title: Distribution and expression of porcine endogenous retroviruses in multi-transgenic pigs generated for xenotransplantation.
abstract: BACKGROUND
  Multi-transgenic pigs produced for use in xenotransplantation have to be screened for the presence and expression of porcine endogenous retroviruses (PERV) to select animals with low PERV load. The production of transgenic pigs may also be associated with the integration of the transgene adjacent to or into the locus of a PERV provirus, potentially leading to an enhanced virus expression.
  
  
  METHODS
  Non-transgenic animals, single-transgenic, and multi-transgenic pigs were screened for the presence of PERV-A, -B, and -C and recombinant PERV-A/C using polymerase chain reaction (PCR). PERV expression was determined by real time reverse transcriptase-PCR. An assay based on the activation of PERV in peripheral blood mononuclear cells by mitogens was used to discriminate between low and high PERV producer animals.
  
  
  RESULTS
  All animals carried PERV-A and -B. A total of 176 from 181 (97.2%) animals carried PERV-C in the germ line and 18 from 64 animals carried PERV-A/C in the genome of lymphoid cells but not in the germ line. The expression of PERV was very low in all animals and not different between transgenic pigs and non-transgenic animals. PERV expression differed between various pig lines. The highest expression was found in mini-pigs and crossing other pig lines with mini-pigs resulted in increased PERV expression in the progeny. However, expression of viral proteins and particle release were not observed in all transgenic animals.
  
  
  CONCLUSIONS
  No evidence for elevated PERV expression in (multi-) transgenic pigs was observed. Differences in PERV expression correlated with the genetic background of the animals, not with the specific transgene. Mini-pigs consistently had the highest level of PERV expression and animals with a mini-pig background had a higher level of expression compared with animals without mini-pig background.
authors.affiliation: Robert Koch-Institute, Nordufer 20, Berlin, Germany.
authors.forename: Britta
authors.initials: B
authors.lastname: Dieckhoff
authors.forename: Barbara
authors.initials: B
authors.lastname: Kessler
authors.forename: Danny
authors.initials: D
authors.lastname: Jobst
authors.forename: Wilfried
authors.initials: W
authors.lastname: Kues
authors.forename: Björn
authors.initials: B
authors.lastname: Petersen
authors.forename: Alexander
authors.initials: A
authors.lastname: Pfeifer
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kurth
authors.forename: Heiner
authors.initials: H
authors.lastname: Niemann
authors.forename: Eckhard
authors.initials: E
authors.lastname: Wolf
authors.forename: Joachim
authors.initials: J
authors.lastname: Denner
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified / Q000821:virology*; D002460:Cell Line; D020077:Endogenous Retroviruses / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000821:virology; D008297:Male; D012367:RNA, Viral / Q000235:genetics; D034421:Sus scrofa; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D019562:Viral Load
chemical_list: D012367:RNA, Viral