BLACKSBURG, Va. (AP) — The company that cloned Dolly the sheep announced Monday that it has cloned a calf, using cells from a fetus rather than cells of an adult animal.
The calf was produced by PPL Therapeutics Inc. of Blacksburg, a subsidiary of PPL, based in Edinburgh, Scotland. It was delivered here at the Virginia-Maryland College of Veterinary Medicine on Feb. 16 and named Mr. Jefferson — in honor of Thomas Jefferson.
“He is proof that the technology developed in sheep can be adapted and applied successfully in another species,” said Willard Eyestone, a senior scientist in PPL’s Blacksburg laboratory.
Mr. Jefferson, a healthy black-and-white Holstein, was delivered through Caesarian section and is being bottle fed in a pen at the veterinary hospital, he said.
While PPL was the first to clone a sheep, the company lost the race to clone the first calf.
Advanced Cell Technology of Massachusetts said in January that it cloned three calves using the technique used to clone Dolly’s offspring. Also, ABS Global Inc. of Wisconsin announced in August that it cloned a calf using a significantly different method.
Caird Rexroad, assistant deputy administrator for the U.S. Department of Agriculture’s research service, said PPL’s accomplishment is significant because it’s important that science is repeatable.
But he added, “It’s not quite as exciting after the first go-round.”
Dolly, the sheep PPL cloned in Scotland last year, was created from a cell taken from the udder of a 6-year-old ewe.
Mr. Jefferson was cloned from cells taken from a 55-day-old calf fetus. Advanced Cell Technology and ABS also used fetal cells, and scientists said no other company has succeeded in cloning a mammal from an adult cell.
PPL produces therapeutic human proteins, including blood components, that are extracted from the milk of genetically engineered sheep in Scotland and pigs, cows and rabbits in Blacksburg. Human genes, micro-injected into animal embryos during in-vitro fertilization, instruct the animals’ mammary glands to produce milk containing the human protein.
PPL believes cloning will be a more efficient and useful way to produce genetically modified livestock than micro-injecting embryos. And it is focusing on cows because they can produce about 20 times as much human milk protein as sheep.
PPL said the cloned calf and the cloned sheep were produced by a process called somatic cell nuclear transfer. Somatic cells develop into tissue and organs, unlike less sophisticated cells that develop into eggs and sperm.
Here’s how it works:
After an unfertilized egg is taken from a cow on PPL’s ranch outside Blacksburg and brought to the lab, a technician removes the nucleus and replaces it with the nucleus of a somatic cell from a fetus. That skin cell is already fertilized, so bulls are unnecessary in this process.
If the cells are replicating, the cloned egg is implanted into a surrogate mother.
Despite the success with Dolly, cloning is very difficult and has a high failure rate. Before Dolly was created, there had been 277 unsuccessful attempts, and some of the lambs were stillborn or had fatal defects.
Eyestone said there were some calf embryos transferred to surrogate mothers that did not complete gestation, but he declined to say how many failures there were.