2011 - Ralph M. Steinman - United States and Canada - "for his discovery of the dendritic cell and its role in adaptive immunity". He was a Canadian immunologist and cell biologist working at Rockefeller University, Posthumous awards are not allowed. However, unknown to the committee, Steinman had died three days before the announcement. The committee decided that since the prize was awarded "in good faith," it would be allowed to stand. Source Nobelprize.org.