Absence of Replication-Competent Human-Tropic Porcine Endogenous Retroviruses in the Germ Line DNA of Inbred Miniature Swine

Abstract

The potential transmission of porcine endogenous retroviruses (PERVs) has raised concern in the development of porcine xenotransplantation products. Our previous studies have resulted in the identification of animals within a research herd of inbred miniature swine that lack the capacity to transmit PERV to human cells in vitro. In contrast, other animals were capable of PERV transmission. Xenotransplantation carries the concerns of cross-species transmission of infectious pathogens present in the donor species (7,17,18,23). Studies indicate that many exogenous microorganisms can be eliminated from the donor herd by using various barrier methods and specialized qualified-pathogenfree rearing techniques (3,25,26). However, porcine endogenous retroviruses (PERVs) are an exception to this rule, as proviral copies are inherited through the germ line DNA.

Evidence and Consequence of Porcine Endogenous Retrovirus Recombination

“…Similar recombined forms of the env gene, containing PERV-A and -C sequences at the 5Ј and 3Ј ends, respectively, have been obtained as parts of human-tropic PERV isolated by transmission to a human cell line from miniature swine PBMC (28,55). Such recombinant env genes have not been detected in miniature swine genomic DNA by extensive screenings (40). Each of these recombined env genes had different A-to-C crossover points (Fig.…”

“…1 (middle and bottom panels, respectively). It has been proposed that such recombination may rescue replication-defective endogenous PERV-A env, whose TM appears to be truncated (40). The U3-R tree, 3Ј to this recombination point, demonstrates that A463, A42, and Ap60, unlike other PERV-A and -C genomes with so-called repeatless LTR, contain the PERV-B type LTR with enhancer repeats (51) (Fig.…”

“…PERV transmission experiments by cocultivation of activated miniature swine PBMC with human 293 cells have led to the isolation of several PERV able to replicate in human 293 cells (28,40,54). All these isolates, including PERV-A 14/220, appear to have hybrid env genes consisting of PERV-A-and -C-like sequence (28,55).…”

“…However, studies on PERV recombination in terms of its genetic nature, biological effects, and implication for xenotransplantation have been limited. Notably, data from partial sequencing of the PERV genome revealed evidence for possible recombination events (28,40,55) but not a genetic characterization of the whole genome of recombinant PERV. In contrast, studies analyzing longer genome sequences (17)(18)(19) have not directly linked genetic recombination with its effect on biological activity of PERV.…”

Isolation and Characterization of an Infectious Replication-Competent Molecular Clone of Ecotropic Porcine Endogenous Retrovirus Class C

“…The HTRC PERV derived ex vivo from inbred miniature swine have been recombinants between PERV-A and PERV-C (11,14,20,21). There is no evidence of inherited recombinations between PERV-A and PERV-C (15). The recombined env gene bore the receptor-binding domain of PERV-A on a PERV-C background (3,11,20).…”