CALM-AF10 fusion gene in leukemias: simple and inversion-associated translocation (10;11)

A translocation (10;11)(p12;q14) was observed in two children, one with acute eosinophilic leukemia and the other with acute T-cell lymphoblastic leukemia. The presence of CALM-AF10 fusion was ascertained by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Fluorescence in situ hybridization (FISH) analysis showed that AF10 gene splitting was associated with partial inversion of chromosome 11 in the first patient. In addition, FISH analysis also determined the orientation of the CALM gene, 5' telomere to 3' centromere on 11q.

Low glucocorticoid receptor alpha/beta ratio in T-cell lymphoblastic leukemia

Glucocorticoid therapy is pivotal in the treatment of acute lymphoblastic leukemia (ALL); it reduces cell proliferation, promotes cell cycle arrest, and induces cell death by apoptosis. The sensitivity of leukemic cells to glucocorticoids was previously related to the cell concentration of 3[H]dexamethasone-binding sites. The latter represents the classic glucocorticoid receptor (GR) isoform alpha that binds ligand and modulates the transcription rates of glucocorticoid-responsive genes. In ALL, lymphoblasts of T-lineage are less sensitive to glucocorticoids than cells of the B-lineage. The alternatively spliced GR isoform (GRP), which exerts a dominant negative effect on GRalpha-mediated transcriptional activity, has been proposed as a possible mediator of glucocorticoid resistance. In this study, we determined the amount of GRalpha and GRbeta in mononuclear cells from 13 newly diagnosed and untreated children with ALL and 9 controls by quantitative Western analysis. Generally, leukemic patients expressed 6 times less GRalpha (ALL= 0.54 +/- 1.1; controls = 3.1 +/- 0.9; p < 0.01) than controls, but the same amount of GRbeta (ALL=3.62 +/- 3.3; controls = 3.6 +/- 3.4). ALL patients with T-cell disease had a much lower GRalpha (0.09 +/- 0.1; p < 0.01) but a similar or slightly higher GRbeta (5.98 +/- 3.9; p = 0.1) expression than controls, with a GRalpha/GRbeta ratio 15 times smaller than controls. Mononuclear leukocytes of T-cell lineage expressed significantly lower GRalpha (p = 0.04) and higher GRbeta (p < 0.01) than cells of the pre-B immunophenotype, with a 10 times smaller ratio. We conclude that the combination of low GRalpha and normal-to-high GRbeta expression in leukemic lymphoblasts might represent one of the mechanisms responsible for their reduced glucocorticoid sensitivity; this is more pronounced in T-lineage cells.

T-ALL with monoclonal gammopathy and hairy cell features

The presented case is a boy with T-cell acute lymphoblastic leukemia (ALL) with hairy cell (HC) features and monoclonal gammopathy. The disease process had an acute onset and followed a rapid, progressive course. The patient had minimal splenomegaly and bicytopenia, but the bone marrow displayed increased numbers of reticulin fibers. The blasts were positive for tartrate-resistant acid phosphatase (TRAP) and CD11c. Molecular analysis revealed rearrangement of immunoglobulin heavy chain genes and a rearranged T-cell receptor (TcRbeta) beta gene. The patient responded to conventional ALL therapy. Acute T-cell ALL with HC features in childhood has not been reported previously, either alone or in association with monoclonal gammopathy. We propose "T-ALL with hairy cell features" to describe this case.

Mutation analysis of mitotic checkpoint genes (hBUB1 and hBUBR1) and microsatellite instability in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a neoplasm of T-lymphocytes, and human T-cell lymphotropic virus type-I (HTLV-I) is etiologically considered as the causative virus of ATLL. The karyotypes of ATLL are very complex in both number and structure, although no specific karyotype abnormalities have been identified. HTLV-I is thought to integrate its provirus into random sites in host chromosomal DNA and induces chromosomal instability. The BUB gene is a component of the mitotic checkpoint in budding yeast. Recently, human homologues of the BUB were identified and mutant alleles of hBUB1 and hBUBR1 were detected in two colorectal tumor cell lines, which showed microsatellite instability (MIN). In vitro, BUB proteins form a complex of monomers. These proteins interact with the human MAD1 gene product, a target of the HTLV-1 tax oncogene. We examined the role of checkpoint gene in the chromosomal abnormalities of ATLL by investigating mutations of hBUB1 and hBUBR1, and MIN of replication errors of BAX, insulin-like growth factor, and transforming growth factor beta type II. We analyzed ten cases with ATLL and eight B-cell lymphomas (five diffuse large cell lymphomas, three follicular lymphomas). Complex chromosomal abnormalities were detected in ATLL, while B-cell lymphomas showed only simple or minimal chromosomal abnormalities. Significant mutations/deletion of hBUB1 or hBUBR1 were detected in four of ten cases with ATLL, including two heterozygous point mutations, one homozygous point mutation, and one with a 47 bp deletion. In contrast, only one of eight B-cell lymphomas showed nonsense mutation of hBUBR1. None of the ATLL and B-cell lymphomas showed MIN. In the multistage process of leukemogenesis of ATLL, our findings indicate that mutations of mitotic checkpoint genes may play an important role in the induction of complex chromosomal abnormalities.

TEL-AML1 fusion gene frequency in paediatric acute lymphoblastic leukaemia in Brazil

We analysed 67 samples from Brazilian children of diverse ethnic origins with acute lymphoblastic leukaemia (ALL) for the presence of the TEL-AML1 fusion gene transcripts using reverse transcription polymerase chain reaction (RT-PCR). All 12 positive cases (20% of the 60 B-cell precursor ALL) had common (CD10+) ALL with a mean age of 4 years (range 1-10 years). We conclude that the frequency, age, distribution and clinical features of the TEL-AML1 fusion gene-positive ALL is similar in the diverse ethnic backgrounds of the Brazilian children to that in other countries with predominantly white Caucasian or oriental ethnicity. Apparent exceptions to this generality are discussed.

New recurring cytogenetic abnormalities and association of blast cell karyotypes with prognosis in childhood T-cell acute lymphoblastic leukemia: a pediatric oncology group report of 343 cases

To further define the cytogenetic differences between B-cell lineage (B-lineage) acute lymphoblastic leukemia (ALL) and T-cell lineage ALL (T-ALL) and to determine the prognostic value of cytogenetics in childhood T-ALL, the blast cell karyotypes of 343 cases of pediatric T-ALL, the largest series reported to date, were evaluated. Cytogenetics were performed in a single central laboratory, and the children were treated using a single Pediatric Oncology Group protocol. Clear differences between the karyotypic characteristics of B-lineage ALL and T-ALL were confirmed. This study suggests that there may be survival differences associated with some T-ALL blast cell karyotypes. Better survival is associated with only normal karyotypes and with t(10;14) (translocation of chromosomes 10 and 14); worse survival is associated with the presence of any derivative chromosome. Two new recurring chromosome aberrations previously not reported in T-ALL were found: del(1)(p22) and t(8;12)(q13;p13). Ten aberrations found in this series, which were reported only once previously in T-ALL, can now be considered recurring abnormalities in T-ALL. All 12 of these new recurring aberrations are targets for discovery and characterization of new genes that are important in T-cell development and leukemogenesis.

Detection of T cell receptor delta gene rearrangements in childhood B and T lineage acute lymphoblastic leukaemia by southern blot and PCR: technical comparison of two methods of analysis

Molecular analysis of antigen receptor genes (Ig and TCR) has been useful for clonal studies in acute lymphoblastic leukaemia (ALL) patients. Rearrangements of these genes can be used to track the persistence of the leukaemic clone during the therapy. The purpose of our study was to analyse the percentage and the pattern of the rearrangements at the TCR D locus in a series of ALL patients, comparing the results obtained by Southern blot and PCR. Genomic DNA was extracted from mononuclear BM cells of 40 paediatric ALL cases, digested with different restriction enzymes and hybridized to TCRDJ1 probe to study the TCR delta locus. Amplification of the rearranged TCR delta genes was performed by PCR to define the gene segments involved. The junctional region was deduced from the sequence to obtain patient-specific primers. Among the 31 B lineage ALL samples, one or two TCR delta alleles proved to be rearranged in 53% of cases. Two different types of rearrangements were chiefly detected: Vdelta2Ddelta3 and Ddelta2Ddelta3. In T-ALL patients, the predominant rearrangement involved the Vdelta1 and the Jdelta1 gene segments.

Human T-cell leukemia virus type I tax activates transcription of the human monocyte chemoattractant protein-1 gene through two nuclear factor-kappaB sites

Infection by human T-cell leukemia virus type (HTLV) I leads to adult T-cell leukemia and is also associated with the neurodegenerative disease HTLV-I-associated myelopathy/tropical spastic paraparesis. Leukocytes are attracted to sites of inflammation by chemokines. One such chemokine is monocyte chemoattractant protein (MCP)-1, a member of the C-C subfamily of chemokines. We investigated whether HTLV-I infection causes up-regulation of MCP-1, which may in turn cause recruitment of leukocytes to HTLV-I-infected areas. We now report that MCP-1 mRNA levels are elevated in HTLV-I-infected T-cell lines, when compared with uninfected ones. We further confirmed secretion of MCP-1 by HTLV-I-infected T-cell lines. MCP-1 mRNA was also expressed in leukemic cells from patients with adult T-cell leukemia. The 5' transcriptional regulatory region of the MCP-1 gene was activated by the HTLV-I-encoded transactivator Tax in the human T-cell line Jurkat, in which endogenous MCP-1 is induced by Tax. By using site-specific point mutations, we have identified two closely spaced nuclear factor (NF)-kappaB sites, A1 and A2, to be important for Tax-mediated transactivation of the MCP-1 gene. Through the use of an electrophoretic mobility shift assay, we demonstrated that Tax induced NF-kappaB binding to both MCP-1 kappaB sites. This is the first report to demonstrate that Tax can transactivate the MCP-1 gene through the induction of NF-kappaB. Our results thus reveal how Tax disrupts the normally regulated MCP-1 gene and leads to its constitutive expression in HTLV-I-infected cells. These findings may have important implications for our understanding of HTLV-I-associated diseases.

[Southern blot hybridization analysis for lymphoid neoplasms]

The recent remarkable progress of molecular biology gave us new tools for examination of the etiology and pathology of many diseases. Hence, the introduction of such techniques in our clinical laboratory area is becoming more important and indispensable year by year. In addition to morphological and phenotypical analysis, we are now establishing a molecular diagnosis system to support the clinical diagnosis of hematological malignancies. In the present study, we show our ongoing results focusing on adult T-cell leukemia(ATL). Southern blot analysis for detection of the monoclonal integration of HTLV-I proviral genome, a causative agent of ATL, was performed using digoxigenin-labeled probe. The sensitivity was equivalent to RI-labeled probe and was enough for clinical use. We are also doing Southern blot analysis for immunoglobulin heavy chain gene and T-cell receptor beta chain gene as custom service for the diagnosis of B-lymphoproliferative disorders and non-ATL T-lymphoproliferative disorders. We are reporting such results to the clinical site with our interpretation. Since the band size of the HTLV-I provirus obtained by Southern blot differed in each case and was sometimes smaller than the size of the complete virus, we further analyzed the structure of HTLV-I using long and accurate PCR(LA-PCR) and sequence-target-site PCR(STS-PCR). We found that the integrated HTLV-I provirus is divided into two subtypes, complete virus and defective virus. The incidence of defective virus was high in acute-type ATL compared with that in chronic- or lymphoma-type ATL. Although there are several difficulties in introducing such molecular analyses into the clinical laboratory area, we think that the need is increasing together with the progression of gene therapy and evidence-based medicine.

Kinetics of early therapeutic response as measured by quantitative PCR predicts survival in a murine xenograft model of human T cell acute lymphoblastic leukemia

The identification of prognostic parameters and surrogate markers for defining patient risk has been beneficial in effectively guiding therapy and increasing the survival of leukemia patients. It has been hypothesized that the therapeutic response, as measured by a change in tumor burden during therapy, might serve as a new surrogate marker of survival. Here we describe the development of a murine SCID xenograft model of human T cell acute lymphoblastic leukemia (T-ALL), and the use of a sensitive, quantitative PCR assay for the measurement of tumor levels to investigate the relationships between tumor burden quantification, therapeutic response and survival. Animals engrafted with the CCRF-CEM (CEM) human T-ALL cell line develop leukemia that closely resembles the human disease. Quantitative PCR detects the expanding tumor mass in the peripheral blood of the animals several weeks before death. In response to induction therapy with chemotherapeutic agents, both the level of minimal residual disease (MRD) in peripheral blood at the end of therapy and the rate of tumor reduction in peripheral blood during therapy strongly correlated with animal survival. Thus, these surrogate markers, which can be measured during the early stages of therapy, may help improve patient survival through dynamic risk stratification.

Pattern of immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements in childhood acute lymphoblastic leukemia in India

In 120 cases of acute lymphoblastic leukemia (median age 8 years), IgH chain gene was rearranged in 99% B-Cell Precursor (BCP) ALLs and 13% T-ALLs. One or the other TCR locus was rearranged not only in all T-ALLs, but also in 87% of BCP-ALLs. TCR-beta rearrangement in BCP-ALL was associated with a higher mean age at presentation (8.7 vs. 6.2 years, P=0.008), lower mean platelet counts (61.2x10(9)/l vs. 103.7x10(9)/l, P=0.003) and a poorer DFS (% cummulative survival 0 vs. 88.9+/-10.5, P=0.004). TCR-gamma rearrangement in T-ALL was associated with a higher mean WBC count (186.3x10(9)/l vs. 63. 4x10(9)/l, P=0.002). Also, the pattern of rearrangement of these genes appeared to be different from the West; viz. TCR-beta rearrangement in a higher proportion of BCP-ALLs (58%, 95% confidence intervals 45-69%), invariable deletion of Cgamma1 and only monoallelic rearrangement for TCR-delta locus. This repertoire of gene rearrangement may have a bearing on the poor treatment outcome reported previously from our geographic region.

T cell receptor gamma (TCRG) gene rearrangements in T cell acute lymphoblastic leukemia refelct 'end-stage' recombinations: implications for minimal residual disease monitoring

The T cell receptor gamma (TCRG) gene configuration was established in a large series of 126 T cell acute lymphoblastic leukemia (T-ALL) patients using combined Southern blotting (SB) and heteroduplex PCR analyses. The vast majority of TALL (96%) displayed clonal TCRG gene rearrangements, with biallelic recombination in 91% of patients. A small immature subgroup of CD3- T-ALL (n = 5) had both TCRG genes in germline configuration, three of them having also germline TCRD genes. In five patients (4%) combined SB and PCR results indicated oligoclonality. In five rearrangements detected by SB, the Vgamma gene segment could not be identified suggesting illegitimate recombination. Altogether, 83% of TCRG gene rearrangements involved either the most upstream Vgamma2 gene (including four cases with interstitial deletion of 170 bp in Vgamma2) and/or the most downstream Jgamma2.3 segment, which can be perceived as 'end-stage' recombinations. Comparative analysis of the TCRG gene configuration in the major immunophenotypic subgroups indicated that TCRgammadelta+ T-ALL display a less mature immunogenotype as compared to TCRalphabeta+ and most CD3- cases. This was reflected by a significantly increased usage of the more downstream Vgamma genes and the upstream Jgamma1 segments. Comparison between adult and pediatric T-ALL patients did not show any obvious differences in TCRG gene configuration. The high frequency, easy detectability, rare oligoclonality, and frequent 'end-stage' recombinations make TCRG gene rearrangements principal targets for PCR-based detection of minimal residual disease (MRD) in T-ALL. We propose a simple heteroduplex PCR strategy, applying five primer combinations, which results in the detection of approximately 95% of all clonal TCRG gene rearrangements in T-ALL. This approach enables identification of at least one TCRG target for MRD monitoring in 95% of patients, and even two targets in 84% of T-ALL.

A heterozygous frameshift mutation in the Fanconi anemia C gene in familial T-ALL and secondary malignancy

BACKGROUND

Patients with Fanconi Anemia (FANC) have a well documented increased risk to develop malignancies, especially Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS). The risk for heterozygous individuals is not clear, epidemiological data are inconsistent. If the risk for heterozygous individuals to develop malignancies was increased, they should be found in groups of patients with AML or MDS at higher proportion than in the normal population. We are currently screening a pediatric population with hematologic malignancies for mutations in the FANCA, FANCC and FANCG gene, and report here on siblings carrying a heterozygous frameshift mutation in the FANCC Gene.

PATIENTS AND METHODS

Using PCR based single strand conformational analysis we screened the DNA from pediatric patients suffering from 1 degree or 2 degrees MDS, CMML/JMML or AML for mutations in the FANCA (43 exons), FANCC (14 exons) and FANCG (14 exons) gene, and included one patient with refractory T-ALL, being the brother of a patient with T-ALL and MDS transforming into AML. Aberrant PCR products were directly sequenced. Flowcytometric measurement of mitogen-sensitivity and G2-phase arrest is used to evaluate cultured stimulated lymphocytes from individuals carrying FANC-mutations.

RESULTS

A novel heterozygous frame-shift mutation, 377-378delGA in the FANCC gene was found in 2 siblings, both suffering from T-ALL with subsequent MDS transforming to AML in one of them. No other mutation was found by direct sequencing of the complete FANCC gene. Both patients died under therapy. The parents (first degree cousins) and one healthy brother are also carriers. Their lymphocytes show a higher mutagen sensitivity than normal, but do not get blocked in G2 phase as being typical for Fanconi Anemia.

CONCLUSION

As the mutation causes a premature Stopcodon within exon 4 of the FANCC gene it has to be regarded as a causal FANCC gene defect. The findings within this family support the hypothesis of an increased risk to develop malignancies in heterozygous carriers of FANC-mutations. A systematic screening of further patients is needed, and we are currently examining a larger cohort to get a better estimate of the true risk of heterozygosity.

Rapid and reliable quantification of minimal residual disease in acute lymphoblastic leukemia using rearranged immunoglobulin and T-cell receptor loci by LightCycler technology

The detection of minimal residual disease (MRD) using immunoglobulin and T-cell receptor (TCR) rearrangements as PCR targets provides important prognostic information on the in vivo effectiveness of treatment in acute lymphoblastic leukemia (ALL). Here we report on the real-time quantification of MRD in 25 ALL patients using LightCycler technology. We designed and adapted allele-specific oligonucleotide (ASO)-PCR protocols that enabled the detection of >90% of the IGH, IGK, TCRD, and TCRG rearrangements observed in ALL patients. In all patients, at least two suitable markers could be identified (average, 3.4 markers/patient). We applied ASO-PCR with 35 immunoglobulin and TCR rearrangements (11 IGH, 6 IGK, 12 TCRG, and 6 TCRD) and compared the sensitivity and practicability of the LightCycler strategy with conventional ASO-PCR on a block thermocycler followed by quantification with gel electrophoresis. The LightCycler measured leukemia-specific PCR products at each cycle (real-time) by staining the PCR product with the DNA-binding dye SYBR Green I. LightCycler technology showed a higher sensitivity than the conventional method in eight cases, whereas the sensitivity of the other markers matched exactly. The detection level varied between 10(-4) and 10(-6) leukemic cells. Furthermore, we determined the MRD status of 27 bone marrow follow-up samples from 15 ALL patients by both methods and revealed comparable results. However, the LightCycler also allowed accurate quantification in samples containing relatively high levels (>10(-3)) of residual leukemia cells. The conventional ASO-PCR technique comprises various laborious and time-consuming PCR experiments and post-PCR steps to determine the number of cycles with the optimal linearity and sensitivity of the PCR. Real-time quantification through LightCycler technology obviates these post-PCR steps, provides the highest sensitivity via software analysis, and therefore represents a rapid, reliable, sensitive, and cost-effective technique for the routine monitoring of MRD in ALL patients.

Constitutive activation of transcription factor AP-1 in primary adult T-cell leukemia cells

Human T-cell leukemia virus type-I (HTLV-I) is the etiologic agent of adult T-cell leukemia (ATL). This study examined the status of the oncogenic transcription factor AP-1 in leukemic cells freshly isolated from patients with ATL. Leukemic cells from peripheral blood of all patients with ATL exhibited constitutive AP-1 DNA binding activity, whereas mononuclear cells from normal individuals did not. In agreement with previous studies, HTLV-I transforming protein, Tax, was found to stimulate the DNA binding activity of AP-1 in a T-cell line. However, HTLV-I genes, including Tax, were not significantly expressed in leukemic cells freshly obtained from patients with ATL. Moreover, all T-cell lines derived from leukemic cells of patients with ATL also displayed constitutive AP-1 DNA binding activity, but expressed little Tax protein. Thus, leukemic cells of patients with ATL appear to have Tax-independent mechanisms that induce AP-1 activity, both in vivo and in vitro. In antibody supershift experiments, AP-1 in fresh leukemic cells and ATL-derived cell lines were found to contain JunD. Consistently, all primary ATL cells and ATL-derived cell lines expressed high levels of JunD messenger RNA. Our results suggest that AP-1 is activated in leukemic cells of patients with ATL through a Tax-independent mechanism and this may play a role in the deregulated phenotypes of ATL leukemic cells. (Blood. 2000;95:3915-3921)

p53 stabilization and functional impairment in the absence of genetic mutation or the alteration of the p14(ARF)-MDM2 loop in ex vivo and cultured adult T-cell leukemia/lymphoma cells

Human T-cell lymphotropic virus type I (HTLV-I) transforms T cells in vitro, and the viral transactivator Tax functionally impairs the tumor suppressor p53 protein, which is also stabilized in HTLV-I-infected T cells. Thus, the functional impairment of p53 is essential to maintain the viral-induced proliferation of CD4+ mature T cells. However, in the CD4+ leukemic cells of patients with adult T-cell leukemia/lymphoma (ATLL), the viral transactivator does not appear to be expressed, and p53 mutations have been found only in a fraction of patients. We sought to investigate whether p53 function is impaired, in ex vivo samples from patients with ATLL, in the absence of genetic mutations. Here we demonstrate that the p53 protein is stabilized also in ex vivo ATLL samples (10 of 10 studied) and that at least in 2 patients p53 stabilization was not associated with genetic mutation. Furthermore, the assessment of p53 function after ionizing radiation of ATLL cells indicated an abnormal induction of the p53-responsive genes GADD45 and p21(WAF1) in 7 of 7 patients. In 2 of 2 patients, p53 regulation of cell-cycle progression appeared to be impaired as well. Because p53 is part of a regulatory loop that also involves MDM2 and p14(ARF), the status of the latter proteins was also assessed in cultured or fresh ATLL cells. The p97 MDM2 protein was not detected by Western blot analysis in established HTLV-I-infected T-cell lines or ex vivo ATLL cell lysates. However, the MDM2 protein could be easily detected after treatment of cells with the specific proteasome inhibitor lactacystin, suggesting a normal regulation of the p53-MDM2 regulating loop. Similarly, p14(ARF) did not appear to be aberrantly expressed in ex vivo ATLL cells nor in any of the established HTLV-I-infected T-cell lines studied. Thus, p53 stabilization in HTLV-I infection occurs in the absence of genetic mutation and alteration of the physiologic degradation pathway of p53. (Blood. 2000;95:3939-3944)

Flow cytometric detection of CD79a expression in T-cell acute lymphoblastic leukemias

We evaluated the lineage specificity of CD79a in acute leukemias using 3-color flow cytometry in 58 consecutive cases. A panel of cell-surface antigens, including myeloid-associated markers, B-cell-associated markers, and T-cell-associated markers, was used. All cases of acute myeloid leukemia were CD79a-, whereas all cases of B-lineage acute lymphoblastic leukemia (ALL) were CD79a+. Three of 8 cases of T-cell ALL showed variable CD79a expression, indicating the presence of a blast subset expressing a relatively high level of CD79a. We investigated the clinical and pathologic characteristics of these 3 cases. All 3 cases had L1 or L2 morphology and expressed surface CD3. None of the other B-cell-associated markers were positive, although 1 case expressed CD13 and CD33. Uncommon random karyotypic abnormalities were identified in all 3 cases. Molecular studies demonstrated monoclonal gene rearrangement of T-cell receptor gamma in 2 of 3 cases. All 3 patients were 18 years old or younger; 1 patient did not enter remission, and 1 had disease relapse in 8 months. Our findings provide further support for the existence of a subset of T-cell ALL coexpressing CD3 and CD79a. Further study of the clinical and biologic significance of this subset may be warranted.

t(4;11)(q21;p15) translocation involving NUP98 and RAP1GDS1 genes: characterization of a new subset of T acute lymphoblastic leukaemia

Two cases of T acute lymphoblastic leukaemia (T-ALL) with an identical t(4;11)(q21;p15) translocation were identified within a prospective study on the biological and clinical features of adult ALL patients enrolled into the therapeutic protocol ALL0496 of the GIMEMA Italian Group. In both cases, the molecular characterization showed an involvement of the NUP98 gene on 11p15 which rearranges with the RAP1GDS1 gene on 4q21. The morphological and immunological features of the leukaemic cells, as well as the clinical behaviour and response to induction therapy, were the same in both patients. Based on the available data, the t(4;11)(q21;p15) translocation involving the NUP98-RAP1GDS1 fusion gene emerges as a new highly specific genetic abnormality that characterizes a subset of T-ALL.

Deletion of the p16INK4A gene in ex vivo acute adult T cell lymphoma/leukemia cells and methylation of the p16INK4A promoter in HTLV type I-infected T cell lines

The stoichiometry of the p16INK4A and p15INK4B proteins bound to the cyclin D-CDK4/6 complex regulates the entry of cells into the G1 phase of the cell cycle. Thus, their level of expression is essential in maintaining regulated cell growth. In several tumors, deletion of these genes has been reported and, more recently, promoter methylation has been suggested as an alternative mechanism to decrease the expression of these cell cycle inhibitor proteins. Here, we studied the methylation status and the integrity of the p16INK4A and p15INK4B genes in 8 chronically HTLV-I-infected T cell lines and in ex vivo cells from 14 ATLL patients. Deletion of the locus carrying both genes was not found in the HTLV-I-infected T cell lines but was found in seven of eight acute ATLL cases and in none of the PBMCs from the chronic cases or the affected lymph nodes of the lymphoma type. In contrast, partial or complete methylation of one or both genes was found only in chronically HTLV-I T cells. Thus, HTLV-I infection targets the p16INK4A and p15INK4B loci both in vitro and in vivo, although the mechanisms may differ.

Detection of methylthioadenosine phosphorylase (MTAP) and p16 gene deletion in T cell acute lymphoblastic leukemia by real-time quantitative PCR assay

Methylthioadenosine phosphorylase (MTAP) deficiency in tumors can be therapeutically exploited for selective therapy. Many tumors lacking MTAP have been found to homozygously delete the chromosome 9p region containing the p16 tumor suppressor gene. Several methods have been used to detect chromosome 9p deletions in primary tumors. However, the accurate diagnosis of chromosome 9p deletions has been hampered by the presence of contaminating normal cells. In search of an accurate and sensitive diagnostic method, we have developed the real-time polymerase chain reaction assay using the TaqMan chemistry for quantitative detection of MTAP and p16 gene deletions. The assay's feasibility was tested with peripheral blood leukocytes (PBL) from 29 patients with adult T cell leukemia (ATL) previously analyzed with Southern blot analysis and validated on 39 PBL or bone marrow samples from childhood T cell acute lymphoblastic leukemia (T-ALL). Homozygous deletions of MTAP and p16 genes were detected respectively in six (20.7%) and eight (27.6%) of 29 ATL samples and in 15 (38.5%) and 23 (59%) of 39 T-ALL samples. The results correlated well with those of Southern blot analysis. It is of significance that the newly developed method can successfully detect homozygous deletions of these genes in samples containing as low as 33% blast cells. This rapid and sensitive method may be useful in searching for candidates for selective therapy targeting MTAP deficiency.

Universal inactivation of both p16 and p15 but not downstream components is an essential event in the pathogenesis of T-cell acute lymphoblastic leukemia

p16/p15 regulate the cell cycle pathway by inhibiting the cyclin Ds-CDK4/6 mediated phosphorylation of pRb. We reported previously that in T-cell acute lymphoblastic leukemia (T-ALL), p16 and p15 were frequently (approximately 70%) inactivated at the DNA level by deletion, mutation, or hypermethylation. Therefore, we hypothesize that inactivation of the cell cycle regulatory pathway may be essential in the pathogenesis of T-ALL, and that the remaining T-ALL with a wild-type p16/p15 gene likely harbor inactivation of these genes at RNA or protein levels. Alternatively, the downstream components of the pathway including CDK4/6, cyclin Ds, and pRb may be deregulated. In 124 primary T-ALLs, we found inactivation of the p16 and p15 genes at the DNA level in 79 (64%) and 64 (52%) samples, respectively. Only 9 of the 45 samples with wild-type p16 expressed p16 protein, whereas the remaining 36 lacked p16 expression at the RNA or protein level. In the 60 samples with an intact p15 gene, only 2 expressed p15 mRNA, and the only one analyzed lacked p15 protein. Overall, the abrogation rates for p16 and p15 at DNA/RNA/protein levels were 93% (115 of 124) and 99% (123 of 124), respectively. Although no alterations were evident in cyclin Ds or CDK4/6, pRb was hyperphosphorylated in the majority of samples investigated. These findings strongly support that both p16 and p15 are specific targets in the deregulation of the cell cycle pathway in T-ALL and that the inactivation of these genes is most likely essential in the pathogenesis of this disease.

T-cell lineage acute lymphoblastic leukemia with chromosome 5 abnormality in a patient with Crohn's disease and lipoid nephrosis

We describe a 17-year-old patient with a documented history of Crohn's disease (CD) and of minimal-change nephrotic syndrome (MCNS) in whom a diagnosis of T-cell acute lymphoblastic leukemia (ALL) was made. The diagnosis of ALL was established by morphological examination of bone-marrow aspirates and confirmed by means of immunophenotypic analysis showing the involvement of T-cell lineage leukemic cells. The lymphoid clone showed a karyotypic abnormality involving the long arm of chromosome 5 in a translocation (5;6). Few cases of CD complicated by ALL have been previously reported. The present one is the first case combining CD and ALL in a patient with a past history of MCNS. This raises the possibility of a relationship among those diseases. The possible mechanisms for such a relationship are discussed here.

The t(14;21)(q11.2;q22) chromosomal translocation associated with T-cell acute lymphoblastic leukemia activates the BHLHB1 gene

We have cloned the genomic breakpoints for a balanced t(14;21)(q11. 2;q22) chromosomal translocation associated with T-cell acute lymphoblastic leukemia. Sequence analysis of the genomic breakpoints indicated that the translocation had been mediated by an illegitimate V(D)J recombination event that disrupted the T-cell receptor (TCR) alpha locus and placed the TCR alpha locus enhancer on the derivative 21 chromosome. We identified a previously unreported transcript, designated BHLHB1 (for basic domain, helix-loop-helix protein, class B, 1) that had been activated by the translocation. BHLHB1 mapped to the region of chromosome 21 that has been proposed to be responsible, at least in part, for the learning deficits seen in children with Down's syndrome. Although BHLHB1 expression normally is restricted to neural tissues, T-cell lymphoblasts with the t(14;21)(q11.2;q22) also expressed high levels of BHLHB1 mRNA. Expression of BHLHB1 dramatically inhibited E2A-mediated transcription activation in NIH 3T3 fibroblasts and Jurkat T cells. This observation suggests that BHLHB1, similar to SCL/TAL1, may exert a leukemogenic effect through a functional inactivation of E2A or related proteins.

Molecular diagnosis in pediatric acute leukemias

This article summarizes the tremendous progress currently achieved in understanding the molecular basis of the pediatric acute leukemias. The article is organized from the perspective of the most frequently encountered pediatric acute leukemia genetic abnormalities in a molecular diagnostics laboratory setting. For each specific entity, the basic molecular biology, putative mechanisms of leukemogenesis, detection methods, and clinical significance are reviewed. Emphasis is placed on discussing the fusion genes generated from common nonrandom chromosomal translocations in B-lineage acute lymphoblastic leukemia (ALL), although brief summaries of T-lineage and myeloid leukemia, as well as the use of the antigen receptor gene rearrangement for residual disease monitoring in acute lympocytic leukemia are also presented. Finally, an overview of emerging technologies of potential importance in the laboratory diagnosis and evaluation of the pediatric acute leukemias is provided.