Immunobiology of acute leukemia

Acute leukemias are commonly defined as the expansion of immature cells that are derived from rare transformed hematopoietic progenitor cells, termed the leukemic stem cells (LSC) or leukemia-initiating cells (LIC), which have the capacity of self-renewal, a defining characteristic also of normal hematopoietic stem cells [1]. As an alternative to originating in a primitive stem cell, leukemias may be derived from transformation of a committed progenitor cell, and, to date, there are well-characterized examples for both concepts among leukemia subtypes. In addition to loss of long-term repopulating potential, also the phenotypic features of the LSC blast cell progeny that invade the bone marrow and the peripheral blood of leukemia patients are different from those of the LSC and typically characterized by different morphology (FAB classification) and antigen profiles. Most interestingly, while the phenotypes of blast cell populations differ based on distinct molecular aberrations, the antigen expression patterns of LSCs for these various subtypes of leukemias, at least in acute myeloid leukemia (AML), are very similar [2].