Sir

The Asilomar moratorium on applications of recombinant DNA research, agreed to by molecular biologists in 1974, marked a turning point in the approach of biologists to their responsibilities to the public in developing a technology with unpredictable consequences.

That the worst-case scenarios envisaged at the time did not materialize in no way detracts from the merit of the caution taken. Today, we are once again faced with a similarly perplexing quandary.

Xenotransplantation, the transplantation of animal organs, tissues and cells, promises substantial benefits in the long term1,2 yet also creates a risk that infectious agents from the donor animal might jump the species barrier to man, not just infecting transplant recipients but also spreading to the general population3. We believe that a decision on whether to proceed at present with clinical trials of xenotransplantation should not be left to the traditional technical-based approaches that regulatory agencies use to evaluate new medical technologies.

Given the potential risk to the public, the issue is first and foremost an ethical one. Before introducing a regulatory framework driven by technical considerations, an informed public debate is needed so that the public can decide whether it wishes to consent to clinical xenotransplantation at all and, if so, under what conditions.

Until such a review is completed in the United States, we advocate a moratorium on all forms of clinical xenotransplantation, a recommendation discussed more fully elsewhere4. At the same time, fundamental research in xenotransplantation should be actively supported, given that it promises not only to advance our understanding of the immune and vascular systems, but also to fill some of the many gaps in our understanding of the problems, benefits and risks of potential clinical application of this technology.