LAUSR

he biological concept of a long-lived T “stem cell” population that can both self-renew and give rise to differentiated cellular progeny was first proposed by embryologists in the 19th century. However, experimental evidence that such stem cells actually existed in mammals was scant until 2 Canadians at the University of Toronto performed a series of now-classic experiments in irradiated mice, inspired in part by Cold War-era fears of nuclear catastrophe. James Edgar Till was born on a farm in Lloydminster, a rural community that straddles the border of Saskatchewan and Alberta, on August 25, 1931. He attended the University of Saskatchewan on a scholarship from the Standard Oil Corporation, and received a bachelor’s degree in 1952 and master’s degree in physics in 1954. Till then went on to Yale University for a PhD in biophysics, which he obtained in 1957. He was recruited to the University of Toronto by cobalt-60 radiotherapy pioneer Harold Johns (19151998) for post-doctoral work, and spent the rest of his career in Toronto. Ernest Armstrong “Bun” McCulloch was born into a wealthy family in Toronto on April 27, 1926, studied at the elite Upper Canada College, and received his medical degree in 1948 from the University of Toronto. His father and 2 uncles were physicians. After medical school graduation, he trained in hematology at Toronto General