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

Purpose: The feasibility of using cryopreserved lymphocytes to detect inter -individual differences in chromosomal radiosensitivity was investigated. T ypically, such studies are conducted with fresh blood samples but, in a cli nical setting, when availability of samples is unpredictable, this is not a lways convenient. The sensitivity of 23 normal healthy donors, 11 breast ca ncer patients who had shown severe acute skin reactions to radiotherapy and seven ataxia telangiectasia (A-T) heterozygotes was determined. Materials and methods: Thawed lymphocytes were exposed to high (HDR) or low dose rare (LDR) gamma irradiation (3.5 Gy) in G(0), stimulated with PHA, t reated with cytochalasin-B 24 h later and then harvested at 90 h for the de termination of micronucleus (MN) yields in binucleate cells. Results: Each normal donor was tested one to three times. Mean MN yields we re 76.1 +/- 9.3/100 cells at HDR and 44.5 +/- 5.3 at LDR, giving an LDR spa ring effect of 39.6 +/- 9.3%. A relatively high proportion of tests failed to yield sufficient binucleate cells for analysis. Inter-experimental varia bility was also high and it was not possible to demonstrate inter-individua l differences in sensitivity in spite of the use of an internal control sam ple from a single normal donor in each experiment. There was a small bur si gnificant increase in radiation-induced MN in the breast cancer patients co mpared with the normals at LDR (but not at HDR), but a complete overlap wit h the normal range. There was no increase in sensitivity in the A-T heteroz ygotes at HDR. The LDR samples failed because the LDR protocol reduced prol iferation rates, and radiation-induced mitotic inhibition in this group was higher than in normals. Conclusions: In comparison with previous experience with fresh blood sample s, the use of frozen lymphocytes is not as satisfactory because: (1) experi mental failures are higher; (2) inter-experiment variability is higher: (3) dose-rate sparing is lower, suggesting poorer repair and (4) the ability t o discriminate between breast cancer cases and normals is probably lower.