Comparison of radiosensitivity between human hematopoietic cell lines derived from patients with Down's syndrome and from normal persons

Increased radiosensitivity of cell lines derived from a Down's syndrome patient with ocular telangiectasia

Studies on radiosensitivity of cells from Down's syndrome (DS) patients were stimulated by the observation of their increased susceptibility to leukemia. While lymphocytes from DS patients were found to consistently show increased chromosomal aberrations after exposure to ionizing radiation, conflicting reports have been published on the radiosensitivity of fibroblasts and lymphoblastoid cell lines (LCL) derived from these patients. In the present study, cultured skin fibroblast lines developed from a DS patient with ocular telangiectasia and five normal subjects were compared for both cell killing and chromosomal aberrations (breaks, translocations, inversions, dicentrics, and rings) after low dose-rate gamma-irradiation. The LCLs developed from the patient and two normal persons were also compared for chromosomal radiosensitivity using the same irradiation protocol. A comparison of the D10 (radiation dose resulting in 10% survival) values estimated from the survival curves and the frequencies of induced chromosome aberrations in different cell lines showed that the DS cells were more radiosensitive than the respective controls. The increased cellular radiosensitivity of the DS patient reported here could be due to a combination of genetic factors (DS plus a gene for hypersensitivity to radiation) and, thus, may not be representative of all DS patients. Alternatively, the use of low dose-rate irradiation could be a factor in revealing the radiosensitivity of DS fibroblasts in general.

Radiosensitive Down syndrome lymphoblastoid lines have normal ionizing-radiation-induced inhibition of DNA synthesis

The extent of X-ray-induced inhibition of DNA synthesis was determined in radiosensitive lymphoblastoid lines from 3 patients with Down syndrome and 3 patients with ataxia telangiectasia (AT). Compared to 6 normal control lines, the 3 AT lines were abnormally resistant to X-ray-induced inhibition of DNA synthesis, while the 3 Down syndrome lines had normal inhibition. These results demonstrate that radiosensitive human cells can have normal X-ray-induced inhibition of DNA synthesis and provide new evidence for the dissociation of radiosensitivity from radioresistant DNA synthesis.

Radiation effects on cultured human lymphoid cells. Analysis using the growth extrapolation method

The cloning efficiency of human normal and malignant lymphoid cells is usually low. Radiation effects in vitro on such cells can therefore not be analysed with conventional cloning. However, this problem can be circumscribed by using the growth extrapolation method. A panel of human leukemia-lymphoma cell-lines representing Epstein-Barr virus carrying lymphoblastoid cells of presumed nonneoplastic derivation and neoplastic T- and B-lymphocytes was used to test the efficiency of this method. The sensitivity to radiation could be determined for all these cell types. The growth extrapolation method gave generally the same result as conventional cloning demonstrated by comparison with one exceptional cell-line with capacity for cloning in agar. The sensitivity varied largely between the different cell types. A common feature was that none of the cell lines had a good capacity to accumulate sublethal radiation injury.