Radiosensitivity of CD4 and CD8 positive human T lymphocytes by an in vitro colony formation assay

The recent development of an in vitro lymphocyte colony assay provides a new opportunity to examine possible variations in human radiosensitivity using peripheral blood lymphocytes (PBL) in place of the hitherto used skin fibroblast assay. Our recent study showed that most of the colonies consisted of lymphocytes bearing CD4 or CD8 antigens. Since the fraction of CD4+ and CD8+ cells in PBL differs among individuals, it was suspected that individual radiosensitivity might be biased by the different subset frequencies if the dose-survival curves of the CD4+ and CD8+ cells differed. In the present study, CD4+ lymphocytes (helper/inducer T cells) and CD8+ lymphocytes (suppressor/cytotoxic T cells) were isolated from PBL and their dose-survival curves were determined. The results showed that the D10 (the dose required to reduce the surviving fraction to 10 %) was quite similar for these two types of cells (3.13 ± 0.10 Gy [mean ±SD] for CD4+, 3.34 ± 0.50 Gy for CD8+ and 3.07 ± 0.05 Gy for the unsorted cells), supporting the use of a whole PBL population for screening of individuals with altered radiosensitivity. (author)