Cryopreserving whole blood for functional assays using viable lymphocytes in molecular epidemiology studies

There is an increasing need for viable lymphocytes in performing phenotypic assays for biomarker studies. Both fresh and cryopreserved lymphocytes hav e been used for cell culture-based functional assays. However, fresh lympho cytes do not allow assays to be done in batches and cryopreservation of iso lated lymphocytes results in a considerable loss of viable cells. To invest igate the feasibility of using cryopreserved whole blood as a source of via ble lymphocytes in molecular epidemiology studies, two well-established bio markers, the host-cell reactivation (HCR) and mutagen sensitivity assays, w ere used to compare the method of cryopreserving whole blood with the tradi tional methods. In 25 paired blood samples assayed for DNA repair capacity (DRC) by the HCR assay, the DRC values of frozen whole blood (mean +/- SD, 11.59 +/- 3.07) were similar to those of frozen isolated lymphocytes (11.08 +/- 3.50). The correlation between the paired DRC values was 0.77 (P < 0.0 01). In 31 paired blood samples assayed for the <gamma>-radiation-induced c hromatid breaks by the mutagen sensitivity assay, there was no significant difference between the baseline level of chromatid breaks in lymphocytes fr om frozen blood (0.05 +/- 0.03) and fresh blood (0.06 +/- 0.03). The blasto genic rate and mitotic index of the cells used for the two assays were comp ared between the different processing methods. The lymphocytes from frozen whole blood were more sensitive to gamma -radiation, with a higher mean lev el of chromatid breaks (0.68 +/- 0.21) than that in fresh blood (0.42 +/- 0 .12, P < 0.01), and the correlation between the numbers of chromatid breaks in the paired samples was statistically significant (r = 0.61, P < 0.001). These data suggest that within the limits of the parameters investigated h ere, cryopreserved whole blood is a good source of viable lymphocytes for b iomarker assays in molecular epidemiological studies. (C) 2001 Elsevier Sci ence Ireland Ltd. All rights reserved.