The central cells of the immune system include three lymphocyte populations: T cells, B cells, and natural killer cells. These lymphoid cells as well as all myeloid cells -- such as granulocytes, macrophages, megakaryocytes, and erythrocytes -- are derived from hematopoietic stem cells that are capable of self-renewal to maintain the immune system for life. Prof. Koichi Akashi has isolated the earliest stem cells on lymphoid and myeloid pathways in the bone marrow. He also found rare stem cell populations that can generate eosinophils, basophils or mast cells, all of which play a critical role in development of allergic disorders. Using these highly purified stem cell populations, he is attempting to identify critical genes involved in generation of these different cell types. He also showed that these cells are susceptible to transformation into acute leukemia. He is therefore trying to isolate cellular surface antigens specific for each stem cell population. The identification of cellular and genetic target might be the key to develop new therapeutic approaches for human hematopoietic malignancy and allergic disorders. Furthermore, understanding the developmental mechanism from stem cells to mature progeny by his model should be critical to develop future regenerative medicine.