The use of cryopreserved lymphocytes in assessing inter-individual radiosensitivity with the micronucleus assay

The feasibility of using cryopreserved lymphocytes to detect inter-individual differences in chromosomal radiosensitivity was investigated. Typically, such studies are conducted with fresh blood samples but, in a clinical setting, when availability of samples is unpredictable, this is not always convenient. The sensitivity of 23 normal healthy donors, 11 breast cancer patients who had shown severe acute skin reactions to radiotherapy and seven ataxia telangiectasia (A-T) heterozygotes was determined.

Thawed lymphocytes were exposed to high (HDR) or low dose rate (LDR) gamma irradiation (3.5 Gy) in Go, stimulated with PHA, treated with cytochalasin-B 24 h later and then harvested at 90 h for the determination of micronucleus (MN) yields in binucleate cells.

Each normal donor was tested one to three times. Mean MN yields were 76.1 +/- 9.3/100 cells at HDR and 44.5 +/- 5.3 at LDR, giving an LDR sparing effect of 39.6 +/- 9.3%. A relatively high proportion of tests failed to yield sufficient binucleate cells for analysis. Inter-experimental variability was also high and it was not possible to demonstrate inter-individual differences in sensitivity in spite of the use of an internal control sample from a single normal donor in each experiment. There was a small but significant increase in radiation-induced MN in the breast cancer patients compared with the normals at LDR (but not at HDR), but a complete overlap with the normal range. There was no increase in sensitivity in the A-T heterozygotes at HDR. The LDR samples failed because the LDR protocol reduced proliferation rates, and radiation-induced mitotic inhibition in this group was higher than in normals.

In comparison with previous experience with fresh blood samples, the use of frozen lymphocytes is not as satisfactory because: (1) experimental failures are higher; (2) inter-experiment variability is higher: (3) dose-rate sparing is lower, suggesting poorer repair; and (4) the ability to discriminate between breast cancer cases and normals is probably lower.