The TeloDIAG: how telomeric parameters can help in glioma rapid diagnosis and liquid biopsy approaches

BACKGROUND

In glioma, TERT promoter mutation and loss of ATRX (ATRX loss) are associated with reactivation of telomerase or alternative lengthening of telomeres (ALT), respectively, i.e. the two telomere maintenance mechanisms (TMM). Strangely, 25% of gliomas have been reported to display neither or both of these alterations.

MATERIALS AND METHODS

The C-circle (CC) assay was adapted to tumor (formalin-fixed paraffin-embedded and frozen) and blood samples to investigate the TMM.

RESULTS

We constructed a CC-based algorithm able to identify the TMM and reported a sensitivity of 100% and a specificity of 97.3% (n = 284 gliomas). By combining the TMM, the mutational status of the isocitrate dehydrogenase 1/2 (IDH) gene (IDHmt), and the histological grading, we propose a new classification tool: TeloDIAG. This classification defined five subtypes: tOD, tLGA, tGBM_IDHmt, tGBM, and tAIV, corresponding to oligodendroglioma, IDHmt low-grade astrocytoma, IDHmt glioblastoma, and IDHwt glioblastoma (GBM), respectively; the last class gathers ALT+ IDHwt gliomas that tend to be related to longer survival (21.2 months) than tGBM (16.5 months). The TeloDIAG was 99% concordant with the World Health Organization classification (n = 312), and further modified the classification of 55 of 144 (38%) gliomas with atypical molecular characteristics. As an example, 14 of 69 (20%) of TERTwt, ATRXwt, and IDHwt GBM were actually tAIV. Outstandingly, CC in blood sampled from IDHmt astrocytoma patients was detected with a sensitivity of 56% and a specificity of 97% (n = 206 gliomas and 30 healthy donors).

CONCLUSION

The TeloDIAG is a new, simple, and effective tool helping in glioma diagnosis and a promising option for liquid biopsy.

OS02.6.A The TeloDIAG: How telomeric parameters can help in glioma rapid diagnosis and liquid biopsies approaches

BACKGROUND

The integration of molecular markers into the WHO 2016 classification has clarified the complex diagnosis of gliomas. Among these biomarkers, the TERT promoter mutation and the loss of ATRX (ATRX loss) are mutually exclusive alterations associated with re-activation of telomerase or alternative lengthening of telomeres (ALT), respectively. Strangely, 25% of gliomas display neither or both these alterations, a situation referred to as abnormal telomere maintenance mechanism (aTMM).

MATERIAL AND METHODS

To investigate the TMM actually involved in gliomas, the C-circle (CC) assay was adapted to tumor (FFPE and frozen) samples.

RESULTS

We constructed a CC-based algorithm able to identify the TMM of 284 gliomas with either TERT or ATRX alteration, with a sensitivity of 100% and a specificity of 97.3%, and succeeded in deciphering the TMM involved in 122 aTMM gliomas. Additionally, the combination of the TMM, the mutational status of the Isocitrate dehydrogenase 1/2 (IDH) gene, and the histological grading was used as base for a new classification: TeloDIAG. Six subtypes are defined in this classification: tOD, tLGA, tGBM_IDHmt, tGBM, and tAIV, corresponding to oligodendroglioma, IDHmt low grade astrocytoma, IDHmt glioblastoma, and IDHwt glioblastoma, respectively, the last class gathers ALT+ IDHwt glioma. The TeloDIAG diagnosis is 99% concordant with the WHO classification for glioma displaying typical molecular characteristics (N=312). It modified the classification of 38% (N=156) discordant tumors, such as IDHwt Astrocytoma, aTMM tumors, or gliomas with unexpected TMM (e.g. TERTwt oligodendroglioma, ATRX loss GBM). Interestingly, 20% (N=69) of TERTwt, ATRXwt, or IDHwt GBM were actually tAIV, which is remarkable as tAIV-glioma patients’ survival tended to be longer (21.2 months) than tGBM patients’ survival (16.5 months). Importantly, CC in blood sampled from IDHmt astrocytoma patients was detected with a sensitivity of 56% and a specificity of 95% (N = 206).

CONCLUSION

In sum, the TeloDIAG is a new, simple, and efficient tool helping in glioma diagnosis and a promising option for liquid biopsy

Prognostic value of Dicer expression in human breast cancers and association with the mesenchymal phenotype

BACKGROUND

Dicer, a ribonuclease, is the key enzyme required for the biogenesis of microRNAs and small interfering RNAs and is essential for both mammalian development and cell differentiation. Recent evidence indicates that Dicer may also be involved in tumourigenesis. However, no studies have examined the clinical significance of Dicer at both the RNA and the protein levels in breast cancer.

METHODS

In this study, the biological and prognostic value of Dicer expression was assessed in breast cancer cell lines, breast cancer progression cellular models, and in two well-characterised sets of breast carcinoma samples obtained from patients with long-term follow-up using tissue microarrays and quantitative reverse transcription-PCR.

RESULTS

We have found that Dicer protein expression is significantly associated with hormone receptor status and cancer subtype in breast tumours (ER P=0.008; PR P=0.019; cancer subtype P=0.023, luminal A P=0.0174). Dicer mRNA expression appeared to have an independent prognostic impact in metastatic disease (hazard ratio=3.36, P=0.0032). In the breast cancer cell lines, lower Dicer expression was found in cells harbouring a mesenchymal phenotype and in metastatic bone derivatives of a breast cancer cell line. These findings suggest that the downregulation of Dicer expression may be related to the metastatic spread of tumours.

CONCLUSION

Assessment of Dicer expression may facilitate prediction of distant metastases for patients suffering from breast cancer.

Allele-specific binding to the -308 single nucleotide polymorphism site in the tumour necrosis factor-alpha promoter

Single nucleotide polymorphisms in the tumour necrosis factor alpha (TNF-alpha) promoter region may modulate TNF-alpha gene transcriptional activity by modifying the binding of transcription factors. Here we confirm that a specific DNA complex binds preferentially the variant TNF2 allele in various cell types and demonstrate that activating protein (AP)-2, myeloid zinc finger gene 1 (MZF-1) and Sp1 are not involved in this complex.

FLRG, an activin-binding protein, is a new target of TGFbeta transcription activation through Smad proteins

The FLRG gene encodes a secreted glycoprotein that binds to activin and is highly homologous to follistatin, an activin ligand. We cloned the promoter region of the human FLRG gene, and defined the minimal region necessary for transcription activation in a reporter-system assay. We showed that the fragment between positions -130 and +6, which consists of multiple consensus Sp1-binding sites, is required for the constitutive expression of the FLRG gene. We demonstrate here that FLRG mRNA expression is rapidly induced by TGFbeta or by transfection with Smad protein expression vectors in human HepG2 cells. We investigated the transcription-regulation mechanism of FLRG expression in HepG2 cells following treatment with TGFbeta. By deletion and point-mutation analysis of the FLRG promoter, we identified a Smad-binding element involved in the TGFbeta-inducible expression of the FLRG gene. Moreover, transactivation of the FLRG promoter by TGFbeta was compromised by dominant-negative mutants of Smad3 and Smad4 proteins. In addition, gel electrophoresis mobility-shift assays demonstrated the specific interaction of Smad3 and Smad4 proteins with the Smad-binding element consensus motif found in the FLRG promoter. Taken together, our data imply that Smad proteins participate in the regulation of expression of FLRG, a new target of TGFbeta transcription activation.

Relationships of the antiproliferative proteins BTG1 and BTG2 with CAF1, the human homolog of a component of the yeast CCR4 transcriptional complex: involvement in estrogen receptor alpha signaling pathway

We have reported previously the physical interaction of B-cell translocation gene proteins (BTG)1 and BTG2 with the mouse protein CAF1 (CCR4-associated factor 1) and suggested that these proteins may participate, through their association with CAF1, in transcription regulation. Here we describe the in vitro and in vivo association of these proteins with hPOP2, the human paralog of hCAF1. The physical and functional relationships between the BTG proteins and their partners hCAF1 and hPOP2 were investigated to find out how these interactions affect cellular processes, and in particular transcription regulation. We defined their interaction regions and examined their expression in various human tissues. We also show functional data indicating their involvement in estrogen receptor alpha (ERalpha)-mediated transcription regulation. We found that BTG1 and BTG2, probably through their interaction with CAF1 via a CCR4-like complex, can play both positive or negative roles in regulating the ERalpha function. In addition, our results indicate that two LXXLL motifs, referred to as nuclear receptor boxes, present in both BTG1 and BTG2, are involved in the regulation of ERalpha-mediated activation.

Expression of FLRG, a novel activin A ligand, is regulated by TGF-beta and during hematopoiesis [corrected]

OBJECTIVE

The human gene FLRG, identified from a B-cell chronic lymphocytic leukemia bearing a t(11;19) translocation, encodes a secreted glycoprotein highly homologous with follistatin. Activin A is a TGF-beta family member involved in the regulation of growth and differentiation of various types of cells, such as those of the hematopoietic system. Its biological activity is antagonized by binding with follistatin. We investigated the binding of FLRG to activin A and the expression pattern of FLRG, follistatin, and activin A during hematopoiesis.

MATERIALS AND METHODS

The binding of FLRG with activin A was investigated by immunoprecipitation and Far-Western blot analysis. Gene expression was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) and Northern Blot in purified hematopoietic populations.

RESULTS

We demonstrate that FLRG, like follistatin, is able to bind to activin A. In bone marrow stromal cells, both mRNA and protein FLRG levels were found to be dramatically increased by TGF-beta. FLRG and activin A are expressed in the same cells, with a higher level of expression in the myeloid cells compared with the erythroid and megakaryocytic cells. FLRG and follistatin expression were different in the hematopoietic subpopulations tested. Moreover, we observed that FLRG and activin A expression was up-regulated during hematopoiesis.

CONCLUSION

FLRG and activin A are expressed in the same hematopoietic cells and regulated by TGF-beta. Moreover, FLRG interacts with activin A, suggesting that FLRG, like follistatin, participates in the diverse regulatory functions of activin A, such as those in hematopoiesis.

AF15q14, a novel partner gene fused to the MLL gene in an acute myeloid leukaemia with a t(11;15)(q23;q14)

In haematopoietic malignancies the MLL gene, located on chromosome 11q23, is frequently disrupted by chromosome rearrangement, generally resulting in fusion to various partner genes. We have previously reported a t(11;15)(q23;q14) in a case of acute myeloblastic leukaemia. Here, we report the cloning of a novel MLL partner, AF15q14, at chromosome 15q14. In this translocation, the breakpoint occurred in exon 8 of MLL and exon 10 of AF15q14. The normal AF15q14 transcripts of approximately 8.5 kb in size, are expressed in different tumoral cell lines, in a variety of normal tissues, and in all the foetal tissues tested. Sequencing of AF15q14 cDNA revealed a putative open reading frame of 1833 amino acids that had no homology with any other known protein. The C-terminal end of the putative AF15q14 contained a bipartite nuclear localization site. The translocation t(11;15) preserved the open reading frame between MLL and the 3' end of AF15q14. The contribution of AF15q14 to the fusion protein was only 85 amino acids. Immunofluorescence staining experiments with expression vectors encoding these 85 amino acids confirmed the functionality of the predicted nuclear localization site.

The IgG Fc receptor, FcgammaRIIB, is a target for deregulation by chromosomal translocation in malignant lymphoma

Rearrangement of chromosomal bands 1q21-23 is one of the most frequent chromosomal aberrations observed in hematological malignancy. The genes affected by these rearrangements remain poorly characterized. Typically, 1q21-23 rearrangements arise during tumor evolution and accompany disease-specific chromosomal rearrangements such as t(14;18) (BCL2) and t(8;14) (MYC), where they are thus thought to play an important role in tumor progression. The pathogenetic basis of this 1q21-23-associated disease progression is currently unknown. In this setting, we surveyed our series of follicular lymphoma for evidence of recurring 1q21-23 breaks and identified three cases in which a t(14;18)(q32;q21) was accompanied by a novel balanced t(1;22)(q22;q11). Molecular cloning of the t(1;22) in a cell line (B593) derived from one of these cases and detailed fluorescent in situ hybridization mapping in the two remaining cases identified the FCGR2B gene, which encodes the immunoreceptor tyrosine-based inhibition motif-bearing IgG Fc receptor, FcgammaRIIB, as the target gene of the t(1;22)(q22;q11). We demonstrate deregulation of FCGR2B leading to hyperexpression of FcgammaRIIb2 as the principal consequence of the t(1;22). This is evidence that IgG Fc receptors can be targets for deregulation through chromosomal translocation in lymphoma. It suggests that dysregulation of FCGR2B may play a role in tumor progression in follicular lymphoma.

Hypermethylation of calcitonin gene in adult acute leukemia at diagnosis and during complete remission

Hypermethylation of the calcitonin gene has been described in various hematologic malignancies. In order to assess its frequency and potential usefulness as a marker for leukemic cells and to detect potential clinical correlations, 180 adult patients (aged > 15 years) with newly diagnosed acute leukemia including 133 cases of acute myeloid leukemia (AML) and 47 cases of acute lymphoblastic leukemia (ALL) were tested for its presence in leukemic blasts at diagnosis by Southern blot technique and polymerase chain reaction (PCR) using 3 sets of primers (P550, P566, P1400), amplifying the most frequent sites of hypermethylation upstream or within the gene. In AML, 92 patients (69%) had hypermethylation detected by Southern blot at diagnosis. This hypermethylation could be confirmed by PCR in 18 of 36 tested cases (50%). Hypermethylation was not significantly associated to any clinical or hematological characteristic of the disease. In ALL, 44 patients (94%) had hypermethylation detected by Southern blot at diagnosis. This hypermethylation could be confirmed by PCR in 33 of the 43 tested cases (77%). Sensitivity of PCR assessed by dilution was 1 to 0.1%. Hypermethylation was not either significantly related to any clinical or hematologic characteristics of the disease. Seven ALL cases which were positive by PCR at diagnosis and achieved cytological CR could be tested during CR. Five cases were negative and did not relapse after 3 to 27 months in CR. One case was positive at the beginning of CR and became negative after autologous transplant. However, he relapsed after 9 months in CR, 3 months after the last negative test. PCR for Bcr/Abl was also negative at this time. We conclude that hypermethylation of the calcitonine gene is frequent at diagnosis in adult acute leukemia, particularly in ALL.

FLRG (follistatin-related gene), a new target of chromosomal rearrangement in malignant blood disorders

We report here the molecular study of a t(11;19)(q13;p13) translocation observed in a case of B-cell chronic lymphocytic leukemia. This translocation leads to the juxtaposition of the CCND1 gene on chromosome 11 to a new transcriptional unit on chromosome 19. The cDNA of this new evolutionarily conserved gene (named FLRG for Follistatin-Related Gene) codes for a secreted glycoprotein of the follistatin-module-protein family. FLRG is expressed in a wide range of human and murine adult tissues and its expression seems to be tightly regulated during murine embryogenesis. Its transcripts could not be detected in hematopoietic cells from all lineages and in particular in cells from lymphoid B and T lineage except in the t(11;19)-carrying leukemia described here. A great variability of expression is observed among the other tumoral cell lines analysed. Besides the t(11;19)-carrying leukemia described in this work, structural rearrangements of the FLRG locus have been found in a non-Hodgkin lymphoma, suggesting that it may play a role in leukemogenesis.

Low frequency of TSG101/CC2 gene alterations in invasive human breast cancers

Large intragenic deletions of the TSG101/CC2 gene were recently reported in seven of 15 primary metastatic breast cancers. Although the number of samples was small, this observation suggested that TSG101/CC2 alterations were a major event in breast carcinogenesis. To study the frequency of these deletions in invasive breast cancers we analysed 189 primary invasive breast tumours and 59 breast cancer metastases. We detected intragenic rearrangements in only three samples (two primary tumours and one metastasis). Northern blot analysis of 43 tumours without rearrangements failed to detect any abnormalities. Furthermore, we studied TSG101/CC2 in 11 human breast adenocarcinoma cell lines by Southern blot, RT-PCR and sequencing of the entire coding region of the gene, and detected no abnormalities. These results show that genetic alteration of TSG101/CC2 is a rare event in breast cancer.

Clinical and biological characteristics of adult de novo and secondary acute myeloid leukemia with balanced 11q23 chromosomal anomaly or MLL gene rearrangement compared to cases with unbalanced 11q23 anomaly: confirmation of the existence of different entities with 11q23 breakpoint

Although the presence of a chromosome 11q23 breakpoint is of recognized poor prognosis in acute lymphoblastic leukemia, its prognostic significance in acute myeloid leukemia (AML) has been the object of conflicting reports, perhaps reflecting the possibility of different entities. It has been found that only typical and generally balanced 11q23 chromosomal anomalies involve the MLL gene while atypical and generally unbalanced do not. To determine whether these two categories of AML patients had different initial characteristics and evolution, supporting different pathogenetic mechanisms, we analyzed clinical and biologic characteristics of newly diagnosed AML patients with balanced 11q23 breakpoint and/or MLL rearrangement seen over a 10-year period in our institution and compared them to cases with unbalanced 11q23 anomaly seen over the same period. These two categories of patients were compared with newly diagnosed patients with normal karyotype and no MLL rearrangement when tested, seen over the same period of time and treated similarly. Over this period, 442 newly diagnosed adult (> 15 years) AML seen in our institution had a successful karyotype performed before any therapy. Thirty-six cases (8%) had a chromosome 11q23 breakpoint including 19 cases with a balanced translocation or inversion and 17 cases with an unbalanced anomaly. Eighty-seven recently diagnosed cases of AML, for whom frozen cellular material was available, were analyzed by Southern blot for the presence of MLL gene rearrangement. Fourteen cases (16% of the tested cases) had a rearrangement of the MLL gene, including seven cases with an apparently successful karyotype not showing any 11q23 breakpoint and two cases with no available karyotype. The only case with unbalanced 11q23 chromosomal anomaly which was tested had no MLL rearrangement. There was a clear-cut clinical difference between the 28 patients having a balanced 11q23 anomaly/MLL rearrangement and the 17 patients having an unbalanced chromosomal anomaly: AML with unbalanced 11q23 anomalies occurred in older patients (P = 0.07) tended to be less frequently associated with previous exposure to topoisomerase II-active drugs and with M4/M5 FAB cytological subtypes, were always associated with other chromosomal anomalies (P < 0.0001), expressed more frequently the CD34 antigen (P = 0.05) and were of considerably poorer prognosis for achievement of CR (P = 0.005) and survival (P = 0.0005). When compared to the control population, patients with balanced anomalies had more frequent history of toxic exposure (P = 0.0003) particularly to topoisomerase II-active drugs, tended to be more frequently of M4/M5 FAB subtypes (P = 0.07), expressed more frequently HLA-DR antigen (P = 0.02) and had shorter DFS (P = 0.02). Patients with unbalanced anomalies had more frequent splenomegaly (P = 0.009), lower WBC count (P = 0.04), and much poorer prognosis for CR achievement (P = 0.0001), survival (P < 0.0001) and DFS (P = 0.01). This study confirms the high frequency of 11q23 chromosomal breakpoint/MLL rearrangement in adult AML and the probable existence of two different entities with different clinical features according to the presence of a balanced or unbalanced cytogenetic abnormality, the latter being not associated with MLL rearrangement.

Unbalanced X;autosome translocation (X;18)(q13;p11) in a case of aggressive natural killer non-Hodgkin lymphoma

Recent evidence has shown that rare cases of aggressive non-Hodgkin lymphomas (NHL) derive from cells belonging to the natural killer (NK) lymphocyte lineage and a new clinico pathologic entity has been proposed. Though well documented in B- and T-cell NHL, chromosome abnormalities are rare findings in NK-NHL and to date, no recurrent cytogenetic abnormality has been described. The present study reports the clinical data, cytogenetic and fluorescence in situ hybridization (FISH) analysis of a new case of typical NK-NHL characterized by a primary unbalanced translocation (X;18) (q13;p11). Recent data of X;autosome translocation in malignant lymphomas have proposed Xp22 and Xq28 as the location of NHL-related oncogenes. According to other published reports on the involvement of the Xq13 region in NHL and particularly in aggressive forms, we hypothesize the existence of additional putative lymphoma-associated oncogenes at the band Xq13.

Molecular analysis of cyclin-dependent kinase inhibitors in human leukemias

Recurrent anomalies of the short arm of chromosome 9, including interstitial deletions and translocations, have often been described. Recently two cyclin-dependent kinase inhibitors, known as P16 (INK4A/MTS1) and P15 (INK4B/MTS2), which map to 9p21, have been found deleted in a wide range of tumors and particularly in leukemic cells. We report here Southern blot analyses of cyclin-dependent kinase inhibitors (P16, P15, P21, and P27) status in primary tumoral cells of 121 patients with acute lymphoblastic leukemias, 85 patients with acute myeloid leukemias and 42 patients with B-chronic lymphocytic leukemias. P16 inactivation was found in 25 of 38 T-ALLs and in 28 of 83 B-lineage ALLs. In eight cases (three T-ALLs and five B-lineage ALLs), one or both alleles of P16 locus were rearranged. In these cases, breakpoints occurred within the two major breakpoints cluster regions previously described in T-ALLs. Homozygous P16 deletions were observed in two of 85 AMLs but in none of the 42 B-CLL cases tested. Our results suggest that P16 inactivation are the most frequent event observed in ALL (44%), are quite rare in AML (<2%) and seem to be absent in CLL. Search for P27 and P21 deletion was negative in B/T-lineage ALLs and monoallelic deletions of P27 were found in four AML cases (5%).

Involvement of a human endogenous retroviral sequence (THE-7) in a t(7;14)(q21;q32) chromosomal translocation associated with a B cell chronic lymphocytic leukemia

B cell chronic lymphocytic leukemias (B-CLL) like other blood cell malignancies are characterized by chromosomal anomalies directly involved in tumor pathogenesis. We report here the molecular characterization of a t(7;14)(q21;q32) chromosomal translocation observed during the course of a B-CLL. We show that this translocation led to the juxtaposition of the immunoglobulin heavy chain locus on chromosome 14 to an endogenous retroviral sequence belonging to the THE family (transposable-like human element) on chromosome 7q21. RT-PCR analysis demonstrated that this sequence is transcribed in most of the tumoral and normal tissue analyzed and in the B-CLL described here. These data raise the question of the role of transposable elements in the pathogeny of some leukemias or at least, in the occurrence of chromosomal rearrangements. Structural rearrangements of the 7q21-22 region are frequently encountered in myeloid disorders, and the work presented here could help in their characterization.

FISH analysis of translocations involving the short arm of chromosome 9 in lymphoid malignancies

Deletion of the short arm of chromosome 9 (9p), resulting in the loss of the p16INK4a/MTS1 gene, now called CDKN2, has been found to occur frequently in acute lymphoblastic leukemia, even in the absence of a microscopically visible deletion. In this study, we have used YAC probes encompassing the CDKN2 locus to analyze by fluorescence in situ hybridization patients with leukemia and lymphoma and translocations involving 9p in order to establish the CDKN2 status in relation to the karyotype. We found that, in leukemic cells exhibiting loss of heterozygosity at the CDKN2 locus, the deleted allele was from the cytogenetically normal chromosome 9, whereas the other allele was located on a rearranged chromosome. This finding suggests that CDKN2 gene loss is nonrandomly associated with 9p translocation in lymphoid proliferations. Genes Chromosom.

Cloning of the mouse BTG3 gene and definition of a new gene family (the BTG family) involved in the negative control of the cell cycle

It is well known that loss of tumor suppressor genes and more generally of antiproliferative genes plays a key role in the development of most tumors. We report here the cloning of the mouse BTG3 gene and show that its human counterpart maps on chromosome 21. This evolutionarily conserved gene codes for a 30 kDa protein and is expressed in most adult murine and human tissues analyzed. However, we demonstrate that its expression is cell cycle dependent and peaks at the end of the G1 phase. This gene is homologous to the human BTG1, BTG2 and TOB genes which were demonstrated to act as inhibitors of cell proliferation. Its description allowed us to define better this seven gene family (the BTG gene family) at the structural level and to speculate about its physiological role in normal and tumoral cells. This family is mainly characterized by the presence of two conserved domains (BTG boxes A and B) of as yet undetermined function which are separated by a non-conserved 20-25 amino acid sequence.

Identification of BTG2, an antiproliferative p53-dependent component of the DNA damage cellular response pathway

Cell cycle regulation is critical for maintenance of genome integrity. A prominent factor that guarantees genomic stability of cells is p53 (ref. 1). The P53 gene encodes a transcription factor that has a role as a tumour suppressor. Identification of p53-target genes should provide greater insight into the molecular mechanisms that mediate the tumour suppressor activities of p53. The rodent Pc3/Tis21 gene was initially described as an immediate early gene induced by tumour promoters and growth factors in PC12 and Swiss 3T3 cells. It is expressed in a variety of cell and tissue types and encodes a remarkably labile protein. Pc3/Tis21 has a strong sequence similarity to the human antiproliferative BTG1 gene cloned from a chromosomal translocation of a B-cell chronic lymphocytic leukaemia. This similarity led us to speculate that BTG1 and the putative human homologue of Pc3/Tis21 (named BTG2) were members of a new family of genes involved in growth control and/or differentiation. This hypothesis was recently strengthened by the identification of a new antiproliferative protein, named TOB, which shares sequence similarity with BTG1 and PC3/TIS21 (ref. 7). Here, we cloned and localized the human BTG2 gene. We show that BTG2 expression is induced through a p53-dependent mechanism and that BTG2 function may be relevant to cell cycle control and cellular response to DNA damage.

Differential expression of cell proliferation regulatory proteins in B- and T-lineage acute lymphoblastic leukaemias

In order to better understand the molecular background of differences between the clinical picture of T- and B-lineage ALLs, we studied the expression of several proteins involved in the regulation of cell proliferation in bone marrow blast cells from 30 cases of previously untreated acute lymphoblastic leukaemia (ALL); 14 cases were T- and 16 B-cell lineage ALLs. We studied several cyclin-dependent kinases (cdk1, cdk2, cdk4, cdk6) and cyclins (cyclin A, cyclin B1, cyclin D3 and cyclin E). We also studied proliferating cell nuclear antigen (PCNA) and Bcl-2 expression, the latter protein known to be involved in the prolonged survival of B-lineage ALL blasts. Proteins obtained from cell lysates were resolved on polyacrylamide gel followed by immunodetection and densitometry of specific bands. Expression of cdk1 and PCNA, markers of proliferative activity, was significantly higher in T- than in B-lineage ALL. Cdk6, which was highly correlated to PCNA, was also higher in T-cell ALL. In contrast, B-lineage ALL displayed a higher expression of anti-apoptotic protein Bcl-2. We hypothesize that those particularities may reflect differential roles of cell multiplication and apoptosis in the neoplastic proliferation of B- and T-lineage ALL.

dic(4;17)(p11;p11): a new recurrent chromosomal abnormality in chronic B-lymphoid disorders

We describe a new nonrandom rearrangement, dic(4;17)(p11;p11), which was identified in three patients with small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL). All three cases had in common atypical morphological features with a significant component of prolymphocytes, an unusual clinical outcome, and were refractory to chemotherapy. To further define the cytogenetic breakpoints, we investigated the cases by whole chromosome painting and fluorescence in situ hybridization (FISH) with centromeric probes. FISH analysis detected the same cytogenetic rearrangement in all patients, suggesting that the dic(4;17)(p11;p11) is a recurrent translocation in SLL/CLL. Moreover, FISH analysis showed a monoallelic deletion of the TP53 gene in all cases, suggesting a correlation with the aggressive course of the disease and the clinical outcome observed in these patients.

Implication of cyclin D1 in malignant lymphoma

The chromosomal translocation t(11;14)(q13;q32) is observed in a number of lymphoid malignancies but is specifically associated with a particular subtype of non-Hodgkin's lymphoma called mantle cell lymphoma, where it is observed in up to 70% of cases. This translocation juxtaposes IGH sequences at 14q32 to a region variously termed BCL1/PRAD1 at 11q13, on the derivative chromosome 11. Detailed molecular analysis identified BCL1 to be a gene coding for the G1 cyclin, cyclin D1, which is an important regulator of the G1/S transition of the cell cycle. Cyclin D1 overexpression is observed in a vast majority of mantle cell lymphoma and lymphoid malignancies with 11q13 rearrangement, thereby confirming BCL1, now referred to as CCND1, as the gene targeted by these rearrangements. In this review, following a brief discussion of the role of cyclin D1 in cell cycle regulation, we discuss the mechanisms and pathogenetic impact of cyclin D1 activation in lymphoproliferative disorders with 11q13 rearrangement. We also review a number of the diagnostic strategies available for detection of CCND1 rearrangement/overexpression, with particular emphasis on applications for mantle cell lymphoma.

Expression of cell cycle regulatory proteins in chronic lymphocytic leukemias. Comparison with non-Hodgkin's lymphomas and non-neoplastic lymphoid tissue

The expression of certain cell cycle regulatory proteins: cdk1, cdk2, cdk4, cyclin A, cyclin B, cyclin E, Bcl2 and PCNA was examined in peripheral blood lymphocytes (PBL) from 25 cases of chronic lymphocytic leukemias (CLL) in order to analyze a possible cell cycle involvement of CLL lymphocytes. For comparison, we also studied the expression of these proteins in: 23 samples of non-Hodgkin's lymphoma (NHL) tissue of different histological types, 10 samples of non-neoplastic lymphoid tissue (NLT), non-stimulated PBL (NS-PBL) and PHA-stimulated PBL (PHA-PBL) from three healthy donors. Samples were lysed and proteins were resolved on polyacrylamide gel followed by Western blot. The expression of cdk4 and cyclin E, both known to act in early cell cycle stage, was approximately on the same level in all groups of lymphoid pathology examined. In particular, we found that that 19 out of 24 CLL cases were cyclin E positive and all but one were cdk4 positive, ie they expressed these markers over twice the level of non-stimulated healthy PBL. The cdk1 expression was above the level seen in NS-PBL in 14 (56%) cases, but the average expression was significantly lower than in the other tissues examined, including low-grade lymphomas. Cdk2 expression was comparable in CLL and in low malignancy grade NHL, but weaker than in other NHL and in NLT. Cyclins A and B, normally observed in advanced cell cycle phases, were not seen in any CLL case. The presence of cdk4 and cyclin E in the blood cells of the majority of CLL cases studied, as well as cdk1 and cdk2 in some cases, indicate that the CLL cells are not quiescent, but are blocked in an early stage of the G1 cell cycle phase, and/or that the expression of these proteins is pathologically deregulated.

Cdk1 is a marker of proliferation in human lymphoid cells

To better understand the relationship between the proliferation of human lymphoid cells and the expression of cdk1, a catalytic subunit of the histone H1 kinase (H1K), we examined its mRNA and protein content in 3 B-cell lines: Ramos, Reh-6 and IARC 963. Cells were elutriated according to their position in the cell cycle. Cell fractions were analyzed for cdk1 mRNA and protein cellular content by Northern blot and immunoblot, respectively, as well as for H1K activity. Both mRNA and protein amounts and H1K activity varied according to cell cycle phase, the lowest values being observed in G1-enriched fractions. For comparison, elutriated fractions were also tested for the expression of cdk2 and cdk4 proteins. Both showed some variations among fractions, but they were less clear than those of cdk1. We also tested 29 samples of lymphoid neoplastic and non-neoplastic tissues for proliferative activity (percentage of S and G2/M cells estimated by flow cytometry) and expression of cdk1, cdk2 and cdk4 proteins. We found a significant correlation between the percentage of cells in S or S + G2/M phases and cdk1 protein content but not cdk2 or cdk4 content. We conclude that cdk1 expression in human lymphoid cells varies during the cell cycle at both mRNA and protein levels.

Heterogeneity of t(1;19)(q23;p13) acute leukaemias. French Haematological Cytology Group

The t(1;19)(q23;p13) translocation occurs commonly in B-lineage ALL. Previous reports have demonstrated a predominance of cases with expression of cytoplasmic Ig mu (C mu+), and FAB L1/L2 phenotype, a poor prognosis and expression of a fusion transcript involving the E2A and PBX1 genes in C mu+ but not in C mu- cases. Of 38 patients with karyotypically proven t(1;19) (q23;p13) leukaemias, we extensively analysed 18 patients with acute leukaemia including 16 B-lineage ALLs, one T-ALL and one AML M4. The AML was associated with a classic E2A-PBX1 fusion transcript and may represent the human counterpart of the AMLs induced by E2A-PBX1 retroviral infection of murine marrow progenitors. The T-ALL was E2A-PBX1 negative and neither the E2A nor the LYL-1 genes, both situated at chromosome 19 p13, were rearranged. Of the 16 B-lineage ALLs, four had cytological features resembling an 'L3-like' phenotype classically associated with Burkitt's lymphoma, two at diagnosis and relapse and two exclusively at relapse. E2A-PBX1 fusion transcripts were detected by RT-PCR in all 13 C mu+ patients and in 2/3 C mu- cases. The 'L3-like' phenotype did not correlate with a particular stage of maturation arrest (one sIg+, one C mu+, one C mu-) or type of E2A-PBX1 transcript, but was associated in all cases with a trisomy 8. Translocation, rearrangement, amplification or over-expression of the c-myc gene was not observed in these cases, demonstrating that the apparent association with trisomy 8 is not due to deregulation of this gene. We therefore show that the E2A-PBX1 transcript, although occurring predominantly in C mu+ pre-B ALL, also occurs in C mu- early pre-B ALL, sIg+ B-ALL and even in AML. These results suggest that the stage of maturation arrest, and indirectly the prognosis, are not solely due to the type of fusion transcript associated with the t(1;19).

Rearrangement of CCND1 (BCL1/PRAD1) 3' untranslated region in mantle-cell lymphomas and t(11q13)-associated leukemias

Rearrangement and overexpression of CCND1 (BCL1/PRAD1), a member of the cyclin G1 gene family, are consistent features of t(11q13)-bearing B-lymphoid tumors (particularly mantle-cell lymphoma [MCL]). Its deregulation is thought to perturb the G1-S transition of the cell cycle and thereby to contribute to tumor development. As suggested by previously published studies, rearrangement of the 3' untranslated region (3' UTR) of CCND1 may contribute to its activation in some lymphoid tumors. To define further the prevalence of such rearrangements, we report here the result of the molecular study of 34 MCL and six t(11q13)-associated leukemias using a set of probes specific to the different parts of the CCND1 transcript. We also sequenced the entire cDNA of the overexpressed CCND1 transcripts in a t(11q13)-associated leukemia. DNA from four of these 40 patients showed rearrangement of the 3' UTR of CCND1 coexisting with major translocation cluster (MTC) rearrangement. Southern blot and sequence analyses showed that, as a result of these rearrangements, the 3' AU-rich region containing sequences involved in mRNA stability and in translational control is eliminated. Moreover, the finding that the CCND1 mRNA half-life was greater than 3 hours (normal tissues, 0.5 hours) in three t(11q13)-associated cell lines stresses the importance of posttranscriptional derangement in the activation of CCND1. Finally, we did not observe any mutation in the coding frame of the CCND1 cDNA analyzed.

Detection of the chromosomal translocation t(11;14) by polymerase chain reaction in mantle cell lymphomas

The t(11;14)(q13;q32) and its molecular counterpart, BCL1 rearrangement, are consistent features of mantle cell lymphoma (MCL). Rearrangement is thought to deregulate the nearby CCND1 (BCL1/PRAD1) proto-oncogene, a member of the cyclin G1 gene family, and thereby to contribute to tumorigenesis. We and others have previously shown that the BCL1 locus is rearranged in 55% to 60% of MCL patients and that, on chromosome 11, more than 80% of the breakpoints are localized within a 1-kbp DNA segment known as the major translocation cluster (MTC). We have determined the nucleotide sequence for a portion of the MTC region, and constructed chromosome 11-specific oligonucleotides that were in conjunction with a consensus immunoglobulin (Ig) heavy chain joining region (JH) primer used to perform the polymerase chain reaction (PCR) to amplify t(11;14) chromosomal junctional sequences in DNA from 16 MCL patients with breakpoints in the MTC region. 15 of the 16 breakpoints that occurred at the MTC region were amenable to PCR detection. The sizes of the amplified bands, the existence or not of a Sac I site in the PCR products, and nucleotide sequencing of the amplified DNA from four patients showed that the breakpoints share a remarkable tendency to tightly cluster within 300 bp on chromosome 11, some of them occurring at the same nucleotide. On chromosome 14, the breakpoints were localized within the Ig JH. Our findings indicate that a BCL1 rearrangement can be detected using this approach in roughly one half of the MCL patients. This has implications for both the diagnosis and the clinical management of MCL.

Localization of two tyrosine kinase receptor genes with respect to the 5q35 chromosomal breakpoint of Ki-1 lymphoma cell lines

The consistency of the breakpoint on chromosome 5 at band 5q35 occurring in Ki-1 non-Hodgkin's lymphomas is highly suggestive of the involvement of a locally altered gene in this disease. In this study, we analyzed the potential involvement, in the translocation, of two receptor tyrosine kinase genes and putative oncogenes, FLT4 and FGFR4, previously localized near this breakpoint. Fluorescence in situ chromosomal hybridization allowed us to refine their localization to sub-band 5q35.3 and to show that both genes are translocated to the derivative chromosomes in Ki-1 cell lines containing either a t(2;5) or a t(3;5). Pulsed-field gel electrophoresis showed that the FLT4 and FGFR4 genes are not physically linked, nor are they altered by the translocation. Finally, Northern blot analysis showed that neither FLT4 nor FGFR4 is expressed in the Ki-1 cell lines, suggesting that they are not implicated in the genesis of Ki-1 lymphomas.

Rearrangement and overexpression of the BCL-1/PRAD-1 gene in intermediate lymphocytic lymphomas and in t(11q13)-bearing leukemias

The t(11;14)(q13;q32) translocation and its molecular counterpart, BCL-1 rearrangement, are consistent features of intermediate lymphocytic lymphoma (ILL). Rearrangement is thought to deregulate the nearby PRAD-1/BCL-1 proto-oncogene that is a newly identified member of the cyclin family. To characterize further the association between rearrangement of chromosome 11q13 and over-expression of BCL-1. Southern blot analysis was performed in 33 cases of ILL, 5 cases of t(11;14)-associated leukemias, and 1 case of leukemia carrying a variant translocation t(11;19)(q13;q13) using three separate BCL-1 locus probes. When RNA was available, BCL-1 expression was assessed by Northern blot analysis. DNA from 19 of 33 ILL (57%) showed BCL-1 rearrangement, 16 involving the major translocation cluster (MTC) region and 3 involving a new breakpoint cluster located in the 5' flanking region of the BCL-1 gene. DNA from 3 of 6 t(11q13)-associated leukemias demonstrated a rearrangement involving the MTC. Northern blot analysis showed that BCL-1 was overexpressed in 14 of 15 ILL and in all leukemias analyzed (included the t(11;19) leukemia) relative to normal and malignant lymphoid tissues. These results constitute additional elements in favor of the role of BCL-1 in lymphoid neoplasia and allow us to speculate about its mechanisms of activation.

FVT-1, a novel human transcription unit affected by variant translocation t(2;18)(p11;q21) of follicular lymphoma

Variant t(2;18) and t(18;22) chromosome translocations observed in B-cell chronic lymphocytic leukemias and in follicular lymphomas have been reported to consistently involve the 5' region of the BCL-2 gene on chromosome 18 and various regions on the lg light chain loci. We show here that a variant t(2;18)(p11;q21) translocation observed in a case of follicular lymphoma leads to the juxtaposition of a J kappa segment to a chromosome 18 transcriptional unit located 10 kpb upstream of the BCL-2 locus. The cDNA of this new evolutionarily conserved gene, termed FVT-1 for follicular-variant-translocation gene, codes for a putatively secreted protein of 36 Kd that is not homologous with any described protein. The FVT-1 gene is weakly expressed in all the analyzed normal hematopoietic tissues but a very high rate of transcription is observed in some T-cell malignancies and in phytohemagglutinin-stimulated lymphocytes. The proximity of FVT-1 to the BCL-2 locus suggests that in the t(14;18) currently observed in follicular lymphomas, both genes would participate in the tumoral process.

Prevalent skipping of an individual exon accounts for shortened protein 4.1 Presles

An asymptomatic shortened variant of protein 4.1 (-8.5 Kd) was first recognized in the red blood cells and designated protein 4.1 Presles. We show here that the missing segment belongs to the 22/24 Kd domain. Protein 4.1 cDNA from reticulocytes was amplified, mapped, and sequenced. The truncation appeared to result from the prevalent skipping of an individual and alternatively spliced exon, also called motif II, whereas this motif is preferentially retained under normal conditions. The same phenomenon was observed in lympho-blastoid cells. Sequencing over 80 bp of intronic sequences 5' and 3' of motif II failed to reveal any change. A new alternative splice site was incidently found 81 nucleotide downstream of motif II in both normal and truncated 4.1 mRNA.

t(2;18) and t(18;22) variant chromosomal translocations in B cell malignancies

Variant translocations (2;18 and 18;22) are described in this review. The chromosomal and molecular findings of these translocation of BCL2 and their effect on possible BCL2 gene activation is discussed. Unanswered questions still remain and these include why this is so rare compared to the 25% incidence recorded for translocations in Burkitt's lymphoma. Further studies are obviously still needed in order to determine the true frequency of these findings and their distribution in the various B-cell disorders.

BTG1, a member of a new family of antiproliferative genes

The BTG1 gene locus has been shown to be involved in a t(8;12)(q24;q22) chromosomal translocation in a case of B-cell chronic lymphocytic leukemia. We report here the cloning and sequencing of the human BTG1 cDNA and establish the genomic organization of this gene. The full-length cDNA isolated from a lymphoblastoid cell line contains an open reading frame of 171 amino acids. BTG1 expression is maximal in the G0/G1 phases of the cell cycle and is down-regulated when cells progress throughout G1. Furthermore, transfection experiments of NIH3T3 cells indicate that BTG1 negatively regulates cell proliferation. The BTG1 open reading frame is 60% homologous to PC3, an immediate early gene induced by nerve growth factor in rat PC12 cells. Sequence and Northern blot analyses indicate that BTG1 and PC3 are not cognate genes. We then postulate that these two genes are the first members of a new family of antiproliferative genes.

Isolation and mapping of a polymorphic DNA sequence (R7) on chromosome 12 (D12S52)

Images

A chromosome 12 coding region is juxtaposed to the MYC protooncogene locus in a t(8;12)(q24;q22) translocation in a case of B-cell chronic lymphocytic leukemia

We performed molecular cloning and sequencing of the breakpoints of a new chromosomal translocation involving the MYC protooncogene locus. This secondary t(8;12)(q24;q22) was associated with a primary t(11;14)(q13;q32) translocation in a case of B-cell chronic lymphocytic leukemia (CLL) in blastic transformation. In this leukemia, Northern blot and nuclease analyses SI showed that MYC was strongly expressed with initiation of the transcription at both the 5' and 3' promoters as observed in Burkitt's lymphomas; no coding change was observed in MYC putative regulatory sequences. The breakpoint on chromosome 8 mapped to the 3' end of the MYC locus, in a region containing a potential Z-DNA tract, and where we identified two DNase 1 hypersensitive sites. A rearranged MYC gene fragment was cloned and shown to contain chromosome 12 information by Southern blot analysis and by in situ hybridization. A genomic probe subcloned from the isolated region of the chromosome 12 recognized a 1.8 kb transcript in virtually all the tissues tested but a preferential expression of this new gene, which we termed BTG1 (for B-cell translocation gene 1) was observed in the CLL cells and in tissues of lymphoid origin. This chromosome 12 coding sequence is conserved in evolution and a transcript of similar size is present in murine tissues.

Break in the BCL1 locus is closely associated with intermediate lymphocytic lymphoma subtype

The t(11;14)(q13;q32) is a recurring translocation associated with some chronic B-cell lymphocytic malignancies; the putative protooncogene BCL1, located at the chromosome band 11q13, can be involved during the translocation process. In order to determine if BCL1 rearrangement is associated with a particular subtype of lymphoma, we analysed 131 B-cell non-Hodgkin's lymphoma samples by Southern blot analysis, using a BCL1 probe. The BCL1 locus was rearranged in 9 out of 25 (36%) cases of intermediate lymphocytic cell lymphomas (ILL), in 1 out of 8 cases of diffuse small cleaved cell lymphoma, in 1 out of 12 cases of diffuse mixed cell lymphoma, and in 1 out of 21 cases of diffuse large cell lymphoma. In contrast, BCL1 was never found rearranged in any of the 46 follicular lymphomas analysed. The BCL2 gene was in germ-line configuration in all ILL. Sequential hybridization of Southern blots with JH, C mu, and BCLI probes identified comigrating fragments in only one case of ILL, which suggests that, in all the other cases, either the rearrangement of BCL1 did not result from a t(11;14) translocation or the break on chromosome 14 occurred outside the JH or C mu regions. These results indicate that rearrangement of the BCL1 locus may be closely associated with ILL and could be considered as a genotypic marker of this lymphoma subtype.

CD30-positive large cell lymphomas ('Ki-1 lymphoma') are associated with a chromosomal translocation involving 5q35

A chromosomal translocation involving a breakpoint on the long arm of chromosome 5 at position q35 has been reported previously in 17 cases of neoplasia. In 14 of these cases the translocation involves exchange of material between chromosome 2 p23 and chromosome 5. Most cases had been diagnosed histologically as malignant histiocytosis but it was suggested recently, following the study of three cases in one of the author's laboratories, that such tumours are in reality lymphoid tumours. In the present paper we report on 12 further neoplasms with a translocation involving the 5q35 breakpoint and show that all were large cell lymphomas expressing the CD30 (Ki-1) antigen, often classifiable histologically as 'Ki-1 lymphoma'. In five cases there was evidence, based on antigen expression and/or genotypic studies, that the neoplasm was of T lymphoid derivation. These findings provide further evidence that translocations involving 5q35 are associated not with histiocytic malignancy, but with large cell lymphoid neoplasms, including typical cases of 'Ki-1 lymphoma' or 'anaplastic large cell lymphoma'. Since cell lines have been established from five of these cases it may be possible in the future to clone the breakpoint on chromosome 5 and to investigate whether there is a gene in its vicinity with oncogenic potential.

Double immunocytochemical labeling of cell and tissue samples with monoclonal anti-bromodeoxyuridine

We describe a new monoclonal antibody (designated Bu20a) against bromodeoxyuridine (BrdU). This antibody was selected by screening against human tissues using the APAAP technique, and shows no crossreactivity with normal nuclei. It stains BrdU incorporated into the nuclei of a wide range of cell types, including human tonsil lymphoid cells, normal mouse tissues, and human tumors growing in nude mice. A double-labeling technique is described using this antibody in which cell smears or tissue sections are first labeled by an immunoperoxidase procedure for a cellular antigen (e.g., mouse or human histocompatibility class II antigen, T-lymphocyte antigen, keratin) and BrdU is then detected by indirect immunofluorescence. This procedure, which was applied to a variety of human and animal cells and tissues, is of wide potential value in analyzing the phenotype of S-phase cells and in co-localizing antigen expression and BrdU incorporation in tissue sections.

Isolation and mapping of a polymorphic DNA sequence (pB3.811) on chromosome 12 [D12S33]

Images

A translocation involving a specific breakpoint (q35) on chromosome 5 is characteristic of anaplastic large cell lymphoma ('Ki-1 lymphoma')

Two cases of non-Hodgkin's lymphoma are reported in which a chromosomal translocation was observed involving the same site (q35) on the long arm of chromosome 5. The other breakpoint involved in the translocation was chromosome 2 (p23) in one case and chromosome 3 (q12) in the other. Both cases were large cell lymphomas expressing CD30 antigen ('Ki-1 lymphoma'). One was clearly of T lymphoid origin, the other probably B cell derived. One other case of a Ki-1 lymphoma with 2;5 translocation (involving the same breakpoint on chromosome 5) has been reported previously, and it is suggested that this cytogenetic abnormality may be specifically associated with Ki-1 lymphoma. The literature contains a further eight cases of lymphoid neoplasms with a translocation involving a breakpoint at q35 on chromosome 5. They have all been described as cases of 'malignant histiocytosis', but the present findings make it likely that these cases were in reality also examples of Ki-1 lymphoma. The breakpoint at the q35 region on chromosome 5 is close to the position of the fms proto-oncogene, suggesting that an abnormality affecting this gene might possibly play a causal role in 'Ki-1 lymphoma'. However, DNA restriction fragment analysis of the present cases showed no evidence that the breakpoint on chromosome 5 involves the fms gene or its immediate vicinity.

Initial clonal acute lymphoblastic transformation of chronic lymphocytic leukemia with (11;14) and (8;12) chromosome translocations and acquired homozygosity

A 69-year-old woman presented with chronic lymphocytic leukemia (CLL) diagnosed after bone marrow recovery following intensive chemotherapy for acute lymphoblastic leukemia. The retrospective diagnosis of initial blastic transformation of CLL was made. The patient eventually died, 5 months after initial blastic phase, from a blastic relapse of her CLL. Immunologic and karyotypic studies of the lymphoid cells at different times during the evolution of the disease provided evidence that both the small lymphocytes and the large blastic cells originated from the same clone since they carried the same surface markers and the same (11;14) (q13;q32) translocation. A subpopulation of cells carried in addition a t(8;12) (q24;q22) together with the loss of the normal chromosome 8 and homozygosity for the abnormal der(8). The possibility that this second population might correspond to the blast cells and that the occurrence of the t(8;12) with homozygosity might be linked to blastic transformation of the CLL is discussed.

Chromosomal R-banding with a monoclonal antidouble-stranded DNA antibody

A monoclonal anti-DNA antibody (HB2) specific for poly dG- poly dC nucleotides was used to stain metaphasic lymphocyte or amniotic cell human chromosomes. HB2 fixation was revealed using either a peroxidase- or a rhodamine-labeled anti-mouse immunoglobulin antiserum. The staining pattern of the chromosomes was dependent on the HB2 concentration: R-banding could be observed at high antibody dilution. Previous trypsinization of metaphasic preparations demonstrated a precise and reproducible typical R-banding independent of the HB2 concentration. This technique appears to be an interesting alternative to other R-banding procedures. The specificity of the antibody allows a better understanding of the biochemical mechanism of R-banding.