It has emerged that Ralph Steinman, who was awarded the Nobel Prize for medicine this morning, died of pancreatic cancer last week.The honour is not normally given posthumously. The award committee has not commented, but will be releasing a statement shortly.Prof Steinman received the award for revolutionising the understanding of the immune system.He discovered the dendritic cell, which helps the body fight off infection.A statement on the Rockefeller University website, where Prof Steinman worked, said the scientist died on September 30 at the age of 68.He was diagnosed with pancreatic cancer four years ago.Marc Tessier-Lavigne, president of the university, said: "The Rockefeller University is delighted that the Nobel Foundation has recognized Ralph Steinman for his seminal discoveries concerning the body's immune responses."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."Prof Steinman was being treated with a dendritic-cell based therapy which stemmed from his own research. SharedThree pioneers of the immune system shared this year's award for medicine.Profs Bruce Beutler and Jules Hoffman discovered how the body's first line of defence was activated.The Nobel prize committee said: "Together Bruce Beutler, Jules Hoffmann and Ralph Steinman have revoluntionised understanding of the immune system by discovering key principles for its activation."They have opened up new avenues for prevention and therapy."The Nobel Foundation said it was preparing an announcement after the news of Prof Steinman's death.Its rules state: "Work produced by a person since deceased shall not be considered for an award. If, however, a prizewinner dies before he has received the prize, then the prize may be presented.