B-CLL
Hematological Malignacy

B CELL CHRONIC LYMPOCYTIC LEUKEMIA (B CLL)

DEFINITION

A chronic leukemia characterized by abnormal B-lymphocytes and often generalized lymphadenopathy. In patients presenting predominately with blood and bone marrow involvement it is called chronic lymphocytic leukemia (CLL); in those predominately with enlarged lymph nodes it is called small lymphocytic lymphoma. These terms represent spectrums of the same disease.

B cell chronic leukemia (B-CLL) is a monoclonal disorder. It is characterized by the relentless accumulation in the blood, marrow and lymphoid tissues of mature monoclonal B lymphocytes that express the CD5 surface molecule. The leukemic CLL B cell accumulation appears to be a result of defective apoptosis rather than uncontrolled proliferation.

EPIDEMIOLOGY

It is the most common leukemia in the western world and it represent 25-35% of all human leukemia. This disease:

• has an incidence higher in males than in females, with a male-to-female ratio of 1.7:1.
• primarily affects olderly individuals, with the majority of cases reported in individuals older than 50 years.

SYMPTOMS

The symptoms usually develop gradually. Early in the disease, B CLL generally has little effect on a person’s well being. It may only be discovered after an abnormal blood count shows up during the course of a routine medical exam or while a person is being treated for an unrelated condition. Some signs and symptoms of B CLL include: tiring more easily, shortness of breath during normal activities, swollen lymph nodes or spleen, infections, weight loss, pressure under the left ribs from enlargement of the spleen, bone pain, unusual bleeding. Some patients may also have other symptoms, such as aches, fever or night sweats, overall itching, side pain, and lumps in the armpit.

PATHOGENESIS

The clinical outcome of B-CLL is very variable: some patients experience a very stable condition and never require treatment, whereas others become symptomatic very quickly and soon require cytostatic therapies. Therefore, although the median overall survival of CLL patients is 10 years, individual patients present extremely heterogeneous prognosis that can vary from a very short to a normal life span.

Prognostic Markers

• The mutational status of immunoglobulin genes (IgVH) expressed in the leukemic population has been identified as a very good prognostic marker of CLL clinical outcome. ** The mutated CLL cases (≥2%) have a more favorable prognosis and require less treatment than the unmutated ones. Moreover, in multivariate analyses, the Ig mutational status appears to be the best prognostic marker of clinical outcome with respect to other parameters such as CD38 expression, genomic aberrations or thymidine kinase serum concentration.
• The B-CLL receptor (BCR) is a multimeric complex located on the surface of B cell. The IG glycoprotein is composed by two identical heavy chains (μ, δ, α, γ or ε) and two identical light chains: κ or λ. Both heavy and light chains have two variable regions (IGHV or IGV) that mediates antigen contact and vary extensively between IG, along with a constant region that is responsible for the effector activities. For heavy chain, the variable region is encoded by three gene segments: variable (IGHV), diversity (IGHD) and joining (IGHJ), whereas the variable regions of the light chains are generated from IGV and IGJ segments. Both for heavy and light chains, the segments involved in V(D)J recombination confer diversity by random and imprecise rearrangement during B-cell development in the bone marrow. The consequent protein sequences mainly differ in the complementary-determining-region-3 of the heavy (HCDR3) and light (K/LCDR3) chains. The BCR has always been a key molecule to understanding CLL, initially only due to the surface IG that were utilized to make or support a correct diagnosis. Studies of the molecular structure of the BCR in CLL are suggesting evidences of a promoting role of the antigen encounter. CLL have a biased use of some specific gene segments. For example, a preferential use of IGHV1-69 in the unmutated CLL and IGHV4-34 and IGHV3-23 in the mutated CLL groups. The clusters, of particular clinical interest is a cluster composed by unmutated CLL with stereotyped BCR expressing genes from the IGHV1 gene family other than IGHV1-69. Of particular interest is a group of IGHV3-21 CLL, composed by cases with either unmutated or mutated IGHV genes, that expressed a stereotyped BCR characterized by an unusually short and highly homologous HCDR3 associated with IGLV3-21. Unlike many forms of chronic and acute leukemia, CLL lacks recurrent reciprocal chromosomal translocations and distinctive patterns of oncogene or tumor suppressor gene expression. The most common abnormality is deletion of 13q, which occurs in more than 50% of patients. The pathogenetic role of 13q deletion in CLL is not fully clear. The deleted region always comprises the locus coding for two microRNAs (miRNAs), hsa-mir-16-1 and hsa-mir-15a. mir-16-1 and mir-15a are deleted or downregulated in the majority (about 70%) of CLL. Over-expression of the anti-apoptotic BCL2, due to the reduced negative regulation by mir-16-1 and mir-15a, has been proposed along with other several genes often involved in cell cycle and/or programmed cell death regulation such as MCL1, ETS1 and JUN. The presence of trisomy 12, which is observed in 15% of patients, is associated with atypical morphology and progressive disease. Deletion in the short arm of chromosome 17 has been associated with rapid progression, short remission, and decreased overall survival in chronic lymphocytic leukemia. 17p13 deletions are associated with loss of function of the tumor suppressor gene p53. Deletions of bands 11q22-q23, observed in 19% of patients, are associated with extensive lymph node involvement, aggressive disease, and shorter survival. CD38 is a 45-kDa type II membrane glycoprotein first described as an activation antigen whose expression coincided with discrete stages of human T and B lymphocyte differentiation. CD38 behaves simultaneously as a cell surface enzyme and as a receptor. Engagement of CD38 by its ligand CD31 or by specific agonist antibodies induces activation and differentiation signals in T, B and NK cells. CD38 expression was heterogeneous among CLL cases. By using a given percentage of CLL cells expressing the antigen (30% of positive cells), significant prognostic differences were found by investigating both chemotherapy requirements and overall survival. Zap70 is a cytoplasmic tyrosine kinase whose expression has been associated with a poor prognosis. Cells with germline IgV H often have an increased expression of Zap70; however, studies have shown discordance rates of 10-20% between IgV H mutational status and Zap70 expression levels. Elevated levels of Zap70 are believed to decrease the threshold for signaling through bcl2, thereby facilitating the antiapoptotic effects of bcl2. Zap70 function also appears to be dependent on heat shock protein 90 (hsp90), whose inhibition may provide a future therapeutic option.

Prognostic Factors in B CLL

REFERENCES

Chiorazzi N, Allen SL, Ferrarini M. Clinical and laboratory parameters that define clinically relevant B-CLL subgroups. Curr Top Microbiol Immunol. 2005, 294:109-33

Dal-Bo M., Bertoni F., Forconi F., Zucchetto A., Bomben R., Marasca R., Deaglio S., et al. Intrinsic and extrinsic factors influencing the clinical course of B-cell chronic lymphocytic leukemia: prognostic markers with pathogenetic relevance. J Transl Med. 2009; 7: 76

Damle RN, Wasil T, Fais F, et al. Ig V gene mutation status and CD38 expression as novel prognostic indicators in chronic lymphocytic leukemia. Blood. 1999;94:1840-1847

Rassenti LZ, Jain S, Keating MJ, Wierda WG, Grever MR, Byrd JC, Kay NE et al. Relative value of ZAP-70, CD38, and immunoglobulin mutation status in predicting aggressive disease in chronic lymphocytic leukemia. Blood. 2008 Sep 1;112(5):1923-30. Epub 2008 Jun 24.

Scheda realizzata da Marianna Spunton e Valentina Griggio

A MOUSE MODEL FOR CLL BASED ON EXPRESSION OF THE SV40 LARGE T ANTIGEN

SV40 T antigenis a potent oncogene able to transform many cell types by inactivating p53 and Rb proteins and inducing genomic instability. It has been implicated in the etiology of various cancers. Transgenic expression of the SV40 T gene under the control of the IgH enhancer induced hyperproliferation of the multilineage hematopoiesis, reminiscent of myelodysplastic syndromes in humans. In this report the aim is to accomplish sporadic SV40 T gene expression in the B-cell lineage in mice; they introduced the SV40 T gene without its promoter and in opposite transcriptional orientation between the IgH chain D and JH segments. It is possible that in the mouse model SV40 T is expressed as a part of a large antisense transcript in early pro B-cells that have not yet performed IgH D to JH recombination. In almost pro B-cells the SV40 will be excised during normal IgH D to JH rearrangment. Only in rare B-cells (the non productive targeted allele has a germline configuration and still contains the SV40 T gene) is possible to express the gene in more mature B-cell stages. It is conceivable that V(D)J mediated reinsertion of D- JH circles containing the SV40 T oncogene compromises genomic integrity, leading to tumor formation. The espression of SV40 T antigen is associated with the development of B-cell malignancies with striking similarities to human B CLL. Tumor formation appears to result from the retention of the targeted germline allele and concomitant antisense transcripion of SV40 large T in mature B-cells. Brugge et al. generated two different mouse model by homologous recombination in ES cells (embryonic stem cells). The SV40 large and small T antigen coding unit was inserted in the IgH locus with (TEμ) or without (T) an extra copy of the IgH intronic enhancer Eμ. Sv40 T gene insertion in the IgH chain locus did not affect B-cell development or chain usage and that in a fraction of mature B cells SV40 T is retained and transcribed.

IgH T and IgH TEμ mice showed the presence of a population of the mature CD19+ B-cells with increased cell size compared with wild type control cells. These cells have retained the targeted IgH allele in the germline configuration. Leukemic cells present in these mice displayed many characteristics also found in human B-CLL, in particular in the subgroup of patients with germline IgH V regions associated with poor prognosis. These features include a mature CD19/CD5 phenotype, VH regions with predominantly germline-encoded sequences, nonstochastic VH-family usage, and CDR3 regions with high serine/tyrosine content. The model replicates the human B-CLL BCR sequences that closely resemble those of known autoreactive or polyreactive antibodies. They found that VH regions were either unmutated, with preferential usage of the VH11 family, or manifested extensive somatic hypermutation and used VHJ558. IgH.TEμ mice manifested a substantially higher tumor incidence than IgH.T mice, the presence of an extra copy of Eμ within the D-JH region may increase the level of antisense transcription. Thus, efficient transformation might be dependent on synergistic effects of Eμ and the IgH enhancers that lead to up-regulation of SV40 T expression in more mature B-cell stages. SV40 large T protein interacts with numerous cellular proteins and pathways, most notably the Rb and p53 pathways but may also induce cell survival via Akt activation. In the mouse model, animals that lack p53 show accelerated tumor formation, even though SV40 large T inactivation of p53 is thought to be necessary to generate lymphoid tumors. This implies that, in the presence of p53, some of the potential transforming properties of large T are inhibited or diminished, as was shown in a mouse model of pancreatic islet carcinogenesis. As a preclinical model to test novel treatment strategies for CLL, the leukemia model has the advantage that tumor progression can be monitored by an IgM allotype-specific flow cytometry assay. Finally, gene profiling studies have shown that the SV40 T antigen genetic signature is composed primarily of genes regulating cell replication, proliferation, DNA repair, and apoptosis, does not reflect a general cancer signature, and is uniquely activated primarily in tumors with aberrant expression of p53, Rb, or Brca1 and not in tumors initiated through Myc or ras overexpression. As human breast, lung, and prostate tumors expressing this set of genes represent subsets of tumors with the most aggressive phenotype, SV40 large T-dependent CLL model should allow the identification of genes that are associated with treatment resistance and poor prognosis.

A mouse model for chronic lymphocytic leukemia based on expression of the SV40 large T antigen. 2009

Scheda realizzata da Marianna Spunton e Valentina Griggio

CpG ISLAND METHYLATION PATTERNS IN B CLL

Epigenetic refers to mitotically and meiotically heritable changes in gene function mediated by mechanisms other than alterations in the primary nucleotide sequence; epigenetic disturbances in human cancer comprise DNA methylation, histone modification and RNA interference. Interactions between these factors have been implicated in neoplastic development. DNA methylation is the covalent binding of a methyl group to DNA at the 5-carbon of the cytosine ring and aberrant methylation in association with transcriptional silencing has been detected for a broad variety of genes in almost all malignancies. Promoter hypermethylation has been described in CLL with specific distribution patterns. The CpG island hypermethylation may affects cellular patterns that regulate the limitless replicative potential, the insensivity to anti-growth signals, the self-sufficiency in growth signals, apoptosis, angiogenesis and capability to invade and metastatize of the cancer cells. The set of tumor suppressor genes hypermethylated in cancer has been shown to be specific for its tissue of origin. Altered DNA methylation patterns may provide a source of potential biomarkers for molecular detection, assessment of prognosis and prediction of response to therapy.

In the study of Seeliger et al. using a candidate gene approach, they determined the methylations status of 15 cancer-related genes in 32 patients with CLL.
The genes selected by a candidate approach and analized by MSP (methylation-specific polymerase chain reaction) were: p15, p16, p,73, tissue inhibitors of metalloproteinase’s 2 and 3 (TIMP-2, TIMP-3), E-chaderin (E-cad), O6-methylguanine DNA methyltransferase (MGMT), human Mut.L homolog 1 (hMLH1), retinoic acid receptor β2 (RARβ2), suppressor of cytokine signalling 1 (SOCS-1), deadh-associated protein kinase 1 (DAPK1) and secreted frizzled-related proteins (SFRP1, -2, -4, -5). The frequency of gene hypermethylation among the 32 primary samples of patiens with CLL was very variable.

Hypermethylation occurred in all Rai stages without a preference for advanced stages. The methylation patters in CLL are disease-specific, because the profile is not similar to other hemopoietic malignancies. The higher frequency of CpG island hypermetthylation discovered they discovered in SFRP1 gene (68,8%). Wnt signalling plays an important role in the stem cell self-renewal as well as in differentiation and proliferation of hematopoietic progenitor cells; aberrant activation of the Wnt pathway has been demonstred to contribute to the development of lymphoid and myeloid malignancies and epigenetic silencing of negative regulators of Wnt signalling has been found in AML and ALL. Despite a growing knowledge about the Wnt pathway, the role of SFRP proteins in normal and malignant hematopoiesis is still poorly defined. DAPK1 hypermethylation (50,0% of samples) has been shown to occur very frequently in B-cell malignancies, but not in T-cell malignancies or myeloid leukemia; Hypermethylation of DAPK1 is characteristic of the transformed B-cell but not of normal B-cells or immortalized B-lymphoblasts. The epigenetic silencing and germline mutations in DAPK1 are present in familial CLL and DAPK1 is epigenetically silenced in the majority of sporadic cases of CLL. DAPK1 is a mediator in apoptotic signalling and loss of its function in CLL cells promotes resistance to apoptosis. Epigenetic changes are pharmacologically reversible and therapeutic approaches with demethylating agents may contribute to reactivation of SFRP1, SFRP2 or DAPK1 function in patients with methylation-associated silencing of those genes. Genetic and epigenetic changes may also function as networks generating numerous alterations in multiple cancer-related pathways. It is necessary to elucidate the complex network of epigenetic and genetic regulatory mechanisms contributing to the development of CLL from earlies stages. The high frequency of epigenetically silenced genes in CLL suggests that DNA methylation changes are required in the development of CLL and that they may act synergistically with genetic alterations. The aberrant CpG island methylation affecting genes involved in fundamental cellular pathways is a common phoenomenon in CLL. Data show that DNA hypermethylation is a frequent event in all CLL stages and that concomitant promoter hypermethylation may occur in multiple cancer-related pathways. The high frequency of DNA methylation in CLL and the variety of genes involved reflect the critical role of epigenetic disturbances in CLL initiation and progression.

CpG island methylation patterns in chronic lymphocytic leukemia. 2009

Scheda realizzata da Marianna Spunton e Valentina Griggio