Prize committee member Hans-Gustav Ljunggren told The Associated Press that drug companies are using the discoveries to develop better vaccines, though none are on the market yet.

``Some vaccines against hepatitis are coming out, large clinical trials are being done today,'' Ljunggren. ``More vaccines against infectious diseases are coming and long-term it will also be possible to use it to improve the treatment of cancer, auto-immunity and chronic inflammatory diseases.''

Beutler, born in 1957, is professor of genetics and immunology at The Scripps Research Institute in La Jolla, California. 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 so-called T-cells. Those cells have a key role in adaptive immunity, producing antibodies that destroy infections. Once the infection has been stopped, the immune system maintains a memory that helps it mobilize its defenses next time it comes under a similar attack.

The trio's discoveries have enabled the development of new methods for treating and preventing diseases, including improved vaccines and in attempts to help the immune system to attack tumors, the committee said.

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.