Transmission of porcine endogenous retroviruses in severe combined immunodeficient mice xenotransplanted with fetal porcine pancreatic cells

Background. Xenotransplantation using pig organs or tissues may alleviate t he human donor organ shortage, However, one concern is the potential transm ission of pig pathogens to humans, especially pig endogenous retroviruses ( PERV), which infect human cell lines in vitro, In this report, the cross-sp ecies in vivo transmission of PERV by xenotransplantation was studied using a severe combined immunodeficient (SCID) mouse model. Methods. Twenty-one SCID mice were transplanted with fetal pig pancreatic c ells and left for periods from three to 41 weeks before being killed. DNA a nd RNA were extracted from liver, spleen, and brain of these mice, and exam ined for PERV using nested polymerase chain reaction (PCR) and reverse tran scriptase-PCR. The pig mitochondrial cytochrome oxidase II subunit gene (CO II) was also amplified to monitor the presence of pig cell microchimerism i n xenotransplanted tissues, and a housekeeping gene was included to monitor the DNA quality and quantity. Results. Examination of 39 DNA samples from tissues of the 21 xenografted m ice identified two mouse tissues (M4-liver and M19-spleen) that were positi ve for PERV but negative for COII. A total of 23 (59%) of the mouse tissues were positive for both PERV and COII, 6 (16%) were negative for both, and 8 (20%) were positive for COII only. PCR and direct sequencing of the PCR p roducts identified three PERV variants, which were different from the PERV sequence detected by PCR direct sequencing from the pig donor cells. Conclusions. The PERV+/COII- results from M4-liver and M19-spleen indicated the presence of PERV transmission from pig to mouse tissue. The PERV varia nts detected in the mouse tissues indicated that different PERVs were trans missible from the pig to mouse tissue during xenotransplantation. The negat ive reverse transcriptase-PCR results for PERV from three mouse samples inc luding M4-liver and M19-spleen suggest there was no active PERV transcripti on in the mouse tissues, although this would need to be studied further.