PERV genetic characteristics as selective breeding criteria - developing a pig breed suitable for xenotransplantation

Abstract

The risk of a zoonotic infection by porcine endogenous retrovirus (PERV) has been a major impediment to the xenotransplantation field ever since the discovery that PERV can infect human cells in vitro. The aim of this thesis was to evaluate different aspects of PERV biology and employ these results as a collective strategy to help assess and ultimately reduce the risk of PERV zoonosis within a potential donor herd. This strategy presupposes that pigs can be selectively bred based upon the following criteria, 1) the presence or absence of transmissible PERV sequences and sequences that may contribute to recombinant formation, 2) PERV copy number per cell, 3) level of reverse transcriptase activity and PERV viral expression within various tissues and 4) in vitro infectivity of both eco-tropic and xeno-tropic PERV virus. These criteria were assessed within a designated pathogen free (DPF) herd derived from the Auckland Island (AI) pig breed. Results confirmed that the AI pig breed does not retain PERV recombinants within its genome and lacks the ability to infect human or pig cells in vitro. PERV expression amongst all tested pigs from all tissues occurs at very low levels (<3% of the expression found in the infectious porcine kidney cell line PK15). PERV copy number was shown to be variable, facilitating the identification of numerous low copy number individuals. Similarly, PERV C negative animals were also present albeit at very low frequencies (1.2 %). These data suggest that the AI pigs present minimal PERV infectious risk and possess several targets for selective breeding that can be used to diminish this risk even further. As a breed the AI pigs are ideal for use in xenotransplantation. In general terms the breeding strategy described here demonstrates considerable utility for the accurate and reliable verification of pig breeds as suitable donors of xenograft material.