In 1988, pathologist Irving Weissman from Stanford Medicine isolated a rare mouse cell, known as the hematopoetic stem cell, which gives rise to all the cells of the blood and immune systems.

His laboratories also discovered the human HSC, a human brain-forming stem cell population, mouse skeletal muscle stem cells, and an osteochondral stem cell in mice. His work and discoveries on stem cell aging contributed to the understanding of cancer stem cells and the immune system and are pioneering achievements with far-reaching clinical applications.