But some cautious researchers wondered whether the success might not be a flash in the pan. After all, the Scottish workers had to try 277 times before they succeeded in producing the clone, named Dolly. Unless the efficiency of the cloning process could be greatly improved, it seemed unlikely to become a common technique for producing improved strains of livestock. Moreover, Dolly's birth did not prove that cloning could be used to create animals from cells that had been genetically manipulated. Unless cloning could be combined with sophisticated genetic manipulation, the technique seemed unlikely to realize its full potential.
Just six months later, it seems clear that doubts are unfounded. While the debate focused on Dolly, a number of other corporate and academic laboratories were quietly pushing ahead with similar projects. At least two U.S. companies--ABS Global of De Forest, Wisc., and Advanced Cell Technology of Worcester, Mass.--have successfully impregnated cows and pigs using cloned cells. In addition, the work over the past six months has demonstrated that cloning works perfectly well on cells that have been genetically altered.
Both corporate contenders claim that their cloning techniques are highly efficient. And neither is making any bones about its commercial intentions. In early August, ABS Global simultaneously introduced a six month old bull named Gene and announced it had formed a new subsidiary, called Infigen, to "commercialize applications of cloning technologies in the cattle breeding, pharmaceutical, nutraceutical and xenotransplantation fields."
Separately, Neal First of the University of Wisconsin at Madison has established, at least transiently, pregnancies in five different species using cloned adult cells. First says he has developed a "universal cloning system" based on cow egg cells that he has used to impregnate cows, sheep, rats, pigs and monkeys.
In cloning procedures generally, nuclei are extracted from cultured cells that might have come originally from an embryo, a fetus or an adult organism. The nuclei are inserted into egg cells which have had their original nucleus removed, a process called nuclear transfer. In the initial work at the Roslin Institute, the egg cells along with their transplanted nuclei were then implanted directly into a foster mother, where they developed and, in the case of Dolly, resulted in a viable offspring.
Researchers at Infigen use a variation on the Roslin approach, explains research director Michael D. Bishop. Rather than transferring just the nucleus, the ABS workers fuse a whole donor cell with an enucleated (nucleus removed) egg cell, a process that is helped along with a jolt of electricity. These donor cells are relatively unspecialized cells taken from fetuses.
When the resulting embryo has divided into about sixteen cells, it is broken up, or disaggregated, into its component cells. The resulting cells are themselves fused with other enucleated egg cells. These second-generation cells are then implanted into foster mothers to develop, which many of them do successfully. The calf "Gene" was cloned from fetal cells using this technique; the company expects to announce the births of cattle cloned from adult cells shortly. By selectively making copies of genetically superior animals, Infigen's corporate parent hopes to boost its share of the lucrative market for bull semen. It might eventually begin selling cloned, genetically-altered animals, says Bishop.
Advanced Cell Technology, for its part, has initiated dozens of clone pregnancies in cows and some in pigs. The company says it anticipates the first births in the near future. For these clones, the donor cells were fibroblasts taken from fetuses. The genomes of these cells can be relatively easily and precisely manipulated through a technique known as targeted gene replacement. "Advanced Cell Technology has the ability to produce transgenic animals using fetal fibroblast nuclear transfer," claims Steve Parkinson, president and chief executive officer.
Parkinson contends that targeted gene replacement produces cells having specific genetic alterations far more effectively than the traditional technique for making transgenic animals, which entails injecting DNA into cell nuclei. He reports that Advanced Cell Technology plans to clone genetically altered animals whose neural tissue would be immunologically compatible with that of humans. Clinical trials of such tissue on patients with Parkinson's disease could start by 1999, he says.
Cloning progress is not restricted to the U.S. Since the February breakthrough, PPL Therapeutics of Edinburgh, which collaborates with the Roslin Institute, has produced five lambs from fetal cells that were genetically modified to carry marker genes and genes for human proteins. Lambs produced from the genetically manipulated cells produce foreign proteins; such animals may be able to manufacture large quantities of medically valuable human proteins in their milk. The result "brings nearer the human benefits from nuclear transfer work," says Ron James, managing director of PPL. The same company is also working on cloned cattle in the U.S.
Dolly, then, was more than just an overnight sensation. Rather, cloning seems set to become a vital technology for agriculture and medicine. "I think the possibility is there that it might really move large-animal transgenic work forward much more rapidly," says Vernon Pursell of the U.S. Department of Agriculture. In other words, better forget the jokes and starting looking at the stock prices.