Comparison of tritiated thymidine labeling and suicide indices in acute nonlymphocytic leukemia.

Leukemic cells were obtained from the bone marrow or peripheral blood of patients with acute myelocytic leukemia or one of its variants. The tritiated thymidine labeling index of the leukemic cells and the suicide index of the cells that produce clusters in vitro were compared. The suicide index was 5 times greater than the labeling index (S.E.) [54 +/- 8% versus 12 +/- 3%], demonstrating the presence of a highly proliferative subpopulation of leukemic cells (in vitro colony-forming unit) among the relatively slowly proliferating leukemic cells. Since the leukemic in vitro colony-forming unit appears to be the progenitor of the recognizable leukemic cell population, the proliferative characteristics of the recognizable leukemic cells may not be reflective of that of leukemic stem cells.