The frequency of illegitimate TCRβ/γ gene recombination in human lymphocytes: influence of age, environmental exposure and cytostatic treatment, and correlation with frequencies of t(14;18) and hprt mutation

Abstract

Chromosome translocations in lymphoid malignancies often involve V(D)J recombinase mediated events giving rise to aberrant T-cell receptor (TCR) and immunoglobulin genes, which have been suggested to be useful as markers of genomic instability, genotoxic exposure and cancer risk. Illegitimate rearrangements involving the TCRβ/γ loci on chromosome 7 create TCRβ/γ hybrid genes which occur at low frequency in peripheral blood lymphocytes (PBLs) of normal healthy individuals. To evaluate the utility of this marker, we studied the possible effects of age and genotoxic exposures on the TCRβ/γ gene variant frequency (VF), and compared the frequencies of hypoxanthine guanine phosphoribosyl transferase ( hprt) mutation, hprt exon 2/3 deletion, t(14;18) and TCRβ/γ gene rearrangements in cells from the same donors. The TCRβ/γ VF ranged five-fold among 16 middle aged blood donors with a mean of 0.74±0.29/10 5 PBLs, which is consistent with our previous estimate in healthy subjects. The TCRβ/γ VF was found to increase from birth until early adult life, and then to decrease with increasing age. Four testis cancer patients, who 6 years earlier had been treated with etoposide and other cytostatic drugs, showed TCRβ/γ VF similar to that in healthy controls. No increase of the TCRβ/γ VF was found among non-smoking PAH-exposed aluminum smelter workers compared to non-smoking controls. Smoking smelter workers showed decreased TCRβ/γ VF compared to non-smoking workers and controls, but in a follow-up study 2 years later the difference was no longer statistically significant, although the smoking smelter workers still showed a lower TCRβ/γ VF than the controls. No correlation was obtained between the TCRβ/γ VF and the t(14;18) or hprt mutant frequency (MF) in a group of healthy individuals. However, there was a statistically significant correlation between the TCRβ/γ VF and the hprt exon 2/3 deletion frequency in PBL DNA from the same donors. These results show that the TCRβ/γ VF in healthy individuals changes with age and correlates with the frequency of hprt exon 2/3 deletion, another marker of aberrant V(D)J recombination in T-cells. However, no effect of smoking or present or previous exposure to genotoxic agents on TCRβ/γ VF was observed in this study. Thus, further studies are needed to prove the utility of TCRβ/γ gene rearrangement as a marker of genotoxic exposure.