Infant acute lymphoblastic leukaemia with t(11; 19)

Clinical and biological importance of cytogenetic abnormalities in childhood and adult acute lymphoblastic leukemia

Among the approximately 7,000 cytogenetically abnormal childhood and adult B- and T-lineage acute lymphoblastic leukemias (ALL) published to date, numerous recurring chromosomal aberrations and abnormality patterns have been identified, and it has been clearly shown that the cytogenetic features often correlate closely with specific morphologic, immunophenotypic, and clinical parameters. Thus, karyotypic investigations are now routinely performed for diagnostic and prognostic purposes in ALL, with the chromosomal abnormalities/cytogenetic patterns playing a major role for proper risk assessment and choice of treatment. At the same time, the cytogenetic analyses have resulted in the identification of more than 70 different genes, located at the breakpoints of ALL-associated structural chromosomal abnormalities, that are causally implicated in the leukemogenic process. Hence, the genetic studies have also improved our understanding of the mechanisms of leukemogenesis. However, the almost staggering amount of cytogenetic information presently available has made it increasingly difficult to obtain a general overview of the clinical and biological importance of karyotypic patterns in ALL. Here, we summarize and review the cytogenetic features of childhood and adult ALL, with emphasis on their molecular genetic consequences and their clinical impact.

A t(11;15) fuses MLL to two different genes, AF15q14 and a novel gene MPFYVE on chromosome 15

The mixed lineage leukemia gene (MLL, also known as HRX, ALL-1 and Htrx) located at 11q23 is involved in translocations with over 40 different chromosomal bands in a variety of leukemia subtypes. Here we report our analysis of a rare but recurring translocation, t(11;15)(q23;q14). This translocation has been described in a small subset of cases with both acute myeloblastic leukemia and ALL. Recent studies have shown that MLL is fused to AF15q14 in the t(11;15). Here we analyse a sample from another patient with this translocation and confirm the presence of an MLL-AF15q14 fusion. However, we have also identified and cloned another fusion transcript from the same patient sample. In this fusion transcript, MLL is fused to a novel gene, MLL partner containing FYVE domain (MPFYVE). Both MLL-AF15q14 and MLL-MPFYVE are in-frame fusion transcripts with the potential to code for novel fusion proteins. MPFYVE is also located on chromosome 15, approximately 170 kb telomeric to AF15q14. MPFYVE contains a highly conserved motif, the FYVE domain which, in other proteins, has been shown to bind to phosphotidyl-inositol-3 phosphate (PtdIns(3)P). The MLL-MPFYVE fusion may be functionally important in the leukemia process in at least some patients containing this translocation.

Antigen expression patterns reflecting genotype of acute leukemias

Multi-parameter flow cytometry, molecular genetics, and cytogenetic studies have all contributed to new classification of leukemia. In this review we discuss immunophenotypic characteristics of major genotypic leukemia categories. We describe immunophenotype of: B-lineage ALL with MLL rearrangements, TEL/AML1, BCR/ABL, E2A/PBX1 translocations, hyperdiploidy, and myc fusion genes; T-ALL with SCL gene aberrations and t(5;14) translocation; and AML with AML1/ETO, PML/RARalpha, OTT/MAL and CBFbeta/MYH11 translocations, trisomies 8 or 11 and aberrations of chromosomes 7 and 5. Whereas some genotypes associate with certain immunophenotypic features, others can present with variable immunophenotype. Single molecules (as NG2, CBFbeta/SMMHC and PML/RARalpha proteins) associated with or derived from specific translocations have been described. More often, complex immunophenotype patterns have been related to the genotype categories. Most known associations between immunophenotype and genotype have been defined empirically. Therefore, these associations should be validated in independent patient cohorts before they can be widely used for prescreening of leukemia. Progress in our knowledge on leukemia will show how the molecular-genetic changes modulate the immunophenotype as well as how the expressed protein molecules further modulate cell behavior.

Transcription factor fusions in acute leukemia: variations on a theme

The leukemia-associated fusion proteins share several structural or functional similarities, suggesting that they may impart a leukemic phenotype through common modes of transcriptional dysregulation. The fusion proteins generated by these translocations usually contain a DNA-binding domain, domains responsible for homo- or hetero-dimerization, and domains that interact with proteins involved in chromatin remodeling (e.g., co-repressor molecules or co-activator molecules). It is these shared features that constitute the 'variations on the theme' that underling the aberrant growth and differentiation that is the hallmark of acute leukemia cells.

Pediatric Acute Lymphoblastic Leukemia: Challenges and Controversies in 2000

This article discusses ways in which pediatric patients with acute lymphoblastic leukemia (ALL) can be stratified to receive intensive and less intensive therapies in order to decrease morbidity and mortality. Specifically, the focus may shift away from current intensive therapies for ultra low-risk patients and away from transplantation for certain patients at relapse. In contrast, infants with ALL comprise an ultra high-risk population in need of specialized approaches.

In Section I Dr. Lange describes the need to identify ultra low-risk children. Groups around the world have improved the outcome of children with ALL by identifying the basic “total therapy” model of the 1970s and stratifying treatment according to risk of relapse. Current first-line treatment cures about 85% of children with standard-risk ALL and 70% of children with high-risk disease. However, all children receive anthracyclines, alkylating agents, or moderate- to high-dose antimetabolite infusions. While randomized clinical trials prove that these intensifications reduce relapses, they also show that half of all children with ALL can be cured with the modest therapy of the 1970s and early 1980s. The patients curable with lesser therapy may be considered an ultra low-risk group. Attempts to use age, gender, white count, morphology, and karyotype to identify the ultra low-risk group of patients with a 90-95% cure rate with minimal therapy have failed. An expanded repertoire of tools such as pharmacogenetic profiling, PCR measurement of minimal residual disease and microarray technology may make this goal achievable in this decade.

In section II Dr. Chessells addresses the management of children with relapsed ALL. The chance of successful re-treatment with conventional chemotherapy for relapse depends on the duration of first remission and the site of relapse. Bone marrow transplantation from a histocompatible sibling or other suitable donor, which is widely accepted as the treatment of choice for children with a first remission of < 24 months, is associated with a high risk of relapse. Bone marrow transplantation for later bone marrow relapse improves leukemia-free survival but has significant short-term and long-term toxicities. The challenges are to develop more effective treatment for early relapse and to identify those children with relapsed ALL who are curable with chemotherapy or, failing this, those children who would be candidates for bone marrow transplantation in third remission.

In Section III Dr. Felix addresses the problem of infant ALL. ALL of infancy is clinically aggressive, and infants continue to have the worst prognosis of all pediatric patients with ALL. High white blood cell count, younger age, bulky extramedullary disease, and CNS disease at diagnosis are unfavorable characteristics. These features occur with MLL gene translocations. The probability of an MLL gene translocation and the probability of poor outcome both are greatest in younger infants. Specialized intensive chemotherapy approaches and bone marrow transplantation in first remission for this disease may lead to improved survival.

Refined recognition of pediatric patients with ALL who need more and less intensive therapies is necessary to increase survival and decrease toxicities.

Pediatric Acute Lymphoblastic Leukemia: Challenges and Controversies in 2000

This article discusses ways in which pediatric patients with acute lymphoblastic leukemia (ALL) can be stratified to receive intensive and less intensive therapies in order to decrease morbidity and mortality. Specifically, the focus may shift away from current intensive therapies for ultra low-risk patients and away from transplantation for certain patients at relapse. In contrast, infants with ALL comprise an ultra high-risk population in need of specialized approaches.

In Section I Dr. Lange describes the need to identify ultra low-risk children. Groups around the world have improved the outcome of children with ALL by identifying the basic “total therapy” model of the 1970s and stratifying treatment according to risk of relapse. Current first-line treatment cures about 85% of children with standard-risk ALL and 70% of children with high-risk disease. However, all children receive anthracyclines, alkylating agents, or moderate- to high-dose antimetabolite infusions. While randomized clinical trials prove that these intensifications reduce relapses, they also show that half of all children with ALL can be cured with the modest therapy of the 1970s and early 1980s. The patients curable with lesser therapy may be considered an ultra low-risk group. Attempts to use age, gender, white count, morphology, and karyotype to identify the ultra low-risk group of patients with a 90-95% cure rate with minimal therapy have failed. An expanded repertoire of tools such as pharmacogenetic profiling, PCR measurement of minimal residual disease and microarray technology may make this goal achievable in this decade.

In section II Dr. Chessells addresses the management of children with relapsed ALL. The chance of successful re-treatment with conventional chemotherapy for relapse depends on the duration of first remission and the site of relapse. Bone marrow transplantation from a histocompatible sibling or other suitable donor, which is widely accepted as the treatment of choice for children with a first remission of < 24 months, is associated with a high risk of relapse. Bone marrow transplantation for later bone marrow relapse improves leukemia-free survival but has significant short-term and long-term toxicities. The challenges are to develop more effective treatment for early relapse and to identify those children with relapsed ALL who are curable with chemotherapy or, failing this, those children who would be candidates for bone marrow transplantation in third remission.

In Section III Dr. Felix addresses the problem of infant ALL. ALL of infancy is clinically aggressive, and infants continue to have the worst prognosis of all pediatric patients with ALL. High white blood cell count, younger age, bulky extramedullary disease, and CNS disease at diagnosis are unfavorable characteristics. These features occur with MLL gene translocations. The probability of an MLL gene translocation and the probability of poor outcome both are greatest in younger infants. Specialized intensive chemotherapy approaches and bone marrow transplantation in first remission for this disease may lead to improved survival.

Refined recognition of pediatric patients with ALL who need more and less intensive therapies is necessary to increase survival and decrease toxicities.

Prednisone Response Is the Strongest Predictor of Treatment Outcome in Infant Acute Lymphoblastic Leukemia

To define prognostic factors in infant acute lymphoblastic leukemia (ALL), the outcome of 106 infants (age ≤12 months) during 3 consecutive multicenter trials of the Berlin-Frankfurt-Münster group (ALL-BFM 83, 86, and 90) was retrospectively analyzed according to presenting features and early in vivo response to prednisone. The prednisone response was defined as the cytoreduction (number of blood blasts per microliter at day 8) to a 7-day prednisone prephase and 1 intrathecal dose of methotrexate on day 1. Prednisone good responder (PGR; <1,000 blasts/μL) received conventional therapy and prednisone poor responder (PPR; ≥1,000 blasts/μL) received intensified therapy. Infant ALL was characterized by a high incidence of a white blood cell count greater than 100 × 103/μL (57%), central nervous system leukemia (24%), lack of CD10 expression (59%), 11q23 rearrangement (49%) including the translocation t(4;11) (29%), and a comparatively high proportion of PPR (26%), which were all significantly associated with inferior outcome by univariate analysis. The estimated probability for an event-free survival at 6 years (pEFS) was by far better for PGR compared with PPR, who had a dismal prognosis despite intensified treatment (pEFS, 53% ± 6%v 15% ± 7%, P = .0001). Infant PGR, who were less than 6 months of age (n = 40), lacked CD10 expression (n = 43), and/or had an 11q23 rearrangement (n = 17) fared significantly better compared with corresponding PPR, as indicated by a pEFS of 44% ± 8%, 49% ± 8%, and 41% ± 12%, respectively. In multivariate analysis, PPR was the strongest adverse prognostic factor (relative risk, 3.3; 95% confidence interval, 1.9 to 5.8; P< .0001). Infants with PGR, comprising a major subgroup (74%) among infants, might successfully be treated with conventional therapy, whereas PPR require new therapeutic strategies, including early treatment intensification or bone marrow transplantation in first remission.

Prednisone Response Is the Strongest Predictor of Treatment Outcome in Infant Acute Lymphoblastic Leukemia

To define prognostic factors in infant acute lymphoblastic leukemia (ALL), the outcome of 106 infants (age ≤12 months) during 3 consecutive multicenter trials of the Berlin-Frankfurt-Münster group (ALL-BFM 83, 86, and 90) was retrospectively analyzed according to presenting features and early in vivo response to prednisone. The prednisone response was defined as the cytoreduction (number of blood blasts per microliter at day 8) to a 7-day prednisone prephase and 1 intrathecal dose of methotrexate on day 1. Prednisone good responder (PGR; &lt;1,000 blasts/μL) received conventional therapy and prednisone poor responder (PPR; ≥1,000 blasts/μL) received intensified therapy. Infant ALL was characterized by a high incidence of a white blood cell count greater than 100 × 103/μL (57%), central nervous system leukemia (24%), lack of CD10 expression (59%), 11q23 rearrangement (49%) including the translocation t(4;11) (29%), and a comparatively high proportion of PPR (26%), which were all significantly associated with inferior outcome by univariate analysis. The estimated probability for an event-free survival at 6 years (pEFS) was by far better for PGR compared with PPR, who had a dismal prognosis despite intensified treatment (pEFS, 53% ± 6%v 15% ± 7%, P = .0001). Infant PGR, who were less than 6 months of age (n = 40), lacked CD10 expression (n = 43), and/or had an 11q23 rearrangement (n = 17) fared significantly better compared with corresponding PPR, as indicated by a pEFS of 44% ± 8%, 49% ± 8%, and 41% ± 12%, respectively. In multivariate analysis, PPR was the strongest adverse prognostic factor (relative risk, 3.3; 95% confidence interval, 1.9 to 5.8; P&lt; .0001). Infants with PGR, comprising a major subgroup (74%) among infants, might successfully be treated with conventional therapy, whereas PPR require new therapeutic strategies, including early treatment intensification or bone marrow transplantation in first remission.

Critical study of prognostic factors in childhood acute lymphoblastic leukaemia: differences in outcome are poorly explained by the most significant prognostic variables. Fralle group. French Acute Lymphoblastic Leukaemia study group

We determined the proportion of survival variability explained by the usual prognostic factors in childhood acute lymphoblastic leukaemia (ALL) during a prognostic study of 1552 patients enrolled in three consecutive Fralle group protocols (Fralle 83, Fralle 87 and Fralle 89). The event-free survival rates at 5 years were 54.8% (SD 1.9), 43.1%) (SD 2.7) and 55.6% (SD 2.2), respectively. In the univariate analysis the following variables were predictive of poor outcome: male gender, elevated leucocytosis (> 50 x 10(9)/l), circulating blastosis. haemoglobin >12 g/dl, platelet count <100 x 10(9)/l, age under 1 year or over 9 years, enlarged mediastinum, nodes, spleen and liver, T phenotype, absence of CD10+ cells; testicular and meningeal involvement, poor response to induction therapy (CCSG M3), and LDH >400 U/l. Among the cytogenetic features, hyperdiploidy had a protective effect, whereas hypodiploidy, translocation and other structural abnormalities had a negative influence, particularly in cases of t(9;22) or t(4;11). Multivariate analysis summarized the prognostic information in terms of four variables: age, gender, leucocytosis and cytogenetic features. Missing data had little influence on the results. However, despite their significance in the multivariate analysis, these four variables each had very low predictive power (1.1% for gender, 2.0% for age, 3.5% for leucocytosis, and 1.6% for cytogenetic features). Thus, the most significant prognostic factors in childhood ALL each explain no more than 4% of the variability in prognosis. This may explain the disappointing practical value of these factors and underlines the need for prognostic tools in childhood ALL.

MLL/ENL fusion in congenital acute lymphoblastic leukemia with a unique t(11;18;19)

To elucidate the events leading to a unique complex translocation involving chromosomes 11, 18, and 19 in a congenital progenitor B-cell acute lymphoblastic leukemia, we have performed comprehensive cytogenetic and fluorescence in situ hybridization (FISH) analyses as well as molecular genetic studies on the DNA and RNA level. We were able to confirm the cytogenetic interpretation of this complex t(11;18;19)(q23;q22;p13.3) by chromosome painting. Involvement of the MLL gene on 11q23 became evident by Southern blot analysis as well as by FISH with a YAC clone containing the respective gene. Despite the fact that the additional signals of the split YAC clone were observed on the abnormal chromosome 18, reverse transcription polymerase chain reaction (RT-PCR) revealed a MLL/ENL hybrid mRNA, which is specific for a t(11;19)(q23;p13.3). This gene fusion most probably represents the critical part of this rearrangement. The transfer of the translocated part of the split YAC clone onto chromosome 18 indicates that the second break must have occurred in the vicinity of the first one, at a distance too close to be resolved by FISH. Whether this break took place within chromosome 11 or 19 sequences, up- or downstream of the MLL/ENL fusion, and whether this translocation results from a concerted simultaneous exchange of material or from two separate sequential events in consecutive cell generations remains open.

Expression of N-CAM (CD56) on acute leukemia cells: relationship with disease characteristics and outcome

Expression of CD56 was analyzed by indirect immunofluorescence method on bone marrow samples from 94 newly diagnosed patients with acute leukemia (AL), including 59 acute myelogenous leukemias (AML) and 35 acute lymphoblastic leukemias (ALL). CD56 was expressed on 17 +/- 18% (range: 0-72%) of AML cells and 24 +/- 24% (range: 0-98%) of ALL cells, without significant differences between FAB subtypes in AML, nor immunologic subtypes in ALL. Expression of CD56 was not associated with any clinical or biological characteristic at diagnosis, nor with prognosis in AML or ALL. We do not confirm previously described relationships between CD56 expression and initial characteristics and evolution of acute leukemia.

Complex MLL rearrangement in a patient with T-cell acute lymphoblastic leukemia

MLL (also known as ALL-I, HTRX, or HRX) gene translocations are among the most common chromosomal abnormalities recognized in both B-lineage acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). However, MLL gene rearrangements are uncommon in T-cell ALL. We recently detected an MLL gene rearrangement in a patient with typical T-cell ALL. We recently detected an MLL gene rearrangement in a patient with typical T-cell ALL (CD2+, CD4+, CD5+, CD7+, CD8+, HLA DR-) and an apparently normal karyotype (46,XX). The rearrangement was cloned and characterized; a DNA fragment distal to the breakpoint was mapped by fluorescence in situ hybridization (FISH) to 19p13, indicating that the leukemic blasts had undergone a cytogenetically undetected rearrangement involving chromosomes 11 and 19. A reverse transcriptase-polymerase chain reaction (RT-PCR) assay demonstrated an in-frame fusion mRNA between the amino terminus of MLL and the carboxy terminus of ENL (also known as MLLT1 or LTG19), a gene that has been mapped to 19p13. In addition, MLL sequences distal (telomeric) to the breakpoint were deleted from the genome, which precludes the formation of a reciprocal ENL/MLL fusion protein. These findings suggest that an MLL/ENL fusion protein (and not a reciprocal ENL/MLL fusion) was likely to be pathogenic in this patient, and they reinforce previous studies showing that leukemic blasts with apparently normal karyotype may harbor MLL rearrangements. Additionally, this report provides the first conclusive evidence of an MLL/ENL gene fusion characterized at a molecular level in a patient with T-cell ALL.

Molecular analysis of the chromosomal breakpoint and fusion transcripts in the acute lymphoblastic SEM cell line with chromosomal translocation t(4;11)

The chromosomal breakpoint and fusion transcripts of the pre-B-leukaemia-derived SEM cell line carrying a reciprocal t(4;11)(q21;q23) translocation were analysed. The breakpoint from derivative chromosome der4 was cloned and sequenced. The crossover site was localized in intron 7 of the ALL-1 gene on chromosome 11q23 and in a large intron of the AF-4 (FEL) gene. RNA transcripts from both wild-type genes and both hybrid genes were detected by reverse transcriptase polymerase chain reaction (RT-PCR) assays. In addition, alternatively spliced mRNA species derived from the der4 chromosome were found. They were generated by using the exon 5' of the breakpoint on der4 as a common splice donor site and the 5' boundaries of exons 8 or 9 of the ALL-1 gene as alternative splice acceptor sites. The hypothesis is proposed that selective pressure operators to maintain the presence of both derivative chromosomes as important elements in the leukaemogenic process.

The role of immunophenotype in acute lymphoblastic leukemia of infant age

The prognosis of acute lymphoblastic leukemia in infants is still significantly worse than that of older children. This is thought to be due to both clinical and biological factors, such as high white blood cell (WBC) counts at diagnosis, irregular or immature phenotypes, and molecular and cytogenetical abnormalities. In order to focus the significance of immunophenotypic analysis, we have reviewed the immunophenotypic studies of 145 infants under 18 months of age treated at the AIEOP centers from 1984 to 1992. Children have been divided in three age groups of six months each; WBC count at diagnosis has been evaluated both as mean values and within different categories (< 10.10(9)/L, > 100.10(9)/L). These have been studied in correlation with immunophenotype and with the expression of single, specific markers. A significant correlation has been found between young age, high WBC count and immature phenotypes. Common ALL was more frequent in older children and showed lower WBC counts. Moreover, event-free survival was significantly better in older children with WBC count < 100.00/mm3, with CD10+, MyAg- ALL. Therefore, we suggest that immunophenotypic analysis is still an important prognostic factor and can be usefully used, together with simple clinical data, to plan therapy for ALL in infants.

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

BACKGROUND

Translocations involving chromosome band 11q23 are very frequent in both acute lymphoblastic and acute myeloid leukemias and are the most common genetic alteration in infants with leukemia. In all age groups and all phenotypes of leukemia, an 11q23 translocation carries a poor prognosis. A major question has been whether one or several genes on band 11q23 are implicated in these leukemias. Previously, we identified the chromosomal breakpoint region in leukemias with the common 11q23 translocations and subsequently cloned a gene named MLL that spans the 11q23 breakpoint.

METHODS

We isolated a 0.74-kb BamHI fragment from a complementary DAN (cDNA) clone of the MLL gene. To determine the incidence of MLL rearrangements in patients with 11q23 abnormalities, we analyzed DNA from 61 patients with acute leukemia, 3 cell lines derived from such patients, and 20 patients with non-Hodgkin's lymphoma and 11q23 aberrations.

RESULTS

The 0.74-kb cDNA probe detected DNA rearrangements in the MLL gene in 58 of the patients with leukemia, in the 3 cell lines, and in 3 of the patients with lymphoma. All the breaks occurred in an 8.3-kb breakpoint cluster region within the MLL gene. The probe identified DNA rearrangements in all 48 patients with the five common 11q23 translocations involving chromosomes 4, 6, 9, and 19, as well as in 16 patients with uncommon 11q23 aberrations. Twenty-one different chromosomal breakpoints involving the MLL gene were detected.

CONCLUSIONS

MLL gene rearrangements were detected with a single probe and a single restriction-enzyme digest in all DNA samples from patients with the common 11q23 translocations as well as in 16 patients or cell lines with other 11q23 anomalies. The ability to detect an MLL gene rearrangement rapidly and reliably, especially in patients with limited material for cytogenetic analysis, should make it possible to identify patients who have a poor prognosis and therefore require aggressive chemotherapy or marrow transplantation.

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.

In situ hybridisation analysis of a homogeneously staining region at 11q23-24 in an acute myeloid leukaemia (M5) using yeast artificial chromosomes

An example of a homogeneously staining region (hsr), occurring in an acute myeloid leukaemia (M5) on chromosome 11 in the region of bands q23-q24, has been analysed. In situ hybridisation using yeast artificial chromosome (YAC) DNA demonstrated that the amplification did not include the CD3 gene cluster and did not affect the human trithorax gene known to be disrupted by translocations at 11q23. In contrast, the amplification was shown to include the sequence D11S543 which has been previously mapped to chromosome band 11q24. High resolution analysis using confocal microscopy allowed the individual amplicons to be visualised, and it was shown that the hsr consisted of an 8-fold amplification of the region surrounding the probe D11S543. From previous estimates of human chromosome size it was possible to calculate that the hsr was composed of amplicons approximately 10 megabases in length. It was concluded that the region amplified did not extend as far as the translocation breakpoints occurring at 11q23 in acute leukaemias.

Structure and expression of the human trithorax-like gene 1 involved in acute leukemias

The human trithorax-like gene 1 (Htrx1 gene) is disrupted in 11q23 translocations that are associated with acute leukemias. Sequencing of a partial human cDNA revealed an open reading frame encoding 1012 amino acids with extensive homology to the Drosophila trithorax protein, particularly in the zinc finger-like domains. Htrx1 gene appears to be unique in the human genome and has been conserved during evolution. Use of the human cDNA as a probe demonstrates that this gene is interrupted in both infant and adult acute myeloid (AML) and lymphoid (ALL) leukemia patients with 11q23 translocations. The structure of the Htrx1 gene around the breakpoints shows that this part of the human gene is interrupted by nine introns. As a result of the rearrangement, zinc finger domains are translocated in both ALL and AML patients. Expression studies reveal that the Htrx1 gene differentially expresses three transcripts within the normal lymphocyte cell lineage.

A t(11;12) 11q23 leukemic breakpoint that disrupts the MLL gene

Translocations involving 11q23 have been shown to be a consistent finding in human hematopoietic malignancies and in some constitutional abnormalities. The identification of a gene, MLL (myeloid/lymphoid or mixed-lineage leukemia), that spans the breakpoints in four different recurrent 11q23 translocations was recently reported. We describe a rare (11;12)(q23;p13) translocation, observed in leukemic cells from a patient with acute lymphoblastic leukemia, which also disrupts this gene.

Molecular cloning of 19p13 breakpoint region in infantile leukemia with t(11;19)(q23;p13) translocation

We studied the breakpoint regions involved in t(11;19)(q23;p13) translocation associated with infantile leukemias. Southern blot analysis with the partial cDNA clone for the MLL gene at 11q23 which we had isolated previously detected gene rearrangements in all three cell lines and three leukemia samples from the patients with t(11;19) translocation, indicating that these breakpoints were clustered within the 8.5 kb BamHI germline fragment detected by the probe. To study the breakpoint region, a genomic library of one of the cell lines, KOCL-33, was made. We have isolated the der(19) allele containing the breakpoint as well as the germline alleles at 19p13 and 11q23. Using the genomic probes on chromosome 19 near the breakpoint, Southern blot analysis was performed. The breakpoints at 19p13 of the two other cell lines and the three leukemia samples were not located within 36 kilobases of the KOCL-33 breakpoint, although pulsed-field gel electrophoresis showed that the breakpoints of all three cell lines were on the same NruI fragment of 230 kilobases. These results showed that the breakpoints at 19p13 were not clustered like those at 11q23 in t(11;19) translocation.

Stem cell origins of leukaemia and curability

It is suggested that most childhood acute lymphoblastic leukaemias and some other paediatric cancers are chemo-curable because they arise in stem cell populations that are functionally transient, chemosensitive and programmed for apoptosis. Most adult acute leukaemias are chemo-incurable at least in part because they originate in relatively drug resistant stem cells with extensive self-renewal capacity. The latter property in turn increases the probability of clones evolving with multi-drug resistance. Particular mutations may superimpose additional adverse features on leukaemic cells.

Phenotypic and genotypic characterization of 14 leukemia and lymphoma cell lines with 11q23 translocations

11q23 translocation is the most popular chromosomal abnormality in infant leukemia. In adults, it is often encountered in non-Hodgkin's lymphoma (NHL). In this study, we analyzed the phenotypic and genotypic characteristics of 9 acute leukemic cell lines with 11q23 translocations and one with deletion of the 11q23 locus, nine of which were established by researchers in this group, together with 4 NHL cell lines with 11q23 translocations. All lines were considered to belong to the B-cell lineage at different stages. All 10 leukemic lines showed clonal rearrangement of the immunoglobulin heavy chain (IgH) gene: two corresponded to the B-precursor stage (CD19+, cytoplasmic mu-), while the other 8 corresponded to the pre-B stage (cytoplasmic mu+). All 4 NHL lines showed rearrangements of both the IgH and Ig kappa genes with three expressing surface Ig; specifically, mature B-cell phenotype. As for myelocytic-monocytic markers, at least one out of 4 antigens examined were positive in 8 of the 10 leukemic cell lines, while only one of the 4 NHL lines was reactive. There were essentially no clear phenotypic or genotypic differences between t(4;11) and t(11;19) cell lines, supporting the view that both diseases have similar clinicopathological characteristics. These cell lines are also valuable for cloning genes at the chromosomal breakpoints.

Cytogenetic features of neonatal leukemias

We reviewed a series of 41 neonatal leukemias (NL), including published cases karyotyped by banding techniques, but excluding Down syndrome-associated cases and analyzed distribution of cytogenetic anomalies with respect to other clinical variables and outcome. The most frequent chromosomal changes in this age group involve rearrangements of 11q23, which is correlated with high white blood cell (WBC) count at onset and type of leukemia. A discrete heterogeneity of cytogenetic abnormalities is also evident, however, possibly reflecting other specific pathways in NL development. With respect to prognosis, cytogenetic abnormalities are a strong indicator of poor prognosis.

Molecular cloning and analysis of chromosome band 11q23 involved in leukaemia-associated translocations

Three overlapping yeast artificial chromosomes (YACs) spanning a 780 kb region of DNA around the CD3 locus on chromosome 11 have been isolated and characterised. The individual cloned regions have been mapped by in situ hybridisation to chromosome band 11q23, and a restriction enzyme map of this region has been constructed. The positions of these clones in relation to a series of leukaemia-associated chromosomal translocations has also been determined. It was concluded that, although two clones lay entirely proximal to the breakpoints examined, the third clone (13HH4) encompassed the breakpoints for the translocations t(4;11), t(6;11), and t(9;11). The t(9;11) was observed in an acute myeloid leukaemia in a patient previously treated for an unrelated malignancy. It would thus appear that the breakpoints at chromosome band 11q23 occurring in therapy-related leukaemias are in the same region as those found in adult and childhood acute leukaemias and may result from a common underlying mechanism.

A trithorax-like gene is interrupted by chromosome 11q23 translocations in acute leukaemias

Some acute lymphocytic leukaemias, particularly those in young children, are associated with a t(4;11)(q21;q23) reciprocal translocation. We have cloned the translocation breakpoint on chromosome 11q23 and isolated corresponding RNA transcripts from this region. The translocation occurs within a cluster of Alu repetitive elements located within an intron of a gene that gives rise to 11.5 (kb) transcript spanning the translocation breakpoint. The 11.5 kb transcript encodes a protein that is highly homologous to the Drosophila trithorax gene, a developmental regulator. An analysis of a series of leukaemic patients carrying t(4;11) and t(9;11) translocations indicate that the majority of breakpoints in infant leukaemias lie within a 5 kb region.

The immunophenotype in infant acute lymphoblastic leukaemia: correlation with clinical outcome. An Italian multicentre study (AIEOP)

A detailed analysis of immunophenotype of 112 infants aged less than 18 months with acute lymphoblastic leukaemia (ALL) was performed. Patients were divided into three groups on the basis of age at presentation (under 6 months: group 1: 6-12 months: group 2; 13-18 months: group 3). There were three cases of T-ALL (2.6%). The proportion of other subtypes was: common ALL in 59 patients (52.68%), pre-B ALL in 15 patients (13.3%), pre-pre-B ALL in 27 (24.1%) and acute undifferentiated leukaemia (AUL) in eight patients (7.14%). In non-T ALL, positivity to CD10 (corresponding to C-ALL and pre-B ALL) was distributed in the three age groups as follows: 38.88% (group I) 65.38% (group II) and 86.36% (group III). Conversely, immature phenotypes (pre-pre-B and AUL) were found more often in the younger patients of groups I and II, as well as anomalous phenotypes, such as the presence of myeloid antigens (MyAg) and of CD7. Prognostic significance was evaluated as event-free survival (EFS) by statistical analysis. A better outcome in CD10-positive ALL than in CD10-negative ones (48% v. 25% of long-term survivors) was demonstrated in all infants. Similarly, EFS was significantly better in MyAg-negative than in MyAg-positive cases. These results were confirmed also when adjusting for white blood cell count. This allowed the identification of CD10-negative, MyAg-positive ALL, which were relatively more frequent in infants and had a poorer clinical outcome with the current therapies. This study stresses the prognostic relevance of the immunological study in infant leukaemias and its utility in choosing different therapeutic modalities for poor risk phenotypes.

The 11q23 breakpoint in acute leukemia with t(11;19)(q23;p13) is distal to those of t(4;11), t(6;11) and t(9;11)

Thirteen cosmid probes were mapped on the long arm of chromosome 11 between 11q22 and 11q24 by nonradioactive in situ hybridization. Starting with these localizations and those of other probes mapped to 11q23, four acute leukemias with translocations involving 11q23 were studied with the same method. The translocation breakpoints of the t(4;11)(q21;q23), t(6;11)(q27;q23), t(9;11)(p21-p22;q23), and t(11;19)(q23;p13) were confirmed to be distal to CD3D. The probe cC111-304 was proximal to the t(11;19) breakpoint while distal to the breakpoints of the other rearrangements. In view of the diversity of chromosomal abnormalities involving band 11q23, our finding extends the molecular heterogeneity of the breakpoint localization in leukemias with rearrangements involving 11q23.

CD3G is within 200 kb of the leukemic t(4;11) translocation breakpoint

The t(4;11)(q21;q23) has been associated with acute lymphocytic leukemia (ALL) especially in infants. The t(4;11) breakpoint on chromosome 11 is cytogenetically indistinguishable from breakpoints for other leukemia-associated translocations affecting 11q23. The molecular basis of the t(4;11) is unknown although a number of genes have been mapped to 11q23. The CD3D, G, and E genes have been positioned proximal to the 11q23 breakpoint of the 4;11 translocation while the THY1 and ETS1 genes have been mapped distal to this breakpoint. We report evidence that CD3G is within 200 kb of the 4;11 breakpoint as observed by pulsed field gel analysis. A rearrangement of the CD3G gene has been observed in a cell line derived from a patient with the t(4;11) translocation and in a hybrid cell line containing the derivative 11q chromosome derived from this cell line, using the restriction enzymes SacII and ClaI. Similar rearrangements using SacII were observed in 2 further patients with ALL and the t(4;11) translocation. No rearrangements in the same DNA were observed using ETS1, THY1, and D11S29 and a range of rare cutter restriction enzymes. CD3G thus provides a tool for the cloning and analysis of the 4;11 translocation, and poses a question of its possible involvement at long range with this translocation.

Chromosomes in childhood acute lymphoblastic leukaemia: karyotypic patterns in disease subtypes

To define further the clinical importance of cytogenetic analysis in acute lymphoblastic leukaemia (ALL) a prospective study was performed on 139 unselected children. Analyses were considered adequate in 104, of whom 35 were normal and 69 had clonal abnormalities. Abnormalities were categorised according to banded chromosome analysis as well as chromosome count. Karyotypes were correlated with clinical and laboratory features at diagnosis and with survival. Of the successful analyses, thirty five (34%) children had no abnormalities; this group contained an excess of T cell disease. Twenty five (24%) had a "characteristic" hyperdiploid karyotype and as a group had lower presenting white counts, a tendency to CD10, and periodic acid schiff positivity of the blast cells and smaller spleens. None was an infant and only one was over 10 years old. Seven (7%) children with t(9; 22), t(8; 14), or t(4; 11) translocations were grouped together as "specific" translocations. Collectively they had a significantly worse prognosis than the remainder. Nine children developed central nervous system relapse, six of whom had either t(4; 11) or abnormalities of 9p or 19p. A descriptive classification taking into account chromosome bonding pattern is cytogenetically more appropriate and may be more clinically useful than grouping children simply by chromosome number. As knowledge and techniques improve, the classification of cytogenetic abnormalities in ALL will need to be kept under frequent review.

Gene mapping by microdissection and enzymatic amplification: heterogeneity in leukaemia associated breakpoints on chromosome 11

A new strategy for mapping chromosome translocation breakpoints in relation to known genes has been developed. This approach is based on the amplification by the polymerase chain reaction (PCR) of specific target sequences from small numbers of microdissected chromosome fragments. This method has been applied to leukaemia-associated translocations affecting the q23 region of chromosome 11. In two independent leukaemias, the t(6;11) translocation was distinguished from the t(9;11) and t(4;11) translocations by demonstrating that the former breakpoint on chromosome 11 lay proximal to the CD3D gene while the latter breakpoints lay distal to CD3D. All three translocation breakpoints were found to lie proximal to ETSI and THYI. The data suggest that although these leukaemia-associated breakpoints on chromosome 11 are cytogenetically identical they may involve disruption of different genes. This approach offers a rapid alternative to mapping by hybridisation of probes either in situ to chromosomes or to somatic cell hybrids containing the appropriate derivative chromosomes.

Mapping of translocation breakpoints on the short arm of chromosome 19 in acute leukemias by in situ hybridization

Non-random translocation involving the short arm of chromosome 19 are frequently observed in acute leukemias. Recent studies have shown that the 19p13 genes E2A and LYLl, both of which encode helix-loop-helix proteins, lie at two different translocation breakpoints in acute lymphoblastic leukemias (ALL). The E2A gene is involved by the t(1;19)(q23;p13) in acute pre-B-cell leukemias and the LYL1 gene is structurally altered by a t(7;19)(q34;p13) in T-cell ALL. To assess the role of these genes in other leukemia-associated translocations we mapped their locations with respect to the t(11;19)(q23;p13) and t(4;19)(q21;p13) translocation breakpoints carried by T-ALL cell lines SUP-T13 and SUP-T8a, respectively. In situ hybridization studies indicated that the E2A and LYL1 genes are physically distinct from the t(4;19) and t(11;19) breakpoints. Using these and other 19p13 translocation breakpoints as landmarks, we established a partial physical map of 19p: 19pter-E2A-INSR-LYL1-[t(4;19)]-19cen. These data should help guide molecular studies to further characterize 19p13 breakpoints and mapping of genes in this chromosomal region.