Rearrangement of the MLL gene in acute lymphoblastic and acute myeloid leukemias with 11q23 chromosomal translocations

Molecular genetics, natural history and the demise of childhood leukaemia

The patterns of genetic change, clonal evolution, natural history and latency are very different in the paediatric leukaemias compared with adult epithelial cancers but are similar to those in other childhood cancers of mesenchymal stem cell origin. This distinction has a biological logic in the context of the selective pressures for clonal emergence in different developmental and cellular contexts and has a major impact on curability. Most childhood leukaemias and some other mesenchymal stem cell tumours are of fetal origin and can metastasize without corruption of restraints on cell proliferation or bypassing apoptosis. In marked contrast to most invasive or metastatic epithelial carcinomas in adults, these former cancers then retain sensitivity to therapeutic apoptosis. Moreover, their abbreviated and less complex evolutionary status is associated with less genetic diversity and instability, minimising opportunity for clonal selection for resistance. A minority of leukaemias in children and a higher fraction in adults do, however, have genetic alterations that bypass cell cycle controls and apoptosis imposition. These are the 'bad news' genotypes. The cellular and molecular diversity of acute leukaemia impacts also on aetiology. Paediatric acute leukaemias can be initiated prenatally by illegitimate recombination and fusion gene formation in fetal haemopoiesis. For acute lymphoblastic leukaemia (ALL) in children, twin studies suggest that a secondary postnatal molecular event is also required. This may be promoted by an abnormal or delayed response to common infections. Even for a classic case of a cancer that is intrinsically curable by systematic chemotherapy i.e. childhood ALL, prevention may turn out to be the preferred option.

Increased karyotype precision using fluorescence in situ hybridization and spectral karyotyping in patients with myeloid malignancies

We studied seven patients with various malignant hematologic disorders using fluorescence in situ hybridization (FISH) and one of these patients with spectral karyotyping (SKY). With appropriate probes, the t(8;21) and inv(16) were confirmed in two patients and the karyotypic precision was increased in five others using FISH and SKY. Two of three patients with 12p rearrangements had a deletion of one TEL allele. Thus, these newer techniques are an important adjunct to accurate chromosome analysis in malignancy.

Acute myeloid leukemia with hypergranular cytoplasm accompanied by t(X;11)(q24;q23) and rearrangement of the MLL gene

This report describes a unique case of acute myeloid leukemia with hypergranular cytoplasm and t(X;11)(q24;q23). The breakpoint on 11q23 was identified within the MLL gene. The hypergranular cytoplasm of leukemic cells and the associated coagulopathy resembled a characteristic of acute promyelocytic leukemia, despite the absence of RARalpha gene rearrangement in this case. The Xq24 site possibly played a role in this atypical blast phenotype.

Involvement of MLL gene in a t(10;11)(q22;q23) and a t(8;11)(q24;q23) identified by fluorescence in situ hybridization

We describe two cases of acute myeloblastic leukemia, classified as M4 and M5 in the French-American-British nomenclature, with an 11q23 rearrangement at karyotypic analysis. The involvement of the MLL gene with two new partner loci on chromosome 10q22 and 8q24, respectively, was demonstrated by fluorescence in situ hybridization using a YAC clone B22B2L.

A combined cytogenetic and molecular approach to diagnosis in a case of desmoplastic small round cell tumor with a complex translocation (11;22;21)

Desmoplastic small round cell tumor (DSRCT) has recently been described as a discrete tumor entity. It is distinguished from other small round cell tumors by its prominent desmoplastic quality, its preponderance in adolescent males, its almost exclusive intraabdominal location, a multi-immunophenotypic profile, and its aggressive nature. Diagnosis on histology alone is not always unequivocal. A recurrent t(11;22)(p13;q12) translocation has recently been described in this tumor, and a chimeric RNA fusion product formed from the WT1 and EWS genes is detectable by reverse transcriptase-polymerase chain reaction (RT-PCR). We describe the use of a multi-faceted approach using conventional G-banding, fluorescence in situ hybridization (FISH) and RT-PCR to assist the diagnosis of a case of DSRCT with a complex variant t(11;22;21)(p13;q12;q22.1) translocation and demonstrate the value of a combined approach to genetic investigation of solid tumors.

Molecular abnormalities in myeloid leukemias and myelodysplastic syndromes

Analysis of chromosome translocations in human myeloid leukemias and myelodysplastic syndromes has identified a number of genes involved in the pathogenesis of these diseases. Most of the genes identified to date can be grouped into one of three major classes--transcription factors, tyrosine kinases or nuclear pore proteins. Recent insights into the molecular basis of these leukemias is presented using selected examples from these groups.

An In Vivo Topoisomerase II Cleavage Site and a DNase I Hypersensitive Site Colocalize Near Exon 9 in the MLLBreakpoint Cluster Region

The human myeloid-lymphoid leukemia gene, MLL (also calledALL-1, Htrx, or HRX ), maps to chromosomal band 11q23. MLL is involved in translocations that result in de novo acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), mixed lineage leukemia, and also in therapy AML (t-AML) and therapy ALL (t-ALL) resulting from treatment with DNA topoisomerase II (topo II) targeting drugs. MLL can recombine with more than 30 other chromosomal bands, of which 16 of the partner genes have been cloned. Breaks in MLL occur in an 8.3-kb breakpoint cluster region (BCR) encompassing exons 5 through 11. We recently demonstrated that 75% of de novo patient breakpoints in MLL mapped in the centromeric half of the BCR between two scaffold-associated regions (SAR), whereas 75% of the t-AML patient breakpoints mapped to the telomeric half of the BCR within a strong SAR. We have mapped additional structural elements in the BCR. An in vivo DNA topo II cleavage site (induced with several different drugs that target topo II) mapped near exon 9 in three leukemia cell lines. A strong DNase I hypersensitive site (HS) also mapped near exon 9 in four leukemia cell lines, including two in which MLL was rearranged [a t(6;11) and a t(9;11)], and in two lymphoblastoid cell lines with normalMLL. Two of the leukemia cell lines also showed an in vivo topo II cleavage site. Our results suggest that the chromatin structure of the MLL BCR may influence the location of DNA breaks in both de novo and therapy-related leukemias. We propose that topo II is enriched in the MLL telomeric SAR and that it cleaves the DNase I HS site after treatment with topo II inhibitors. These events may be involved in recombination associated with t-AML/t-ALL breakpoints mapping in the MLL SAR.

An In Vivo Topoisomerase II Cleavage Site and a DNase I Hypersensitive Site Colocalize Near Exon 9 in the MLLBreakpoint Cluster Region

The human myeloid-lymphoid leukemia gene, MLL (also calledALL-1, Htrx, or HRX ), maps to chromosomal band 11q23. MLL is involved in translocations that result in de novo acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), mixed lineage leukemia, and also in therapy AML (t-AML) and therapy ALL (t-ALL) resulting from treatment with DNA topoisomerase II (topo II) targeting drugs. MLL can recombine with more than 30 other chromosomal bands, of which 16 of the partner genes have been cloned. Breaks in MLL occur in an 8.3-kb breakpoint cluster region (BCR) encompassing exons 5 through 11. We recently demonstrated that 75% of de novo patient breakpoints in MLL mapped in the centromeric half of the BCR between two scaffold-associated regions (SAR), whereas 75% of the t-AML patient breakpoints mapped to the telomeric half of the BCR within a strong SAR. We have mapped additional structural elements in the BCR. An in vivo DNA topo II cleavage site (induced with several different drugs that target topo II) mapped near exon 9 in three leukemia cell lines. A strong DNase I hypersensitive site (HS) also mapped near exon 9 in four leukemia cell lines, including two in which MLL was rearranged [a t(6;11) and a t(9;11)], and in two lymphoblastoid cell lines with normalMLL. Two of the leukemia cell lines also showed an in vivo topo II cleavage site. Our results suggest that the chromatin structure of the MLL BCR may influence the location of DNA breaks in both de novo and therapy-related leukemias. We propose that topo II is enriched in the MLL telomeric SAR and that it cleaves the DNase I HS site after treatment with topo II inhibitors. These events may be involved in recombination associated with t-AML/t-ALL breakpoints mapping in the MLL SAR.

Seminars from the University of Minnesota. Chromosome translocations: dangerous liaisons

Many chromosome abnormalities, especially translocations or inversions, are closely associated with a particular morphologic or phenotypic subtype of leukemia, lymphoma, or sarcoma. Cloning the genes at the breakpoints of these rearrangements has provided critical tools for more-precise diagnosis; in some cases the particular diagnosis has prognostic implications. In addition, many of the genes had not been previously identified; their discovery has had a major impact on our understanding of the molecular biology of cancer. One such gene is MLL (myeloid-lymphoid or mixed-lineage leukemia), which is located at chromosome band 11q23. This gene is involved in the 4;11 and 11;19 (p13.3) translocations in acute lymphoblastic leukemia and in the 6;11, 9;11, and 11;19 (p13.1) translocations in acute myeloblastic leukemia. It is also involved in most translocations in infants (under 1 year of age) with acute leukemia and in patients with acute leukemia who were previously treated with drugs that inhibit toposiomerase II. The target gene of MLL is unknown at present, but because of its homology to the trithorax gene in Drosophila, and based on experimental data from mice, it appears to be involved in maintaining the function of some of the homeobox genes. The development of cytogenetic and molecular probes for MLL rearrangements has confirmed that translocations involving MLL are associated with a very poor prognosis. Thus physicians can identify patients with MLL involvement and can institute treatment for these high-risk patients. An increasing understanding of MLL should lead to more-effective targeted therapy.

Partial Tandem Duplications of the MLL Gene Are Detectable in Peripheral Blood and Bone Marrow of Nearly All Healthy Donors

Partial tandem duplication within the MLL gene has recently been described as a novel genetic alteration in acute myeloid leukemia (AML). It has been associated with trisomy of chromosome 11, but was also identified in AML patients with normal karyotypes. The current study was performed to investigate whether MLL duplications are restricted to AML, and hence whether they may also occur in normal hematopoietic cells. MLL-duplication transcripts were analyzed by nested reverse-transcriptase polymerase chain reaction (RT-PCR) in peripheral blood in two groups of 45 and 20 patients, respectively, as well as in two bone marrow samples from healthy volunteers. Duplications were detected in two independent nested RT-PCR experiments in the peripheral blood samples of 38 of 45 (84%) and 20 of 20 (100%) of the two groups and in both bone marrow samples. On this basis, MLL duplications seem to occur frequently in a subset of cells in normal hematopoiesis. The type of partially duplicated MLL transcripts varied substantially. Three transcripts were identical to those known from AML. In addition, four new transcripts were characterized. Three of these four were in frame and potentially translatable. MLL duplications were also detected by seminested genomic PCR with intron 9– and intron 1–specific primers in 20 of 20 peripheral blood samples studied, indicating that the duplications are genomically fixed at the DNA level and are not an RT-PCR artifact. In summary, MLL duplications are regularly generated by homologous ALU recombination in a small number of hematopoietic cells of most or even all healthy donors. These data suggest that MLL duplications are not implicated in the malignant transformation in AML, or alternatively, that only a few cells will acquire additional oncogenic mutations necessary to establish the malignant phenotype of AML.

© 1998 by The American Society of Hematology.

Partial Tandem Duplications of the MLL Gene Are Detectable in Peripheral Blood and Bone Marrow of Nearly All Healthy Donors

Partial tandem duplication within the MLL gene has recently been described as a novel genetic alteration in acute myeloid leukemia (AML). It has been associated with trisomy of chromosome 11, but was also identified in AML patients with normal karyotypes. The current study was performed to investigate whether MLL duplications are restricted to AML, and hence whether they may also occur in normal hematopoietic cells. MLL-duplication transcripts were analyzed by nested reverse-transcriptase polymerase chain reaction (RT-PCR) in peripheral blood in two groups of 45 and 20 patients, respectively, as well as in two bone marrow samples from healthy volunteers. Duplications were detected in two independent nested RT-PCR experiments in the peripheral blood samples of 38 of 45 (84%) and 20 of 20 (100%) of the two groups and in both bone marrow samples. On this basis, MLL duplications seem to occur frequently in a subset of cells in normal hematopoiesis. The type of partially duplicated MLL transcripts varied substantially. Three transcripts were identical to those known from AML. In addition, four new transcripts were characterized. Three of these four were in frame and potentially translatable. MLL duplications were also detected by seminested genomic PCR with intron 9– and intron 1–specific primers in 20 of 20 peripheral blood samples studied, indicating that the duplications are genomically fixed at the DNA level and are not an RT-PCR artifact. In summary, MLL duplications are regularly generated by homologous ALU recombination in a small number of hematopoietic cells of most or even all healthy donors. These data suggest that MLL duplications are not implicated in the malignant transformation in AML, or alternatively, that only a few cells will acquire additional oncogenic mutations necessary to establish the malignant phenotype of AML.

© 1998 by The American Society of Hematology.

ABI-1, a Human Homolog to Mouse Abl-Interactor 1, Fuses theMLL Gene in Acute Myeloid Leukemia With t(10;11)(p11.2;q23)

Recurrent translocation t(10;11) has been reported to be associated with acute myeloid leukemia (AML). Recently, two types of chimeric transcripts, MLL-AF10 in t(10;11)(p12;q23) andCALM-AF10 in t(10;11)(p13;q14), were isolated. t(10;11) is strongly associated with complex translocations, including invins(10;11) and inv(11)t(10;11), because the direction of transcription of AF10 is telomere to centromere. We analyzed a patient of AML with t(10;11)(p11.2;q23) and identified ABI-1 on chromosome 10p11.2, a human homolog to mouse Abl-interactor 1 (Abi-1), fused with MLL. Whereas the ABI-1 gene bears no homology with the partner genes of MLL previously described, the ABI-1 protein exhibits sequence similarity to protein of homeotic genes, contains several polyproline stretches, and includes asrc homology 3 (SH3) domain at the C-terminus that is required for binding to Abl proteins in mouse Abi-1 protein. Recently, e3B1, an eps8 SH3 binding protein 1, was also isolated as a human homolog to mouse Abi-1. Three types of transcripts of ABI-1 gene were expressed in normal peripheral blood. Although e3B1 was considered to be a full-length ABI-1, the MLL-ABI-1fusion transcript in this patient was formed by an alternatively spliced ABI-1. Others have shown that mouse Abi-1 suppresses v-ABL transforming activity and that e3B1, full-length ABI-1, regulates cell growth. In-frame MLL-ABI-1 fusion transcripts combine the MLL AT-hook motifs and DNA methyltransferase homology region with the homeodomain homologous region, polyproline stretches, and SH3 domain of alternatively spliced transcript of ABI-1. Our results suggest that the ABI-1 gene plays a role in leukemogenesis by translocating to MLL.

© 1998 by The American Society of Hematology.

ABI-1, a Human Homolog to Mouse Abl-Interactor 1, Fuses theMLL Gene in Acute Myeloid Leukemia With t(10;11)(p11.2;q23)

Recurrent translocation t(10;11) has been reported to be associated with acute myeloid leukemia (AML). Recently, two types of chimeric transcripts, MLL-AF10 in t(10;11)(p12;q23) andCALM-AF10 in t(10;11)(p13;q14), were isolated. t(10;11) is strongly associated with complex translocations, including invins(10;11) and inv(11)t(10;11), because the direction of transcription of AF10 is telomere to centromere. We analyzed a patient of AML with t(10;11)(p11.2;q23) and identified ABI-1 on chromosome 10p11.2, a human homolog to mouse Abl-interactor 1 (Abi-1), fused with MLL. Whereas the ABI-1 gene bears no homology with the partner genes of MLL previously described, the ABI-1 protein exhibits sequence similarity to protein of homeotic genes, contains several polyproline stretches, and includes asrc homology 3 (SH3) domain at the C-terminus that is required for binding to Abl proteins in mouse Abi-1 protein. Recently, e3B1, an eps8 SH3 binding protein 1, was also isolated as a human homolog to mouse Abi-1. Three types of transcripts of ABI-1 gene were expressed in normal peripheral blood. Although e3B1 was considered to be a full-length ABI-1, the MLL-ABI-1fusion transcript in this patient was formed by an alternatively spliced ABI-1. Others have shown that mouse Abi-1 suppresses v-ABL transforming activity and that e3B1, full-length ABI-1, regulates cell growth. In-frame MLL-ABI-1 fusion transcripts combine the MLL AT-hook motifs and DNA methyltransferase homology region with the homeodomain homologous region, polyproline stretches, and SH3 domain of alternatively spliced transcript of ABI-1. Our results suggest that the ABI-1 gene plays a role in leukemogenesis by translocating to MLL.

© 1998 by The American Society of Hematology.

Characteristic Pattern of Chromosomal Gains and Losses in Primary Large B-Cell Lymphomas of the Gastrointestinal Tract

In contrast to low-grade B-cell lymphomas originating in the gastrointestinal (GI) tract, only few cytogenetic data are available for the large cell, highly malignant variants. We studied 31 large B-cell lymphomas of the GI tract by comparative genomic hybridization (CGH) and fluorescence in situ hybridization using specific DNA probes (FISH). The most frequent aberrations were gains of all or of parts of chromosomes 11 (11 cases), 12 (9 cases), 1q (4 cases), and 3q (4 cases). Losses of parts of chromosome 6q and of parts of the short arm of chromosome 17 (6 cases each) were found most frequently. In four cases a total of seven high-level DNA amplifications was detected. In two of these cases, involvement of specific protooncogenes (RELand MYC) was shown. Some genetic aberrations seemed to be associated with an inferior clinical course: patients with ≥2 aberrations had a significantly shorter median survival. Furthermore, all patients with gains of all or parts of chromosome arm 1q and with high-level DNA amplifications as well as seven of nine patients with gains of all or parts of chromosome 12 died of lymphoma. In conclusion, the pattern of chromosomal gains and losses in large B-cell lymphomas was different from data reported for low-grade (MALT) lymphomas of the stomach and bowel, especially with respect to the high incidence of partial gains of chromosome arm 11q and of all or parts of chromosome 12 and the low frequency of polysomy 3. In addition, our data suggest that chromosomal gains and losses detected by CGH and FISH may predict for the outcome of patients with this tumor entity.

Characteristic Pattern of Chromosomal Gains and Losses in Primary Large B-Cell Lymphomas of the Gastrointestinal Tract

In contrast to low-grade B-cell lymphomas originating in the gastrointestinal (GI) tract, only few cytogenetic data are available for the large cell, highly malignant variants. We studied 31 large B-cell lymphomas of the GI tract by comparative genomic hybridization (CGH) and fluorescence in situ hybridization using specific DNA probes (FISH). The most frequent aberrations were gains of all or of parts of chromosomes 11 (11 cases), 12 (9 cases), 1q (4 cases), and 3q (4 cases). Losses of parts of chromosome 6q and of parts of the short arm of chromosome 17 (6 cases each) were found most frequently. In four cases a total of seven high-level DNA amplifications was detected. In two of these cases, involvement of specific protooncogenes (RELand MYC) was shown. Some genetic aberrations seemed to be associated with an inferior clinical course: patients with ≥2 aberrations had a significantly shorter median survival. Furthermore, all patients with gains of all or parts of chromosome arm 1q and with high-level DNA amplifications as well as seven of nine patients with gains of all or parts of chromosome 12 died of lymphoma. In conclusion, the pattern of chromosomal gains and losses in large B-cell lymphomas was different from data reported for low-grade (MALT) lymphomas of the stomach and bowel, especially with respect to the high incidence of partial gains of chromosome arm 11q and of all or parts of chromosome 12 and the low frequency of polysomy 3. In addition, our data suggest that chromosomal gains and losses detected by CGH and FISH may predict for the outcome of patients with this tumor entity.

Lack of TEL/AML1 fusion in pediatric AML: further evidence for lineage specificity of TEL/AML1

BACKGROUND

The TEL/AML1 fusion associated with t(12;21)(p13;q22) is the most common gene rearrangement in childhood malignancy, occurring in approximately 25% of pediatric acute lymphoblastic leukemia. The TEL/AML1 rearrangement is cryptic at the cytogenetic level but confers a favorable prognosis. The AML1 gene was first identified by virtue of its involvement in adult and pediatric acute myeloid malignancies associated with t(8;21) and t(3;21)(q26;q22.1). We have therefore determined the frequency of the TEL/AML1 fusion in pediatric myeloid leukemias by RT-PCR analysis.

METHODS

Total RNA was isolated from cryopreserved bone marrow samples of 38 pediatric patients with AML. RNA quality was controlled for by amplification of the TEL gene. An RT-PCR assay was then used to test for the presence of the TEL/AML1 fusion.

RESULTS

29 patients had adequate RNA for analysis. Zero out of 29 pediatric AML patients had evidence for the TEL/AML1 fusion by RT-PCR.

CONCLUSIONS

The TEL/AML1 fusion does not occur in children with AML and suggests that the TEL/AML1 rearrangement is restricted in pediatric hematologic malignancy to B lineage ALL.

Pseudo-rearrangement of the MLL gene at chromosome 11q23: a cautionary note on genotype analysis of leukaemia patients

AIMS

The MLL gene on chromosome 11q23 is frequently disrupted by chromosomal translocations in association with haematological malignancies. Recently, a specific site within the 8.3 kb MLL break-point cluster region that is cleaved during the early stages of apoptosis has been identified. Because MLL gene rearrangements are used to identify patients with high risk leukaemia, it was the aim of this study to determine whether this DNA cleavage event could be triggered in diagnostic bone marrow samples solely through ex vivo incubation at room temperature.

METHODS

Pretreatment bone marrow samples were collected from six paediatric leukaemia patients. Genomic DNA for Southern blot analysis of MLL gene rearrangements was isolated immediately after samples were obtained and compared to genomic DNA isolated after incubation of specimens for 24-60 hours at room temperature, simulating delays in processing that might occur when samples are delivered to reference laboratories. In addition, cryopreserved samples from 70 paediatric leukaemia patients were screened for evidence of site specific MLL cleavage.

RESULTS

After ex vivo incubation of bone marrow samples, site specific MLL cleavage resulting in a pseudo-rearrangement of the MLL gene was detected in two of six patients. In addition, a third patient with a similar MLL pseudo-rearrangement in cryopreserved cells was identified.

CONCLUSIONS

Pseudo-rearrangement of the MLL gene at chromosome 11q23 was caused by ex vivo incubation of bone marrow samples. This novel phenomenon, which could lead to misclassification of leukaemia patients, might also be of importance for genotype analysis by Southern blotting at other loci.

Malignant histiocytosis. Histologic, cytochemical, chromosomal, and molecular data with a nosologic discussion

Although myelomonoblastic leukemia is thought to originate from a malignant transformation of the stem cell of the mononuclear phagocyte system, malignant histiocytosis (MH) is classically assumed to represent a malignant change of the terminal and fixed elements of this system. Indeed, MH is characterized by the proliferation of large, clear, pleomorphic, "histiocytic-like" HLADR and CD30+ cells resulting in a nodal and extranodal disseminated neoplasm affecting preferentially and severely children and young adults. Although there is broad agreement on the clinicopathologic presentation of this condition, there is currently quite a controversy over the T-lymphoid or histiocytic origin of the proliferative cells that results in a nosologic discussion between the anaplastic large cell lymphoma (ALCL) advocates and the MH supporters. This article has dealt mainly with this nosologic discussion and with the contributions provided by the investigations performed on MH permanent cell lines. These in vitro studies have demonstrated that the proliferation is characterized by a unique chromosomal abnormality, the 5q35bp usually associated with a t(2;5) translocation generating a fusion gene NPM/ALK and the subsequent translation of p80 protein. Although it is known that no single chromosomal abnormality is strictly restricted to a cell lineage, this 5q35bp and associated translocations seem today to represent the hallmark for this condition. In view of these chromosomal aberrations, the CD30+ ALCLs represent a heterogeneous group because 15% to 50% express the NPM/ALK fusion gene. In addition, these in vitro investigations have shown that 5q35bp proliferative cells are glass-adherent, can develop an immunodependent phagocytosis, and are able to reduce NBT and produce TNF-alpha. More significantly, they express constitutively the c-fms (the receptor of the macrophage growth factor) and, under TPA stimulation, are able to modulate the expression of this receptor and its ligand, as well as TNF-alpha and IL-1. None of these cell lines express CD3, but several express CD68 and CD71. In contrast, genomic investigations have shown the underlying existence of monoallelic and even biallelic gene rearrangements for TCR beta and IgJH. In view of these discrepancies between the genomic and phenotypic features of these cells, the histogenetic debate should remain open but must take into account these new chromosomal and molecular data.

Large granular lymphocytic leukaemia with a mixed T-cell/B-cell phenotype

We report a case of large granular lymphocytic leukaemia (LGLL) with mixed T-cell/B-cell phenotypes. The LGLL cells expressed T-cell markers such as CD1, CD2, CD3, CD5, CD7, CD8 and CD57. The CD8+ LGLL cells coexpressed B-cell markers including CD20 and PCA-1, and a fraction of purified CD8+ LGLL cells secreted double isotypes of immunoglobulins (IgG-kappa and IgA-kappa). Both TCRB and IGH genes were clonally rearranged. The LGLL cells could be divided into at least three subpopulations that were cytogenetically distinct, and all subpopulations involved the 11q23. The expression of both T- and B-cell markers on the LGLL cells suggests the involvement of a putative common lymphoid progenitor in leukaemic transformation.

Scaffold-associated regions in the human type I interferon gene cluster on the short arm of chromosome 9

Scaffold-associated regions (SARs) function at the level of modeling or shaping the chromatin of DNA into loop domains. We have mapped 36 SARs in the human type I interferon (IFN) gene complex on chromosome 9, band p21-22, to examine the overall structure of this gene complex. A total of 29 strong SARs and 7 weak SARs were mapped to the flanking regions of the different interferon genes. Twenty-two strong SARs mapped to the flanking regions of 13 interferon (IFNA) alpha genes; 2 strong SARs mapped to one interferon omega (IFNW) gene; 2 strong SARs mapped to one interferon alpha pseudogene (IFNAP); and 3 strong SARs mapped to two interferon omega pseudogenes (IFNWP). One weak SAR mapped to the flanking region of one IFNA gene, whereas 6 weak SARs flanked four IFN pseudogenes (P11, P12 P20, P23). The IFN SAR structure was comparable between the BV173 leukemia cell line and the U373 glioma cell line. Analysis of two glioma deletion breakpoint junctions, where breaks occur within and outside the IFN gene cluster, revealed an association with SARs. IFN SARs showed evidence for cooperativity among the SARs, while DNA sequence analysis revealed a series of clustered A-tracts within strong SARs. These data suggest that the IFN genes may be organized into a series of small (2-10 kb) DNA loop domains, with each loop containing a coding region flanked by SARs. In our model, the SAR enrichment and the clustering of A-tracts observed at the SARs within the IFN gene complex represent a higher level of chromatin organization, which may predispose this region to breakage.

Backtracking leukemia to birth: identification of clonotypic gene fusion sequences in neonatal blood spots

Epidemiological evidence has suggested that some pediatric leukemias may be initiated in utero and, for some pairs of identical twins with concordant leukemia, this possibility has been strongly endorsed by molecular studies of clonality. Direct evidence for a prenatal origin can only be derived by prospective or retrospective detection of leukemia-specific molecular abnormalities in fetal or newborn samples. We report a PCR-based method that has been developed to scrutinize neonatal blood spots (Guthrie cards) for the presence of numerically infrequent leukemic cells at birth in individuals who subsequently developed leukemia. We demonstrate that unique or clonotypic MLL-AF4 genomic fusion sequences are present and detectable in neonatal blood spots from individuals who were diagnosed with acute lymphoblastic leukemia at ages 5 months to 2 years and, therefore, have arisen during fetal hematopoiesis in utero. This result provides unequivocal evidence for a prenatal initiation of acute leukemia in young patients. The method should be applicable to other fusion genes in children with common subtypes of leukemia and will be of value in attempts to unravel the natural history and etiology of this major subtype of pediatric cancer.

Adult Patients With De Novo Acute Myeloid Leukemia and t(9; 11)(p22; q23) Have a Superior Outcome to Patients With Other Translocations Involving Band 11q23: A Cancer and Leukemia Group B Study

Following reports of childhood acute myeloid leukemia (AML) showing that patients with t(9; 11)(p22; q23) have a better prognosis than those with translocations between 11q23 and other chromosomes, we compared response to therapy and survival of 24 adult de novo AML patients with t(9; 11) with those of 23 patients with other 11q23 translocations [t(11q23)]. Apart from a higher proportion of French-American-British (FAB) M5 subtype in the t(9; 11) group (83% v 43%, P = .006), the patients with t(9; 11) did not differ significantly from patients with t(11q23) in terms of their presenting clinical or hematologic features. Patients with t(9; 11) more frequently had an extra chromosome(s) 8 or 8q as secondary abnormalities (46% v 9%, P = .008). All patients received standard cytarabine and daunorubicin induction therapy, and most of them also received cytarabine-based intensification treatment. Two patients, both with t(9; 11), underwent bone marrow transplantation (BMT) in first complete remission (CR). Nineteen patients (79%) with t(9; 11) and 13 (57%) with t(11q23) achieved a CR (P = .13). The clinical outcome of patients with t(9; 11) was significantly better: the median CR duration was 10.7 versus 8.9 months (P = .02), median event-free survival was 6.2 versus 2.2 months (P = .009), and median survival was 13.2 versus 7.7 months (P = .009). All patients with t(11q23) have died, whereas seven (29%) patients with t(9; 11) remain alive in first CR. Seven of eight patients with t(9; 11) who received postremission regimens with cytarabine at a dose of 100 (four patients) or 400 mg/m2 (2 patients) or who did not receive postremission therapy (2 patients) have relapsed. In contrast, 7 (64%) of 11 patients who received intensive postremission chemotherapy with high-dose cytarabine (at a dose 3 g/m2) (5 patients), or underwent BMT (2 patients) remain in continuous CR. We conclude that the outcome of adults with de novo AML and t(9; 11) is more favorable than that of adults with other 11q23 translocations; this is especially true for t(9; 11) patients who receive intensive postremission therapy.

TEL gene rearrangements in myeloid malignancy

The TEL gene is a recently described, "promiscuous" gene with a role in both myeloid and lymphoid malignancy. It is unusual since there may be more than one mechanism by which its rearrangement through chromosomal translocation is leukemogenic. This article discusses the four potential mechanisms of TEL-mediated transformation. It is conceivable that the TEL gene is the common target for various translocations precisely because of this pleiotropy of pathogenic mechanisms by which TEL gene rearrangements can lead to cell transformation.

Adult Patients With De Novo Acute Myeloid Leukemia and t(9; 11)(p22; q23) Have a Superior Outcome to Patients With Other Translocations Involving Band 11q23: A Cancer and Leukemia Group B Study

Following reports of childhood acute myeloid leukemia (AML) showing that patients with t(9; 11)(p22; q23) have a better prognosis than those with translocations between 11q23 and other chromosomes, we compared response to therapy and survival of 24 adult de novo AML patients with t(9; 11) with those of 23 patients with other 11q23 translocations [t(11q23)]. Apart from a higher proportion of French-American-British (FAB) M5 subtype in the t(9; 11) group (83% v 43%, P = .006), the patients with t(9; 11) did not differ significantly from patients with t(11q23) in terms of their presenting clinical or hematologic features. Patients with t(9; 11) more frequently had an extra chromosome(s) 8 or 8q as secondary abnormalities (46% v 9%, P = .008). All patients received standard cytarabine and daunorubicin induction therapy, and most of them also received cytarabine-based intensification treatment. Two patients, both with t(9; 11), underwent bone marrow transplantation (BMT) in first complete remission (CR). Nineteen patients (79%) with t(9; 11) and 13 (57%) with t(11q23) achieved a CR (P = .13). The clinical outcome of patients with t(9; 11) was significantly better: the median CR duration was 10.7 versus 8.9 months (P = .02), median event-free survival was 6.2 versus 2.2 months (P = .009), and median survival was 13.2 versus 7.7 months (P = .009). All patients with t(11q23) have died, whereas seven (29%) patients with t(9; 11) remain alive in first CR. Seven of eight patients with t(9; 11) who received postremission regimens with cytarabine at a dose of 100 (four patients) or 400 mg/m2 (2 patients) or who did not receive postremission therapy (2 patients) have relapsed. In contrast, 7 (64%) of 11 patients who received intensive postremission chemotherapy with high-dose cytarabine (at a dose 3 g/m2) (5 patients), or underwent BMT (2 patients) remain in continuous CR. We conclude that the outcome of adults with de novo AML and t(9; 11) is more favorable than that of adults with other 11q23 translocations; this is especially true for t(9; 11) patients who receive intensive postremission therapy.

Defects in Yolk Sac Hematopoiesis in Mll-Null Embryos

Translocations involving the mixed lineage leukemia gene (MLL ), the human homolog of the Drosophila gene trithorax, are one of the most common genetic alterations in human acute leukemias. Each translocation involving MLL results in loss of one functional copy of MLL and the generation of a chimeric fusion protein with potential dominant negative or neomorphic activity. Mll is a positive regulator of Hox genes, which have been implicated in both axial skeleton patterning and hematopoietic development. Previous studies indicated that Hox gene expression is altered in Mll heterozygous (+/−) and homozygous (−/−) deficient mice. To study the role of Mll in hematopoiesis and to obtain insights into leukemogenesis, we have examined the effects of haplo-insufficiency or absence of Mll by in vitro differentiation of Mll +/+, +/−, and −/− yolk sac progenitor cells. Mll −/− colonies were fewer in number, took longer to develop, and contained fewer cells than their wild-type and heterozygous counterparts. Formation of colony-forming unit-granulocyte, erythroid, macrophage, megakaryocyte (CFU-GEMM), colony-forming unit-macrophage (CFU-M), and burst-forming unit-erythroid (BFU-E) was markedly decreased in Mll −/− cultures, while numbers of colony-forming unit-erythroid (CFU-E), colony-forming unit-granulocyte (CFU-G), and colony-forming unit-granulocyte macrophage (CFU-GM) were essentially unaffected. Despite the decreased numbers of colonies present, Mll −/− cultures showed all cell types without morphologic evidence of maturation arrest. These studies indicate that Mll is required for normal numbers of hematopoietic progenitors and their proper differentiation, especially along the myeloid and macrophage pathways.

Chromosome 8 tetrasomies and pentasomies--a clonal abnormality closely associated with acute monocytic leukaemia

We report four cases of polysomy 8 (one tetrasomy and three pentasomies) observed in acute monocytic leukemia (FAB M4 and M5). Three of them showed a rearrangement of 11q23 identified by conventional cytogenetic analysis and/or chromosome painting. Our cases as well as a review of the literature, suggest that polysomy 8 is preferentially associated with monocytic differentiation (24/31). These polysomies have been observed in 21 de novo leukemias and in 10 secondary hematological disorders. A 11q23 rearrangement has been detected in 9 out of 32 patients, by conventional cytogenetic techniques in 7 and by FISH in 2. We suggest that these cases should be analysed by FISH and molecular studies in order to detect a rearrangement of MLL/11q23. Monocytic differentiation is often associated with a change of the MLL gene and the polysomy 8 might be a particular clonal evolution secondary to 11q23 abnormality.

MLL is fused to CBP, a histone acetyltransferase, in therapy-related acute myeloid leukemia with a t(11;16)(q23;p13.3)

The recurring translocation t(11;16)(q23;p13.3) has been documented only in cases of acute leukemia or myelodysplasia secondary to therapy with drugs targeting DNA topoisomerase II. We show that the MLL gene is fused to the gene that codes for CBP (CREB-binding protein), the protein that binds specifically to the DNA-binding protein CREB (cAMP response element-binding protein) in this translocation. MLL is fused in-frame to a different exon of CBP in two patients producing chimeric proteins containing the AT-hooks, methyltransferase homology domain, and transcriptional repression domain of MLL fused to the CREB binding domain or to the bromodomain of CBP. Both fusion products retain the histone acetyltransferase domain of CBP and may lead to leukemia by promoting histone acetylation of genomic regions targeted by the MLL AT-hooks, leading to transcriptional deregulation via aberrant chromatin organization. CBP is the first partner gene of MLL containing well defined structural and functional motifs that provide unique insights into the potential mechanisms by which these translocations contribute to leukemogenesis.

Partial duplication of the MLL gene in acute myelogenous leukemia without karyotypic aberration

Partial duplication of the MLL gene is a recently characterized novel genetic mechanism for leukemogenesis. A close association with trisomy 11 has been observed. A case of acute myelogenous leukemia (AML) M6 without karyotypic abnormality was found to have rearrangement of the MLL gene. Southern analysis with an MLL exon 2 probe revealed partial duplication of the MLL gene, with a duplicated MLL transcript amplified by reverse transcription polymerase chain reaction (RT = PCR). The presence of trisomy 11 was excluded by fluorescence in situ hybridization (FISH). Few cases of AML with MLL gene duplication have been reported, and they showed involvement of the M1, M2, and M4 subtypes. This case is the first reported case with an M6 phenotype, and highlights the importance of investigating for MLL gene mutations in all subtypes of AML, as they may carry prognostic significance.

Diagnosis and treatment of childhood acute myelogenous leukemia

Acute myelogenous leukemia (AML) accounts for about 20% of the acute leukemias seen in children. In contrast to childhood acute lymphoblastic leukemia (ALL), there has only been a modest improvement in the cure rate of children with AML during the past two decades. Approximately 40% of children treated with chemotherapy alone are long-term survivors. The outcome is somewhat better for those children who are given bone marrow transplants from histocompatible sibling donors early in the first remission. During the last decade, however, new insights into the molecular basis of AML has increased our understanding of the pathogenesis and biology of this group of leukemias and are beginning to provide us with new therapeutic strategies.

Minimal residual disease in acute monocytic leukemia patient with trisomy 11 and partial tandem duplication of MLL

We studied MLL rearrangements in five patients with myeloid hematologic malignancies with trisomy 11. Two had acute monocytic leukemia (AMoL), one had chronic myelomonocytic leukemia, one had refractory anemia, and the other had juvenile chronic myelogenous leukemia. Only one patient, a 15-year-old boy with AMoL and simple trisomy 11, showed rearrangement of MLL. He did not respond to chemotherapy, and successfully underwent bone marrow transplantation, but suffered a relapse 22 months later. Reverse transcription-polymerase chain reaction (RT-PCR) and sequencing analyses of bone marrow cells revealed a tandem duplication of MLL, and his relapse was predictable by sequential RT-PCR studies before it was clinically evident. Of 16 acute myeloid leukemia patients with trisomy 11 and rearrangement of MLL reported, our patient was the youngest in age and the only one with AMoL.

DNA cleavage within the MLL breakpoint cluster region is a specific event which occurs as part of higher-order chromatin fragmentation during the initial stages of apoptosis

A distinct population of therapy-related acute myeloid leukemia (t-AML) is strongly associated with prior administration of topoisomerase II (topo II) inhibitors. These t-AMLs display distinct cytogenetic alterations, most often disrupting the MLL gene on chromosome 11q23 within a breakpoint cluster region (bcr) of 8.3 kb. We recently identified a unique site within the MLL bcr that is highly susceptible to DNA double-strand cleavage by classic topo II inhibitors (e.g., etoposide and doxorubicin). Here, we report that site-specific cleavage within the MLL bcr can be induced by either catalytic topo II inhibitors, genotoxic chemotherapeutic agents which do not target topo II, or nongenotoxic stimuli of apoptotic cell death, suggesting that this site-specific cleavage is part of a generalized cellular response to an apoptotic stimulus. We also show that site-specific cleavage within the MLL bcr can be linked to the higher-order chromatin fragmentation that occurs during the initial stages of apoptosis, possibly through cleavage of DNA loops at their anchorage sites to the nuclear matrix. In addition, we show that site-specific cleavage is conserved between species, as specific DNA cleavage can also be demonstrated within the murine MLL locus. Lastly, site-specific cleavage during apoptosis can also be identified at the AML1 locus, a locus which is also frequently involved in chromosomal rearrangements present in t-AML patients. In conclusion, these results suggest the potential involvement of higher-order chromatin fragmentation which occurs as a part of a generalized apoptotic response in a mechanism leading to chromosomal translocation of the MLL and AML1 genes and subsequent t-AML.

MLL Gene Rearrangement, Cytogenetic 11q23 Abnormalities, and Expression of the NG2 Molecule in Infant Acute Myeloid Leukemia

To study prognostic factors in infant acute myeloid leukemia (AML), we analyzed 44 children treated on Childrens Cancer Group protocols for MLL gene rearrangement by Southern blot, cytogenetic 11q23 abnormalities, and reactivity with monoclonal antibody 7.1. This antibody detects the human homologue of the rat NG2 chondroitin sulfate proteoglycan molecule, which has previously been reported to be expressed on human melanoma. NG2 has been found to be expressed on human leukemic blasts but not on other hematopoietic cells. In childhood AML, NG2 cell surface expression correlated with poor outcome and with some but not all 11q23 rearrangements. In childhood acute lymphoblastic leukemia, NG2 expression correlated with poor outcome and with balanced 11q23 translocations. In this study, 29 of 44 (66%) of infants with AML showed MLL rearrangement and, as expected, this group had a high incidence of French-American-British M4/M5 morphology (22/29). Of the cases tested, 35.1% (13/37) were NG2 positive. All (13/13) NG2-positive cases were rearranged at MLL, whereas only 46% (11/24) of NG2-negative cases had MLL rearrangement. NG2 expression did not correlate with poor outcome (P = .31); there was a trend towards a worse outcome with MLL rearrangement (P = .13). Thus monoclonal antibody 7.1 does not detect all cases of MLL rearrangement in infant AML.

MLL Gene Rearrangement, Cytogenetic 11q23 Abnormalities, and Expression of the NG2 Molecule in Infant Acute Myeloid Leukemia

To study prognostic factors in infant acute myeloid leukemia (AML), we analyzed 44 children treated on Childrens Cancer Group protocols for MLL gene rearrangement by Southern blot, cytogenetic 11q23 abnormalities, and reactivity with monoclonal antibody 7.1. This antibody detects the human homologue of the rat NG2 chondroitin sulfate proteoglycan molecule, which has previously been reported to be expressed on human melanoma. NG2 has been found to be expressed on human leukemic blasts but not on other hematopoietic cells. In childhood AML, NG2 cell surface expression correlated with poor outcome and with some but not all 11q23 rearrangements. In childhood acute lymphoblastic leukemia, NG2 expression correlated with poor outcome and with balanced 11q23 translocations. In this study, 29 of 44 (66%) of infants with AML showed MLL rearrangement and, as expected, this group had a high incidence of French-American-British M4/M5 morphology (22/29). Of the cases tested, 35.1% (13/37) were NG2 positive. All (13/13) NG2-positive cases were rearranged at MLL, whereas only 46% (11/24) of NG2-negative cases had MLL rearrangement. NG2 expression did not correlate with poor outcome (P = .31); there was a trend towards a worse outcome with MLL rearrangement (P = .13). Thus monoclonal antibody 7.1 does not detect all cases of MLL rearrangement in infant AML.