RADIOSENSITIVITY OF PROGENITOR CELLS OF THE HEMATOPOIETIC MICRO-ENVIRONMENT

The radiosensitivity of cells which transfer hematopoietic microenvironment was studied in a model in which femoral bone marrow is transplanted under the renal capsule of a mouse. For in vitro 137Cs γ irradiation, the D0 for the hematopoietic microenvironment transferring units (HMTU) was 444 ± 5 rad and the extrapolation number (n) was 5.2. The value of the quasi-threshold dose (D(q)) was approximately 500 rad which reflects the high capacity of HMTU for repair of sublethal injury. After in vivo exposure to γ rays, HMTU radiosensitivity was somewhat higher (D0 of 325 ± 25 rad, n of 3.5, and D(q) of 635 rad). For in vitro irradiation with fast neutrons, the D0 was 161± 19 rad and n, 1.4. On the basis of the fraction of transplant failures after exposure to different radiation doses it was calculated that one femoral marrow plug contains about 50 HMTU.