James ‘Jim’ Till is a biophysicist who collaborated with haematologist Ernest McCulloch on research that led to proof of the existence of stem cells. These primitive cells can evolve into specialised cells or divide into further stem cells. They are critical to foetal development and act as a repair system for adult tissues.

Jim and Ernest observed small lumps in the spleens of irradiated mice following injections of bone marrow cells. They called the lumps ‘spleen colonies’. Further experiments demonstrated that the colonies were clones derived from single cells. These results were published in the journal Nature in 1963. Additional experiments showed that the colony-forming cells were capable of self-renewal, as expected from a functional definition of stem cells.

Jim and Ernest’s work on stem cells revolutionised our understanding of human biology and disease and helped to found the field of modern haematology, which focuses on diseases related to the blood. Jim now posts frequently to Twitter, using the hashtags #cancerSC and #OpenAccess.