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

Abstract

Purpose: The increased level of illegitimate V(D)J recombination at the T-cell receptor (TCR) loci in lymphoid tumours as well as in T lymphocytes of ataxia telangiectasia patients and humans exposed to carcinogens in vivo suggest that site-specific interlocus recombination events could serve as markers of genomic instability and early genetic changes associated with carcinogenesis. The purpose of this study was to investigate the ability of ionizing 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 3Gy of either X- or gamma irradiation in vitro. Growth factor-stimulated cell cultures were established, and cell samples for DNA extraction were taken immediately after exposure and at several time points during long-term growth. A PCR-based method was used to measure the frequency of variant cells with V gamma -J beta 1 TCR rearrangements. Results: The frequency of TCR beta / gamma -variant cells was not significantly different in the irradiated and control cultures at any time studied up to 55 days after PHA-stimulation, indicating that V(D)J-mediated V gamma -J beta 1 rearrangement is not induced by X- or gamma -irradiation under these conditions. However, in both irradiated and non-irradiated cultures, the frequency of TCR beta / gamma variants increased approximately fourfold after mitogen stimulation, from a normal background level of 0.3-0.4 10 -5 to 1.3-1.6 10 -5 at days 4-9. These levels then gradually declined during prolonged cultivation, and after 2-4 weeks the frequency of variant cells was below the detection limit (<0.13 10 -5). Conclusions: These results provide no evidence that TCRbeta/gamma gene rearrangements can be induced by X- or gamma -irradiation in vitro. However, in contrast with cells with normal TCR receptors, TCR beta / gamma -variant cells display a relative growth advantage for 1-2 weeks, followed by gradual loss of proliferative capacity. Eventually, they are eliminated from the cell population or outnumbered by cells with normal TCR. If there are similar differences in vivo between cells with hybrid and normal TCR, this may explain the previously reported time- and seasondependent changes in the frequency of cells with hybrid TCR in occupationally exposed populations and individuals receiving cytostatic treatment.