Two new translocations involving the 11q23 region map outside the MLL locus in myeloid leukemias

BACKGROUND AND OBJECTIVES: In acute leukemias, chromosomal translocations involving the 11q23 band are frequently, but not invariably, associated with MLL gene rearrangement and their finding is associated with a poor prognosis. We observed two new translocations with a breakpoint in the 11q23 region at standard cytogenetic analysis: a previously undescribed t(3;11)(q21;q23) in a 70-year old woman with a fulminating form of AML-M1 and a new translocation t(6;11)(q15;q23) in a 61-year old man with an atypical chronic myelogenous leukemia. In these two patients, involvement of the MLL gene was analyzed by molecular cytogenetic techniques which also allowed a more precise mapping of the breakpoints. DESIGN AND METHODS: The MLL gene was analyzed by Southern blot and by fluorescent in situ hybridization (FISH) with a double-color MLL probe. A panel of 11q, 3q and 6q cosmid/YAC probes mapping around the breakpoints was used for breakpoint mapping. RESULTS: In both patients, FISH analysis and Southern blot showed that the MLL gene was not rearranged; in patient 1, MLL was retained on the 11q+ derivative, whereas in patient 2 it moved to the 6q- chromosome. In the t(3;11) we localized the chromosome 11 breakpoint at 11q23.3, in a region flanked by CP-939H3 and cos1p3, distal to the MLL locus; in the t(6;11) the break occurred at 11q21, in a region flanked by CP-819A5 and CP-829A6, proximal to the MLL locus. INTERPRETATION AND CONCLUSIONS: Our cases add two new translocations to the list of chromosomal anomalies involving the long arm of chromosome 11, and show that apparent translocation t(11q23) may involve loci and genes other than MLL. Characterizing the molecular heterogeneity of 11q23 translocations may identify some prognostic significance.     

Acute lymphoblastic leukemias with deletion of 11q23 or a novel inversion (11)(p13q23) lack MLL gene rearrangements and have favorable clinical features

Balanced translocations affecting the 11q23 region are among the most frequent chromosomal abnormalities in childhood acute lymphoblastic leukemia (ALL), comprising 5% to 6%. These cases consistently have a rearranged MLL gene and are associated with high-risk presenting features, hyperleukocytosis and younger age, and a poor treatment outcome. To assess the clinical and biologic significance of 11q23- associated structural chromosomal abnormalities other than translocations, we studied 17 cases of childhood ALL [14 with del(11)(q23) and 3 with inv(11)(p12q23)] that were identified among 785 cases with successful chromosome analysis. In contrast to reported cases with 11q23 and MLL gene rearrangement, our series was characterized by relatively low leukocyte counts (median, 15.1 x 10(9)/L), expression of CD10 antigen but not myeloid-associated CD15 and CDw65 antigens, a relatively high frequency of T-cell immunophenotypes, and a generally favorable prognosis. All 13 cases with interpretable molecular analysis lacked MLL gene rearrangements. We suggest that most cases with deletions or inversions affecting the 11q23 region represent clinically and biologically different entities as compared with those defined by 11q23 translocation.     

Rearrangements of the MLL gene in therapy-related acute myeloid leukemia in patients previously treated with agents targeting DNA- topoisomerase II

Chromosome band 11q23 is frequently involved in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) de novo, as well as in myelodysplastic syndromes (MDS) and lymphoma. Five percent to 15% of patients treated with chemotherapy for a primary neoplasm develop therapy-related AML (t-AML) that may show rearrangements, usually translocations involving band 11q23 or, less often, 21q22. These leukemias develop after a relatively short latent period and often follow the use of drugs that inhibit the activity of DNA-topoisomerase II (topo II). We previously identified a gene, MLL (myeloid-lymphoid leukemia or mixed-lineage leukemia), at 11q23 that is involved in the de novo leukemias. We have studied 17 patients with t-MDS/t-AML, 12 of whom had cytogenetically detectable 11q23 rearrangements. Ten of the 12 t-AML patients had received topo II inhibitors and 9 of these, all with balanced translocations of 11q23, had MLL rearrangements on Southern blot analysis. None of the patients who had not received topo II inhibitors showed an MLL rearrangement. Of the 5 patients lacking 11q23 rearrangements, some of whom had monoblastic features, none had an MLL rearrangement, although 4 had received topo II inhibitors. Our study indicates that the MLL gene rearrangements are similar both in AML that develops de novo and in t-AML. The association of exposure to topo II- reactive chemotherapy with 11q23 rearrangements involving the MLL gene in t-AML suggests that topo II may play a role in the aberrant recombination events that occur in this region both in AML de novo and in t-AML.     

Therapy-related acute myeloid leukemia-like MLL rearrangements are induced by etoposide in primary human CD34+ cells and remain stable after clonal expansion

Rearrangements involving the MLL gene on chromosome band 11q23 are a hallmark of therapy-related acute myeloid leukemias following treatment with topoisomerase II poisons including etoposide. Therapy-related and de novo genomic translocation breakpoints cluster within a well-characterized 8.3-kb fragment of MLL. Repair of etoposide-stabilized DNA topoisomerase II covalent complexes may initiate MLL rearrangements observed in patients. We used a culture system of primary human hematopoietic CD34+ cells and inverse polymerase chain reaction to characterize the spectrum of stable genomic rearrangements promoted by etoposide exposure originating within an MLL translocation hotspot in therapy-related leukemia. Alterations to the region were observed at a readily detectable frequency in etoposide-treated cells. Illegitimate repair events after minimal repair included MLL tandem duplications and translocations, with minor populations of deletions or insertions. In stably repaired cells that proliferated for 10 to 14 days, the significant majority of illegitimate events were MLL tandem duplications, and several deletions, inversions, insertions, and translocations. Thus, etoposide promotes specific rearrangements of MLL consistent with the full spectrum of oncogenic events identified in leukemic samples. Although etoposide-initiated rearrangements are frequent, only a small subset of translocations occurs in cells that proliferate significantly.     

Clonal, nonconstitutional rearrangements of the MLL gene in infant twins with acute lymphoblastic leukemia: in utero chromosome rearrangement of 11q23

Rearrangements of chromosome band 11q23 are common in infant leukemias, comprising more than 70% of the observed chromosome abnormalities in children less than 1 year of age. The MLL gene, which is located at the 11q23 breakpoint in infant, childhood, and adult acute leukemias, has been cloned and has homology to the Drosophila trithorax gene. The breakpoints in MLL are restricted to an 8.3-kilobase pair (kb) region of the gene that is involved in translocations with as many as 29 other chromosomal regions in a number of phenotypically distinct acute leukemias. We have detected an identical, clonal, nonconstitutional rearrangement of the MLL gene in peripheral blood cells from a pair of female infants twins with acute lymphoblastic leukemia (ALL) and a t(11;19)(q23;p13.3). The detection of nonidentical IGH rearrangements suggests that the MLL rearrangement took place in a B-cell precursor or hematopoietic stem cell in one twin which was transferred in utero to the other fetus resulting in ALL with an identical aneuploid karyotype in both infants. We speculate that the other MLL-related infant leukemias may also develop in utero, and that the rearrangements may occur consistently in stem cells or early precursor cells, accounting for the frequency of mixed-lineage leukemia in infants.     

A novel gene, AF1q, fused to MLL in t(1;11) (q21;q23), is specifically expressed in leukemic and immature hematopoietic cells

Translocations involving chromosomal band 11q23 are associated with leukemias. These translocations fuse the MLL, a gene with sequence homology to the Drosophila trithorax, to genes from a number of other chromosomal loci. We have characterized two t(1;11)(q21;q23) translocations that fuse the MLL gene to a novel gene, AF1q on chromosomal band 1q21, in two infants with acute myelomonocytic leukemia (AMMOL). In one of these patients, der(11) represents an inframe fusion of the N-terminal portion of MLL gene to the complete AF1q open reading frame, whereas der(1) does not give rise to an open reading frame. This observation suggests that the N-terminal portion of MLL gene is critical for leukemogenesis in translocations involving band 11q23. The predicted wild-type AF-1q product is a 9-kD protein with no similarity to any other protein in the data banks. The AF1q mRNA is highly expressed in the thymus but not in peripheral lymphoid tissues. In contrast to its restricted distribution in normal hematopoietic tissue, AF1q was expressed in all leukemic cell lines tested.     

Successful Outcome of Mismatched Hematopoietic Stem Cell Transplantation from a Related Donor in an Infant with Acute Lymphoblastic Leukemia and 9;11 Translocation: Case Report and Review of the Literature

Although infants with acute lymphoblastic leukemia (ALL) and MLL gene rearrangements have a poor prognosis, those with acute myeloid leukemia (AML) have been shown to have a superior outcome with intensive chemotherapy alone despite the presence of MLL gene rearrangements. We report the case of an ALL infant with t(9;11), a common cytogenetic abnormality in infant AML, who after relapse underwent successful hematopoietic stem cell transplantation (HSCT) from her HLA 2-loci-mismatched mother. Analysis of the outcome among ALL infants with MLL gene rearrangements registered in the Japan Infant Leukemia Study between 1996 and 1999 showed the event-free survival of patients with t(9;11) was not different from that of those with other 11q23 translocations. Most of the patients with t(9;11) described in the reviewed literature also experienced either induction failure or early relapse after achievement of complete remission, but some of them were rescued with subsequent HSCT. These findings suggest that infant ALL with t(9;11) has features distinct from those of infant AML with the same karyotype and that the prognosis among these patients can be improved only with the combination of intensive chemotherapy and HSCT An appropriate strategy for the treatment of ALL infants with different 11q23 translocations must be clarified.     

Rearrangement of the MLL gene confers a poor prognosis in childhood acute lymphoblastic leukemia, regardless of presenting age

MLL gene rearrangements are associated with an extremely poor prognosis in infants with acute lymphoblastic leukemia (ALL), but little is known about their clinical significance in older children. Therefore, we studied 45 cases of childhood ALL with abnormalities of chromosome 11q23 for rearrangement of the MLL gene to determine if this feature confers a uniformly poor prognosis. MLL gene rearrangements were detected in all 18 cases with the common t(4;11), t(9;11) or t(11;19) translocations, whereas only 5 of 12 patients with either unbalanced or uncommon balanced translocations demonstrated a rearrangement. Abnormalities of the MLL gene were not detected in any of the 15 cases with a deletion or inversion of the chromosomes 11q23 region. The presence of an MLL rearrangement was significantly associated with age less than 1 year (P < .001), leukocyte count >50 x 10(9)/L (P = .003), and the absence of leukemic cell CD10 expression (P < .001). In a stratified statistical analysis adjusted for age and treatment protocol, MLL gene rearrangement was correlated with an inferior treatment outcome (P = .028). The 4-year event-free survival estimate (+/- SE) was 10% +/- 6.5% for cases with a rearranged MLL gene and 64% +/- 19.2% for other cases. When infants were excluded from the analysis, MLL rearrangement was still significantly associated with a poor outcome (P = .02), and remained so with the exclusion of t(4;11)- positive cases (P = .05). Thus, regardless of presenting age, MLL gene rearrangement identifies a high-risk subgroup of patients who are not likely to be cured with conventional treatment.     

急性白血病11q23/MLL基因易位重排及其临床意义

目的：研究11q23/MLL基因易位重排在急性白血病（AL）中的发生率、产生融合基因的常见类型及其临床意义.方法：用荧光原位杂交技术，MLL双色断裂分离重排探针检测50例AL患者（49例初治，1例难治）的11q23/MLL基因，用流式细胞仪检测免疫表型，对于11q23/MLL基因易位重排阳性的患者，用巢式RTPCR方法检测11q23/MLL基因易位重排形成的6种常见融合基因类型.结果：6例AL有11q23/MLL基因易位重排，发生率为12%，2例为AML-M5，4例为ALL且均为B-ALL.2例11q23/MLL基因易位重排阳性的AML M5患者融合基因均为MLL/AF9，其中1例为初治，发病时左侧小腿有白血病细胞浸润，本例患者化疗1疗程获CR;1例为难治性AL患者，于第3个疗程化疗后才达CR.4例11q23/MLL基因易位重排阳性的B-ALL患者中有2例于诊断后3周内死于全身衰竭和感染，化疗未获CR，其中1例患者的融合基因为MLL/ENL，1例未扩出融合基因产物;1例于诊断后第2天因DIC脑出血死亡，未进行化疗，其融合基因为MLL/AF9;1例发病时胸椎有白血病细胞浸润，1疗程化疗后获CR，其融合基因产物未扩出.结论：荧光原位杂交技术是检测AL11q23/MLL基因易位重排快速、灵敏的方法，巢式RT-PCR是检测11q23/MLL基因易位重排所产生的融合基因类型简便可行的方法;有11q23/MLL基因易位重排的AL患者临床症状凶险，预后差。     

Human homologue of the rat chondroitin sulfate proteoglycan, NG2, detected by monoclonal antibody 7.1, identifies childhood acute lymphoblastic leukemias with t(4;11)(q21;q23) or t(11;19)(q23;p13) and MLL gene rearrangements

Monoclonal antibody 7.1, which recognizes the chondroitin sulfate proteoglycan molecule NG2, was used to screen prospectively blast cells from 104 consecutive children at initial presentation with acute lymphoblastic leukemia (ALL). Reactivity with this antibody was found in 9 cases (8.6%), of whom 5 had a t(4;11)(q21;q23) and 4 had a t(11;19)(p13;q23). None of the NG2- cases had either translocation. Southern blot analysis disclosed MLL gene rearrangement in only the 9 cases with 7.1 reactivity plus the t(4;11)(q21;q23) or t(11;19)(q23;p13) translocation. MLL gene rearrangements were not detected in 89 patient leukemic samples that did not express NG2, including 7 patients with del(11)(q23) or inv(11)(p13q23). As expected from the association with t(4;11) and t(11;19), NG2+ cases were significantly more likely to be infants, to have hyperleukocytosis and central nervous system involvement, to be CD10-, and to express myeloid- associated antigens CD15 and CD65. Despite short follow-up duration, 3 of the NG2+ cases have relapsed while the other 101 patients remain in remission. Thus, blast cell surface expression of NG2 is useful for identifying patients with ALL having t(4;11) or t(11;19) translocations that are associated with poor prognosis, especially in the infant age group.     

Distribution of 11q23 breakpoints within the MLL breakpoint cluster region in de novo acute leukemia and in treatment-related acute myeloid leukemia: correlation with scaffold attachment regions and topoisomerase II consensus binding sites

A major unresolved question for 11q23 translocations involving MLL is the chromosomal mechanism(s) leading to these translocations. We have mapped breakpoints within the 8.3-kb BamHI breakpoint cluster region in 31 patients with acute lymphoblastic leukemia and acute myeloid leukemia (AML) de novo and in 8 t-AML patients. In 23 of 31 leukemia de novo patients, MLL breakpoints mapped to the centromeric half (4.57 kb) of the breakpoint cluster region, whereas those in eight de novo patients mapped to the telomeric half (3.87 kb). In contrast, only two t-AML breakpoints mapped in the centromeric half, whereas six mapped in the telomeric half. The difference in distribution of the leukemia de novo breakpoints is statistically significant (P = .02). A similar difference in distribution of breakpoints between de novo patients and t-AML patients has been reported by others. We identified a low- or weak-affinity scaffold attachment region (SAR) mapping just centromeric to the breakpoint cluster region, and a high-affinity SAR mapping within the telomeric half of the breakpoint cluster region. Using high stringency criteria to define in vitro vertebrate topoisomerase II (topo II) consensus sites, one topo II site mapped adjacent to the telomeric SAR, whereas six mapped within the SAR. Therefore, 74% of leukemia de novo and 25% of t-AML breakpoints map to the centromeric half of the breakpoint cluster region map between the two SARs; in contrast, 26% of the leukemia de novo and 75% of the t-AML patient breakpoints map to the telomeric half of the breakpoint cluster region that contains both the telomeric SAR and the topo II sites. Thus, the chromatin structure of the MLL breakpoint cluster region may be important in determining the distribution of the breakpoints. The data suggest that the mechanism(s) leading to translocations may differ in leukemia de novo and in t-AML.     

Acute leukemias of different lineages have similar MLL gene fusions encoding related chimeric proteins resulting from chromosomal translocation.

The MLL gene, on human chromosome 11q23, undergoes chromosomal translocation in acute leukemias, resulting in gene fusion with AF4 (chromosome 4) and ENL (chromosome 19). We report here translocation of MLL with nine different chromosomes and two paracentric chromosome 11 deletions in early B cell, B- or T-cell lineage, or nonlymphocytic acute leukemias. The mRNA translocation junction from 22 t(4;11) patients, including six adult leukemias, and nine t(11;19) tumors reveals a remarkable conservation of breakpoints within MLL, AF4, or ENL genes, irrespective of tumor phenotype. Typically, the breakpoints are upstream of the zinc-finger region of MLL, and deletion of this region can accompany translocation, supporting the der(11) chromosome as the important component in leukemogenesis. Partial sequence of a fusion between MLL and the AFX1 gene from chromosome X shows the latter to be rich in Ser/Pro codons, like the ENL mRNA. These data suggest that the heterogeneous 11q23 abnormalities might cause attachment of Ser/Pro-rich segments to the NH2 terminus of MLL, lacking the zinc-finger region, and that translocations occur in early hematopoietic cells, before commitment to distinct lineages.     

Transient myeloproliferative disorder with 11q23 aberration in two neonates with Down syndrome

 Infants with Down syndrome may develop a transient myeloproliferative disorder (TMD) with the features of acute leukemia but resolving in a spontaneous remission. Chromosomal aberrations in addition to trisomy 21 have only rarely been described. In many cases of infant acute leukemia band q23 of chromosome 11 is involved in nonrandom translocations, often resulting in a rearrangement of the ALL-1 (MLL, HRX, HTRX 1) gene. Generally, this translocation carries a bad prognosis. We describe two newborn girls with Down syndrome and TMD in whom the constitutional trisomy 21 was combined with an acquired abnormality of chromosome 11. During the TMD the morphological and immunologic features were consistent with those of megakaryoblastic leukemia. The chromosome 11 abnormalities were del(11)(q23), but rearrangements of the ALL-1 gene were not found. Our patients had remissions that occurred spontaneously or after a mild chemotherapy. The important finding is that additional chromosomal changes may occur during TMD in Down syndrome. The fact that the abnormality was in region 11q23 raises the question of whether the risk for developing leukemia is increased under these conditions. Received: December 1, 1997 / Accepted: May 19, 1998     

Heterogeneity of breakpoints of 11q23 rearrangements in hematologic malignancies identified with fluorescence in situ hybridization

Twenty-four patients whose cells contained a variety of 11q23 rearrangements, including translocations, insertions, and an inversion, were studied using fluorescence in situ hybridization with cosmid, phage, and plasmid probes mapped to 11q22-24. In 17 patients, the breakpoints of the common 11q23 translocations involving chromosomes 4, 6, 9, and 19 as well as some uncommon translocations involving 3q23, 17q25, 10p11, and an insertion 10;11 were all located in the breakpoint cluster region of the MLL gene, regardless of age, phenotype of disease, or involvement of a third chromosome. The breakpoints in 11q23 in the other 7 patients with a t(7;11)(p15;q23), inv(11)(p11q23), t(4;11)(q23;q23), der(5)t(5;11)(q13;q23), ins(10;11)(p11;q23q24), t(11;14)(q23;q11), or t(11;18;11) (p15;q21;q23) were located either centromeric to CD3D or telomeric to THY1. Thus, although most 11q23 rearrangements, involve the same breakpoint cluster region of MLL, there is heterogeneity in the breakpoint in some of the rare rearrangements.