Increased somatic cell mutant frequency in atomic bomb survivors

Medical management of three workers following a radiation exposure incident

The medical management of three individuals involved in an exposure incident to whole-body radiation at a nuclear generating plant of a Canadian electrical utility is described. The exposure incident resulted in the two highest whole-body radiation doses ever received in a single event by workers in a Canadian nuclear power plant. The individual whole-body doses (127.4 mSv, 92.0 mSv, 22.4 mSv) were below the threshold for acute radiation sickness but the exposures still presented medical management problems related to assessment and counseling. Serial blood counting and lymphocyte cytogenetic analysis to corroborate the physical dosimetry were performed. All three employees experienced somatic symptoms due to stress and one employee developed post-traumatic stress disorder. This incident indicates that there is a need in such radiation exposure accidents for early and continued counseling of exposed employees to minimize the risk of development of stress-related symptoms.

Congenital anomalies in children of patients who received chemotherapy for cancer in childhood and adolescence

BACKGROUND

Many patients who have been treated successfully for childhood cancer with regimens that contain one or more mutagenic chemotherapeutic agents are concerned that their own treatment during childhood or adolescence may adversely affect their children.

METHODS

To determine the effect of chemotherapy for cancer during childhood and adolescence on the outcome of subsequent pregnancies, we reviewed the records of 306 men and women who had been treated for pediatric cancer and who responded to our questionnaire. One hundred of the 306 patients reported 202 pregnancies. Among the patients who had received chemotherapy as part of their treatment for cancer, 60 patients or wives of patients had had one or more pregnancies of 20 or more weeks' gestation. The 60 former patients had a total of 100 live-born and 2 stillborn children.

RESULTS

The frequency of congenital anomalies was 8.1 percent (5 of 62) among the live-born children of the women and 7.9 percent (3 of 38) among the live-born children of the men. Structural congenital cardiac defects were identified in 10.0 percent (2 of 20) of the children of women who had been treated with dactinomycin, as compared with 0.6 percent (144 of 24,153) among the children in a multicenter survey of fetal anomalies (P = 0.0126). We found no relation between the number of mutagens received or the cumulative dose of any agent received and the frequency of congenital anomalies in the children.

CONCLUSIONS

These data suggest that treatment of children and adolescents with mutagenic chemotherapeutic agents, in the dose ranges we examined, does not increase the frequency of congenital anomalies in the children subsequently born to the former patients. However, the possible adverse effect of dactinomycin on the children of such patients requires further study.

International Commission for Protection Against Environmental Mutagens and Carcinogens. ICPEMC publication No. 18. Review of the genotoxicity and carcinogenicity of antischistosomal drugs; is there a case for a study of mutation epidemiology? Report of a task group on mutagenic antischistosomals

One of the interests of ICPEMC is to identify situations in which the possible induction of inherited defects in man by mutagen exposure could actually be studied. The large-scale use of mutagenic drugs in field programmes against schistosomiasis, mainly during the 1970's, was considered a possible case. An ICPEMC task group approached the problem by (1) updating the genetic toxicology data base for antischistosomal drugs, and (2) reviewing possible study areas. Expertise was combined from genetic toxicology, mutation epidemiology and tropical medicine. It was considered that: (a) if any, hycanthone would be the most appropriate candidate drug for study; (b) it would be virtually impossible to meet the basic requirements of an appropriate mutation epidemiology study, in endemic countries; (c) as more defined genetic endpoints would be selected (e.g. sentinel phenotypes) the required large sample sizes would seem prohibitive, since documentation on past programmes is limited and local demography would render the reliable tracking of substantial numbers of offspring of treated persons an almost impossible task; (d) in most endemic countries proper diagnosis and registration of inherited defects is largely lacking; (e) the problems encountered in demonstrating inherited effects in humans after heavy or chronic exposure to established animal mutagens such as ionizing radiation and cancer chemotherapy, in combination with the ambiguous nature of the animal germ cell data with hycanthone, do not particularly warrant large expectations; (f) since non-mutagenic antischistosomal drugs are now in use, the problem is academic and of low priority in the endemic countries whose medical and research resources are often limited. Thus, studying offspring of hycanthone-treated people to demonstrate the mutagenic potential of the drug in man is not a viable enterprise.

Detection of 6-thioguanine-resistant spleen lymphocytes in different mouse strains by autoradiography

The variant frequencies for 6-thioguanine-resistant spleen cells in different mouse strains have been estimated by autoradiography for animals without chemical treatment and in cases of in vivo mutagen dosage with ethylnitrosourea and cyclophosphamide, respectively. In untreated mice, the following variant frequencies have been found: C57Bl/6J, 2.84 x 10(-5);NMRI, 3.04 x 10(-5);DBA/2J, 5.91 x 10(-5). The selective concentration of 6-thioguanine was 100 microM for strains NMRI and DBA, while in the case of C57Bl with this concentration, no variant cells could be counted and a selective concentration of 50 microM was chosen. Treatment with 70, 140, and 210 mg/kg ethylnitrosourea resulted in increased variant frequencies in cells isolated 8 or 15 days later. On the other hand, doses of 20, 60, and 120 mg/kg cyclophosphamide did not result in a clear dose-response relationship of variant frequency in cells isolated 1, 8, 15, 22, and 29 days after treatment. These data are discussed with respect to findings in human populations exposed occupationally to cyclophosphamide.

Nuclear medicine patients do not have higher mutant frequencies after exposure to thallium-201

The HPRT-lymphocyte clonal assay has been used to detect mutants induced in vivo in humans. This method has previously detected a rise in mutant frequency among nuclear medicine patients following exposure to technetium-99m, at a dose corresponding in theory to 5.1 mGy. In the present study, nuclear medicine patients were sampled before and after exposure to thallium-201, corresponding to a whole-body dose of 4.2 mGy. No rise in mutant frequency was found. We suggest that a difference in the effective dose received by the patients' lymphocytes accounts for the apparent contradiction with earlier results.

6-Thioguanine-resistant T-lymphocyte autoradiographic assay. Determination of variation frequencies in individuals suspected of radiation exposure

We used the autoradiographic assay to assess human in vivo somatic cell gene mutation at the hypoxanthine guanine phosphoribosyl transferase (HGPRT) locus in T-lymphocytes. Cells able to incorporate tritiated thymidine in vitro in the presence of 6-thioguanine were enumerated in order to determine 6-thioguanine-resistance (TGr) variant frequencies in cryopreserved lymphocytes from 17 normal control individuals, from 3 persons suspected to have been exposed to 60Co in an accident in Cd. Juárez (Mexico), studied 24 months after the accident, and from 4 individuals who were in Kiev during the radiation accident in Chernobyl (U.S.S.R.); 2 of them were studied 1 month after the accident, and again 1 year after the first sampling, the other 2 were studied 13 months after the accident. The data obtained indicate that this assay may be useful in any laboratory of cytogenetics for human population monitoring and that its use following accidental exposure to ionizing radiation should be further evaluated.

Review of the molecular characteristics of gene mutations of the germline and somatic cells of the human

Molecular analyses of the limited number of de novo germinal mutations identified in humans indicate that an array of alterations in gene structure can be generated. Similar conclusions are derived from the large data set obtained from molecular analyses of alleles that segregate in the human population and cause genetic diseases. The molecular alterations include nucleotide substitutions as well as insertions, deletions and other rearrangements of the DNA. The lesions may be located in the coding or the noncoding regions of genes or may involve the flanking sequences. The insertions and deletions involve fragments ranging from single nucleotides to many kilobases, and involve both unique sequences and repetitive elements. The nature of the lesions observed to date as either de novo mutations or segregating variants suggests there are locus-specific characteristics of the alterations in DNA structure that are recovered as genetic diseases. Differences in mutation spectra among genetic loci appear to reflect both the structure of the target sequences and the relationship between gene structure and gene function. No induced germinal mutations have been identified, thus no data are available that reveal the relationships between mutagenic exposures and the molecular fingerprints of the lesion induced in the human germ cell and transmitted to the subsequent generations. In contrast, the prospects for analyzing the roles of genetic target, exposure history and individual responsiveness to exposure in creating particular molecular lesions in somatic cells are excellent, both for alterations of single nucleotides and for major alterations of gene structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Spontaneous mutation rate in retinoblastoma

A novel approach was used to estimate the in vivo mutation rate of the retinoblastoma gene. A mathematical formula can be used to calculate the probability of neoplasia induced by one or more mutations in a population of dividing cells. This formula can then be applied to epidemiological data on hereditary and sporadic retinoblastoma. The analysis yields an estimate of the in vivo mutation rate of 8 x 10(-8)/gene/cell division (range 5.5 x 10(-8) to 1.3 x 10(-7]. The estimated non-replication association in vivo mutation rate is 2.4 x 10(-8)/gene/year (range 0 to 6.8 x 10(-8]. The formula is an improvement on previous attempts to produce a model of the process of mutation during cell generation. It can be applied to neoplastic disease in both children and adults.

In vitro induction, expression and selection of thioguanine-resistant mutants with human T-lymphocytes

Conditions have been defined to measure the in vitro induction of mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in human T-lymphocytes by a cell cloning assay. The in vitro growth of mass cultures as well as cell cloning is accomplished by the use of crude T-cell growth factor (TCGF) and irradiated human lymphoblastoid feeder cells. These initial studies employed irradiation of G0 phase peripheral blood mononuclear cells from a single individual. After exposure to gamma-irradiation from a 137Cs source, the cells were stimulated with the mitogen phytohemagglutinin (PHA) and maintained in exponential growth with exogenous TCGF to allow phenotypic expression of the 6-thioguanine-resistant (TGr) mutants. The mutant frequency was determined by measuring cell cloning efficiency in microtiter dishes in the absence and presence of TG, with an optimal selection density of 1 X 10(4) cells/well. The development of this in vitro assay should allow direct study of susceptibility to gamma-irradiation in the human population in terms of both cytotoxicity and mutation induction.

Increased frequency of 6-thioguanine-resistant lymphocytes in peripheral blood of workers employed in cyclophosphamide production

The frequency of 6-thioguanine-resistant peripheral blood lymphocytes has been determined by autoradiography in a control population and a population of cyclophosphamide-exposed individuals. The mean variant frequency in a non-exposed population was found to be 2.76 +/- 1.48 X 10(-5). Subpopulations of smokers and non-smokers revealed statistically significant differences in the variant frequencies, i.e. 3.52 +/- 1.55 X 10(-5) and 2.07 +/- 1.05 X 10(-5) respectively. In 20 out of a total of 23 individuals employed in cyclophosphamide synthesis and manufacturing, the variant frequency of 6-thioguanine-resistant lymphocytes was found to be higher than the maximum individual frequency found in the control population. The mean variant frequency in the cyclophosphamide-exposed population was 13.64 +/- 13.56 X 10(-5), a statistically significant increase as compared to the mean control frequency. There was no correlation between variant frequency and duration of employment suggesting that this test reflects the actual exposure and not a cumulative effect.

In vivo hprt mutant frequencies in T-cells of normal human newborns

Mutation at the hypoxanthine-guanine phosphoribosyl transferase locus (hprt; HPRT enzyme) in the human fetus was studied by clonal assay of placental cord blood samples from full-term newborns. Conditions for determining hprt mutant frequencies, as defined for adults, were also optimal for studies in newborns. The mean mutant frequency for 45 normal human newborns (37 male, 8 female) was 0.64 X 10(-6) (SD = 0.41 X 10(-6); median value = 0.58 X 10(-6). These values are approx. 10-fold lower than corresponding adult hprt mutant frequency values. Factors such as limiting-dilution cloning efficiencies, delay prior to study of sample, sex, cryopreservation or technician performing the assay did not significantly affect assay results. Maternal smoking did not result in elevated mutant frequency values. Most wild-type and mutant clones studied were CD4 surface antigen positive (helper/inducer). All hprt mutants analyzed lacked HPRT activity.

Molecular analyses of in vivo hprt mutations in human T-lymphocytes. III. Longitudinal study of hprt gene structural alterations and T-cell clonal origins

The hprt clonal assay detects mutations occurring in vivo in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene of human T-lymphocytes. Analysis of 94 wild-type and 326 hprt mutant clones from 3 normal males was performed using Southern blotting with hprt and T-cell receptor (TCR) gene probes. Gross structural alterations of the hprt gene occurred in approximately 14% of the in vivo derived mutants. Breakpoints were randomly distributed across the gene with one possible mutational "hot spot" observed. Most hprt mutants were independent as judged by TCR gene rearrangement patterns indicating that the measured hprt mutant frequency is a good measure of the actual hprt mutation frequency. However, sibling mutants (generally doublets and triplets except for one nonamer) were detected. Information on the timing in vivo of the hprt mutational events and the persistence in vivo of sibling mutants was also obtained.

Frequency of variant erythrocytes at the glycophorin-A locus in two Bloom's syndrome patients

Blood type MN is determined by a glycoprotein termed glycophorin A (GPA) which exists on the surface of erythrocytes, and the difference between the M and N types is derived from the presence of 2 different amino acids in the amino-terminal portion (Furthmayer, 1978). Using a pair of fluorescence-labeled monoclonal antibodies specific to each GPA, somatic mutations in erythrocytes of MN heterozygotes at the GPA-M and -N alleles can be quantitatively determined using a flow sorter (Langlois et al., 1986). Our results for 2 Bloom's syndrome (BS) patients showed that variants either lost expression of one allele (simple gene inactivation or loss) or expressed only one allele at twice the normal level (most probably somatic recombination) occurring at a frequency of about 1-3 per 10(3) erythrocytes. The flow cytometric patterns of erythrocytes from the BS patients showed a typical smear of variants bearing intermediate levels of expression of one GPA allele, indicating that the real variant frequency is even greater than that measured. On the other hand, the parents heterozygous for the BS gene showed variant frequencies (1-8 x 10(-5)) within the normal range. These data strongly support the hypothesis that the cancer proneness of BS patients is due to their increased frequency of spontaneous mutations and somatic recombination.

A chromosome study of 6-thioguanine-resistant mutants in T lymphocytes of Hiroshima atomic bomb survivors

Cytogenetic characterizations were made of lymphocyte colonies established from somatic mutation assays for 6-thioguanine (TG) resistance in Hiroshima atomic bomb survivors. G-banded chromosomes were analyzed in both TG-resistant (TGr) and wild-type colonies. Included were 45 TGr and 19 wild-type colonies derived from proximally exposed A-bomb survivors, as well as colonies from distally exposed control individuals who did not receive a significant amount of A-bomb radiation (18 TGr and 9-wild type colonies). Various structural and numerical chromosome abnormalities were observed in both TGr and wild-type colonies. Aberrations of the X chromosome, on which the hypoxanthine guanine phosphoribosyl transferase (HPRT) locus is present, were found in 6 colonies: 2 resistant colonies from controls (45,X/46,XX; 46,X,ins(X)), 3 resistant colonies (45,X/46,XX/46,X, + mar; 46,X,t(Xq +;14q-); 46,Y,t(Xq-;5q +)), and 1 wild-type colony (45,X/47,XXX) from proximally exposed persons. In cases with exchange aberrations, each of the break points on the X chromosome was situated proximally to band q26 where the HPRT locus is known to be assigned. DNA-replicating patterns were also studied, and it was found that abnormal X chromosomes showed early replicating patterns, while normal X chromosomes showed late replicating patterns.

Cloning of phenotypically different human lymphocytes originating from a single stem cell

By using hypoxanthine guanine phosphoribosyltransferase (hprt) gene alterations and chromosome aberrations as in vivo cellular markers, human T, NK, and B cells originating from a single stem cell have been successfully cloned from the peripheral blood of an atomic bomb survivor from Hiroshima. These mutant lymphocytes were selectively cloned, taking advantage of their resistance to a purine analogue, 6-thioguanine. The cloned lymphocytes possessed the same hprt gene alterations and the same chromosome aberration (20q-), but exhibited different surface or functional phenotypes and different rearrangements of TCR or Ig genes. The chromosome aberration patterns strongly suggested that the original stem cell initiated differentiation into each cell type after exposure to atomic bomb radiation. Since the person studied here was exposed to the bomb at 17 yr age, the results suggested that common stem cells exist in adults for at least T, NK, and B cells. The use of hprt gene alterations as specific cellular markers provides a novel method for identifying stem cells in the lymphocyte lineage and for studying lymphocyte differentiation in humans.

Cloning of in vivo-derived thioguanine-resistant human B cells

In vivo-derived thioguanine-resistant (TGr) B cells have been cloned from peripheral blood mononuclear cells (PBMC) of 4 healthy adults. This was done by using Epstein-Barr (EB) virus transformation of B cells enriched from a large number of PBMC obtained with a blood cell separator. The cloned TGr B cells lacked hypoxanthine guanine phosphoribosyltransferase (HPRT) enzyme activity. The frequency of in vivo TGr B cells was estimated to be 8.6-13.1 X 10(-6) for the 4 individuals by comparing the cloning efficiency of non-selected cells and TG-selected cells. This frequency is somewhat higher but comparable to the in vivo frequency of TGr T cells. Because the cloned TGr B cells can be easily expanded in vitro, this procedure provides a large amount of material for the precise characterization of in vivo mutations in humans.

Somatic mutation in peripheral lymphocytes of former workers at the Okunojima poison gas factory

The former workers at the Okunojima poison gas factory comprise a high risk group for malignant tumors such as respiratory tract cancer. Demonstration of injury to somatic cell genes in this group may provide important data for evaluating the association between mustard gas and malignant tumors. So we measured the frequency of T lymphocytes lacking the hypoxanthine guanine phosphoribosyl transferase (HGPRT) activity, by cloning with interleukin 2 (IL2). In this study, we performed cloning of T lymphocytes lacking the HGPRT activity using recombinant IL2 (rIL2) and observed an increased frequency of somatic mutation in poison gas workers who had had more chances to be exposed to mustard gas and those who had worked for a longer period. This result suggested that inhalation of small amounts of mustard gas damaged somatic cell genes, resulting in carcinogenesis.