A few months ago, in the teeth of ferocious opposition, the British parliament passed a law authorising the creation of human-animal hybrid embryos. The idea was to create clones using hollowed-out animal eggs and human genetic material. Now MPs may feel that they wasted their time in an ethical Battle of the Somme: the debate was pointless because the "cybrids" almost certainly will not work.

Earlier this month, Robert Lanza of Advanced Cell Technology, a California stem-cell company, published a paper in the journal Cloning and Stem Cells, which showed that human–cow, human–mouse and human–rabbit hybrid embryos fail to grow beyond 16 cells. "there is no evidence that patient-specific human stem cells can be generated using animal oocytes," his team concluded. Genes thought to be critical for pluripotency — the ability to develop into a wide variety of cell types – also failed to express properly. "At first we thought it would just be a matter of tweaking the culture conditions," Lanza told Nature. But "the problem was far more fundamental".

Critics of the hybrids felt vindicated. A British scientist commented on Nature’s blog recalled that "Those who questioned the ethics or the prospects of this technology had to face angry patients who had been convinced that cybrids would be the holy grail that would cure them." He contended that "high profile public hyping of very speculative proposals, like cybrids, is a disservice to the public and to science".

But it was a bitter disappointment for scientists who had hoped that they could get pluripotent stem cells without having to use human eggs, which have proved all but impossible to obtain ethically in the vast quantities required for serious research. The unpalatable conclusion seems to be that the supernova of "therapeutic cloning" is fading. ~ AFP, Feb 2; Nature, Feb 3; Cloning and Stem Cells