After the circus procession of cloned sheep, cows, mice, and goats in the past couple years, humans seemed likely to join the list soon. Now this sobering news: A cloned calf in France dropped dead seven weeks after its birth.
The calf appeared healthy until days before her death; then she developed severe anemia and collapsed. An autopsy revealed a withered thymus gland, where white blood cells mature, suggesting that her immune system never started working. Jean-Paul Renard of the National Institute for Agronomic Research in Jouy-en-Josas, who cloned her, thinks a defective donor cell might be at fault. He points out that the cloning process can work fine--other clones produced with his technique are thriving--but concedes that 30 to 50 percent of cloned calves die shortly before and immediately after birth. "If we want to apply this technique outside of research," he says, "such a high rate of abortion and mortality will not be acceptable."
Failure is actually the norm in the cloning business. Ryuzo Yanagimachi at the University of Hawaii has had perhaps the greatest success, producing five generations of cloned mice. Recently he created the first male clone, also a mouse. Yet Yanagimachi and his team had to transplant 274 embryos just to produce three live male mice, two of which died almost immediately. That's not much of an improvement over the 276 failures that preceded Dolly the sheep, the first mammal clone.
There are other signs of trouble. The cloned mice were born with mild breathing problems. More disturbing is that Dolly's chromosomes are worn down at the edges, possibly showing signs of premature aging. It is not clear if she will die early. For now, she appears healthy and has given birth to four lambs, also doing fine. But Margaret Mellon of the Washington, D.C.-based Union of Concerned Scientists warns: "There are many things that could be seriously wrong with her that would be very difficult to detect."
