Myeloid lineage involvement in acute lymphoblastic leukemia: a morphology antibody chromosomes (MAC) study.

We looked for clonal chromosomal abnormalities in myeloid cell lineages in the bone marrow aspirates from six children with acute lymphoblastic leukemia (ALL). The study was carried out using a combination of MAC (morphology, antibody, chromosomes) and in situ hybridization procedures. In patients whose leukemic cells expressed only lymphoid antigens, we found chromosomal aberrations in CD10- and CD20/22-positive lymphoid cells. Mature CD22+ and CD3+ lymphocytes did not have the chromosomal aberrations. In one patient whose leukemic cells also expressed myeloid-associated antigens, the clonal chromosome aberrations were seen not only in the CD10+ and CD19+ blasts, but also in glycophorin A-positive morphologically nonleukemic erythroblasts.

Micronucleus assay in lymphocytes as a tool to biomonitor human exposure to aneuploidogens and clastogens.

The analysis of micronuclei (MN) in cultured human lymphocytes is, in principle, able to detect exposure to clastogens and aneuploidogens alike. There is, however, no clear evidence from human biomonitoring studies or animal experiments showing that in vivo exposure of resting lymphocytes to an aneuploidogen could actually be expressed as MN in cultured lymphocytes. In vitro, a pulse treatment of human lymphocytes with vinblastine, an aneuploidogen, did result in MN induction even if performed before mitogen stimulation, although a much more pronounced effect was obtained in actively dividing lymphocyte cultures. On the other hand, it is probable that a considerable portion of "spontaneous" MN contain whole chromosomes, their contribution increasing with age. It also seems that cytochalasin B, used for the identification of second cell cycle interphase cells in the MN assay, is able to slightly increase the level of MN with whole chromosomes. If MN harboring chromosome fragments represent a minority of the total MN frequency, there may be difficulties in detecting a weak effect in this fraction of MN against the background of MN with whole chromosomes. This would reduce the sensitivity of the assay in detecting clastogens, unless MN with whole chromosomes and chromosome fragments are distinguished from each other. That a problem may exist in sensitivity is suggested by the difficulty in demonstrating MN induction by smoking, an exposure capable of inducing chromosome aberrations. The sensitivity of the lymphocyte MN assay could be increased by detecting kinetochore or centromere in MN, or by automation, allowing more cells to be analyzed.

Distribution of radiation-induced exchange aberrations in human chromosomes 1, 2 and 4.

PURPOSE: To examine the distribution of radiation-induced breakpoints in chromosomes 1, 2 and 4 both in relation to their DNA content and by localization of the breaks along each chromosome. MATERIAL AND METHODS: The work consisted of two studies, one with chromosomal aberrations found in persons after accidental exposure in Estonia in 1994 and another involving aberrations seen in in vitro-irradiated lymphocytes. Localization of breakpoints in painted chromosomes involved in complete exchange-type aberrations was conducted by applying a computerized measuring system on stored image-files. RESULTS AND CONCLUSIONS: The yield of exchanges in chromosomes 1, 2 and 4 in both studies was equal to that expected from their DNA content. In contrast, the breakpoint location of complete exchanges within these chromosomes was not random. Chromosomes 1 and 4 contained more breaks in the middle parts of the p and q arms, whereas breaks were observed more uniformly along chromosome 2. Complete exchanges, however, were very rare in the terminal regions of all three chromosomes, most probably resulting from limitations in the resolution of small painted pieces.

Comparison of dose-response curves for chromosomal aberrations established by chromosome painting and conventional analysis.

PURPOSE: To establish 60Co gamma-ray dose-response curves for dicentrics and translocations visualized by chromosome painting and for dicentrics analysed after conventional solid staining. MATERIALS AND METHODS: Analysis of chromosomal aberrations was performed on peripheral blood lymphocytes obtained from 48 h old cultures of irradiated whole blood. Dicentrics were scored from Giemsa-stained preparations, and bi-coloured dicentrics and translocations after FISH painting of chromosomes 1, 2 and 4. RESULTS: Equal frequencies of complete dicentrics and translocations, where both members of the exchanges were seen, were observed in the chromosome painting analysis at all doses, resulting in similar calibration curves. Due to differences in scoring criteria, dicentrics scored in conventionally Giemsa-stained slides agreed better with data for total than for complete exchanges. Donor differences for translocations at the control level and at low doses were seen and large uncertainty surrounds the linear component of the dose-response for total translocations. CONCLUSIONS: Dose reconstruction of past exposures in cases of low doses is very dependent on the linear coefficient of the curve. Results indicate that total translocations would give less reliable dose estimates and therefore complete translocations are preferred.

Induction of micronuclei in cultured human lymphocytes treated with vinblastine before and after mitogen stimulation.

The analysis of micronuclei (MN) in cultured human lymphocytes can, in principle, detect exposure to clastogens and aneuploidogens alike. As aneuploidogens such as spindle poisons usually act on dividing cells, it is not clear how an in vivo exposure of resting peripheral lymphocytes to an aneuploidogen could be transmitted and expressed as MN in cultured lymphocytes. This question is fundamental in judging if cultured lymphocytes can be used to detect in vivo exposure to aneuploidogens. In the present study, in vivo exposure of resting lymphocytes to an aneuploidogen was simulated in vitro by a 24-h pulse treatment of human lymphocytes with vinblastine sulfate (VBL) before mitogen stimulation, followed by two washes and culture in the presence of phytohemagglutinin (PHA) for 72 h. This treatment protocol did result in an increased MN frequency, but only at the highest concentration of VBL available for analysis (100 ng/ml). A more effective response, with a significant effect already at 40 ng/ml, was obtained when the 24-h pulse treatment was started at 24 h of PHA-stimulated 72-h cultures. Still much lower concentrations of VBL (1 or 2.5 ng/ml) were effective, when the treatment, started 24 h after culture initiation, was continued for 48 or 72 h (respectively) until cell harvest. These results demonstrate that MN induction by VBL depends, as expected, on the duration and timing of exposure, reflecting the availability of dividing cells during the treatment. The positive MN response obtained in the pulse-treated unstimulated lymphocytes may reflect an effect initiated in the resting stage and retained until mitosis or residual VBL left in the cells or in the cell suspension, despite the washes.