U.S. citizens Mario R. Capecchi and Oliver Smithies and Briton Sir Martin J. Evans won the 2007 Nobel Prize in medicine on Monday for groundbreaking stem cell discoveries that led to a technology known as gene targeting.

The process has helped scientists develop models on mice of human disorders from cardiovascular and neuro-degenerative ailments to diabetes and cancer.

The citation from the Nobel award committee said the three winners had discovered "principles for introducing specific gene modificiation in mice by the use of embryonic stem cells."

The researchers used so-called "knockout mice" — animals whose genetic code has been altered in the lab to either turn on or off certain genes that mice and humans share.

The use of gene targeting has helped expand the knowledge of "numerous genes in embryonic development, adult physiology, aging and disease," the citation said.

Capecchi, 70, was born in Verona, Italy, and moved to the United States with his mother — a Holocaust survivor — after World War II. He did work that "shed light on the cause of several human inborn malformations," the prize citation said, while Evans, 66, applied gene targeting to develop mouse models for human diseases.

Smithies, 82, born in Britain, also used gene targeting to develop mouse models for inherited diseases such as cystic fibrosis and the blood disease thalassemia, and other diseases such as hypertension and atherosclerosis.

All three were informed early Monday that they had won the prize.

"It was a fantastic surprise," Capecchi told The Associated Press in a telephone interview from Salt Lake City, Utah, where he is a professor of human genetics and biology.

He said he was deep asleep when he got the phone call from the Nobel committee at 3 a.m. local time.

"He sounded very serious, so the first reaction was this must be real," Capecchi said.

Smithies told The Associated Press getting award was "very gratifying."

After working on the research for more than 20 years, he said it's "rather enjoyable being recognized at this level."

Smithies, who is a professor at the University of North Carolina at Chapel Hill, said he hopes winning the Nobel Prize will make it easier to secure funding for other work.

The citation said gene targeting has pervaded all fields of biomedicine. "Its impact on the understanding of gene function and its benefits to mankind will continue to increase over many years to come," it said.

The medicine prize was the first of the six prestigious awards to be announced this year. The others are chemistry, physics, literature, peace and economics.

The prizes are handed out every year on Dec. 10, the anniversary of award founder Alfred Nobel's death in 1896.

Last year, the Nobel Prize in medicine went to Americans Andrew Z. Fire and Craig C. Mello for discovering RNA interference, a process that can silence specific genes.