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PERV-C integration, expression and transmission of PERV to human cells

Linda Scobie¹, Ralph Hector¹, Magda Matouskova², Juan Ribes³, Giada Mattiuzzo³, Claire Crossan¹, Jiri Hejnar², Yasu Takeuchi³

¹Glasgow Caledonian University, Department of Biological and Biomedical Sciences, Glasgow, United Kingdom; ²Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague, Czech Republic; ³UCL, Infection and Immunity, London, United Kingdom

Background: Xenotransplantation of organs from miniature swine carries several concerns; one such risk arises from the genetically acquired porcine endogenous retrovirus (PERV). There are three known subtypes of PERV-A, B and C, although a high titre recombinant form (A/C) has also been identified. It has been suggested that these recombinants are exogenous and/or driven by one or more critical loci present in the pig genome. Previous data has shown that miniature swines have three distinct transmission phenotypes and a PERV C locus was identified that appeared to be associated with these phenotypes (Hector et al Xenotransplantation, 14: 222–226,2007).

Methods: We have further analysed the presence and expression of PERV-C proviruses within the genome of a number of pigs, including those known to transmit PERV to both pig and human cells. Splinkerette PCR was used to map integrations within the porcine genome and all integrations were analysed to determine if they were ‘solo-LTR’ sequences or were intact, i.e., possess gag and env sequences.

Results: A total of 132 PERV-C integrations have been mapped within the genomes of different porcine breeds (MP vs LWx), however, only about 24 of these appear to attached to PERV sequence and 18 can be mapped from 5’ to 3’ end. Distribution amongst animals is heterogenous and appears to be breed-specific. One locus, 6SH was identified as absent in animals whose PBMC culture did not produce infectious PERV. Analysis of this locus showed hypo-methylation of the viral control region and a deletion present from nt6292-nt7834 in the envelope gene.

Conclusion: Specific PERV-C loci have been identified which may contribute to the formation of HTRC recombinant PERV. Hypo-methylation indicates this locus may indeed be actively expressed and excluding donor animals which harbour these loci should increase the safety profile.