Effect of hyperthermia on both primary proliferation and self-renewal of human leukemic progenitor cells in vitro: its application to in vitro purging.

Self-renewal, as defined by the capacity to yield new colonies following replating, is an important function of leukemic progenitors (L-CFU) to originate self-maintaining clones. In this work, we studied the effect of hyperthermia (41-44 degrees C) on the growth of human L-CFU derived primary colonies and of secondary colonies formed by replating to evaluate the purging effect of human L-CFU by heat. The survival curves clearly demonstrated much greater hyperthermic sensitivity of L-CFU compared to normal granulocyte-macrophage progenitors (CFU-GM) at all temperatures (41-44 degrees C) studied. At 42 degrees C or higher, L-CFU decreased (by more than 2 log reduction) dramatically and therefore were unable to form colonies in vitro. At 42 degrees C and 43 degrees C, 65 and 30%, respectively, of CFU-GM obtained from remission and normal marrows were left after 1 h exposure. At 44 degrees C, however, CFU-GM derived colonies disappeared after a 2 h exposure. In the four available patients with acute myelogenous leukemia, secondary colonies formed by replating were decreased in proportion to the decreasing primary colonies during heating (42 and 43 degrees C). However, their self-renewal capacity was retained in vitro until the primary colonies disappeared. These observations suggest that heat exposure at 43 degrees C for 1 h could be the most effective conditions for in vitro purging of human L-CFU because of the wide difference between surviving fractions of CFU-GM and L-CFU.