STIMULATED RAPID EXPRESSION IN-VITRO FOR EARLY DETECTION OF IN-VIVO T-CELL RECEPTOR MUTATIONS INDUCED BY RADIATION EXPOSURE

The T-cell receptor (TCR) mutation assay for in vivo somatic mutations is a sensitive indicator of exposure to ionizing radiation. However, this assay cannot be immediately applied after radiation exposure beca use expression of a mutant phenotype may require as long as several mo nths. in the present study, we eliminate this time lag by stimulating lymphocytes with a mitogen that can accelerate the turnover of TCR pro tein expression in T-cells, When lymphocytes obtained from healthy don ors were irradiated with various doses of X-rays and cultured with hum an interleukin-2 after phytohemagglutinin (PHA) pulse stimulation, the mutant frequency (MF) of CD4(+) T-cells increased dose dependently du ring the first 7 days, then decreased rapidly due to the growth disadv antage of mutant cells. This suggests that PHA stimulation can shorten the expression time of a mutant phenotype to within a week after radi ation exposure. The relationship between radiation dose and TCR IMF on the seventh day was best fitted by a linear-quadratic dose-response m odel. We applied this improved TCR mutation assay to gynecological can cer patients who received 5 days of localized radiotherapy, totaling a bout 10 Gy. The in vivo TCR MF in the patients did not change within a week after radiotherapy, whereas the in vitro TCR MF of PHA-stimulate d lymphocytes from the same patients significantly increased 7 days af ter initiating culture. The estimated mean radiation dose to the perip heral blood lymphocytes of the cancer patients was about 0.9 Gy, based on the in vitro linear-quadratic dose-response curve. This estimated dose was close to that described in a previous report an unstable-type chromosome aberrations from cervical cancer patients after receiving the same course of radiotherapy, On the basis of these findings, we pr opose that the improved TCR mutation assay is a useful biological dosi meter for recent radiation exposure.