Proliferation of PHA- and PWM-stimulated lymphocytes measured by sister chromatid differential staining

Analysis of the length of S-phase required to show sister chromatid differential staining

In vitro studies of BrdU-dependent sister chromatid differential staining typically employ two cycles of BrdU incorporation. Experiments are described which determined the actual fraction of both S-phases that the rat embryonic fibroblasts (Rat-1) cells had to traverse in order to show distinctive differential staining. Following synchronization of cells by a combination of serum deprivation and hydroxyurea blockage, sister chromatid differential staining, labelling index, mitotic index, and per cent DNA replication are determined. Results indicate that only approximately 50% of the first S-phase is necessary in order to show distinctive differential staining. The importance of this finding to studies of cellular proliferation using BrdU incorporation is discussed.

Proliferative characteristics of progeny derived from normal human hemopoietic progenitor cells

Cell cycle times of cells derived from human hemopoietic progenitor cells were measured directly by using 5-bromodeoxyuridine (BrdU) incorporation and sister chromatid differential staining. Umbilical cord cells were cultured in the mixed-colony assay for 96 h prior to the addition of BrdU and then harvested at 6-12 h intervals. Individual cell cycle times ranging from 8.5-23.4 h were observed while population mean cell cycle times ranged from 17.5-24 h. These results show that some early progeny of hemopoietic progenitor cells have short cell cycle times and that there is considerable heterogeneity within the proliferating cell population.

Proliferative characteristics and sister chromatid exchange (SCE) of colony-forming cells (CFU-S) in acute myelogenous leukemia

Sister chromatid exchange (SCE) and cell cycle progression of colony-forming cells (CFU-S) from patients with acute myelogenous leukemia were studied using bromodeoxyuridine (BrdU) incorporation and sister chromatid differential staining. The mean SCE rate of CFU-S was 7.99, which is similar to that reported for human peripheral blood lymphocytes. Cultures treated with BrdU at culture initiation and then harvested 72-120 hr later indicated a cell cycle time (TC) of approximately 60 hr. However, cells allowed to proliferate for 72-120 hr prior to the addition of BrdU showed TC values of 12-36 hr. Analysis of serial cultures from one patient revealed a heterogeneous population with a mean TC of 19.5 hr. These cell cycle times are considerably shorter than previously published reports and suggest that leukemic cells have the potential to divide rapidly.

Lymphocyte reactivity in patients with cancer of the oral cavity measured by sister chromatid differential staining

Lymphocyte reactivity in phytohemagglutinin-stimulated peripheral lymphocyte cultures from 22 patients with squamous cell carcinoma of the oral cavity and 29 age- and sex-matched controls was measured by the bromodeoxyuridine-Giemsa method for demonstrating sister chromatid differential staining. One hundred metaphases from each donor were counted, and the proportions of cells in the first, second, and third cycles were scored to estimate the in vitro mitogen responsiveness and cell division rates of the lymphocytes. The in vitro reactivity of peripheral lymphocytes of cancer patients was impaired in comparison with that of the controls, and the degree of reactivity of lymphocytes in cancer patients was not related to the size (greatest diameter) of the primary tumor. Results are discussed in relation to previously existing data.

Chromosome studies on lymphocytes of patients under cytostatic therapy. II. Studies Using the BUDR-labelling technique in cytostatic interval therapy

Lymphocyte cultures from the peripheral blood of 38 patients undergoing a cytostatic interval therapy with a regimen of methyl-CCNU (1-[2-chloroethyl-3-(4-methyl-cyclohexyl)]-1-nitrosourea), 5-fluorouracil, and vincristine (each 5-day course of therapy was followed by a therapy interval of 4 weeks) were supplied with 5-bromodeoxyuridine (BUDR) for the whole culture time to determine the sister chromatid labelling pattern. From a total of 92 individual blood samples sister chromatid exchange (SCE) studies were performed including analyses before the start of the therapy, and immediately and 4 weeks after each course of therapy. In addition, the frequency of first, second, and third metaphases in the 72-h cultures was estimated using the characteristic labelling patterns. A distinct increase of SCE frequency over the control level (i.e., lymphocyte cultures of patients before the start of therapy) was observed at all phases of therapy. It was clearly correlated with the number of courses of therapy up to course 7, later on the SCE rate remained more or less at the level reached. The influence of the composition of each drug regimen on the SCE rate was less pronounced than it was on the breakage rate. Moreover, although a clear correlation existed between the individual rates of breakage and SCE, the formation of the latter appeared to reflect a long-term effect of the therapy rather than did the formation of break aberrations. In addition, as the intercellular variability of the number of SCEs per cell was much higher than that of breaks, the interindividual variability (variation of the mean values for each patient) was small compared to the respective variability of breakage rates. The proportion of first, second, and third metaphases present in 72-h cultures evidently was influenced by single courses of therapy. The observed delay of proliferation was also reflected in different amounts of chromosome damage. Although the BUDR treatment enhanced the cytostatic effect of the therapy on the lymphocytes in culture rendering SCE analysis rather difficult in several cases, the other data of this study and in particular the experiences with the "long-term effect" make it imperative to include BUDR-labelling in further cytogenetic studies in subjects with exceptional exposure to chemicals. However, the SCE method can by no means, replace the classic cytogenetic analysis.

Frequencies of sister-chromatid exchanges in relation to cell kinetics in lymphocyte cultures

The frequency of sister-chromatid exchanges (SCE) was determined on second-division metaphases of lymphocytes stimulated by phytohaemagglutinin (PHA) during 9 days of culture. By using either a continuous or a pulsed bromodeoxyuridine (BUdR) treatment, cells were selected that had divided only twice, or at least twice, after different culture periods. No significant differences were observed in the SCE frequencies among the various samples. The incidence of SCE appears to be independent of the proliferation properties of cultured lymphocytes, such as length of cell cycle, fast or delayed response to PHA and number of divisions performed in vitro.

Lymphocyte proliferation in Down's syndrome measured by sister chromatid differential staining

Lymphocyte proliferation in PHA stimulated cultures from Down's syndrome patients and normals was measured by the BrdU/Giemsa method for demonstrating sister chromatid differential staining. Both Down's syndrome patients and normals had 1st, 2nd and 3rd divisions present. However, Down's syndrome patients had more 3rd division metaphases and fewer 2nd division metaphases than the normals. There was no difference in the mitotic index between the two groups.

Relation between the SCE points and the DNA replication bands

A method for obtaining a combination of differential sister chromatid staining and DNA replication banding is described. Using this method the SCE points can be precisely localized to particular bands of individual chromosomes. It was shown, that SCEs occur not only in the regions of early DNA replication (= euchromatic segments = negative G-bands), but also in the regions of late DNA replication bands (=heterochromatic segments=positive G-bands). SCEs occurred about three times more frequently in the euchromatic segments than in the heterochromatic segments. Furthermore, more SCEs were observed in the early replicating X-chromosome than in the late replicating X-chromosome.

The apparent decrease in thiotepa-induced chromosome aberrations in human lymphocytes caused by an effect of WR2721 on the cell cycle as found by the definitively determined division method

Antimutagenic radioprotective compounds have been reported to decrease the yield of chemically induced chromosome aberrations even when administered long before the chemical mutagen thio-TEPA. Because thio-TEPA can induce aberrations in all parts of the cell cycle, it seemed likely that the apparent decrease in aberrations was the result of an effect of the antimutagen on the progression of cells through the cell cycle so that cells treated in the more sensitive stage would be scored. To test this possibility human lymphocytes were treated with the protective compound WR2721 and then thio-TEPA. The cells were grown in the presence of 5-bromodeoxyuridine, which allows the definitive determination of metaphases from cells that divided once, twice, or three times after treatment. The yield of aberrations observed in first division cells was the same whether or not the protector was present. A decrease in aberration yields appeared only in rapidly cycling cells that were in the second division at the time of fixation. Labeling experiments showed that in this rapidly dividing population fewer of the metaphase cells had been in G2 when thio-TEPA was added. The results indicate that part of the decrease in aberration yields obtained by treatment with an antimutagen several hours before the addition of a mutagen is an artifact of cell selection.