Cloned pigs may not be safe for xenotransplantation

Separate papers published in Science and Nature demonstrated that pigs can be successfully cloned using nuclear transfer with somatic cell donor nuclei, but that organs from pigs may carry infectious porcine endogenous retroviruses (PERV), making pig tissues unsuitable for xenotransplantation. National Institute of Animal Industry (Tsukuba Norin Danchi, Japan) researchers and colleagues published in Science the successful cloning of a pig by microinjection of nuclei from somatic cells (fetal fibroblasts) into mature enucleated oocytes. Following the transfer of 110 cloned embryos to 4 female pigs, a single cloned piglet (named Xena) was born. Also, PPL Therapeutics (LSE:PTH) published in Nature the use of a two-step nuclear transfer cloning procedure to generate five cloned pigs using cultured adult somatic cell nuclei as donors, which the company had previously announced (see BioCentury, March 20).

PTH said that it has isolated pig cells lacking the alpha1-3 galactosyl transferase gene, which is involved with processing of a cell surface antigen that leads to immune responses against pig organs transplanted into humans, and that such cells could be used to clone engineered pigs for xenotransplantation. However, researchers at Genetic Therapy Inc. subsidiary (Gaithersburg, Md.), a subsidiary of Novartis (NVS; SWX:NOVN), and colleagues also published in Nature that PERV are transcriptionally active and infectious cross-species in vivo after transplantation of pig tissues. They showed that pig pancreatic islet cells produce PERV and can infect human cells in culture as well as immune-deficient diabetic mice in vivo. They noted that viruses related to PERV are associated with hematopoietic malignancies, and suggested that there is justified concern over risk of PERV infection following pig tissue xenotransplantation into immunosuppressed human patients. ...