In what seems a particularly cruel twist of fate, Steinman never knew he had been awarded medicine's most sought-after prize, which is shared with American Bruce Beutler and Jules Hoffmann of France.
The Nobel committee had been unaware of Steinman's death Friday when it announced he was to share the award, worth about $1.5 million. Since 1974, the Nobel statutes haven't allowed posthumous awards unless a laureate dies after the announcement but before the Dec. 10 award ceremony.
However, after an emergency meeting Monday, the Swedish foundation said the prize would remain in effect, saying: "The Nobel Prize to Ralph Steinman was made in good faith, based on the assumption that the Nobel laureate was alive."
Officials said the situation was unprecedented and that Steinman's survivors would receive his share of the prize money, but it wasn't immediately clear who would represent him at the ceremony in Stockholm.
Montreal-born Steinman, who was 68 when he died, was cited for his identification of dendritic cells, which help regulate adaptive immunity, an immune system response that purges invading micro-organisms from the body.
It was a discovery he turned to in trying to save his own life, said a statement from Rockefeller University in New York, where the cell biologist had carried out his research since 1970.
"He was diagnosed with pancreatic cancer four years ago, and his life was extended using a dendritic-cell based immunotherapy of his own design," the university said.
In Stockholm, Nobel committee member Goran Hansson said the committee didn't know Steinman had died when it chose him as a winner.
"It is incredibly sad news," Hansson said. "We can only regret that he didn't have the chance to receive the news he had won the Nobel Prize. Our thoughts are now with his family."
Nobel officials said they believe it is the first time a laureate has died before the announcement without the committee's knowledge.
In a statement, Prime Minister Stephen Harper lauded the three winners of the Nobel for medicine and called the award "a fitting final tribute" to Steinman's life's work.
“Dr. Steinman shall be honoured for all time with this achievement," Harper said. "Canadians will mourn his loss.”
The scientist, recently given a gleaming new lab in his role as head of Rockefeller University's Center for Immunology and Immune Diseases, had received many honours for his work, including the Albert Lasker Award for Basic Medical Research in 2007 and the Canadian Gairdner Award in 2003.
"For several years, we've been wondering and hoping that Ralph Steinman might be winning the Nobel Prize, and today when I heard that he won it, I was delighted," said Dr. Lorne Tyrrell of the University of Alberta, chair of the Gairdner Foundation board that selected him as a winner.
"And then I felt cheated and ... it was such a cruel turn of fate to find out that he passed away on Friday, because I think nothing would have made him happier near the end of his life, to have heard that he won the Nobel Prize," Tyrrell said from Kyoto, Japan, where he was attending a conference.
Dr. John Dirks, Gairdner Foundation president and scientific director, said Steinman was a great researcher who knew his science and critiqued it well.
"He liked Canada a lot, loved Canada — his family is still here in large part — and just a great person and almost an ideal image of a creative scientist," Dirks said from Japan.
"We'll miss him in every respect. I can't imagine how sad this is — just a few minutes before everyone hears of this great honour and the next moment we realize that he died over the weekend."
Alan Bernstein, a fellow Canadian who got to know Steinman during his 3 1/2-year tenure as head of the Global HIV Vaccine Enterprise in New York, said he was shocked and saddened to hear of the death of his friend and colleague.
Bernstein said Steinman took him under his scientific wing when he first arrived in New York in 2008 and the two would celebrate Canada Day together each year.
"Ralph was a wonderful human being, so his passing, aside from the Nobel, is very sad news indeed. He was a very warm-hearted individual, very open," Bernstein said Monday from Fethiye, Turkey, where he on vacation.
"And it's very sad that he, I assume, never lived to hear the wonderful news. Knowing Ralph as I do, while it would have been nice for him to hear it, I suspect it wouldn't have been so important as you might think, in the sense that he cared most about the science."
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 defences next time it comes under a similar attack.
The Nobel committee also cited Beutler and Hoffmann for their discoveries in the 1990s of receptor proteins that can recognize bacteria and other micro-organisms as they enter the body, and activate the first line of defence in the immune system, known as innate immunity.
The trio's discoveries have enabled the development of improved vaccines against infectious diseases, said Hansson. In the long term they could also yield better treatments of cancer, rheumatoid arthritis, Type 1 diabetes, multiple sclerosis and chronic inflammatory diseases.
He said their research has 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 tumours," the committee said.
While no vaccines are on the market yet, Hansson said vaccines against hepatitis are in the pipeline.
Beutler, 53, holds dual appointments at University of Texas Southwestern Medical Center in Dallas and as a professor of genetics and immunology at the Scripps Research Institute in San Diego, Calif. 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.
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.
"I am very touched. I'm thinking of all the people who worked with me, who gave everything," Hoffmann said by telephone to a news conference in Paris. "I wasn't sure this domain merited a Nobel."
Beutler said he woke up in the middle of the night, glanced at his cellphone and realized he had a new email message.
"And I squinted at it and I saw that the title line was 'Nobel Prize,' so I thought I should give close attention to that," Beutler said in an interview posted on the Nobel website. "And I opened it and it was from Goran Hansson, and it said that I had won the Nobel Prize, and so I was thrilled."
Still, he was a "little disbelieving" until he checked his laptop, "and in a few minutes I saw my name there and so I knew it was real."
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 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 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 files from The Associated Press.