Three scientists shared the Nobel Prize for medicine Monday for their discoveries about the human immune system that forged the development of new treatments against infectious diseases and cancer.

American Bruce Beutler and French scientist Jules Hoffmann split the 10 million-kronor ($1.5 million) award with Canadian-born Ralph Steinman now affiliated with Rockefeller University, the Nobel committee at Stockholm's Karolinska institute announced Monday.

However, officials with Rockefeller University said that Steinman died of pancreatic cancer on Sept. 30, three days before the announcement on Monday.

Nobel Prizes are typically not given post-humously and Nobel committee member Goran Hansson said that Nobel committee was unaware that Steinman had died when they announced him as winner. Committee officials said they were looking through their regulations.

The Rockefeller University is delighted that the Nobel Foundation has recognized Ralph Steinman for his seminal discoveries concerning the body's immune responses, Rockefeller University President Marc Tessier-Lavigne, said in a press statement. But the news is bittersweet, as we also learned this morning from Ralph's family that he passed a few days ago after a long battle with cancer. Our thoughts are with Ralph's wife, children and family.

Regardless of whether Steinman ultimately keeps the post humous award, the Nobel committee lauded the research for giving insight into human immune systems.

This year's Nobel laureates have revolutionized our understanding of the immune system by discovering key principles for its activation, stated the award panel at Sweden's Karolinska Institute in Stockholm.

Lars Klareskog, the chairman of the prize-giving Nobel Assembly, told Reuters: I am very excited about what these discoveries mean. I think that we will have new, better vaccines against microbes and that is very much needed now with the increased resistance against antibiotics.

I also expect that there will be some development in the area of attacking cancers from the self-immune system. There are some promising things there.

In an unorthodox move, Goran Hansson, Secretary-General of the Nobel Committee, said that the three members hadn't been able to be contacted, so the committee announced the prizes without giving the well-known phone call to the award winners.

The discoveries of the scientists enabled the development of improved vaccines against infectious diseases. In the long term they could also yield better treatments of cancer, rheumatoid arthritis, Type 1 diabetes, multiple sclerosis, and chronic inflammatory diseases, Hansson told The Associated Press.

Beutler and Hoffmann were cited for their discoveries in the 1990s of receptor proteins that can recognize bacteria and other microorganisms as they enter the body, and activate the first line of defense in the immune system, known as innate immunity.

Steinman was honored for the discovery two decades earlier of dendritic cells, which help regulate adaptive immunity, the next stage of the immune system's response, when the invading microorganisms are purged from the body.

The discoveries have helped scientists understand why the immune system sometimes attacks its own tissues, 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 told AP that vaccines against hepatitis are in the pipeline. Large clinical trials are being done today, he said.

Hansson said he hadn't been able to reach any of the winners before the announcement.

Hoffmann for example is traveling in China and is difficult to reach, he said.

Beutler, born in 1957, is professor of genetics and immunology at The Scripps Research Institute in San Diego. 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.

Steinman, 68, has been affiliated with Rockefeller University in New York since 1970, and heads its Center for Immunology and Immune Diseases.

Hoffmann's discovery came in 1996 during research on 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.

Steinman's discovery dates back to 1973, when he found a new cell type, the dendritic cell, which has a unique capacity to activate  T-cells. Those cells have a key role in adaptive immunity, when antibodies and killer cells fight infections. They also develop a memory that helps the immune system mobilize its defenses next time it comes under a similar attack.

The medicine award kicked off a week of Nobel Prize announcements, and will be followed by the physics prize on Tuesday, chemistry on Wednesday, literature on Thursday and the Nobel Peace Prize on Friday. The winners of the economics award will be announced on Oct. 10.

The coveted prizes were established by wealthy Swedish industrialist Alfred Nobel - the inventor of dynamite - except for the economics award, which was created by Sweden's central bank in 1968 in Nobel's memory. The prizes are always handed out on Dec. 10, on the anniversary of Nobel's death in 1896.

Last year's medicine award went to British professor Robert Edwards for fertility research that led to the first test tube baby.

With reporting from the Associated Press.