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[Recent progress in leukemic stem cell research for childhood leukemia].

Leukemic stem cells (LSCs) were originally identified in acute myeloid leukemia (AML) cases by using xenograft models, as a distinct cell population that can initiate leukemia in immunodeficient mice. Since then, many efforts have been made to clarify the identities of LSCs and other cancer stem cells in various cancer types, to both understand their biology and determine the most suitable targets for anti-cancer therapies. LSCs were identified as existing in the immature CD34+CD38- leukemic population in most AML cases, and these cells were found to share some features with normal hematopoietic stem cells. On the other hand, recent studies have shown that in childhood acute lymphoblastic leukemia (ALL), LSCs exist among B-lineage-committed progenitors expressing CD19. In contrast to AML, in which LSCs generate leukemic cells in a hierarchical order with LSCs at the top, leukemia propagation in childhood ALL is better explained by a stochastic model. In B-precursor ALL, LSCs form via acquisition of additional genetic change(s) in CD19+ B-lineage progenitor cells with self-renewing capacity. These LSCs possess a growth advantage and the capacity to produce progeny with the same ability as the LSCs. Identification of genetic and cellular targets in leukemic transformation is necessary to develop improved anti-cancer therapies.