Molecular pathogenesis of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is unique among malignancies since it represents an accumulation of B-lymphocytes resistant to apoptosis. Several factors are thought to confer this unusual feature to a CLL B-cell. Misbalance between cytoplasmic pro-survival and pro-death molecules, such as Bcl-2, Mcl-1 and alike, appears to be one of the key factors defining B-cell longevity. Autocrine pathways, such as vascular endothelial growth factor-receptor pathway, also contribute to survival. The role of B-cell receptor (BCR) is less straightforward. In the last decade it became clear that CLL does not constitute a uniform disease, but, based on the prevalence of mutations in the BCR heavy chain (IgVH), can be classified into two distinct subgroups. Several molecular markers correlate with IgVH mutations. Some of them, like zeta-chain associated protein kinase, are also involved in BCR signaling and influence cell cycle. Yet the primary pathogenic event leading to increased proliferation and survival in CLL is difficult to ascertain. Molecules involved in BCR signaling pathways and cytoplasmic pro-survival players probably act in concert to confer resistance to apoptosis. In this respect, the role of the B-CLL environment, which includes nurse-like cells and T-cells, cannot be underestimated. Nurse-like cells provide stimuli necessary for perpetuation of life in CLL. On the other hand, abnormal T-cell function, whether it is excessive immunosuppression delivered by regulatory T-cells or insufficient anti-tumor immunity rendered by T-helpers, allows malignant CLL cells to go unnoticed by the cellular immune system.     

Biology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) lies at the cross-roads of hematology, immunology and oncology for at least three major reasons: (a) it is the prototype of human malignancies that primarily involve defects in the induction of apoptosis; (b) CLL patients develop a severe immunodeficiency with progressive hypogammaglobulinemia; and (c) they have a high prevalence of autoimmune phenomena. Recent advances in the biology of the malignant cell in CLL lead to a scenario comprised of two basic elements: first, CLL cells are optimally organized to survive in their niches because their ability to undergo apoptosis is severely hampered; second, they have a microenvironment-dependence that promotes their extended survival, a situation that arises most probably through direct cell-to-cell contacts. In addition, CLL cells themselves are the major accessory cells in CLL, but are inefficient antigen-presenting cells. This latter defect may provide a clue to reinterpret the events of immunodeficiency and autoimmunity.     

Polyamine metabolism in chronic lymphocytic leukemia

We have previously shown that polyamines have profound effects on lymphocyte proliferation and function. We now report that the proliferative response of cultured lymphocytes from patients with chronic lymphocytic leukemia is abrogated by the addition of diacetyldiaminohexane (HMBA), the 6-carbon analogue of diacetylputrescine. In addition, this study demonstrates the post-translational modification of proteins by polyamines in CLL-lymphocytes, a decrease in the uptake of exogenous spermidine by CLL-lymphocytes which have been exposed to HMBA, and the significant conversion of spermidine to N1-acetylspermidine in CLL-lymphocytes.     

Monoclonal antibody therapy of chronic lymphocytic leukemia

Cure of patients with chronic lymphocytic leukemia (CLL) has been an elusive goal. The recent availability of active monoclonal antibodies has rekindled enthusiasm for new and innovative therapeutic approaches. Alemtuzumab, induces responses in about a third of patients with relapsed or refractory CLL following therapy with fludarabine and an alkylating agent. Whereas, rituximab has limited activity in previously treated patients, response rates of 50-70% have been reported in those without prior therapy. Recent data on combinations with rituximab and chemotherapy have shown promise for improving patient outcome. Newer antibodies in development include the primatized monoclonal antibody lumiliximab (IDEC-152), directed against CD23. Other biological approaches include the use of antisense oligonucleotides, proapoptic small molecules, and vaccines directed against the malignant B cells. The rational development of combinations of these promising approaches may eliminate the need for chemotherapy, leading to safer and more effective approaches for patients with CLL.     

Genetic features of B-cell chronic lymphocytic leukemia

The genetic features of B-cell chronic lymphocytic leukemia (CLL) are currently being reassessed by molecular cytogenetic techniques such as fluorescence in situ hybridization (FISH). Conventional cytogenetic studies by chromosome banding are difficult in CLL mainly because of the low in vitro mitotic activity of the tumor cells, which leads to poor quantity and quality of metaphase spreads. Molecular genetic analyses are limited because candidate genes are known for only a few chromosomal aberrations that are observed in CLL. FISH was found to be a powerful tool for the genetic analysis of CLL as it overcomes both the low mitotic activity of the CLL cells and the lack of suitable candidate genes for analysis. Using FISH, the detection of chromosomal aberrations can be performed at the single cell level in both dividing and non-dividing cells, thus circumventing the need of metaphase preparations from tumor cells. Probes for the detection of trisomies, deletions and translocation breakpoints can be applied to the regions of interest with the growing number of clones available from genome-wide libraries. Using the interphase cytogenetic FISH approach with a disease specific set of probes, chromosome aberrations can be found in more than 80% of CLL cases. The most frequently observed abnormalities are losses of chromosomal material, with deletions in band 13q14 being the most common, followed by deletions in 11q22-q23, deletions in 17p13 and deletions in 6q21. The most common gains of chromosomal material are trisomies 12q, 8q and 3q. Translocation breakpoints, in particular involving the immunoglobulin heavy chain locus at 14q32, which are frequently observed in other types of non-Hodgkin's lymphoma, are rare events in CLL. Genes affected by common chromosome aberrations in CLL appear to be p53 in cases with 17p deletion and ataxia telangiectasia mutated (ATM), which is mutated in a subset of cases with 11q22-q23 aberrations. However, for the other frequently affected genomic regions, the search for candidate genes is ongoing. In parallel, the accurate evaluation of the incidence of chromosome aberrations in CLL by FISH allows the correlation of genetic abnormalities with clinical disease manifestations and outcome. In particular, 17p abnormalities and deletions in 11q22-q23 have already been shown to be among the most important independent prognostic factors identifying subgroups of patients with rapid disease progression and short survival. In addition, deletion 17p has been associated with resistance to treatment with purine analogs. Therefore, genetic abnormalities may allow a risk assessment for individual patients at the time of diagnosis, thus giving the opportunity for a risk-adapted management.     

miR-34家族在慢性淋巴细胞白血病中的作用

近年来的研究表明microRNAs表达异常直接或间接导致了多种亚型慢性淋巴细胞白血病（chronic lymphocytic leukemia,CLL）的发生。miR-34家族（包括miR-34a、miR-34b与miR-34c）是一个与细胞增殖、分化和癌变高度相关的microRNA家族。近年来,人们发现miR-34家族在p53调控网络和CLL发生中起着重要作用,并具有显著的临床应用价值。将对miR-34家族在慢性淋巴细胞白血病发生中的作用和机制做一综述。     

Galactose-1-phosphate uridylyltransferase activity in chronic lymphocytic leukemia.

Galactose-1-phosphate uridylytransferase (E.C.2.7.12) activity was measured in both lymphoid and erythroid cells from patients with chronic lymphocytic leukemia (CLL). Decreased enzyme activity was found in both cell types using two assay methods. The results suggest the presence of an inhibitor of the enzyme in CLL patients. A correlation between decreased uridyl transferase activity and glycogen accumulation in CLL is postulated.     

Lymphocyte cholesterol synthesis in chronic lymphocytic leukemia

Studies in B and T lymphocytes from two patients with B cell chronic lymphocytic leukemia (CLL) showed that the rate of cholesterol synthesis and hydroxymethylglutaryl (HMG)-CoA reductase activity in the malignant cell--the B lymphocyte--did not differ from that in normals, before or after the treatment. Cholesterol synthesis and HMG-CoA reductase activity in T cells, on the other hand, from one patient (H.E.) before therapy, were only one-fifth of that in normals and in the other patient (J.R.) receiving treatment. Following chemotherapy and treatment with prednisone, T lymphocytes from H.E. exhibited normal cholesterol metabolism.     

Genetic alteration associated with chronic lymphocytic leukemia

The genetics of B-cell chronic lymphocytic leukemia (B-CLL) differ considerably from most other forms of hematologic malignancy which are usually characterized by chromosome translocations. B-CLL typically contains chromosomal deletions and chromosomes 13q14 and 11q22-->q23 are the most common. These two regions appear to share a common ancestral origin (Auer et al., 2007b). Overall, chromosomal abnormalities can be found in the majority of patients with B-CLL when using sensitive techniques (Dohneret al., 2000) and possibly reflects an underlying predisposition, with a small but significant number of familial cases. Although single and consistent abnormalities are most common, multiple rearrangements can occur, often with disease progression (Feganetal., 1995; Dohner et al., 2000). Regions of recurrent deletion suggest the presence of tumor suppressor genes if following Knudson's theoretical 2-hit model. However, despite extensive sequencing analysis over the last decade and lack of pathogenic mutations identified, there has been a move away from this suggested hypothesis and alternative mechanisms of gene inactivation involving epigenetic silencing or haploinsufficiency may be considered as more likely in this disease. This review focuses on the common genetic abnormalities in B-CLL and relates them to some of the more recent hypotheses on inactivation of genes within these regions of deletion.     

B-lymphocyte colony formation in chronic lymphocytic leukemia

A semisolid culture system for B-cell colony formation is described. The system includes pretreatment of B-cells by neuraminidase-galactose oxidase and help of mitomycin-treated T-cells. With this assay system, colony-forming B-cell precursors were detected in all eight patients we studied with B-cell chronic lymphocytic leukemia. These patients' own T-cell helper effect was less than that of normal T-cells.     

Modulation of apoptosis by cytokines in B-cell chronic lymphocytic leukemia.

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the slow and progressive accumulation of monoclonal apparently mature, CD5(+) B lymphocytes. The majority of circulating cells appear to be nondividing, and it has been suggested that a prolonged life span is mainly responsible for the accumulation of the leukemic cells. However, spontaneous programmed cell death by apoptosis occurs when B chronic lymphocytic leukemia cells are cultured in vitro. This may be because of the lack of an unidentified essential cytokine present in vivo. Thus, we investigate interleukin-2 (IL-2), IL-4, IL-6 and IL-10 in vitro effects on apoptosis of B cells from 32 previously untreated patients with B-CLL in initial clinical stages. B cells were isolated from peripheral blood, and apoptosis was measured in these cells immediately after isolation and following incubation in vitro, without and with the different cytokines, for 24 and 48 h. Distribution of cellular DNA content and quantitative analysis of apoptosis were determined by standard propidium iodide staining and flow cytometry. Spontaneous apoptosis occurred in B-CLL cells incubated in vitro in the absence of cytokines. Our results indicate that both IL-2 and IL-4, but not IL-6, inhibit in vitro apoptosis in a large percentage of B-CLL patients. IL-10 increases in vitro apoptotic cell number in stage 0 patients, but not in stage I and II. These data support the hypothesis that IL-2 or IL-4, may be cell survival factors in vivo and that IL-10 might be a candidate for immune therapy of early B-CLL.     

Immunogenotypic characteristics of chronic lymphocytic leukemia patients from northern Italy.

Ig gene analysis, carried out in 25 patients failed to show rearrangement patterns typical of each stage, but, nevertheless, confirmed the monoclonal origin of leukemic cells in these patients. In addition, in 14 of them the pattern of Ig gene rearrangements measured on two different occasions was analyzed. Only in patients who had received chemotherapy, the intensity of the Ig germline band was greater than that of the rearranged bands, indicating the reduction of lymphocytosis after the therapy. Thus, though Ig gene rearrangement could not distinguish the CLL stage, our data confirm the usefulness, at all clinical stages, of Ig gene analysis as a tool in the evaluation of the efficiency of the therapy.     

Therapeutic efficacy of theophylline in chronic lymphocytic leukemia

Theophylline, a methylxanthine commonly used as a treatment for asthma, has been shown to induce apoptosis in chronic lymphocytic leukemia (CLL) cells bothin vitro andin vivo. We have treated three advanced CLL patients with theophylline, and seen responses in two. The clinical courses of the responders are presented, and the literature concerning theophylline as therapy for CLL is reviewed.