Acute hematological tolerance to multiple fraction, whole body, low dose irradiation in an experimental murine system

Using a dose fractionation scheme patterned after the current regimen for treatment of disseminated non-Hodgkin lymphoma, the authors studied the effects of irradiation on progenitor and effector cells for hematopoiesis in five-month-old BC3F1 mice. Fractions of 20 or 50 rad (0.2 or 0.5 Gy) total body irradiation were given twice weekly to a final total dose of 200 or 500 rad (2 or 5 Gy), respectively. Weekly assays revealed a marked, sustained depression of stem cell activity, measured as numbers of spleen colony-forming units (CFU-S) and in vitro colony-forming cells (CFU-C), without corresponding depression of effector cells (red and white cells, and platelets). The lack of correlation between numbers of stem cells and peripheral elements is relevant to clinical assessment of marrow reserve.