(CBS/AP) Key immune system discoveries led three scientists to win the Nobel Prize in medicine on Monday.
The honors - along with a $1.5 million prize - were split among American Bruce Beutler, French scientist Jules Hoffmann, and Canadian-born Ralph Steinman, the Nobel committee at Stockholm's Karolinska institute said.
Rockefeller University in New York City announced in a statement that Steinman had died on September 30, three days before the announcement. Nobel committee member Goran Hansson said the Nobel committee didn't know Steinman was dead when it chose him as a winner - awards are not typically given out posthumously.
The scientists' landmark discoveries enabled the development of improved vaccines against infectious diseases. In the long term they could also help treat cancer, rheumatoid arthritis, type 1 diabetes, multiple sclerosis, and chronic inflammatory diseases, Hansson said.
Beutler and Hoffmann received the Prize for their 1990s discoveries of proteins that can recognize bacteria and other microorganisms as they enter the body, and activate the first line of defense in the immune system, called "innate immunity."
Hoffmann's discovery came in 1996 while researching how fruit flies fight infections. Two years later, Beutler's research on mice showed that fruit flies and mammals activate "innate immunity" in similar ways when attacked by germs.
Hoffmann, 70, headed a research laboratory in Strasbourg, France, between 1974 and 2009 and served as president of the French National Academy of Sciences between 2007-2008. Beutler, 54, serves as professor of genetics and immunology at The Scripps Research Institute in San Diego.
Steinman was cited for discovering a new type of cells called dendritic cells, which help regulate the body's "adaptive immunity" - the next stage of the immune system's response - when the body purges invading microorganisms.
His discovery dates back to 1973, when he discovered these new cells had a unique capacity to activate infection-fighting T-cells. Dendritic cells also develop a memory that helps the immune system mobilize its defenses next time it comes under a similar attack.
Steinman, 68, had been affiliated with Rockefeller University since 1970, and was head of its Center for Immunology and Immune Diseases.
The discoveries have helped scientists understand why the immune system sometimes attacks itself, paving the way for new ways to fight inflammatory diseases.
"They have made possible the development of new methods for preventing and treating disease, for instance with improved vaccines against infections and in attempts to stimulate the immune system to attack tumors," the committee said.
No vaccines are on the market yet, but Hansson said that hepatitis vaccines are in the pipeline. "Large clinical trials are being done today," he said.
Last year's medicine award went to British professor Robert Edwards for fertility research that led to the first test tube baby.