Variations in the frequency of T-cell receptor beta/gamma-interlocus recombination in long-term cultures of non-irradiated and X- and gamma-irradiated human lymphocytes

Purpose: The increased level of illegitimate V(D)J recombination at the T-c ell receptor (TCR) loci in lymphoid tumours as well as in T lymphocytes of ataxia telangiectasia patients and humans exposed to carcinogens in vivo su ggest that site-specific interlocus recombination events could serve as mar kers of genomic instability and early genetic changes associated with carci nogenesis. The purpose of this study was to investigate the ability of ioni zing radiation to induce TCR beta/gamma-interlocus rearrangements in human lymphocytes in vitro. Materials and methods: Peripheral blood lymphocytes (PBL) from two healthy donors were exposed to 3 Gy of either X- or gamma-irradiation in vitro. Gro wth factor-stimulated cell cultures were established, and cell samples for DNA extraction were taken immediately after exposure and at several time po ints during long-term growth. A PCR-based method was used to measure the fr equency of variant cells with V gamma-J beta 1 TCR rearrangements. Results: The frequency of TCR beta/gamma-variant cells was not significantl y different in the irradiated and control cultures at any time studied up t o 55 days after PHA-stimulation, indicating that V(D)J-mediated V gamma-J b eta 1 rearrangement is not induced by X- or gamma-irradiation under these c onditions. However, in both irradiated and non-irradiated cultures, the fre quency of TCR beta/gamma variants increased approximately fourfold after mi togen stimulation, from a normal background level of 0.3-0.4 x 10(-5) to 1. 3-1.6 x 10(-5) at days 4-9. These levels then gradually declined during pro longed cultivation, and after 2-4 weeks the frequency of variant cells was below the detection limit (< 0.13 x 10(-5)). Conclusions: These results provide no evidence that TCR beta/gamma gene rea rrangements can be induced by X- or gamma-irradiation in vitro. However, in contrast with cells with normal TCR receptors, TCR beta/gamma-variant cell s display a relative growth advantage for 1-2 weeks, followed by gradual lo ss of proliferative capacity. Eventually, they are eliminated from the cell population or outnumbered by cells with normal TCR. If there are similar d ifferences in vivo between cells with hybrid and normal TCR, this may expla in the previously reported time- and season-dependent changes in the freque ncy of cells with hybrid TCR in occupationally exposed populations and indi viduals receiving cytostatic treatment.