H-2z homozygous New Zealand mice as a model for B-cell chronic lymphocytic leukemia: elevated bcl-2 expression in CD5 B cells at premalignant and malignant stages

Distinct roles of BCNP1 in B-cell development and activation

B-cell novel protein 1 (BCNP1) has recently been identified as a new B-cell receptor (BCR) signaling molecule but its physiological function remains unknown. Here, we demonstrate that mice deficient in BCNP1 exhibit impaired B-cell maturation and a reduction of B-1a cells. BCNP1-deficient spleen B cells show enhanced survival, proliferation and Ca2+ influx in response to BCR cross-linking as compared with wild-type spleen B cells. Consistently, mutant B cells show elevated phosphorylation of SYK, B-cell linker protein (BLNK) and PLCγ2 upon BCR cross-linking. In vivo, BCNP1-deficient mice exhibit enhanced humoral immune responses to T-independent and T-dependent antigens. Moreover, aged mutant mice contain elevated levels of serum IgM and IgG3 antibodies and exhibit polyclonal and monoclonal B-cell expansion in lymphoid organs. These results reveal distinct roles for BCNP1 in B-cell development, activation and homeostasis.

Murine models for chronic lymphocytic leukaemia

CLL (chronic lymphocytic leukaemia) is characterized by the clonal outgrowth of B-lymphocytes with the distinctive phenotype: CD19(hi)CD5(+)CD23(+)IgM(lo). These malignant B-cells accumulate in the PB (peripheral blood) and lymphoid organs, and are generally arrested at the G(0)/G(1)-phase of cell cycle and display a resistance to apoptosis. To date, most of the CLL research has been carried out using PB samples obtained from patients with established CLL, which have proved instrumental in characterizing the disease. However, while CLL cells appear to have a defect in apoptosis in vivo, they rapidly undergo apoptosis ex vivo, suggesting that CLL cells are dependent on microenvironmental signals to enhance cell survival. One approach used to define the cellular and molecular events that govern CLL has been the development of murine models that replicate the human disease. As well as providing a deeper understanding of the potential triggers for CLL, these models provide preclinical in vivo systems to test novel therapies. The focus of the present review will be to highlight the recent advances in the development of mouse models for CLL.

Murine models of chronic lymphocytic leukaemia: role of microRNA-16 in the New Zealand Black mouse model

Mouse models are valuable tools in the study of human chronic lymphocytic leukaemia (CLL). The New Zealand Black (NZB) strain is a naturally occurring model of late-onset CLL characterized by B-cell hyperproliferation and autoimmunity early in life, followed by progression to CLL. Other genetically engineered models of CLL that have been developed include (NZB x NZW) F1 mice engineered to express IL5, mice expressing human TCL1A, and mice overexpressing both BCL2 and a tumour necrosis factor receptor-associated factor. The applicability to human CLL varies with each model, suggesting that CLL is a multifactorial disease. Our work with the de novo NZB model has revealed many similarities to the human situation, particularly familial CLL. In NZB, the malignant clones express CD5, zap-70, and have chromosomal instability and germline Ig sequence. We also identified a point mutation in the 3'-flanking sequence of Mirn16-1, which resulted in decreased levels of the microRNA, miR-16 in lymphoid tissue. Exogenous restoration of miR-16 to an NZB malignant B-1 cell line resulted in cell cycle alterations, suggesting that the altered expression of Mirn15a/16-1 is an important molecular lesion in CLL. Future studies utilizing the NZB mouse could ascertain the role of environmental triggers, such as low dose radiation and organic chemicals in the augmentation of a pre-existing propensity to develop CLL.

Genome screening for susceptibility loci in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex, multigenic autoimmune disease with a wide spectrum of clinical manifestations. Much of the pathology is attributed to deposition to various tissues of immune complexes continuously formed with autoantibodies; thus, the pathogenesis is related to dysregulation of self-reactive B cells. Recent family linkage studies and allele-sharing linkage analyses of affected sibling pairs have advanced genome screening for susceptibility loci in SLE, and a considerable number of chromosomal intervals with significant or suggestive linkage to SLE have been identified. However, there are still several inherent difficulties in precisely identifying loci and genes, as the complexity of polygenic inheritance of SLE phenotypes is considerable. One must note that each specific aspect of diverse SLE phenotypes (clinical manifestations and immunological abnormalities) is mostly controlled separately by a different set of susceptibility loci. Involvement of positive and negative epistatic gene interactions often puzzles genetic analyses. Studies on SLE using murine lupus models are ongoing to solve some of these difficulties. Comparative studies have identified several syntenic chromosomal intervals with susceptibility loci in both mouse models and humans. Thus, combining knowledge derived from both human and murine studies is vital. The ultimate identification of susceptibility genes and their functions will probably depend largely on studies using genetically manipulated mutant mice, including those with homologous recombination of potent polymorphic target genes. The up-coming completion of genomic sequences in mice and humans is predicted to limit the numbers of potent candidate genes in particular genomic intervals and accelerates this line of studies. Such knowledge will lead to elucidation of genetic and cellular mechanisms involved in the dysregulation of self-reactive lymphocytes in the pathogenesis of SLE. Prophylactic and therapeutic clinical approaches can then be better designed.

A model of chronic lymphocytic leukemia with Ritcher's transformation in severe combined immunodeficiency mice

OBJECTIVE

The major aim of the study was to establish a murine model of chronic lymphocytic leukemia with B-1 cells derived from a New Zealand white mouse.

MATERIAL AND METHODS

Malignant B-1 cells (named CLL-RT cells) derived from a New Zealand white mouse were injected into the peritoneal cavity of severe combined immunodeficiency mice. Upon follow-up of recipient mice, the lymphomas showed characteristics similar to chronic lymphocytic leukemia (CLL) with Ritcher's transformation.

RESULTS

Blood samples from the recipient mice showed that CLL-RT cells increased rapidly in peripheral blood after 5 weeks. Serum interleukin-10 also increased significantly in recipient mice, as in human chronic lymphocytic leukemia patients. These CLL-RT cells showed a high nucleus-to-cytoplasm ratio. These cells could metastasize via circulation in the recipients and form diffuse lymphomas in various tissues. These aggressive and diffuse lymphomas were similar to Ritcher's transformation of human CLL. The cell surface antigens of the spleen and peritoneal resident cells were analyzed by flow cytometry. The CLL-RT cells constantly expressed surface immunoglobulins M and G, and CD5, CD19, B220, and CD40 molecules. They did not express any CD11b, CD3, MAC-3, CD23, NK1.1, or H-2K(d) molecules.

CONCLUSIONS

The characteristics of our animal model are very similar to human CLL. This animal system could be an ideal model for the human disease. We believe the animal model would be valuable in therapeutic studies and aid in the identification of the specific genetic alleles associated with the disease.

Genetic aspects of inherent B-cell abnormalities associated with SLE and B-cell malignancy: lessons from New Zealand mouse models

Genes that predispose to SLE are closely related to key events in pathogenesis of this disease. As much of the pathology can be attributed to high affinity autoantibodies and/or their immune complexes, some of the genes may exert effects in the process of emergence, escape from tolerance mechanisms, activation, clonal expansion, differentiation, class switching and affinity maturation of self-reactive B cells. A number of growth and differentiation factors and signaling molecules, including positive and negative regulators, are involved in this process. Genetic variations associated with functional deficits in some of such molecules can be involved in the susceptibility for SLE. As is the case with SLE, hereditary factors play significant roles in the pathogenesis of B cell chronic lymphocytic leukemia (B-CLL). Patients with B-CLL or their family members frequently have immunological abnormalities, including those associated with SLE. It is suggested that certain genetically determined regulatory abnormalities of B cells may be a crossroad between B-CLL and SLE. A thorough understanding of the genetic pathways in B cell abnormalities leading to either SLE or B-CLL is expected to shed light on their association. New Zealand mouse strains are pertinent laboratory models for these studies. Chromosomal locations of several major genetic loci for abnormal proliferation, differentiation and maturation of B cells and relevant candidate genes, located in close proximity to these intervals and potentially related to the SLE pathogenesis, have been identified in these mice. Further studies make for a wider knowledge and understanding of the pathogenesis of SLE and related B-cell malignancy.

Assessing the potential carcinogenic activity of magnetic fields using animal models

We update our 1997 publication by reviewing 29 new reports of tests of magnetic fields (MFs) in six different in vivo animal models of carcinogenesis: 2-year, lifetime, or multigeneration exposure studies in rats or mice; and promotion/progression models (rat mammary carcinoma, rat liver focus, mouse skin, several models of human leukemia/lymphoma in rats and mice, and brain cancer in rats). Individual experiments are evaluated using a set of data quality criteria, and summary judgments are made across multiple experiments by applying a criterion of rough reproducibility. The potential for carcinogenicity of MFs is discussed in light of the significant body of carcinogenesis data from animal bioassays that now exists. Excluding abstracts, approximately 80% of the 41 completed studies identified in this and our previous review roughly satisfy data quality criteria. Among these studies, the criterion for independent reproducibility is not satisfied for any positive results but is satisfied for negative results in chronic bioassays in rats and mice and for negative results in both promotion and co-promotion assays using the SENCAR mouse skin model. Results of independent replication studies using the rat mammary carcinoma model were conflicting. We conclude that long-term exposure to continuous 50- or 60-Hz MFs in the range of 0.002-5 mT is unlikely to result in carcinogenesis in rats or mice. Though results of most promotion/progression assays are negative, a weak promoting effect of MFs under certain exposure conditions cannot be ruled out based on available data.

Susceptibility Alleles for Aberrant B-1 Cell Proliferation Involved in Spontaneously Occurring B-Cell Chronic Lymphocytic Leukemia in a Model of New Zealand White Mice

B-cell chronic lymphocytic leukemia (B-CLL) and autoimmune disease are a related event, and genetic factors are linked to both diseases. As B-CLL is mainly of B-1 cell type that participates in autoantibody production, genetically-determined regulatory abnormalities in proliferation and/or differentiation of B-1 cells may determine their fate. We earlier found that, in H-2–congenic (NZB × NZW) F1 mice, while H-2d/z heterozygosity predisposes to autoimmune disease, H-2z/z homozygosity predisposes to B-CLL. Studies also suggested the involvement of non–H-2-linked NZW allele(s) in leukemogenesis. Using H-2–congenic NZW and B10 mouse strains, their F1 and backcross progeny, we have now identified three major NZW susceptibility loci for abnormal proliferation of B-1 cells, which form the basis of leukemogenesis; one H-2–linked locus on chromosome 17 and the other two non–H-2-linked loci, each on chromosome 13 and chromosome 17. Each susceptibility allele functioned independently, in an incomplete dominant fashion, the sum of effects determining the extent of aberrant B-1 cell frequencies. The development of leukemia was associated with age-related increase in B-1 cell frequencies in the blood. Thus, these alleles probably predispose B-1 cells to accumulate genetic alterations, giving rise to B-CLL. Potentially important candidate genes and correlation of the findings with autoimmune disease are discussed.

Susceptibility Alleles for Aberrant B-1 Cell Proliferation Involved in Spontaneously Occurring B-Cell Chronic Lymphocytic Leukemia in a Model of New Zealand White Mice

B-cell chronic lymphocytic leukemia (B-CLL) and autoimmune disease are a related event, and genetic factors are linked to both diseases. As B-CLL is mainly of B-1 cell type that participates in autoantibody production, genetically-determined regulatory abnormalities in proliferation and/or differentiation of B-1 cells may determine their fate. We earlier found that, in H-2–congenic (NZB × NZW) F1 mice, while H-2d/z heterozygosity predisposes to autoimmune disease, H-2z/z homozygosity predisposes to B-CLL. Studies also suggested the involvement of non–H-2-linked NZW allele(s) in leukemogenesis. Using H-2–congenic NZW and B10 mouse strains, their F1 and backcross progeny, we have now identified three major NZW susceptibility loci for abnormal proliferation of B-1 cells, which form the basis of leukemogenesis; one H-2–linked locus on chromosome 17 and the other two non–H-2-linked loci, each on chromosome 13 and chromosome 17. Each susceptibility allele functioned independently, in an incomplete dominant fashion, the sum of effects determining the extent of aberrant B-1 cell frequencies. The development of leukemia was associated with age-related increase in B-1 cell frequencies in the blood. Thus, these alleles probably predispose B-1 cells to accumulate genetic alterations, giving rise to B-CLL. Potentially important candidate genes and correlation of the findings with autoimmune disease are discussed.

IFN-γ Receptor Deletion Prevents Autoantibody Production and Glomerulonephritis in Lupus-Prone (NZB × NZW)F1 Mice

(NZB × NZW)F1 female (BW) mice spontaneously develop an autoimmune disease, characterized by the production of autoantibodies (autoAbs) and glomerulonephritis, which can be delayed by neutralizing IFN-γ Abs and accelerated by IFN-γ injections. To define the role of IFN-γ in the pathogenesis of glomerulonephritis, we established a population of BW mice deficient in IFN-γR (BWγR−/−) by repeated crossing; these mice were compared with BWγR+/+ and +/− littermates. Of the BWγR+/+ and +/− mice, 50% showed immune complex glomerulonephritis with heavy proteinuria at 8 mo of age, while only 10% of the BWγR−/− mice were affected at 14 mo. The serum concentration of anti-dsDNA and anti-histone Abs was dramatically reduced in BWγR−/− mice. The role of IFN-γ in promoting class switch to IgG2a and IgG3 could not fully account for the impaired production of anti-dsDNA in BWγR−/− animals since, IgM and IgG1 levels were also reduced. There was a high incidence of B cell lymphoma in the BWγR−/− mice, which might be related to the suppression of autoAb production. Thus, the absence of glomerulonephritis in BWγR−/− mice is likely due to a dramatic yet unexplained effect of the inactivation of IFN-γ signaling on autoAb production.

Altered response to and production of TGF-beta by B cells from autoimmune NZB mice

New Zealand Black (NZB) mice spontaneously develop immune dysfunction manifested as autoimmune hemolytic anemia and systemic lupus erythematosus. In later life, a subset of these mice develop clonal CD5+ B cell tumors analogous to human chronic lymphocytic leukemia (CLL). NZB disease is marked by B cell hyperactivity characterized by spontaneous immunoglobulin secretion and proliferation. Elimination of autoreactive lymphocytes by apoptosis is a vital mechanism to prevent expansion of self-reactive lymphocyte population. TGF-beta appears to be an important factor in normal and abnormal immune regulation and this cytokine may play a role in the development of chronic human B cell tumors. We asked whether the response to or production of TGF-beta by NZB B cells was aberrant and could contribute to disease development. In this study, we demonstrated that the apoptotic response to TGF-beta was increased in B cells from NZB mice compared to B cells from normal BALB/c mice. The increased apoptosis was related to endogenous activation and was possibly mediated through increased expression of the TGF-beta Type II receptor. Despite functional differences between CD5-negative B cells and CD5-positive B cells, TGF-beta induced apoptosis in both populations to a similar extent. NZB B cells also secrete increased active TGF-beta compared to BALB/c B cells. We suggest that the aberrant secretion of active TGF-beta and the increased response to the apoptotic effects of TGF-beta by NZB B cells may play a role in the disease process of these mice, perhaps attempting to limit the autoimmune phenomena, but possibly also contributing to generalized immunosuppression. We also suggest that the CD5(+) tumors in the NZB mouse may not be a fully appropriate model of human CLL, since CLL B cells are abnormally resistant to the apoptotic effects of TGF-beta.

Requirement for increased IL-10 in the development of B-1 lymphoproliferative disease in a murine model of CLL

Malignant B-1 cells derived from NZB mice, a murine model of spontaneous autoimmunity and B cell lymphoproliferative disease, produce significantly higher levels of IL-10 mRNA than normal B-1 or B cells. IL-10 may act as an autocrine growth factor for the expansion of malignant B-1 cells. In order to determine if elevated endogenous production of IL-10 was a required element for the malignant transformation of B-1 cells in NZB mice, backcross animals were studied for the linkage between elevated IL-10 expression and the presence of lymphoid malignancy. The phenotypes of aged (NZB x DBA/2)F1 x NZB animals were determined and a strong correlation was found between the elevated levels of IL-10 mRNA and the development of B-1 malignant clones. In contrast, an increased level of IL-10 message was not associated with elevated serum IgM or the presence of anemia or reticulocytosis which is mainly seen in response to autoantibody production. These results indicate that, at least in NZB, the autoimmunity and lymphoproliferation phenotypes are not linked genetically. IL-10 may enhance proliferation and the development of B-1 cell malignancy rather than antibody production by the B-1 cell subpopulation. Thus, IL-10 plays an important role in B-1 malignancies, and downregulation of IL-10 could be a likely site for intervention in B cell malignancies.

Incidence of 5' bcl-2 rearrangement in patients with B cell chronic lymphocytic leukemia from India

The incidence of B cell chronic lymphocytic leukemia (B-CLL) is lower in Asian countries, including India, when compared with Western countries. The bcl-2 gene rearrangement was restricted to the 5' region and seen in only one of the 20 Indian patients analyzed. The incidence remains similar to that reported from Western and Japanese institutions.

Interference between Neisseria meningitidis and PC-KLH induced anti-phosphorylcholine PFC responses in NZB/W autoimmune mice

In this work, we demonstrate that the simultaneous injection of PC-KLH and Neisseria meningitidis-derived antigens [NMB or PC-(NMB)HI] induced in old NZB/W mice defective responses as does PC-KLH challenge. On the other hand, the simultaneous injection of both immunogenic preparations of N. meningitidis evoked responses similar to those shown by old mice challenged with NMB alone. Alteration in PC-specific PFC responses also affected hapten-free inhibition profiles and their heterogeneities. The increase in PC50s of anti-phosphorylcholine PFC responses and their heterogeneities induced by certain antigens with aging is correlated with a decrease in T15 idiotype expression, suggesting that after the T15 dominant clone disappears no other clone takes control of the anti-PC response. These results suggest that the mechanism(s) involved in the regulation of T15 marker expression play an important role in the inability of old NZB/W mice to mount good anti-PC responses and suggest that regulatory mechanisms induced by PC-KLH dominate those elicited by NMB.

Growth inhibition of malignant CD5+B (B-1) cells by antisense IL-10 oligonucleotide

Malignant B-1 cells derived from NZB mice, a murine model of chronic lymphocytic leukemia, produce significantly higher levels of IL-10 mRNA than normal B-1 or B cells. IL-10 may act as an autocrine growth factor for malignant B-1 cells. By addition of antisense oligodeoxynucleotides specific for IL-10 mRNA, we were able to dramatically inhibit the growth of leukemic B-1 cells in a time and dose dependent manner. Control cell lines which do not depend on IL-10 for growth were not affected. Antisense therapy targeted at the 5' region of the IL-10 mRNA not only resulted in inhibition of malignant B-1 cell proliferation but also inhibited IL-10 production by malignant B-1 cells. Because endogenous IL-10 gene activation is critical for B-1 cell expansion, inactivation of the endogenous IL-10 gene by IL-10 antisense rather than extracellular regulation of the IL-10 gene product should be successful in controlling the malignant growth.