Variations in radiation sensitivity and repair among different hematopoietic stem cell subsets following fractionated irradiation

Abstract

The radiation dose-survival of various hematopoietic cell subsets in murine bone marrow (BM) was determined in the cobblestone area forming cell (CAFC) assay under conditions of single-, split-, and multiple- dose irradiation. A greater recovery in cell survival with decreasing dose per fraction, or increasing fraction number, was observed for primitive CAFC day-28 and day-35 than for CAFC day-6 and day-12 (colony- forming unit (CFU)-granulocyte macrophage and CFU-spleen day-12 equivalents). Linear quadratic (LQ) model analysis of CAFC survival data provided an estimate of the alpha/beta ratio that is an inverse index of the fractionation effect and is known to be lower for late than for acutely responding tissues. This analysis gave decreasing alpha/beta ratios with increasing primitiveness of the CAFC subset. These values were found to be comparatively low (about 4 Gy) for CAFC day-28 and day-35 and are in general agreement with previous studies on long-term repopulation in vivo. In contrast, alpha/beta ratios of CAFC day-6 and day-12 were relatively high (above 6 Gy) and are consistent with values obtained from acute marrow failure. Delayed harvesting of BM after a single dose of 6 Gy showed little evidence of proliferative repopulation over 1 week and hence the differential dose-sparing effect of fractionation among the CAFC subsets appears to be mostly attributable to the influence of sublethal damage repair. These results require a reevaluation of previous notions of marrow stem cell radiosensitivity and repair based on acute marrow lethality (LD50/30) or spleen colony (CFU-S) data, especially when applied to fractionated total body irradiation effects on long-term repopulating stem cells in a BM transplant setting.

Phenotypic and Functional Changes Induced in Hematopoietic Stem/Progenitor Cells After Gamma-Ray Radiation Exposure

“…In contrast to other hematological stresses, c-ray radiation exposure causes immediate damage to all intermediate subsets of the hematopoietic process, with various effects respective to their status in the hematopoietic hierarchy [18][19][20]. Although HSCs appear more resistant than most committed progenitors and precursors [20,21], it was recently shown that ionizing radiation (IR) can induce early apoptosis and long-lasting senescence among KSL stem/progenitor cells [22]. Intriguingly, in this latter study, no KSL cells were detected in the BM of sublethally irradiated mice 3 days after exposure, which is paradoxical because the hematopoietic system can recover from such nonlethal insults.…”

Dermal benzene and trichloroethylene induce aneuploidy in immature hematopoietic subpopulations in vivo

“…The potential hematotoxic effects of bz on stem cell populations have not yet been documented, although damage to these cells may be relevant for bz-induced leukemias. We used the CAFC system of Ploemacher et al [Ploemacher et al, 1991;Down et al, 1995] to monitor the hematotoxic effects of acute bz exposure on a broad range of progenitor and stem cells. Hematotoxicity to all progenitor cell types is observed 0.5 week after bz exposure (Fig.…”

“…2c, d). The effects of bz and TCE on hematopoiesis were also assessed using the CAFC (cobblestone area-forming cell) limiting-dilution assay, which probes a broad spectrum of immature hematopoietic subpopulations, ranging from cells capable of forming spleen colonies (CFU-S) to more primitive hsc with capabilities of multilineage hematopoietic reconstitution [Ploemacher et al, 1991;Down et al, 1995]. In the CAFC assay, subpopulation detection is dependent on culture duration: CAFC enumerated at long culture durations (i.e., Ͼ21 days) reflect proliferation of primitive hematopoietic subpopulations, whereas CAFC at shorter culture intervals (i.e., days 7-20) represent more mature cells (i.e., CFU-S, CFU-GM).…”

“…The low frequency of hsc coupled with the complexity of DNA damage assays has hampered investigation of genotoxin-induced alterations to the hsc genome. Fortunately, methodologies are now available to isolate hsc, assess genomic integrity, and probe the function of multiple hematopoietic subpopulations [Pinkel et al, 1986;Ploemacher et al, 1991;Okada et al, 1992;Down et al, 1995]. We used molecular cytogenetic techniques and hematopoietic functional assays to quantify genomic damage and hematotoxic effects of chemicals associated with environmentally induced leukemia.…”

1 Stem cells: characterization and measurement

“…The recognition of heterogeneity in the HSC compartment and the development of the CAFC assay allowing the estimation of HSC subset frequencies, and thus radiation survival, has led to a more balanced appraisal of the HSC compartment radiosensitivity. It is the CFU-S day-7/CAFC day-7-10 population that shows high radiation sensitivity and lack of SLD repair (Meijne et al, 1991(Meijne et al, , 1992Ploemacher et al, 1992), but with increasing primitivity CAFC subsets are far more radio-resistant and display high levels of SLD repair, matching or surpassing that of lung tissue (Down et al, 1995).…”