The Unique Impact of the Atomic Bomb on Modern Hematology

On August 6, 1945, the United States dropped the first atomic bomb (“Little Boy”) on Hiroshima, and on August 9, 1945, it dropped the second atomic bomb (“Fat Man”) on Nagasaki. Two Canadian scientists, Ernest A. McCulloch and James E. Till, developed the spleen colony method in the 1960s based on their observations of the effects of ionizing radiation. They called the nodules that appeared on mouse spleens “colony-forming units,” or “CFUs.” The spleen colony method defined by Till and McCulloch is regarded as a revolution in hematology. In bone-marrow transplantation studies carried out with chromosome-labeled stem cells, the presence of the same chromosomal markers in cells of the thymus and lymph nodes as in spleen colonies indicated that hematopoietic and immune system cells originate from a common stem cell. McCulloch and Till’s collaboration led to entirely new understandings of the biology of blood cell production. In our understanding of diseases of blood cells in recent decades, basic knowledge in molecular and cell biology has been translated into improved diagnostic and therapeutic methods. The pioneering efforts of Till and McCulloch created a completely new paradigm in stem cell biology, genomics, immunotherapy, cellular therapies, and precision medicine approaches to tailor treatments for hematological disorders.