Heat sensitivity, thermotolerance and protein synthesis of granulocyte and macrophage progenitors from mice and from long-term bone marrow cultures

Ex-vivo purging of leukaemic cells by single or fractionated heating during bone marrow transplantation for acute myeloid or lymphoblastic leukaemias may be possible since many leukaemic cells may be more sensitive to killing by heat than normal bone marrow colony-forming unit-granulocyte and macrophages (CFU-GM). In these studies we have compared heat response, thermotolerance response and heat shock protein (HSP) synthesis of bone marrow progenitors from intact mice or bone marrow obtained from 37°C or 33°C long-term bone marrow cultures (LTBMCs). Such studies were done to examine whether CFU-GM responses to heat are influenced by in vitro growth conditions. In terms of heat response CFU-GM progenitors from LTBMCs showed increased heat sensitivity when compared to CFU-GM from mice, with CFU-GM from 33^CC cultures being more heat-sensitive than those from 37°C cultures. The kinetics of thermotolerance development and decay in CFU-GM were similar from all three systems. Thermotolerance was maximum at 3-9 h, began to decay by 24 h and was absent by 48 h from cells obtained from mice and LTBMCs grown at 37°C. However, CFU-GM from 33°C LTBMCs showed a delay in decay of thermotolerance. The kinetics of die development and decay of thermotolerance remained as above and was independent of incubation conditions whether bone marrow was left in situ or incubated in vitro in medium containing various colony-stimulating factors (CSF) or medium containing no CSF. The synthesis of HSPs was measured by one-and two-dimensional gel electrophoresis. Synthesis of HSP-70 kd was detected following a triggering dose of heat at 0-3 h for bone marrow heated in vivo and 0-6 h for bone marrow from LTBMCs. These studies indicate that CFU-GM heat and thermotolerance response was influenced by the temperature at which the cultures were maintained but not by other differences present in their microenvironment.