James Till

James Edgar Till OC OOnt FRS FRSC (August 25, 1931 – May 18, 2025) was a Canadian biophysicist at the University of Toronto, best known for demonstrating – in a partnership with Ernest McCulloch – the existence of stem cells.

Till was born on August 25, 1931, in Lloydminster, which is located on the border between Saskatchewan and Alberta. The family farm was located north of Lloydminster, in Alberta; the eastern margin of the farm was the Alberta–Saskatchewan boundary.

He attended the University of Saskatchewan with scholarships awarded by the Standard Oil Company and the National Research Council, graduating with a B.Sc. in 1952 and a M.Sc. in physics in 1954. Some of his early work was conducted with Harold E. Johns, a pioneer in cobalt-60 radiotherapy. Till proceeded to Yale University, where he received a Ph.D. in biophysics in 1957. He then became a post-doctoral fellow at the University of Toronto.

Harold E. Johns recruited Till to the Ontario Cancer Institute at Princess Margaret Hospital shortly after he completed his work at Yale. Subsequently, Till chose to work with Ernest McCulloch at the University of Toronto in its Faculty of Medicine. Thus, the older physician's insight was combined with the younger physicist's rigorous and thorough nature.

In the early 1960s, McCulloch and Till started a series of experiments that involved injecting bone marrow cells into irradiated mice. They observed that small raised lumps grew on the spleens of the mice, in proportion to the number of bone marrow cells injected. Till and McCulloch dubbed the lumps 'spleen colonies', and speculated that each lump arose from a single marrow cell: perhaps a stem cell.

In later work, Till & McCulloch were joined by graduate student Andy Becker. They cemented their stem cell theory and in 1963 published their results in Nature. In the same year, in collaboration with Lou Siminovitch, a trailblazer for molecular biology in Canada, they obtained evidence that these same marrow cells were capable of self-renewal, a crucial aspect of the functional definition of stem cells that they had formulated.

In 1969, Till became a Fellow of the Royal Society of Canada.

In the 1980s Till's focus shifted, moving gradually into evaluation of cancer therapies, quality of life issues, and Internet research, including Internet research ethics and the ethics of List mining.

Till held the distinguished title of University Professor Emeritus at the University of Toronto.

Later in life, Till was a vocal proponent of open access to scientific publications.

Until 2019, Till was an editorial member of the open access journal Journal of Medical Internet Research.

Till was a founding member of the Board of Directors of the Canadian Stem Cell Foundation (no longer active).

Till died on May 18, 2025, at the age of 93.

• 1969, he and Ernest A. McCulloch were awarded the Canada Gairdner International Award
• 1993, awarded Robert L. Noble Prize by the National Cancer Institute of Canada, now the research arm of the Canadian Cancer Society
• 1994, made an Officer of the Order of Canada
• 2000, made a Fellow of the Royal Society of London
• 2004, inducted into the Canadian Medical Hall of Fame
• 2005, he and Ernest A. McCulloch were awarded the Albert Lasker Award for Basic Medical Research
• 2006, made a member of Order of Ontario
• 2018, awarded Edogawa-NICHE Prize