Calling it "bittersweet" news, colleagues of Canadian-born Ralph Steinman at New York's Rockefeller University said he had prolonged his own life with a new therapy based on his prize-winning research into the body's immune system.

The 68-year-old physician, who joked last week with his family about hanging on until the annual prize declaration, died Friday after a four-year battle with pancreatic cancer -- a fact the Nobel committee was not told until hours after it announced the 2011 award was shared by Steinman and two others.

He never knew his life's work had been crowned with the highest accolade science can bestow, becoming the first person in half a century to win a posthumous Nobel prize -- after a day of consternation in Stockholm, where the Nobel rules have long insisted, in principle, on recognizing only the living.

Two other pioneers whose work on the immune system has also driven ground-breaking possibilities for curbing infections and cancers, American Bruce Beutler and Jules Hoffman from France, shared the other half of the 10 million-crown prize.