Elimination of porcine endogenous retroviruses from pig cells
Level 5 - mechanism / opinion, no new human data
Narrative commentary reviewing in vitro laboratory gene editing research
OpenAlex W2241849116 · doi:10.1111/xen.12210
What was done
This commentary reviews and analyzes a study by Yang et al. that used CRISPR/Cas9 targeting a conserved sequence in the retroviral pol gene to eliminate porcine endogenous retroviruses (PERVs) in a porcine kidney cell line (PK15). It contextualizes these findings within prior failed attempts using zinc finger nucleases, preclinical and clinical trials with over 200 xenotransplant recipients, and biological challenges remaining before PERV-free pigs can be produced.
What was found
The reviewed study inactivated 62 PERV proviruses in PK15 porcine cells using CRISPR/Cas9 without reported genomic rearrangements or instability. Reverse transcriptase activity was absent in the supernatant of treated cells, and unlike untreated controls, supernatant from CRISPR-treated cells did not infect human cells in vitro. Historical xenotransplantation trials involving >200 patients receiving porcine islet cells or other tissues documented zero in vivo PERV transmissions.
Why it matters
PERVs represent a primary biosafety concern and regulatory hurdle in porcine xenotransplantation because they cannot be eliminated by breeding. Demonstrating that dozens of integrated proviral copies can be simultaneously inactivated without fatal genomic instability provides a technical pathway toward generating safer donor pigs.
Limits
The primary findings were obtained exclusively in an immortalized porcine cell line (PK15) in vitro. The method was not tested in primary porcine cells or stem cells required for cloning live pigs. Provirus copy number varies across pig breeds, and the physiological effects of PERV inactivation on porcine placental development and animal viability were not assessed.
Cited by
- supports George Church's group engineered pig germlines with 42 to 62 simultaneous genome edits targeting porcine endogenous retroviruses and immunological genes for xenotransplantation.