An updated and comprehensive map of human hematopoiesis ― how cells of the immune system develop in the bone marrow ― is presented in a report published online this week in Nature Immunology. This revised map may be useful when evaluating the potential of cells generated in vitro from human hematopoietic stem cells, which will likely be used in future clinical applications.
The immune system contains different types of white blood cells. T cells and B cells are known as lymphoid cells, while monocytes and macrophages are known as myeloid cells. It was previously thought that lymphoid and myeloid cells are generated from precursors with strict lymphoid or myeloid potential, which are derived from stem cells at a very early stage. However, John Dick and colleagues now demonstrate that in humans, similar to mice, lymphoid and myeloid potential separate in a gradual transition, rather than a clear cut dichotomy.