Deletion of chromosome 13 (band q14) but not trisomy 12 is a clonal event in B-chronic lymphocytic leukaemia (CLL)

RFP2, c13ORF1, and FAM10A4 are the most likely tumor suppressor gene candidates for B-cell chronic lymphocytic leukemia

Occurrence of 13q14 deletions between D13S273 and D13S25 in B-cell chronic lymphocytic leukemia (B-CLL) suggests that the region contains a tumor suppressor gene. We constructed a PAC/cosmid contig largely corresponding to a 380-kb 13q14 YAC insert that we found deleted in a high proportion of B-CLL patients. We found seven genes by exon trapping, cDNA screening and analysis/cDNA extension of known expressed sequence tags. One appeared to originate from another region of 13q. Recent publications have focused on two of the genes that most likely do not have a tumor suppressor role. This study evaluates the remaining four genes in the region by mutation scanning and theoretical analysis of putative encoded products. No mutations suggestive of a pathogenic effect were found. The 13q14 deletions may be a consequence of an inherent instability of the region, an idea supported by our finding of a considerable proportion of AluY repeats. Deletion of putative enhancer sequences and/or genes in the region may result in an inactivation of tumor suppression by a haploinsufficiency mechanism. We conclude that RFP2, c13ORF1, and a chromosome 13-specific ST13-like gene, FAM10A4, are the most likely candidates for such a type of B-CLL TSG.

B-chronic lymphocytic leukemia: practical aspects

B-CLL is the most common adult leukemia in the Western world. It is a neoplasia of mature looking B-monoclonal lymphocytes co-expressing the CD5 antigen (involving the blood, the bone marrow, the lymph nodes and related organs). Much new information about the nature of the neoplastic cells, including chromosomal and molecular changes as well as mechanisms participating in the survival of the leukemic clone have been published recently, in an attempt to elucidate the biology of the disease and identify prognostic subgroups. For the time being, clinical stage based on Rai and Binet staging systems remains the strongest predictor of prognosis and patients' survival, and therefore it affects treatment decisions. In the early stages treatment may be delayed until progression. When treatment is necessary according to well-established criteria, there are nowadays many different options. Chlorambucil has been the standard regimen for many years. During the last decade novel modalities have been tried with the emphasis on fludarabine and 2-chlorodeoxyadenosine and their combinations with other drugs. Such an approach offers greater probability of a durable complete remission but no effect on overall survival has been clearly proven so far. Other modalities, included in the therapeutic armamentarium, are monoclonal antibodies, stem cell transplantation (autologous or allogeneic) and new experimental drugs. Supportive care is an important part of patient management and it involves restoring hypogammaglobulinemia and disease-related anemia by polyvalent immunoglobulin administration and erythropoietin respectively.

Deletion analysis of chromosome 13q14.3 and characterisation of an alternative splice form of LEU1 in B cell chronic lymphocytic leukemia

Heterozygous and homozygous deletions of chromosome 13q14.3 are found in 50% of patients with B cell CLL, suggesting the presence of one or more tumour suppressor genes within the deleted region. To identify candidate genes from the region, we constructed a map of 13q14.3 using a combination of genomic and cDNA library screening. The incidence of deletions in CLL patients was 51.5% encompassing a 265 kb region of minimal deletion (RMD) telomeric to markers D13S319. Two CpG islands were identified within the RMD, the telomeric of which is fully methylated whilst the more centromeric is unmethylated. A novel transcript was identified within the RMD that represents an alternative splice version of Leu1. The nine exons of this transcript span a genomic of 436 kb with exon 1 of Leu1 being the common first exon. The remaining exons were shown to be more frequently deleted than Leu1 itself. All splice forms of this transcript were detectable by RT-PCR but Leu1 detected the most abundant message on Northern blotting. Sequence analysis failed to reveal inactivating mutations in patients with heterozygous deletion of 13q14.3, although a polymorphic T to A variant was identified within exon 1 of Leu1 in leukemic and normal controls. As no mutations have been detected for Leu1 or any other transcript so far described, we cannot exclude the existence of control elements within the RMD that may regulate expression of genes lying in this region.

Cytogenetic findings in lymphoplasmacytic lymphoma/Waldenström macroglobulinemia. Chromosomal abnormalities are associated with the polymorphous subtype and an aggressive clinical course

We correlated bone marrow cytogenetic findings with morphologic and immunophenotypic data in 37 patients with lymphoplasmacytic lymphoma (LPL)/Waldenström macroglobulinemia (WM). Each LPL/WM case was classified as lymphoplasmacytoid (n = 18), lymphoplasmacytic (n = 10), or polymorphous (n = 9) using the Kiel criteria. Of 12 cases with chromosomal abnormalities, a single numeric abnormality was present in 4 and a complex karyotype in 8. The most common numeric abnormalities were and -8 in 3 cases each; the most common structural abnormality was del(6q) in 6 cases. Cytogenetic abnormalities were significantly less common in the lymphoplasmacytic and lymphoplasmacytoid groups (5/28 [18%]) compared with the polymorphous group (7/9 [78%]). Clinical follow-up was available for 28 patients for a median of 36 months. Six (67%) of 9 patients with aneuploid tumors, including 4 with polymorphous subtype, subsequently had clinical progression or developed high-grade lymphoma. In contrast, 4 (21%) of 19 patients with diploid tumors, including 1 of polymorphous type, developed clinical progression or high-grade lymphoma. We conclude that abnormal cytogenetic findings in LPL/WM correlate with the polymorphous subtype and poor prognosis.

Aberrant B cell receptor signaling from B29 (Igbeta, CD79b) gene mutations of chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) B cells characteristically exhibit low or undetectable surface B cell receptor (BCR) and diminished responses to BCR-mediated signaling. These features suggest that CLL cells may have sustained mutations affecting one or more of the BCR proteins required for receptor surface assembly and signal transduction. Loss of expression and mutations in the critical BCR protein B29 (Igbeta, CD79b), are prevalent in CLL and could produce the hallmark features of these leukemic B cells. Because patient CLL cells are intractable to manipulation, we developed a model system to analyze B29 mutations. Jurkat T cells stably expressing micro, kappa, and mb1 efficiently assembled a functional BCR when infected with recombinant vaccinia virus bearing wild-type B29. In contrast, a B29 CLL mutant protein truncated in the transmembrane domain did not associate with mu or mb1 at the cell surface. Another B29 CLL mutant lacking the C-terminal immunoreceptor tyrosine activation motif tyrosine and distal residues brought the receptor to the surface as well as wild-type B29 but showed significant impairment in anti-IgM-stimulated signaling events including mitogen-activated protein kinase activation. These findings demonstrate that B29 mutations previously identified in CLL patients can affect BCR-dependent signaling and may contribute to the unresponsive B cell phenotype in CLL. Finally, the features of the B29 mutations in CLL predict that they may be generated by somatic hypermutation.

Prognostic relevance of monosomy at the 13q14 locus detected by fluorescence in situ hybridization in B-cell chronic lymphocytic leukemia

Deletion of the chromosome band 13q14, which contains the putative deleted in B-cell malignancy (DBM) gene, and trisomy 12 have been demonstrated by fluorescence in situ hybridization (FISH) techniques in malignant B-cells from patients with B cell chronic lymphocytic leukemia (B-CLL). However, the prognostic relevance of 13q14 abnormalities as detected by FISH is unknown. We prospectively studied malignant blood cells from 54 consecutive, untreated B-CLL patients using FISH probes to the RB1 locus and DBM (markers D13S25 and D13S319) for band 13q14, as well as probes to chromosome 12. The cells from all cases were CD5+ CD20+, expressed clonally restricted surface immunoglobulin light chain, and had typical features for B-CLL on careful blood smear morphologic evaluation. Patients were followed for a mean of 3.9 years and treatment-free survival (TFS) was used in the prognostic factor analysis. Twenty-four (44%) patients were observed to have monosomy of the RB1 locus and 26 (48%) monosomy of D13S25 and D13S319. The 26 patients who had a deletion at at least one of these loci had a 48.4 month (mo) median TFS vs 31.1 mo for those without evidence of deletion at any 13q14 locus (p = 0.07). The seven patients found to have trisomy 12 had a median TFS of 6.9 mo vs 39.3 mo for those diploid for chromosome 12 (p < 0.01). When these seven patients with trisomy 12 were excluded from the analysis, patients who had a deletion at 13q14 tended to have a longer median TFS (50.1 vs 36.2 mos), but this was not statistically significant (p = 0.2). This study confirms the prevalence of 13q14 deletions in B-CLL and suggests that patients with this abnormality have a better TFS than those with trisomy 12.

Secondary abnormalities of chromosome 6q in B-cell chronic lymphocytic leukemia: a sequential study of karyotypic instability in 51 patients

Although karyotypic abnormalities are well documented in B-cell chronic lymphocytic leukemia (B-CLL), few sequential cytogenetic studies have been done. In this study, peripheral blood lymphocytes from fifty-one patients with B-CLL were sequentially karyotyped over a mean interval of 13.8 months (range, one to 51 months). Cytogenetic clones were detected in 33/51 patients (66%) on initial study, including 17 patients with structural abnormalities of chromosome 13q14, and three patients with trisomy 12. Karyotypic evolution was documented in 22/51 patients (43%). The most common secondarily acquired chromosome aberrations were structural abnormalities of the long arm of chromosome 6 involving the region of 6q21-q24 (six patients). Four patients each had acquired structural abnormalities of 1q, 3p, 12q, and 13q. Disease progression, as measured by advance in Rai stage or death from the disease, was observed more often in the clonal evolution group than in the karyotypically stable group (11/22 vs. 5/29; P = 0.017). Patients with secondary abnormalities of 6q had a significantly decreased progression-free survival interval compared with other patients in the study (P = .023). The authors conclude that clonal karyotypic evolution is common in B-CLL, and that clonal evolution correlates with clinical disease progression. Furthermore, the poor outcomes previously attributed to CLL with 6q abnormalities may be related to the clonal acquisition of these abnormalities over time. Future studies should focus on the relevant genetic events underlying the clinical progression observed with karyotypic evolution of B-CLL.

Trisomy 12 is seen within a specific subtype of B-cell chronic lymphoproliferative disease affecting the peripheral blood/bone marrow and co-segregates with elevated expression of CD11a

In order to delineate the specific morphological and immunophenotypic features of B-cell lymphoproliferative disorders associated with trisomy 12, 172 sequential unselected cases of CD19+CD5+ B-cell disorders, primarily affecting the peripheral blood and bone marrow, were studied. Trisomy 12 was found in 24 cases (13.9%), with all cases morphologically classified as either CLL-PL or CLL-mixed by FAB criteria. Trisomy 12 was not found in any cases of typical CLL. Trisomy 12 cases demonstrated a significant higher expression of CD11a (P<0.0001) and CD20 (P<0.0006) when compared to cases with the equivalent morphology and immunophenotype, but without the chromosomal abnormality. Trisomy 12 cases also demonstrated a higher frequency of FMC7, CD38 expression and moderate to strong surface immunoglobulin staining. However, no correlation was detected between the percentages of trisomy 12 cells and cells expressing CD11a, CD38, FMC7 or sIg mean fluorescent intensity. Cells from trisomy 12 positive cases were sorted according to their CD11a expression using fluorescent activated cell sorting. There was a significant increase in the percentage of trisomy 12 cells within the CD11a+ sorted fraction compared to the unsorted population (P < 0.05), implying that trisomy 12 is associated with increased expression of CD11a. With the highly specific morphological and immunophenotypic features demonstrated by trisomy 12 cases in this study, it is highly likely that these cases constitute a specific group of B-cell lymphoproliferative disorders.

Detailed Molecular Delineation of 13q14.3 Loss in B-Cell Chronic Lymphocytic Leukemia

A region of chromosome 13q14.3, telomeric to the Retinoblastoma gene RB-1 is frequently deleted in patients with B-cell chronic lymphocytic leukemia (B-CLL). A cosmid and P1-derived artificial chromosome (PAC) contig spanning over 600 kb has been constructed, which encompasses this locus. The contig clones have been used to order a number of markers along the minimally deleted region and to localize a series of CpG islands corresponding to possible candidate genes. A novel polymorphic dinucleotide repeat, 6E3.2, present in one of the ordered cosmid clones has been isolated for use in deletion mapping studies of patient DNA. Leukemic samples from 229 CLL patients have been screened for loss of heterozygosity using microsatellite markers and analyzed for hemizygous and homozygous deletions by Southern blot techniques using genomic probes selected from cosmids across the region. Hemizygous deletions were found in 31% of cases with an additional 10% showing homozygous loss. The use of these probes has defined the commonly deleted area to less than 130 kb, centromeric to the locus D13S272.

In B-cell chronic lymphocytic leukaemia chromosome 17 abnormalities and not trisomy 12 are the single most important cytogenetic abnormalities for the prognosis: a cytogenetic and immunophenotypic study of 480 unselected newly diagnosed patients

Of 560 consecutive, newly diagnosed untreated patients with B CLL submitted for chromosome study, G-banded karyotypes could be obtained in 480 cases (86%). Of these, 345 (72%) had normal karyotypes and 135 (28%) had clonal chromosome abnormalities: trisomy 12 (+12) was found in 40 cases, 20 as +12 alone (+12single), 20 as +12 with additional abnormalities (+12complex). Other frequent findings included abnormalities of 14q, chromosome 17, 13q and 6q. The immunophenotype was typical for CLL in 358 patients (CD5+, Slg(weak), mainly FMC7-) and atypical for CLL in 122 patients (25%) (CD5-, or Slg(strong) or FMC7+). Chromosome abnormalities were found significantly more often in patients with atypical (48%) than in patients with typical CLL phenotype (22%) (P < 0.00005). Also +12complex, 14q+, del6q, and abnormalities of chromosome 17 were significantly more frequent in patients with atypical CLL phenotype, whereas +12single was found equally often in patients with typical and atypical CLL phenotype. The cytomorphology of most of the +12 patients was that of classical CLL irrespective of phenotype. In univariate survival analysis the following cytogenetic findings were significantly correlated to a poor prognosis: chromosome 17 abnormalities, 14q+, an abnormal karyotype, +12complex, more than one cytogenetic event, and the relative number of abnormal mitoses. In multivariate survival analysis chromosome 17 abnormalities were the only cytogenetic findings with independent prognostic value irrespective of immunophenotype. We conclude that in patients with typical CLL immunophenotype, chromosome abnormalities are somewhat less frequent at the time of diagnosis than hitherto believed. +12single is compatible with classical CLL, and has no prognostic influence whereas chromosome 17 abnormalities signify a poor prognosis. In patients with an atypical CLL immunophenotype, chromosome abnormalities including +12complex, 14q+, del 6q and chromosome 17 are found in about 50% of the patients, and in particular chromosome 17 abnormalities suggest a poor prognosis.

Cloning and gene mapping of the chromosome 13q14 region deleted in chronic lymphocytic leukemia

Frequent deletions and loss of heterozygosity in a segment of chromosome 13 (13q14) in cases of B-cell chronic lymphocytic leukemia (CLL) have suggested that this malignancy is caused by inactivation of an unknown tumor suppressor gene located in this region. Toward the identification of the putative CLL tumor suppressor, we have constructed a high-resolution physical map of YAC, PAC, and cosmid contigs covering 600 kb of the 13q14 genomic region. In addition to densely positioned genetic markers and STSs, this map was further annotated by localization of 32 transcribed sequences (ESTs) using a combination of exon trapping, direct cDNA selection, sample sequencing of cosmids and PACs, and homology searches. On the basis of these mapping data, allelic loss analyses at 13q14 using CLL tumor samples allowed narrowing of the genomic segment encompassing the putative CLL gene to <300 kb. Twenty-three ESTs located within this minimally deleted region are candidate exons for the CLL-associated tumor suppressor gene.

Interphase cytogenetics in chronic lymphocytic leukemia

The incidence of trisomy 12 and 13q12-q14 abnormalities in patients with chronic lymphocytic leukemia (CLL) was determined by conventional cytogenetics and interphase fluorescence in situ hybridization (FISH). In the analysis of 580 consecutive patients, trisomy 12 was detected by conventional cytogenetics in 39 cases (9%) and 117 cases (20%) by FISH. Trisomy 12 was shown to be associated with advanced clinical stage, atypical morphology, and higher proliferative activity. Combined immunophenotyping and FISH showed that trisomy 12 was present only in a proportion of the clonal B-cells. These data suggest that trisomy 12 is a secondary event associated with features of disease progression. Sequential FISH showed clonal progression of the trisomic clone over time. Three hundred patients also were investigated for 13q deletions using FISH analysis of the RB1 locus (13q14). Monoallelic RB1 deletion was seen in 104 (34%) of cases. One case had a homozygous deletion in 90% of the cells. Dual-color FISH detected the presence of trisomy 12 and RB1 in 17 (5%) cases. DNA probes for 13q12.3 (BRCA2) and 13q14 (RB1 and DBM locus) were used in 35 cases. Twenty-eight (80%) cases showed deletion of a 1Mb 13q12.3 encompassing the BRCA2 locus, whereas 22/35 (63%) were deleted at 13q14. Our data suggest that abnormalities of 13q are more frequent than trisomy 12 in CLL and provide evidence for the presence of a new candidate gene at 13q12.3 that may be involved in the pathogenesis of CLL.

Genes and chromosomes in chronic B-cell leukemia

Cytogenetic analysis of patients with chronic B-cell leukemia (B-CLL) indicates that 50% have chromosome abnormalities, while fluorescence in situ hybridization (FISH) and molecular techniques reveal an even higher incidence. Trisomy 12 and deletions or translocation of chromosome 13q14 are the most common abnormalities, but in neither case has the gene or genes involved in the abnormalities been identified. Combined FISH and immunophenotyping studies suggest that both abnormalities are secondary events in B-CLL. Other recurring chromosome abnormalities include 6q-, 11q- and 12p-, but the genes involved in these abnormalities have not been identified. Involvement of the BCL1, BCL2, and BCL3 genes has been reported, but the numbers are low and the cases tend to be atypical. Trisomy 12 in association with complex karyotypic abnormalities is associated with a poor prognosis, and FISH studies show a strong correlation between trisomy 12, atypical morphology, and advanced disease. Ten to 15% of patients have mutations of p53 which is associated with advanced disease, resistance to treatment, and poor survival.

Cytogenetic findings in 175 patients indicate that items of the Kiel classification should not be disregarded in the REAL classification of lymphoid neoplasms

Cytogenetics have proved to be a valuable tool for classifying systemic lymphatic neoplasms, as this technique allows different stem line aberrations and clonal developments to be distinguished. This study was designed to analyze how far groups defined according to common cytogenetic features correlated with their position in either the Kiel (KC) or the REAL classification. Cytogenetic analyses were performed on material from 175 patients with lymphoid neoplasms (LN). Samples were prepared from peripheral blood and bone marrow in acute lymphoblastic leukemia (ALL), from bone marrow in multiple myeloma (MM), and from lymph node biopsies in lymphomas. The results of this study support the inclusion of ALL, MM, and extranodal lymphomas into a comprehensive classification, because their chromosomal aberrations were always characteristic for LN. From the cytogenetic point of view, a subgroup of ALL appears as a leukemic manifestation of lymphoblastic lymphoma. MM have structural aberrations of chromosomes 1, 11, and 14 and secondary aberrations of chromosomes 3, 6, 7, 12, 13, and 18, all of which are characteristic for lymphatic disease. The groups with follicle center cell lymphoma and mantle cell lymphoma correlate well with our results both in the low-grade subtype and in the blastic variant type, the majority of cases demonstrating t(14; 18) and its variants and t(11; 14), respectively. In contrast, the group of diffuse large B-cell (DLB) lymphomas proved to be heterogeneous on the basis of our cytogenetic results. Accordingly, we would suggest keeping the immunoblastic lymphoma (IB) subtype defined by the KC. IB demonstrates no stem line aberration in common with any other group and seems to be characterized by stem line aberrations involving chromosomes 3 and 6. As some DLB lymphomas have a t(14;18) or variant translocations involving chromosome 18, they should either be separated as a subgroup or included into the group of follicle center lymphomas.