Genomic DNA of leukemic patients: target for clinical diagnosis of MLL rearrangements

Genomic DNA is the optimal resource to analyze questions concerning genetic changes that are related to oncogenesis. This article tries to summarize recent efforts to analyze chromosomal changes that trigger the development of human acute myeloid and lymphoblastic leukemias. The aim of this study was to establish an universal method that enables the identification and characterization of chromosomal translocations of the human MLL gene at the genomic nucleotide level. Chromosomal translocations of the MLL gene are the result of illegitimate recombination events in hematopoietic stem or precursor cells, strictly associated with the onset of highly malignant leukemic diseases. The applied technology was able to identify specific fusion alleles that were generated by chromosomal translocations, chromosomal deletions, chromosomal inversions and partial tandem duplications. Moreover, it allowed us to investigate even highly complex genetic changes by applying systematic breakpoint analyses. On the basis of these analyses, patient-specific molecular markers were established that turned out to be a very good source for monitoring minimal residual disease (MRD). MRD analyses control the efficiency and efficacy of current treatment protocols and have become a very sensitive molecular tool to monitor therapeutic success or failure in individual leukemia patients.     

Neoplastic meningosis in immature cell leukemias and malignant lymphomas

162 patients with acute leukemias or malignant non-Hodgkin lymphomas were examined for meningeal and cerebral manifestations of their disease. A clinically manifest disease could be found in 13 patients, meningosis was additionally detected by autopsy in 32 patients. The highest frequency was found in acute lymphatic leukemia followed by lymphoblastic lymphomas and acute myeloic leukemias. Less frequently there was a meningeal involvement in low-grade malignant lymphomas which becomes clinically manifest only in some rare cases. In this respect, non-lymphoblastic, high grade-malignant lymphomas take an intermediate position. On principle, meningosis prophylaxis is imperative for acute lymphoblastic leukemias and advanced lymphoblastic lymphomas.     

Chromosome 11 rearrangements in various hematological neoplasias

Chromosome 11 abnormalities in leukemic bone marrow cells were observed in 14.0% of the cases of acute lymphoblastic leukemia (ALL), in 18.7% of acute myeloid leukemia (AML) cases, and in 16.7% of refractory anemia (RA) cases. Bands 11pl3, 11pl4, 11pl5 on the short arm and 11ql4, 11q21, 11q23 on the long arm of chromosome 11 were involved in these rearrangements. Rearrangements of band 11q23 were detected most often. Reciprocal translocations were found with the highest frequency, while para-and pericentic inversions and deletions, both terminal and interstitial, occurred less often. In RA cases only deletions were observed. Comparison of clinical features showed no correlation with age and major hematological indexes such as the number of blast cells in the initial period. These results show that the prognosis is poor in cases of abnormalities at both 11q21 and 11q23 in acute leukemia (AL) as well as in 11pl3 and 11pl5 in AML. This is the first observation of these phenomena.     

ML antigen of DBA/2 mouse leukemias: expression of an endogenous murine mammary tumor virus

Spontaneous, transplantable leukemias of DBA/2 mice express an antigen (ML) which cross-reacts with antigens of murine mammary tumor virus (MuMTV). The MuMTV cross-reactive antigen of the DBA/2 leukemias (ML cells) was found to be a glycoprotein of 78,000 molecular weight containing antigenic determinants of the major MuMTV glycoprotein gp52. No MuMTV particles were produced by the ML cells, although they did contain type A particles--the pronucleocapsids of MuMTV. The ML antigen appeared to be an aberrant form of the intracellular MuMTV env precursor molecular prgp70, which was not processed properly but instead acquired extra carbohydrate groups and was expressed in uncleaved form on the cell surface. Isolation of MuMTV core protein p28 from the leukemic cells and subsequent tryptic peptide mapping analysis showed that the p28 from leukemia cells differed from the p28 of MuMTV isolated from DBA/2 mouse milk. These observations indicate that the MuMTV expressed in DBA/2 leukemic spleen cells is of a different strain than the virus secreted in lactating mammary glands of DBA/2 mice and probably represents the expression of an endogenous DBA/2 provirus.     

Structural alterations of the BCR and ABL genes in Ph1 positive acute leukemias with rearrangements in the BCR gene first intron: further evidence implicating Alu sequences in the chromosome translocation.

In the Philadelphia positive bcr negative acute leukemias (Ph1+bcr- AL), the chromosomal breakpoints on chromosome 22 have been shown clustered within 10.8kb (bcr2) and 5kb (bcr3) fragments of the first intron of the BCR gene. We previously reported that the breakpoints were localized in Alu repeats on chromosomes 9 and 22 in a Ph1+bcr- acute lymphoblastic leukemia with a rearrangement involving bcr2. Molecular data of two other Ph1 translocations, one a Ph1+bcr- acute myeloblastic leukemia in the bcr2 region, and the other an acute lymphoblastic leukemia in the bcr3 region are presented. In the former, the breakpoints on chromosomes 9 and 22 are localized in Alu repeats, in regions with two inverted Alu sequences, as in our previously reported case. In the second leukemia, the breakpoints are not located in Alu sequences, but such repeats are found in their vicinity. The implications of these findings are discussed.     

Gene expression profile in bone marrow and hematopoietic stem cells in mice exposed to inhaled benzene

Acute myeloid leukemia and chronic lymphocytic leukemia are associated with benzene exposure. In mice, benzene induces chromosomal breaks as a primary mode of genotoxicity in the bone marrow (BM). Benzene-induced DNA lesions can lead to changes in hematopoietic stem cells (HSC) that give rise to leukemic clones. To gain insight into the mechanism of benzene-induced leukemia, we investigated the DNA damage repair and response pathways in total bone marrow and bone marrow fractions enriched for HSC from male 129/SvJ mice exposed to benzene by inhalation. Mice exposed to 100 ppm benzene for 6h per day, 5 days per week for 2 week showed significant hematotoxicity and genotoxicity compared to air-exposed control mice. Benzene exposure did not alter the level of apoptosis in BM or the percentage of HSC in BM. RNA isolated from total BM cells and the enriched HSC fractions from benzene-exposed and air-exposed mice was used for microarray analysis and quantitative real-time RT-PCR. Interestingly, mRNA levels of DNA repair genes representing distinct repair pathways were largely unaffected by benzene exposure, whereas altered mRNA expression of various apoptosis, cell cycle, and growth control genes was observed in samples from benzene-exposed mice. Differences in gene expression profiles were observed between total BM and HSC. Notably, p21 mRNA was highly induced in BM but was not altered in HSC following benzene exposure. The gene expression pattern suggests that HSC isolated immediately following a 2 weeks exposure to 100 ppm benzene were not actively proliferating. Understanding the toxicogenomic profile of the specific target cell population involved in the development of benzene-associated diseases may lead to a better understanding of the mechanism of benzene-induced leukemia and may identify important interindividual and tissue susceptibility factors.     

Chromosome 11 rearrangements in the different haematological neoplasias

The cases of chromosome 11 abnormalities in leukemic bone marrow cells have constituted 14.0% in acute lymphoblastic leukemia (ALL), 18.7% in acute myeloid leukemia (AML), and 16.7% in refractory anemia (RA). The bands of the short arms 11p13, 11p14, llp15 and the long arms 11q14, 11q21, 11q23 were involved in chromosome rearrangements. The rearrangements of the band 11q23 were detected more often. Reciprocal translocations were found with the highest frequency, while para- and pericentic invertions, terminal and intestitial deletions occured with the lower incidence. Deletions were found in RA cases only. Comparison with the clinical features showed no correlation with the age and the main haematological indexes including the amount of blast cells in the initial period. The results have showed the poor prognosis of the abnormalities not only of 11q21, 11q23 in acute leukemia (AL), but of 11p13, 11p15 in AML as well, while not enough data on this subject is availalbe in the literature.     

Induced leukemias and their connection with radiation exposure

The cytogenetic study of bone marrow cells was performed in 40 patients with secondary leukemias which have arisen after application of cytostatic and/or radiotherapy for primary tumours (Hodgkin's disease, lymphomas, acute lymphoblastic leukemias, breast cancer and other solid tumours). The comparative analysis of results has shown, that the leukemias after irradiating or application of alkylating agents and irradiation, have the quite particular clinico-morphological and cytogenetic characteristics. In 70% of cases these diseases develops as smouldering leukemias with subsequent transformation in M-4, M-6, and rarely M-2 cytochemical variants. Primary cytogenetic events in 60% of researched karyotypes are the losses of long arms or whole chromosomes 5 and 7. In 20% of the researched cases normal karyotype was found, in the left 20%, the changes of a karyotype not including anomalies 5 and 7 chromosomes were detected. The obtained outcomes allow to consider the discharged complex of tags as reference for leukemias, induced by irradiating or chemical agents with similar mechanism of action (alkylating agents, benzene and its derivates). This complex of tags is typical for induced leukemias, and in a combination with definition of a level of stable aberrations in peripheral blood lymphocytes, can be utilised for abjection of radiation-induced leukemias from common mass of cases detected in regions, polluted by radionuclides. In this study in 60% of cases only specific for secondary leukemias chromosomal aberrations, including monosomy 5 and 7, rearrangements of 11q23 were found. On the base of the obtained data the differences in concepts of "secondary" and "induced" leukemias are considered.     

Growth of normal versus leukemic bone marrow cells in long term culture from acute lymphoblastic and myeloblastic leukemias

The ability of the in vitro long-term bone marrow culture (LTBMC) system to impair the survival of leukemic cells and to enhance the growth of normal progenitors has been studied. Bone marrow cells from 19 acute lymphoblastic leukemia (ALL) and 30 acute myeloid leukemia (AML) patients at diagnosis were grown in LTBMC for 4-10 weeks. In half of the cases the leukemic population declined down to undetectable levels and was replaced by putative normal hemopoietic precursors, both in ALL and in AML. In the remaining cases, leukemic cells persisted throughout the culture time and few if any normal hemopoietic cells were detected. These data led us to extend to the lymphoid compartment the previous observation of decreasing leukemic myeloid blasts in LTBMC. The potential of such cultures as an in vitro purging system for autologous bone marrow transplantation in selected poor-prognosis lymphoid malignancies should be explored, as has been done for acute and chronic myeloid leukemias.     

Establishment of leukemia cell lines, BALM-6, BALM-7 and BALM-8 with B-cell characteristics from a patient with acute lymphoblastic leukemia.

Three leukemia cell lines, BALM-6, -7 and -8 were established from the bone marrow of a patient with acute lymphoblastic leukemia. Based on immunophenotypic and the cytogenetic analysis and on the expression of immunoglobulins on both the cell surface and in the cytoplasm, BALM-6, BALM-7 and BALM-8 are clonal leukemic cell populations of B cell origin.     

Rearrangements of chromosome 9 in different hematological neoplasias

In the present article the frequency of anomalies in chromosome 9 among children with hematological neoplasias amounted to 25/112 in acute lymphoblastic leukemia (ALL), 10/83 in acute myeloid leukemia (AML), and 3/20 in myelodysplastic syndrome (MDS). In ALL, deletions are encountered more often than translocations. Deletions are found in both single anomalies and as an element in complex karyotypes. The rearrangements involve the bands 9q34 and 9q22 the most often. The translocation t(9;22)(q34; q11) is encountered in 7.1% of all cases of ALL. In AML, translocation are found more often than deletions. Structural rearrangements most often involved the long arm, at bands 9q22 and 9q34. Deletions, duplications, and translocations were recorded in MDS. No relationship with the initial hematological indicators, including blastosis, were found. The studies attest to different directions of the clinical prognosis in the course of acute leukemia (AL) where there are deletions. Multidrug resistance and the continuing progress of the disease in the course of chemotherapy is found in t(9;22)(q34; q11).     

S1 nuclease hypersensitive sites in an oligopurine/oligopyrimidine DNA from the t(10;14) breakpoint cluster region.

Recurring chromosomal translocations are frequently seen in cancers, especially in leukemias and lymphomas. The genes affected by these chromosomal translocations appear to play an important role in oncogenesis. The mechanism underlying the formation of chromosomal translocation is a subject under extensive study. In chromosomal translocations involving the Ig and TCR loci, complete heptamer-spacer-nonamer signal motifs are usually present at the break of the Ig and TCR genes, indicating the involvement of V-D-J recombinase(s). On the other hand, in only about 50% of the cases signal motif sequences have been found at the break in the other participating chromosome, suggesting that different mechanisms may be involved in the scission of the corresponding chromosome. Here we report the identification of an oligopurine/oligopyrimidine DNA in the t(10;14) breakpoint cluster region associated with T-cell acute lymphoblastic leukemia. S1 nuclease mapping revealed multiple S1 hypersensitive sites in the oligopurine/oligopyrimidine DNA. These data suggest a role for oligopurine/oligopyrimidine sequences (non-B DNA) in the formation of chromosomal translocation.     

Pre-natal origins of childhood leukemia

Chimeric fusion genes derived by chromosome translocation provide stable, sensitive and clone-specific markers for tracking the origins of leukemic cells and the natural history of disease and have been particularly informative in studies with twins concordant for leukemia and in retrospective scrutiny of archived neonatal blood spots. These data have indicated that in pediatric leukemia the majority, but not all, of the chromosome translocations arise, in utero, during fetal hemopoiesis, probably as initiating events. In most cases, functionally complementary and secondary genetic events are also required. These are acquired rapidly, and possibly in utero also, in infant acute lymphoblastic leukemia (ALL) but post-natally for most childhood ALL and acute myeloblastic leukemia (AML). An important consequence of the latter is a very variable and occasionally protracted post-natal latency (1-15 years). Another important corollary is that functional chromosomal translocations and pre-leukemic clones arise at a substantially higher frequency (approximately 100x) before birth than the cumulative incidence or risk of disease. These natural histories provide an important framework for consideration of key etiological events in pediatric leukemia.     

Cytogenetic findings in acute myelogenous leukemias (FAB M 1 to M 6)

The results published in the period from 1973 to 1983 entitled "Cytogenetic findings in acute myeloic leukemias" (M 1 to M 6 of FAB classification) were compiled. In 50-60 per cent of those patients affected with acute myeloic leukemia a deviating karyotype could be detected. With a markedly higher frequency chromosomes 8 and 21 will take part in aberrations, with translocations (8; 21) having the main share with about 30-40 per cent. More than half the male bearers of translocation exhibits a loss of the Y-chromosome, a third of female patients a loss of the X-chromosome. Trisomy 8 and 9 as well as monosomy 7 appear in about 20 per cent. These aberrations can also be found in all other leukemic and preleukemic processes. Patients with karyotypic abnormalities in all their cells will have the slightest average survival time and the worst appeal to therapy. The sole appearance of monosomy 7 or Ph1-chromosome respectively seems to be an unfavourable sign from a prognostic point of view. Children with acute myeloic leukemia will possess an aberrant karyotype more frequently than adults, but they have a longer average life, boys are more frequently affected by this. Acute promyelocytic leukemia can be characterized cytogenetically in 94 per cent of the cases by translocation (15; 17). However, distinct geographical differences can be observed here, the causes of which have not been elucidated. About 40 per cent of the patients with acute myelo-monocytic leukemia developed aberrations. Further investigations will have to show whether the chromosome 11 really took part in it somewhat more frequently than merely at random. Chromosome anomalies have not a visible influence on the course of the disease. In 30-40 per cent of patients with a rarely occurring acute monocytic leukemia, an abnormal karyotype could be found. There was an incidence of 47 per cent for a specific translocation (9; 11) or a similar variant respectively. Erythroleukemia is characterized by a high instability of chromosomes and karyotypical variability, particularly in erythrocyte precursors and by an average survival time of one months. Megakaryoblastic and eosinophilic leukemia are very rare kinds of acute leukemias. The small number of publications allows no general statement to be made concerning karyotypical changes.     

Incidence and phenotypic heterogeneity of Moloney virus-induced leukemias: a multigenic control

The incidence of leukemias was established in mice of different inbred strains inoculated with Moloney leukemia virus (M-MuLV), and a complex genetic control was found. To characterize the different steps of the host-virus relationship further, the degree of viremia, the appearance of leukemia, organ involvement, and the surface phenotype of leukemic cells were studied in individual mice. The results demonstrate that: a) The viremia was controlled by H-2 and non-H-2 genes. Three H-2 genes located in the I and D or T region of the MHC behave like immune-response genes controlling the specific antiviral immune response. Other gene(s) mapped outside the complex also affected the virus production. Both sets of genes influenced leukemia incidence, since leukemias were observed only in highly viremic strains. b) Additional non-H-2 genes, which were not involved in viremia control, were determinants in the induction of malignancies because some sensitive strains do not become leukemic despite high levels of viremia. c) The anatomical type of Moloney virus-induced leukemias varied according to the non-H-2 background. Most of the leukemias arising in B10 congeneic mice involved the thymus and were frequently limited to this organ, whereas BALB mice preferentially developed splenic leukemias. d) In a given inbred strain, the leukemias arising in different animals frequently expressed different phenotypes. It can be concluded that Moloney virus-induced leukemia is a multistep process, viral production being necessary but not sufficient in and of itself to induce a malignant transformation.     

Appearance of B- or T-lymphocyte markers after diffusion chamber culture of acute lymphoblastic leukemia cells

Blast cells derived from blood and marrow samples of a patient with acute lymphoblastic leukemia (ALL), as well as from the Reh line originally established from an ALL patient, were cultured in diffusion chambers implanted i.p. into preirradiated CBA mice. At different intervals over a period of up to 20 days, surface immunoglobulins, ALL antigen, and T-cell antigen were investigated by using direct immunofluorescence. Rosette formation was tested with sheep and mouse erythrocytes. On day 0, the cells expressed only ALL antigen at the surface, and no rosette formation was observed. During culture the patient's lymphoblasts, which originally had cytoplasmic IgM in addition to ALL antigen, expressed surface immunoglobulins as well as mouse erythrocyte receptors. The Reh line cells were ambivalent in two experiments developing T-cell antigens and sheep erythrocyte receptors as well as mouse erythrocyte receptors. Our data suggest that the differentiation arrest in leukemic lymphoblasts can be overcome, thus entailing a surface pattern similar to mature T- or B-lymphocytes.     

Detection of terminal deoxynucleotidyl transferase (TdT) by flow cytometry in leukemic disorders

We applied a new technique to the detection of intracellular TdT in 26 leukemic patients, including 16 non-T acute lymphoblastic leukemia (ALL), four T-ALL, one T-lymphoblastic lymphoma in leukemia phase, one undifferentiated leukemia, one de novo lymphoblastic phase of chronic myeloid leukemia, and three acute monocytic leukemias (AMOL). Mononuclear cell suspensions were incubated in saponin to permeabilize the cell membrane. The cells were then stained by indirect immunofluorescence (IF) using anti-human TdT monoclonal antibodies and were analyzed by flow cytometry (FCM). The TdT results were compared with those obtained by biochemical TdT assay (26 cases), immunoperoxidase determination (PAP) (12 cases), and fluorescence microscopy (seven cases). The results obtained by PAP and fluorescence microscopy were 100% concordant with those obtained by FCM and biochemical assay. TdT determination by FCM allows the analysis of large numbers of cells in a fast, objective, and reliable manner, as compared with biochemical assay, PAP, and fluorescence microscopy determinations.