A Preliminary Study On Biologic Safety With Porcine Endogenous Retrovirus In Xenotransplantation

It is of broad and charming feature that organs, tissues and cells of the pig as donor source for xenotransplantation to human beings. It may alleviate the relative shortage of human donor organs, and provide not only a substitutive therapy for patients suffering from intractable neurologic disorders (Parkinson's disease, Huntington's disease, and epilepsy) and type- I insulin-dependent diabetes mellitus, but also a interim measure for patients suffering from acute fulminant hepatitis with liver failure and acute and chronic renal failure. Since Dr. dive Patience (a principal scientist at BioTransplant Inc.) reported firstly porcine endogenous retrovirus (PERV) might infect human cells in vitro in 1997, extensive attentions have been attracted on the potential hazard of interspecies infection with xenotransplantation to human beings.Patience et al has demonstrated three variants of PERV that could infect human cell in vitro at least. Takeuchi et al has shown that PERV could infect human cell lines in vitro by pseudotyping experiments. Martin et al has confirmed PERV could infect human cell in vitro by infectious trial. More extensive and deeper researches about biological characteristics of PERV have been performed by many of scholars.It has been demonstrated that PERV is a typical mammalian C-type retrovirus with a comlpex structure of gag-pol-env gene. Patience et al seperated natural virus particles from two pig kidney cell lines, and'The project is supported by the national KEY basic research developmental programe. No.G2000016106demonstrated a typical mammalian C-type retrovirus particles. Akiyoshi et al reported the nucleotide sequence of porcine endogenous retrovirus from lymphocytes of miniature swine (PERV-MSL) is a typical mammalian C-type retrovirus of 8,132 bp with the greatest homological nucleic acid sequence to gibbon ape leukemia virus and murine leukemia virus. Constitutive product of PERV-MSL RNA has been detected in normal leukocytes and multiple organs of swine. The open reading frames for gag, pol, and env in PERV-MSL have over 99% homological amino acid sequence identity to those of Tsukuba-1 retrovirus and are highly homologous to those of endogenous retrovirus of cell line PK15 (PK15-ERV). Sources of Pig species are rich in China. Experimental study of biological features of PERV has not been reported domestically so far as we know.Although PERV can infect human cell in vitro has been demonstrated, few research that PERV is transcriptionally active and infectious cross-species in vivo was reported. Van der Laan et al established a model of pig pancreatic islets transplanted into NOD/SCID (non-obese diabetic mellitus, severe combined immunodeficiency) mice. Here they showed that cells of pig pancreatic islets produced PERV and infected human cells in culture. After transplantation into NOD/SCID mice, the expression of PERV RNA in mice was detected. The results showed that various tissues of mice were infected by PERV. This is the first report that PERV is active replication and infectious interspecies in vivo after transplantation of pig tissues. Subsequently, Deng et al transplanted twenty-one SCID mice with fetal pig pancreatic cells and brought up for three to 41 weeks before being killed. DNA and RNA were extracted from the liver, spleen, and brain of these mice, and examined for PERV using nested polymerase chain reaction (PCR) and reverse transcriptase-PCR. The pig mitochondrial cytochrome oxidase II subunit gene (COII) was also amplified to monitor the presence of pig cell microchimerism in xenotransplanted tissues. The results showed the PERV was positive inM4-liver and Ml9- spleen, and COII negative. This indicated that transmission of PERV from pig to mouse had happened. The negative reverse transcriptase-PCR results for PERV from these mouse samples suggest there was no active PERV replication in the mouse tissues. No evidence of infection with PERV was found recently in a several of reports on clinical patients transplanted alive tissues or cell of...