The successful cloning of five bonhams from an adult pig has significant medical potential insofar as it opens the possibility of a new source of organs for transplantation. But much further work remains to be done before the potential can be realised and there will also be much research required to ensure that the act of transplanting tissues from one species to another is both safe and effective.
There have been worries expressed, for instance, that there might be some hitherto undiscovered virus, harmless to pigs, which could become lethally virulent if transferred to humans. Such worries need to be allayed convincingly. But the process of using animal substances to treat human illness has been around for years, most notably, perhaps, in the life-saving use of animal insulins to manage previously fatal diabetes.
It has been apparent to everyone since Dr Christian Barnard transplanted the first human heart that the supply of human organs for transplantation could never be enough to meet the critical needs of those whose lives could be saved by the process. The number of healthy young people who meet with an unexpected death (the likeliest donors of healthy organs) is vastly outstripped by the number of middle- and old-aged people with advanced heart disease and hardening of the arteries. The number of people with kidney failure requiring transplantation also exceeds the number of likely donors in absolute terms. And that is before tissue-typing can identify organs that are at least likely to prove compatible with their sick recipients.
The successful birth just over a week ago of Millie, Christa, Alexis, Carrel and Dotcom, (all but the first and last bonhams named after transplantation pioneers) is simply the opening of a door. But it could lead to very precise genetic engineering techniques which might be applied to cloned pigs to render their tissues non pig-like so that, if transplanted, they would not trigger a sick patient's immune system to reject whatever organ might be transplanted from the pig.
Xenotransplantation (the transfer of organs between different species) has hitherto created catastrophic rejection reactions. There is still a long way to go. Estimates of four years until the first clinical trials of organ transplants from suitably altered pigs to humans seem optimistic at this stage. There are still significant genetic hurdles to be jumped and there is likely to be some hue and cry from people who see ethical problems in the whole process.
But the ultimate prospect of what could become replacement organs virtually on demand for those in need of new hearts must surely bring joyful relief to those families whose members have severe coronary heart disease - most of whom have no prospect whatever of getting life-saving transplants with human organs. Of course, the ultimate answer to chronic heart disease must be prevention rather than replacement. Meanwhile, the birth in Blacksburg, Virginia, of five small pigs using techniques developed by the Roslin Institute in Scotland for cloning may offer realistic hope for sufferers in the interim.