Response of mouse thymic cells to radiation after transfusion of mesenchymal stem cells.

Thymic lymphoma is a highly invasive and even metastatic cancer. This study investigated the effects of mesenchymal stem cells (MSCs) transfusion on cell cycle, cell proliferation, CD3 expression, mutation frequency of T cell receptor using mouse model of thymic lymphoma.C57BL/6J young mouse models of thymoma were injected with MSCs. Six months later, the thymus was taken for pathological examination and flow cytometry studies. The cells were labeled with anti-CD4, CD8, CD3, propidium iodide, or CFDA-SE, cell cycle, proliferation kinetics, and mutation frequency of T cell receptor, respectively.Pathologic results showed that control had clear corticomedular structure with regularly shaped lymphocytes. After radiation, the thymus structure was completely destroyed, with lymphoid tumor cells diffusely distributed and heavily stained, and large nuclei. Transfusion of MSCs resulted in normal thymus structure. Cytometry studies showed that there were more CD4-/CD8- T cells in the thymus of irradiated mice than in control; transfusion of MSCs led to reduced CD4-/CD8- T cells. In irradiated mice, there were less CD4+/CD8+ T cells than in control and MSCs transfusion groups. It was observed that there were more cells arrested in G1 phase in the thymus cells and CD4-/CD8- T cells in irradiated mice than in other 2 groups, whereas there were more cells arrested in S phase in CD4+/CD8+ and CD4+/CD8- T cells in irradiated mice than in the other mice. In the thymus cells, and CD4+/CD8+ and CD4+/CD8- T cells, irradiated mice group had significantly less parent, G2, G3, and G4 cells, and more cells at higher generations, and also higher proliferation index. In CD4-/CD8- T cells, irradiated mice had significantly more parent, G2, and G3 cells, and less G4, G5, G6, and propidium iodide, as compared with the other 2 groups. The expression of CD3 in CD4/CD8 T cells was significantly higher than in control. MSCs transfusion improved CD3 expression, but was still less than the control. Irradiation resulted in very high mutation frequency of T cell receptor, which was barely affected by MSCs transfusion.Mesenchymal stem cell transfusion is able to restore the cell cycle and cell proliferation, but not CD3 expression and mutation frequency of T cell receptor in irradiated mice to control level.

[Frequency of Lymphocytes with Mutations at the Locus of T-Cell Receptor in Residents of Radiation Polluted Bryansk Region 28 Years after the Chernobyl Nuclear Power Plant Accident].

The aim of this study is to assess the level of somatic mutagenesis according to the frequency of lymphocytes bearing mutations at the locus of T-cell receptor (TCR) in the residents of the Bryansk region contaminated with radionuclides as a result of the Chernobyl accident. The study was :conducted in 2014 in two regional centers - Klintsy and Novozybkov (average¹³7Cs pollution density of 322 and 708 kBq/m²,.respectively). The average frequency of the TCR-mutant cells in the total group of examined residents of the Bryansk region (n = 237) was not significantly different from that in the group of agematched control persons living in un- contaminated areas (n = 146): 3.8 x 10⁻4 vs 3.5 x 10⁻4, respectively (p = 0.84). However, after separation of examinees into 3 groups depending on age at the start of irradiation (at.the moment of the Chernobyl acci- dent) it was found that the average frequency of the TCR-mutant cells in the persons exposed in utero was 1.6 higher than that in the control group (p = 0.04). Proportion of persons with an increased frequency of the mutant cells (more than the age norm of this indicator) among prenatally exposed population reached 23.8%; which was about.4 times higher than in the control group (p = 0.04). Proportion of persons with an increased frequency of the TCR-mutant cells in group "0-17 years at the start of irradiation", was about 2 times higher than in controls, but this difference was not statistically significant (8.0% vs 4.3%, respectively, p = 0.33). In the third group "18 or more years old at the start of irradiation" we could not register the difference in the average frequency of theTCR mutant cells or the proportion of persons with an increased frequency of these cells in comparison with the age-matched control group. In general, comparison with earlier data shows that age-related regularities of somatic mutagenesis established 15-18 years after the Chernobyl accident persist at a later date (after 28 years in this study).

Electrically controlled molecular recognition harnessed to activate a cellular response.

Seamless embedment of electronic devices in biological systems is expected to add the outstanding computing power, memory, and speed of electronics to the biochemical toolbox of nature. Such amalgamation requires transduction of electronic signals into biochemical cues that affect cells. Inspired by biology, where pathways are directed by molecular recognition, we propose and demonstrate a generic electrical-to-biological transducer comprising a two-state electronic antigen and a chimeric cell receptor engineered to bind the antigen exclusively in its "on" state. T-cells expressing these receptors remain inactivated with the antigen in its "off" state. Switching the antigen to its "on" state by an electrical signal leads to its recognition by the T-cells and correspondingly to cell activation.

[Establishment and verification of dose effect relation curves between T cell receptor gene mutation frequency and ionizing radiation dose].

OBJECTIVE: To establish the dose-effect curve between TCR MF and ionizing radiation. METHODS: Peripheral lymphocytes were collected from 8 healthy adults (4 males and 4 females) and cultured in vitro with 12 well culture plates. They were stimulated by PHA-P and IL-2 after exposed to different doses of irradiation (0.00 - 8.00 Gy) and cultured for 7 d. The dose-effect curve was established after measuring TCR MF using flow cytometry. Also, using the same method, we separated and cultured the peripheral lymphocytes collected from 16 radiotherapy cancer patients, whose radiation styles and doses were different, and then measured TCR MF to estimate the whole equivalent dose of radiotherapy patients through the dose-effect curve. Peripheral blood was collected and cultured, chromosome aberration (dicentric and ring) was determined under microscope to estimate irradiation dose. RESULTS: The relationship of dose-effect between the TCR MF and ionizing radiation (0.00 - 8.00 Gy) was well, the curve of large dose group (2.00 - 8.00 Gy), low dose group (0.00 - 1.00 Gy) and 0.00 - 8.00 Gy dose group were met with the quadratic polynomial model, the equation was TCR MF = -32.8579 + 20.5436D + 0.6341D(2), TCR MF = 1.796 + 0.017D + 5.155D(2) and TCR MF = -0.6229 + 6.305D + 0.6919D(2), respectively. D was the radiation dose (Gy). Using the established curve and the chromosome aberration method to estimate the systemic exposure dosage, the average relative deviation was 16.8%. CONCLUSION: The curve established by the TCR gene mutation analysis technology can be applied to exposure dose estimation of victims in ionization radiation accidents.

Requirements for effective antitumor responses of TCR transduced T cells.

Adoptive transfer of TCR gene-modified T cells has been proposed as an attractive approach to target tumors for which it is difficult or impossible to induce strong tumor-specific T cell responses by vaccination. Whereas the feasibility of generating tumor Ag-specific T cells by gene transfer has been demonstrated, the factors that determine the in vivo effectiveness of TCR-modified T cells are largely unknown. We have analyzed the value of a number of clinically feasible strategies to enhance the antitumor potential of TCR modified T cells. These experiments reveal three factors that contribute greatly to the in vivo potency of TCR-modified T cells. First, irradiation-induced host conditioning is superior to vaccine-induced activation of genetically modified T cells. Second, increasing TCR expression through genetic optimization of TCR sequences has a profound effect on in vivo antitumor activity. Third, a high precursor frequency of TCR modified T cells within the graft is essential. Tumors that ultimately progress in animals treated with this optimized regimen for TCR-based adoptive cell transfer invariably display a reduced expression of the target Ag. This suggests TCR gene therapy can achieve a sufficiently strong selective pressure to warrant the simultaneous targeting of multiple Ags. The strategies outlined in this study should be of value to enhance the antitumor activity of TCR-modified T cells in clinical trials.

[Transgenerational genomic instability in children of liquidators of the accident at the ChNPP (cytogenetic and immunogenetic characteristics)].

A complex of cytogenetic and of immunogenetic study of the state of the lymphocyte genomes in the liquidators of the ChNPP accident and their unirradiated children has been carried out for the first time. Increased frequencies of the chromosome aberrations, of gene mutations (TCR mutations) and of predictors of apoptosis (cells with CD95+ immunophenotype) have been revealed in both generations. The analysis of correlations between the parameters under study has demonstrated distinctive features characteristic of induction of genomic instability in the organism of unirradiated children as compared to their fathers--liquidators directly exposed to radiation. Individual variability of genome destabilization were observed by all criteria used and manifested themselves in the diverse spectrum of transgenerational mutational effects and in different levels of their expression. The results obtained demonstrate the necessity of integral evaluation of the state of the genome using several genetic criteria to reveal transgenerational genomic instability in children of a special category--the offsprings of irradiated parents.

Radiation sensitivity and genomic instability in the hematopoietic system: Frequencies of micronucleated reticulocytes in whole-body X-irradiated BALB/c and C57BL/6 mice.

Using flow cytometry, we quantified the number of micronucleated reticulocytes in peripheral blood of whole-body X-irradiated mice in order to evaluate the radiation sensitivity and the induced genomic instability of the hematopoietic system. An acute effect of radiation dose as small as 0.1 Gy was detectable 2 days after irradiation, and the radiation dose effect was significantly greater in BALB/c mice than in C57BL/6 mice, that is, 3.0- and 2.3-fold increases in frequencies of micronuclei were noted in the two groups of mice, respectively. Even 1 year after irradiation, mice irradiated with 2.5 Gy of X-rays showed significantly increased frequencies of micronucleated reticulocytes, that is, 1.6- and 1.3-fold increases in BALB/c and C57BL/6 mice, respectively. However, this delayed effect was not apparent when the same mice were analyzed for T-cell receptor mutant frequencies in splenocytes. A significant mouse strain difference in the delayed radiation effect on micronucleated reticulocyte frequencies was noted as well. The results indicate that delayed genomic effects of irradiation on the murine hematopoietic system can persist in vivo for prolonged periods, and that there are mouse strain differences in sensitivity to radiation-induced genomic instability.

Ultraviolet irradiation suppresses T cell activation via blocking TCR-mediated ERK and NF-kappa B signaling pathways.

UV irradiation is carcinogenic and immunosuppressive. Previous studies indicate that UV-mediated alteration of APCs and induction of suppressor T cells play a critical role in UV-induced immune suppression. In this study, we show that UV irradiation can directly (independently of APCs and suppressor T cells) inhibit T cell activation by blocking TCR-mediated phosphorylation of ERK and IkappaB via overactivation of the p38 and JNK pathways. These events lead to the down-modulation of c-Jun, c-Fos, Egr-1, and NF-kappaB transcription factors and thereby inhibit production of cytokines, e.g., IL-2, IL-4, IFN-gamma, and TNF-alpha, upon TCR stimulation. We also show that UV irradiation can suppress preactivated T cells, indicating that UV irradiation does not only impair T cell function in response to T cell activation, but can also have systemic effects that influence ongoing immune responses. Thus, our data provide an additional mechanism by which UV irradiation directly suppresses immune responses.

[Comparative investigation of structural and gene somatic mutations in workers of nuclear chemical plants. II. Frequency of lymphocytes mutant in T-cell receptor loci].

Frequency of lymphocytes mutant at T-cell receptor (TCR) loci was defined in 42 workers of nuclear chemical plants. In 11 persons mainly exposed to external radiation the mean frequency of TCR-mutant lymphocytes was statistically significant by higher compared with control group of unexposed donors: 9.1 x 10(-4) vs 3.5 x 10(-4) correspondently (p < 0.01). Frequency of TCR-mutant lymphocytes did not correlate neither the frequency of structural mutations non doses of external exposure. In group of workers exposed to combined external and internal radiation (n = 31) the average frequency of TCR-mutant lymphocytes was higher compared with control level: 8.9 x 10(-4) vs 3.5 x 10(-4) correspondently (p < 0.01). Correlations between the frequency of TCR-mutant cells and Pu content in organism (r = 0.5; p = 0.005) and between the frequency of chromosome aberration of unstable and stable types (r = 0.5; p = 0.002 and r = 0.6; p = 0.036, correspondently) were set. Comparison of results of analysis of structural and gene mutations allows us to supose that in case of external exposure the observed disturbances can result from genome instability in remote period after irradiation. In case of combined exposure the genetic changes were possibly caused by the constant action of alpha-radiation from Pu containing in the body.

Dose response for T-cell receptor (TCR) mutants in patients repeatedly treated with 131I for thyroid cancer.

The T-cell receptor mutant frequency (TCR-Mf) was measured in 53 young adults, who were treated with radioiodine for thyroid cancer. Patients came from the southern part of Belarus. This region had suffered the most from the Chernobyl Disaster. TCR-Mf was determined by flow cytometry before and after 1 to maximal 10 treatments. Before treatment, TCR-Mf of patients was 2.0 x 10(-14). This Mf value is in the same range as that of young healthy students. After radioiodine therapy (RIT), TCR-Mf increases within about half a year to a maximum. The increase per one mGy to red marrow was 8.7 x 10(-7). After the maximum TCR-Mf declines exponentially. The half-life of TCR mutants was found to be 3.2 years. On the basis of these data, a calibration curve for the use of TCR-Mf as a biological dosimeter is given.

Characterization of a real time H2O2 monitor for use in studies on H2O2 production by antibodies and cells.

It was recently shown that antibodies catalyze a reaction between water and ultraviolet light (UV) creating singlet oxygen and ultimately H2O2. Although the in vivo relevance of these antibody reactions is unclear, it is interesting that among a wide variety of non-antibody proteins tested, the T cell receptor is the only protein with similar capabilities. In clinical settings UV is believed to exert therapeutic effects by eliminating inflammatory epidermal T cells and we hypothesized that UV-triggered H2O2 production is involved in this process. To test the hypothesis we developed tools to study production of H2O2 by T cell receptors with the long-term goal of understanding, and improving, UV phototherapy. Here, we report the development of an inexpensive, real time H2O2 monitoring system having broad applicability. The detector is a Clark oxygen electrode (Pt, Ag/AgCl) modified to detect UV-driven H2O2 production. Modifications include painting the electrode black to minimize UV effects on the Ag/AgCl electrode and the use of hydrophilic, large pore Gelnots electrode membranes. Electrode current was converted to voltage and then amplified and recorded using a digital multimeter coupled to a PC. A reaction vessel with a quartz window was developed to maintain constant temperature while permitting UV irradiation of the samples. The sensitivity and specificity of the system and its use in cell-free and cell-based assays will be presented. In a cellfree system, production of H2O2 by CD3 antibodies was confirmed using our real time H2O2 monitoring method. Additionally we report the finding that splenocytes and Jurkat T cells also produce H2O2 when exposed to UV light.

ELF magnetic fields initiate protein tyrosine phosphorylation of the T cell receptor complex.

The human T cell line Jurkat registers a sinusoidal extremely low frequency (ELF), 0.10 mT magnetic fields (MFs) at the level of the plasma membrane. In this study, the protein tyrosine phosphorylation (PY) of two membrane-associated proteins in Jurkat cells were examined following a short-term MFs exposure, the zeta chains and the Src kinases p56lck. These proteins are interesting to study since the earliest biochemical event upon T cell receptor (TcR) activation is PY of the zeta chains. These signalling chains in the TcR complex was assessed using Western blotting and the activation of the p56lck kinase was analysed by in vitro kinase assay. The MFs exposure of Jurkat for 5 min activated p56lck and resulted in PY of zeta. These findings are in line with earlier reports on how MFs exposure affects signal transduction in Jurkat.

Gamma-irradiation directly affects the formation of coding joints in SCID cell lines.

SCID mice have a defect in the catalytic subunit of the DNA-dependent protein kinase, causing increased sensitivity to ionizing radiation in all tissues and severely limiting the development of B and T cell lineages. SCID T and B cell precursors are unable to undergo normal V(D)J recombination: coding joint and signal joint products are less frequently formed and often will exhibit abnormal structural features. Paradoxically, irradiation of newborn SCID mice effects a limited rescue of T cell development. It is not known whether irradiation has a direct impact on the process of V(D)J joining, or whether irradiation of the thymus allows the outgrowth of rare recombinants. To investigate this issue, we sought to demonstrate an irradiation effect ex vivo. Here we have been able to reproducibly detect low-frequency coding joint products with V(D)J recombination reporter plasmids introduced into SCID cell lines. Exposure of B and T lineage cells to 100 cGy of gamma irradiation made no significant difference with respect to the number of coding joint and signal joint recombination products. However, in the absence of irradiation, the coding joints produced in SCID cells had high levels of P nucleotide insertion. With irradiation, markedly fewer P insertions were seen. The effect on coding joint structure is evident in a transient assay, in cultured cells, establishing that irradiation has an immediate impact on the process of V(D)J recombination. A specific proposal for how the DNA-dependent protein kinase catalytic subunit influences the opening of hairpin DNA intermediates during coding joint formation in V(D)J recombination is presented.

Irradiation-mediated rescue of T cell-specific V(D)J recombination and thymocyte differentiation in severe combined immunodeficient mice by bone marrow cells.

In SCID (severe combined immunodeficient) mice, proper assembly of immunoglobulin and T cell receptor (TCR) genes is blocked by defective V(D)J recombination so that B and T lymphocyte differentiation is arrested at an early precursor stage. Treating the mice with gamma irradiation rescues V(D)J rearrangement at multiple TCR loci, promotes limited thymocyte differentiation, and induces thymic lymphomas. These effects are not observed in the B cell lineage. Current models postulate that irradiation affects intrathymic T cell precursors. Surprisingly, we found that transfer of irradiated SCID bone marrow cells to unirradiated host animals rescues both TCR rearrangements and thymocyte differentiation. These data indicate that irradiation affects precursor cells at an earlier stage of differentiation than was previously thought and suggest new models for the mechanism of irradiation rescue.

[Long-term effects of chronic radiation exposure on the level of somatic mutations in peripheral blood cells]. / Vliianie khronicheskogo radiatsionnogo vozdeistviia na uroven' somaticheskikh mutatsii v kletkakh perifericheskoi krovi liud ei v otdalennye sroki.

The level of comatic mutations was studied at GPA locus and in the TCR system at late times since the onset of radiation exposure in persons exposed to chronic radiation accidents at the Mayak Production Association in the period 1949-1952. Individuals with predominantly external gamma-exposure and those with predominantly internal (mainly due to 90Sr) exposures have been identified among the exposed population. The average dose to red bone marrow made up 121.5 cSv with individual values ranging from 11.0 to 462.7 cSv. An increased frequency of TCR-mutant lymphocytes was noted for exposed subjects. The level of GPA-variant erythrocytes of different types in the study group did not differ from the respective value registered in control. The analysis of TCR status showed no dependence of mutant cell frequency on exposure dose. The assumption is made that the rate of exposure dose and the nature of its formation (chronic exposure) exert a decisive influence on the level of somatic mutations in peripheral blood cells in humans.

[Determination of mutation frequency at loci of glycophorin A and T-cell receptors: informativeness for biological dosimetry of acute and prolonged irradiation]. / Opredelenie chastoty mutatsii po lokusam glikoforina A i T-kletochnogo retseptora: informativnost' dlia biologicheskoi dozimetrii ostrogo i prolongirovannogo oblucheniia.

The frequencies of somatic mutations at loci of glycophorin A (GPA) and T-cell receptor (TCR) were determined in persons exposed professionally to ionizing radiation or a result of accidents at nuclear power plants and in control donors. Dependence of glycophorin A mutant (NO) cell frequency on doses of acute (up to 3.5 Gy) and prolonged (up to 15.0 Gy) irradiation was shown. The slope of linear regression corresponded to increase of NO-mutant frequency by 31.1 x 10(-6)/Gy (r = 0.87, p < 0.0001) for acute irradiation and by 6.3 x 10(-6)/Gy (r = 0.61, p < 0.0001) for prolonged one. The 5-fold decrease of the linear regression slope in the case of prolonged irradiation makes significantly worse permissive ability of the GPA test. Therefore its use for biological dosimetry of prolonged irradiation is not expedient in dose interval up to 1 Gy. The frequency of mutations in genes of T-cell receptor significantly correlated with dose of irradiation only in group of donors with recent radiation exposure (r = 0.75, p = 0.0002). Meanwhile, the TCR method is more sensitive and informative for biological dosimetry of recent radiation, than the GPA test.

[Determination of mutation frequency at loci of glycophorin A and T-cell receptor: study of Chernobyl AES accident cleanup workers]. / Opredelenie chastoty mutatsii po lokusam glikoforina A i T-kletochnogo retseptora: obsledovanie likvidatorov avarii na CHAES.

The frequencies of somatic mutations at loci of glycophorin A (GPA) and T-cell receptor (TCR) were determined in control unexposed donors and Chernobyl clean up workers, who received low doses of irradiation up to 0.25 Gy. High variability of mutant rates for two investigated genes was shown in the clean up workers. No significant difference in the GPA (NO) mutant frequencies was observed between the clean up workers and control donors (p > 0.05), though there is a tendency for increasing the GPA mutation rate in the clean up workers. Meanwhile, the TCR mutation rate was significantly increased the clean up workers (p < 0.01), perhaps because of acceleration of spontaneous mutagenesis and possible genome instability. Persons with elevated levels of mutations at two loci can present a group at high risk in respect to oncological diseases.

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-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 TCRbeta/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. 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 Vgamma-Jbeta1 TCR rearrangements. RESULTS: The frequency of TCRbeta/gamma-variant cells was not significantly different in the irradiated and control cultures at any time studied up to 55 days after PHA-stimulation, indicatin that V(D)J-mediated Vgamma-Jbeta1 rearrangement is not induced by X- or gamma-irradiation under these conditions. However, in both irradiated and non-irradiated cultures, the frequency of TCRbeta/gamma variants increased approximately fourfold after mitogen 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 prolonged 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 TCRbeta/gamma gene rearrangements can be induced by X- or gamma-irradiation in vitro. However, in contrast with cells with normal TCR receptors, TCRbeta/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 season-dependent changes in the frequency of cells with hybrid TCR in occupationally exposed populations and individuals receiving cytostatic treatment.

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 because expression of a mutant phenotype may require as long as several months. In the present study, we eliminate this time lag by stimulating lymphocytes with a mitogen that can accelerate the turnover of TCR protein expression in T-cells. When lymphocytes obtained from healthy donors were irradiated with various doses of X-rays and cultured with human interleukin-2 after phytohemagglutinin (PHA) pulse stimulation, the mutant frequency (MF) of CD4+ T-cells increased dose dependently during the first 7 days, then decreased rapidly due to the growth disadvantage of mutant cells. This suggests that PHA stimulation can shorten the expression time of a mutant phenotype to within a week after radiation exposure. The relationship between radiation dose and TCR MF on the seventh day was best fitted by a linear-quadratic dose-response model. We applied this improved TCR mutation assay to gynecological cancer patients who received 5 days of localized radiotherapy, totaling about 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-stimulated lymphocytes from the same patients significantly increased 7 days after initiating culture. The estimated mean radiation dose to the peripheral 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 on unstable-type chromosome aberrations from cervical cancer patients after receiving the same course of radiotherapy. On the basis of these findings, we propose that the improved TCR mutation assay is a useful biological dosimeter for recent radiation exposure.