Studies on the Hyperthermic Sensitivity of theMurine Hematopoietic Stem Cell Compartment.II. Heat Effect on Donor Stem Cells With Long-Term Repopulating Ability

Variations in hyperthermic sensitivity among different hematopoietic progenitor and stem cell populations of the bone marrow have been previously described for clonogenic subsets responsible for short-term hematopoiesis. However, less is known of the heat sensitivity of more primitive stem cells capable of long-term repopulation in irradiated recipients. In the present study, control and heat-treated (60 minutes at 43 degrees C) donor bone marrow cells from congenic B6-Gpi-1(a) mice were transplanted at different cell doses (10(4), 10(5), 10(6), and 10(7) nucleated cells) in pre-irradiated (6 Gy) BG-Gpi-lb mice. The development and levels of donor marrow engraftment were determined from blood Gpi phenotyping, and the bone marrow dose required for equivalent longterm engraftment at 20 weeks provided an estimate of the surviving fraction corresponding to primitive stem cells of long-term repopulating ability (LTRA). Comparison with previous bone marrow cell survival values demonstrates that LTRA cells are less sensitive to hyperthermic treatment than other hematopoietic subsets, confirming a relationship between the heat sensitivity and the hierarchical structure of the hematopoietic stem cell compartment.