To the editor

It was with interest that I read the article on regenerative medicine in the March 2001 issue (Nat. Biotechnol. 19, 201–206, 2001) and was pleased to see the coverage given to xenotransplantation and other technologies as a potential solution to the chronic shortage of human donor organs and tissues.

In reading your article, however, I noted an inaccuracy. It was reported: “Biotransplant has bred miniature swine free from PERV.” This statement is incorrect and requires further clarification. To assess the potential for the lineages of BioTransplant miniature swine to transmit replication-competent PERV, peripheral blood and aortic endothelial cells were co-cultured with human and porcine target cells using standard assays. In all cases, transmission and replication in the porcine target cells was detected. However, a single line of miniature swine was identified that failed in all tests to establish infection in human cells. As such, these animals are not free from PERV. Rather, they appear not to produce PERV that can establish a productive replication in human cells. This observation (C. Patience, unpublished data) has also been confirmed in two independent laboratories. Defining the genetic basis of this behavior in this line of miniature swine is now the focus of safety research at Immerge BioTherapeutics, a recent joint venture between Novartis Pharma AG and BioTransplant Inc.