LETTER: Man's best friend?

Sir: The Government announcement on new guidelines regulating xenotransplantation may have given the false impression that animal to human transplants will be saving human lives in the imminent future (report, 31 July). In reality, a combination of hype and hope has obscured the fact that the obstacles to xenotransplantation ever becoming a clinical therapy are enormous.

The unpredictable consequences of the introduction of genetically-modified pig tissue into living human subjects and, in particular, the well-reported risk of novel infectious diseases being introduced to the human population as a result of animal-to-human virus transfer overshadow all consideration of this matter. Best present evidence indicates that this latter risk cannot be completely eliminated: the possibility of this potentially devastating eventuality must be balanced against a realistic assessment of the likely success of the procedure.

Animal and human organs differ in numerous ways: in their production of and response to hormones; in their rates of filtration, secretion and absorption of electrolytes, enzymes, and other chemical substances; in their immunological and histological properties; in their physical structure; and not least their expected longevity. Any one of these multiple discrepancies could prove an insurmountable obstacle to the success of this procedure: in combination they are likely to prove fatal to it. A chain is only as strong as its weakest link.

Imutran's claim in 1995 that they were ready to proceed to human clinical trials has been proven irresponsible to the point of recklessness by the stringent regulation the Government has subsequently introduced. The implication now that a cure to the shortage of organs for transplant is only a few animal experiments away raises premature, and almost certainly false, hope. Xenotransplantation is not a panacea: it is speculative, potentially dangerous, and more a product of the financial high risk-high reward principles of commercial biotechnology than a considered and prudent response to the organ shortage.

ALISTAIR CURRIE

Sheffield