Radiation sensitivity of the hemopoietic stem cell

Area of Science:

• Radiobiology
• Hematology
• Stem Cell Biology

Background:

• The LD50/30 after total-body irradiation (TBI) reflects animal radiosensitivity, determined by hemopoietic stem cells.
• Pluripotential stem cells are crucial, with mouse models extensively studied using spleen colony assays.
• In vitro assays like CFU-S and CFU-C quantify stem cells, but show variability in radiosensitivity parameters (D0 and N).

Purpose of the Study:

• To estimate hemopoietic stem cell surviving fractions at higher radiation doses (5-10 Gy) than typically studied.
• To investigate the hypothesis that a radioresistant stem cell subpopulation exists, potentially due to hypoxia.
• To determine the relative biological effectiveness (RBE) of fission neutrons for stem cell survival and lethality.

Main Methods:

• Derived stem cell surviving fractions using peripheral blood cell repopulation data in monkeys and spleen/bone marrow repopulation in mice after high-dose TBI.
• Calculated theoretical D0 values for hemopoietic stem cells.
• Determined RBEs for CFU-S survival and LD50/30 in BCBA mice using fission neutrons.

Main Results:

• Estimates of hemopoietic stem cell surviving fractions were derived for radiation doses between 5 and 10 Gy.
• Data suggest a small subpopulation of hemopoietic stem cells exhibits higher radioresistance than the majority.
• The RBEs for CFU-S survival and LD50/30 were similar, indicating the radioresistance is not due to hypoxia.

Conclusions:

• The radioresistance of the stem cell subpopulation responsible for survival at high doses is not attributable to hypoxic conditions.
• This finding has implications for understanding radiation effects on the hematopoietic system and developing radioprotective strategies.