THE PHENOMENOLOGY AND POSSIBLE MECHANISMS OF A NEW EXPERIMENTAL-METHOD FOR ACCELERATING POSTIRRADIATION RESTORATION OF HEMATOPOIETIC STEM-CELL POTENTIAL

Extraction of bone marrow from one or several bones immediately after irradiation, with or without subsequent incubation for a short period under suitable conditions, and subsequent reimplantation into the same organism can reduce the lethal effect of irradiation in a number of s pecies, Extraction plus a period of incubation is referred to as the r eimplantation method, The effectiveness is roughly relative to the amo unt of bone marrow extracted and transplanted. This effect has been de monstrated by assays of 30-45-day survival and of hemopoietic stem cel l potential. The effectiveness of the reimplantation method has been t ested in a dose range of 6.5 to 8.5 Gy and was found to be 1.2-1.06 in terms of dose reduction factors assayed by bone marrow cellularity 9 days after exposure and 1.18-1.09 for survival of bone marrow colony-f orming units, The favorable effect of incubating irradiated bone marro w with cycloheximide on the stem cell potential has been proven by exp eriments using a donor-recipient method. The positive effect of the re implantation procedure and the partial extraction procedure on the ste m cell potential in irradiated mice can be shown as soon as 2 h after exposure and the procedures. The results suggest that there exist some reserves that can be stimulated to accelerate hemopoietic restoration in a heavily irradiated organism. The recruitment of these reserves s eems to be related to the response of the structures producing cytokin es after lethal irradiation. In addition, repair processes may be invo lved in the rescue of lethally irradiated hemopoietic stem cells. (C) 1996 by Radiation Research Society