Sir

You refer in your Briefing on xenotransplantation (Nature 391, 320–325; 1998) to a study on seroreactivity to porcine viruses in the ten diabetic patients transplanted with fetal pig islets in Stockholm, Sweden, between 1990 and 1993. The study was presented at the Xenotransplantation Congress in Nantes, France, last September.

Your description of the serological findings is correct: a number of patients tested positive for antibodies to various pig viruses. The sera have subsequently been evaluated for possible cross-reactivity with antibodies to human pathogens, and most reactivities have now been accounted for by such cross-reactivity. There remains a weak reactivity against porcine parvovirus in samples from three patients, and these are being reanalysed at the Centers for Disease Control in Atlanta, Georgia.

The statement that one patient is ill with porcine parvovirus infection is, however, false. None of the patients developed any infectious symptoms related to the xenotransplantation. Nor has any of them developed any unusual symptoms of diseases since exposure to the porcine islets. The alleged transmission of viral disease from pig to man has raised considerable concern. There has, however, been no evidence of such disease in our patients.