransplantation studies should consider the danger of highly infectious TRIM5alpha-insensitive human-tropic PERV recombinants.
Journal of General Virology 04/2009; 90(Pt 3):702-9. · 3.13 Impact Factor
[show abstract][hide abstract] ABSTRACT: Gammaretroviral and lentiviral vectors are promising tools for gene therapy, but they can be oncogenic. The development of safer vectors depends on a quantitative assay for insertional mutagenesis. Here we report a rapid, inexpensive, and reproducible assay which uses a murine cell line to measure the frequency of interleukin-3 (IL-3)-independent mutants. Lentiviral and gammaretroviral vectors cause insertional mutagenesis at similar frequencies; however, they use different mechanisms. Human immunodeficiency virus (HIV)-based vectors generate mutants by insertion only into the growth hormone receptor (Ghr) locus. The HIV enhancer/promoter is active in the absence of the HIV Tat protein in this locus, and an HIV/Ghr spliced transcript expresses GHR and cells respond to GH. Deletion of the enhancer/promoter in a self-inactivating HIV-based vector prevents this mechanism of insertional mutagenesis. In contrast, gammaretroviral vectors insert into other loci, including IL-3 and genes identified as common insertion sites in the Retroviral Tagged Cancer Gene Database (RTCGD).
Journal of Virology 11/2008; 83(1):283-94. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Pig-to-human xenotransplantation has taken steps closer to reality through advances in animal engineering to address immunological as well as microbial problems. The most highlighted problem in xenotransplantation safety has been the potential risk for zoonotic infection mediated by porcine endogenous retroviruses. Safety issues regarding viral zoonosis, particularly porcine endogenous retroviruses, are summarized and commented upon.
Several molecular, transgenic strategies to provide safer transplant source animals with less porcine endogenous retrovirus infectivity have been developed. A genomics approach by selective breeding and porcine endogenous retrovirus loci knockout is at least theoretically possible. For other viruses, advances have been made in technologies for virus discovery and identification.
The consequences of possible zoonoses in xenotransplantation are largely unknown. Further work to identify and control potential zoonotic agents based on recent progress will improve the safety profile of xenotransplantation. Advances made should be subjected to cautious testing in well controlled, preclinical and clinical experiments.
Current opinion in organ transplantation 05/2008; 13(2):184-8. · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: Homologous recombination is a dominant force in evolution and results in genetic mosaics. To detect evidence of recombination events and assess the biological significance of genetic mosaics, genome sequences for various viral populations of reasonably large size are now available in the GenBank. We studied a multi-functional viral gene, the adeno-associated virus (AAV) cap gene, which codes for three capsid proteins, VP1, VP2 and VP3. VP1-3 share a common C-terminal domain corresponding to VP3, which forms the viral core structure, while the VP1 unique N-terminal part contains an enzymatic domain with phospholipase A2 activity. Our recombinant detection program (RecI) revealed five novel recombination events, four of which have their cross-over points in the N-terminal, VP1 and VP2 unique region. Comparison of phylogenetic trees for different cap gene regions confirmed discordant phylogenies for the recombinant sequences. Furthermore, differences in the phylogenetic tree structures for the VP1 unique (VP1u) region and the rest of cap highlighted the mosaic nature of cap gene in the AAV population: two dominant forms of VP1u sequences were identified and these forms are linked to diverse sequences in the rest of cap gene. This observation together with the finding of frequent recombination in the VP1 and 2 unique regions suggests that this region is a recombination hot spot. Recombination events in this region preserve protein blocks of distinctive functions and contribute to convergence in VP1u and divergence of the rest of cap. Additionally the possible biological significance of two dominant VP1u forms is inferred.
PLoS ONE 02/2008; 3(2):e1634. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The World Health Organisation (WHO) recommended the development of simple, safe, sensitive and specific neutralization assays for avian influenza antibodies. We have used retroviral pseudotypes bearing influenza H5 hemagglutinin (HA) as safe, surrogate viruses for influenza neutralization assays which can be carried out at Biosafety Level 2.
Using our assay, sera from patients who had recovered from infection with influenza H5N1, and sera from animals experimentally immunized or infected with H5 tested positive for the presence of neutralizing antibodies to H5N1. Pseudotype neutralizing antibody titers were compared with titers obtained by hemagglutinin inhibition (HI) assays and microneutralization (MN) assays using live virus, and showed a high degree of correlation, sensitivity and specificity.
The pseudotype neutralization assay is as sensitive as horse erythrocyte HI and MN for the detection of antibodies to H5N1. It is safer, and can be applied in a high-throughput format for human and animal surveillance and for the evaluation of vaccines.
Influenza and Other Respiratory Viruses 06/2007; 1(3):105-12. · 1.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: The risk of zoonotic infection by porcine endogenous retroviruses (PERV) has been highlighted in the context of pig-to-human xenotransplantation. The use of receptors for cell entry often determines the host range of retroviruses. A human-tropic PERV subgroup, PERV-A, can enter human cells through either of two homologous multitransmembrane proteins, huPAR-1 and huPAR-2. Here, we characterised human PARs and their homologues in the PERV-A resistant rodent species, mouse and rat (muPAR and ratPAR, respectively).
Upon exogenous expression in PERV-A resistant cells, human and rat PARs, but not muPAR, conferred PERV-A sensitivity. Exogenously expressed ratPAR binds PERV-A Env and allows PERV-A infection with equivalent efficiency to that of huPAR-1. Endogenous ratPAR expression in rat cell lines appeared to be too low for PERV-A infection. In contrast, the presence of Pro at position 109 in muPAR was identified to be the determinant for PERV-A resistance. Pro109. was shown to be located in the second extracellular loop (ECL2) and affected PERV-A Env binding to PAR molecules.
The basis of resistance to PERV-A infection in two rodent species is different. Identification of a single a.a. mutation in muPAR, which is responsible for mouse cell resistance to PERV-A highlighted the importance of ECL-2 for the viral receptor function.
[show abstract][hide abstract] ABSTRACT: Recombinant lentiviral vectors (LVs) are commonly used as research tools and are being tested in the clinic as delivery agents for gene therapy. Here, we show that Vesicular stomatitis virus G protein (VSV-G)-pseudotyped LV preparations produced by transient transfection are heavily contaminated with tubulovesicular structures (TVS) of cellular origin, which carry nucleic acids, including the DNA plasmids originally used for LV generation. The DNA carried by TVS can act as a stimulus for innate antiviral responses, triggering Toll-like receptor 9 and inducing alpha/beta interferon production by plasmacytoid dendritic cells (pDC). Removal of TVS markedly reduces the ability of VSV-G-pseudotyped LV preparations to activate pDC. Conversely, virus-free TVS are sufficient to stimulate pDC and act as potent adjuvants in vivo, eliciting T- and B-cell responses to coadministered proteins. These results highlight the role of by-products of virus production in determining the immunostimulatory properties of recombinant virus preparations and suggest possible strategies for diminishing responses to LVs in gene therapy and in research use.
Journal of Virology 02/2007; 81(2):539-47. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: A novel, stable human immunodeficiency virus type 1 vector packaging system, STAR, was tested for its ability to transduce human cord blood CD34+ progenitor cells assayed both in vitro and after transplantation into NOD/SCID mice. Vectors pseudotyped with three different gammaretrovirus envelopes were used: the amphotropic MLV envelope (MLV-A), a modified gibbon ape leukemia virus envelope (GALV+), and a modified feline endogenous virus RD114 envelope (RDpro). Gene transfer to freshly thawed CD34+ cells in the absence of cytokines was very low. Addition of cytokines increased gene transfer efficiency significantly and this was further augmented if the cells were prestimulated for 24 h. Concentration of the vectors (15-fold) by low-speed centrifugation increased gene transfer to CD34+ cells in vitro even further. More than 90% of cells were transduced with a single exposure to the RDpro vector as determined by GFP expression using flow cytometry. The two other pseudotypes transduced approximately 65-70% of the cells under the same conditions. Transplantation of CD34+ cells prestimulated for 24 h and then transduced with a single exposure to concentrated vector revealed that the RDpro vector transduced 55.1% of NOD/SCID repopulating human cells, which was significantly higher than the MLV-A (12.6%)- or GALV+ (25.1%)-pseudotyped vectors.
[show abstract][hide abstract] ABSTRACT: Alphavirus glycoproteins have broad host ranges. Human immunodeficiency virus type 1 (HIV-1) vectors pseudotyped with their glycoproteins could extend the range of tissues that can be transduced in both humans and animal models. Here, we established stable producer cell lines for HIV vectors pseudotyped with alphavirus Ross River virus (RRV) and Semliki Forest virus (SFV) glycoproteins E2E1. RRV E2E1-stable clones could routinely produce high-titer pseudotyped vectors for at least 5 months. SFV E2E1-stable clones, however, produced relatively low titers. We examined the properties of RRV E2E1-pseudotyped vectors [HIV-1(RRV)] and compared them with amphotropic murine leukemia virus Env- and vesicular stomatitis virus glycoprotein G-pseudotyped vectors. HIV-1(RRV) displayed a number of characteristics which would be advantageous in ex vivo and in vivo experiments, including resistance to inactivation by heat-labile components in fresh human sera and thermostability at 37 degrees C. Upon single-step concentration by ultracentrifugation of HIV-1(RRV), we could achieve vector stocks with titers up to 6 x 10(7) IU/ml. HIV-1(RRV) efficiently transduced cells from several different species, including murine primary dendritic cells, but failed to transduce human and murine T cells as well as human hematopoietic stem cells (HSC). These results indicate that HIV-1(RRV) could be used in a number of applications including animal model experiments and suggest that expression of RRV cellular receptors is limited or absent in certain cell types such as T cells and human HSC.
Journal of Virology 03/2005; 79(3):1765-71. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The genetic nature and biological effects of recombination between porcine endogenous retroviruses (PERV) were studied. An infectious molecular clone was generated from a high-titer, human-tropic PERV isolate, PERV-A 14/220 (B. A. Oldmixon, et al. J. Virol. 76:3045-3048, 2002; T. A. Ericsson et al. Proc. Natl. Acad. Sci. USA 100:6759-6764, 2003). To analyze this sequence and 15 available full-length PERV nucleotide sequences, we developed a sequence comparison program, LOHA(TM) to calculate local sequence homology between two sequences. This analysis determined that PERV-A 14/220 arose by homologous recombination of a PERV-C genome replacing an 850-bp region around the pol-env junction with that of a PERV-A sequence. This 850-bp PERV-A sequence encompasses the env receptor binding domain, thereby conferring a wide host range including human cells. In addition, we determined that multiple regions derived from PERV-C are responsible for the increased infectious titer of PERV-A 14/220. Thus, a single recombination event may be a fast and effective way to generate high-titer, potentially harmful PERV. Further, local homology and phylogenetic analyses between 16 full-length sequences revealed evidence for other recombination events in the past that give rise to other PERV genomes that possess the PERV-A, but not the PERV-B, env gene. These results indicate that PERV-A env is more prone to recombination with heterogeneous backbone genomes than PERV-B env. Such recombination events that generate more active PERV-A appear to occur in pigs rather frequently, which increases the potential risk of zoonotic PERV transmission. In this context, pigs lacking non-human-tropic PERV-C would be more suitable as donor animals for clinical xenotransplantation.
Journal of Virology 01/2005; 78(24):13880-90. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Complement activation mediated by the major xenogeneic epitope in the pig, galactosyl-alpha(1-3) galactosyl sugar structure (alpha-Gal), and human natural antibodies could cause hyperacute rejection (HAR) in pig-to-human xenotransplantation. The same reaction on viruses bearing alpha-Gal may serve as a barrier to zoonotic infection. Expressing human complement regulatory proteins or knocking out alpha-Gal epitopes in pig in order to overcome HAR may therefore pose an increased risk in xenotransplantation with regard to zoonosis. We investigated whether amphotropic murine leukemia virus, porcine endogenous retrovirus, and vesicular stomatitis virus (VSV) budding from primary transgenic pig aortic endothelial (TgPAE) cells expressing human CD55 (hCD55 or hDAF) was protected from human-complement-mediated inactivation. VSV propagated through the ST-IOWA pig cell line, in which alpha-galactosyl-transferase genes were disrupted (Gal null), was also tested for sensitivity to human complement. The TgPAE cells were positive for hCD55, and all pig cells except the Gal-null ST-IOWA expressed alpha-Gal epitopes. Through antibody binding, we were able to demonstrate the incorporation of hCD55 onto VSV particles. Viruses harvested from TgPAE cells were relatively resistant to complement-mediated inactivation by the three sources of human sera tested. Additionally, VSV from Gal-null pig cells was resistant to human complement inactivation. Such protection of enveloped viruses may increase the risk of zoonosis from pigs genetically modified for pig-to-human xenotransplantation.
Journal of Virology 07/2004; 78(11):5812-9. · 5.08 Impact Factor