Establishment and characterization of the tumors of chronic lymphocytic leukemia cell line in nude and SCID mice

Identification of unique molecular heterogeneity of human CD79, the signaling component of the human B cell antigen receptor (BCR), and synergistic potentiation of the CD79-targeted therapy of B cell tumors by co-targeting of CD79a and CD79b

We identified unique molecular heterogeneity of CD79 of human B cell antigen receptor (BCR) that may open a new approach to the ongoing CD79b-targeted therapy of B cell tumors. The primary purpose of the present study is to gain new information valuable for the enhanced CD79-targeted therapy. The molecular heterogeneity of CD79 was identified by sequential immunoprecipitation of BCR by use of anti-CD79b monoclonal antibody (mAb) SN8 and anti-CD79a mAb SN8b. SN8 is the antibody component of polatuzumab vedotin, an anti-CD79b antibody drug conjugate, that has been widely used for therapy of diffuse large B-cell lymphoma (DLBCL). The sequential immunoprecipitation shows that anti-CD79b mAb will be able to react only with a subgroup of CD79 molecules while anti-CD79a mAb will react with another subgroup of CD79 molecules; CD79 is a disulfide-linked heterodimer of CD79a and CD79b. Therapeutic study of SCID mice bearing human B-cell tumor shows synergistic potentiation by co-targeting CD79b and CD79a. Furthermore, simultaneous targeting of PD-1 strongly potentiates CD79a/CD79b-targeted therapy of B cell tumors. Flow cytometry analyses of CD79a/CD79b on malignant B cells of patients may provide a method for selection of the candidate patients for the CD79a/CD79b dual targeting therapy.

Common nonmutational NOTCH1 activation in chronic lymphocytic leukemia

Activating mutations of NOTCH1 (a well-known oncogene in T-cell acute lymphoblastic leukemia) are present in ∼4-13% of chronic lymphocytic leukemia (CLL) cases, where they are associated with disease progression and chemorefractoriness. However, the specific role of NOTCH1 in leukemogenesis remains to be established. Here, we report that the active intracellular portion of NOTCH1 (ICN1) is detectable in ∼50% of peripheral blood CLL cases lacking gene mutations. We identify a "NOTCH1 gene-expression signature" in CLL cells, and show that this signature is significantly enriched in primary CLL cases expressing ICN1, independent of NOTCH1 mutation. NOTCH1 target genes include key regulators of B-cell proliferation, survival, and signal transduction. In particular, we show that NOTCH1 transactivates MYC via binding to B-cell-specific regulatory elements, thus implicating this oncogene in CLL development. These results significantly extend the role of NOTCH1 in CLL pathogenesis, and have direct implications for specific therapeutic targeting.

Isolation of a novel chronic lymphocytic leukemic (CLL) cell line and development of an in vivo mouse model of CLL

Leukemic cell lines have become important tools for studies of disease providing a monoclonal cell population that can be extensively expanded in vitro while preserving leukemic cellular characteristics. However, studies of chronic lymphocytic leukemia (CLL) have been impeded in part by the lack of continuous human cell lines. CLL cells have a high spontaneous apoptosis rate in vitro and exhibit minimal proliferation in xenograft models. Therefore, there is a need for development of primary CLL cell lines and we describe the isolation of such a line from the bone marrow of a CLL patient (17p deletion and TP53 mutation) which has been in long term culture for more than 12 months with continuous proliferation. The CLL cell line (termed MDA-BM5) which was generated in vitro with continuous co-culture on autologous stromal cells is CD19+CD5+ and shows an identical pattern of somatic hypermutation as determined in the patient's bone marrow (BM), confirming the origin of the cells from the original CLL clone. MDA-BM5 cells were readily transplantable in NOD/SCID gamma null mice (NSG) with disease developing in the BM, liver and spleen. BM cells from quaternary serial transplantation in NSG mice demonstrated the presence of CD19+CD5+ cells with Ig restricted to lambda which is consistent with the original patient cells. These studies describe a new CLL cell line from a patient with del(17p) that provides a unique model for in vitro and in vivo studies.

Murine genetically engineered and human xenograft models of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a genetically complex disease, with multiple factors having an impact on onset, progression, and response to therapy. Genetic differences/abnormalities have been found in hematopoietic stem cells from patients, as well as in B lymphocytes of individuals with monoclonal B-cell lymphocytosis who may develop the disease. Furthermore, after the onset of CLL, additional genetic alterations occur over time, often causing disease worsening and altering patient outcomes. Therefore, being able to genetically engineer mouse models that mimic CLL or at least certain aspects of the disease will help us understand disease mechanisms and improve treatments. This notwithstanding, because neither the genetic aberrations responsible for leukemogenesis and progression nor the promoting factors that support these are likely identical in character or influences for all patients, genetically engineered mouse models will only completely mimic CLL when all of these factors are precisely defined. In addition, multiple genetically engineered models may be required because of the heterogeneity in susceptibility genes among patients that can have an effect on genetic and environmental characteristics influencing disease development and outcome. For these reasons, we review the major murine genetically engineered and human xenograft models in use at the present time, aiming to report the advantages and disadvantages of each.

Characterization of a new chronic lymphocytic leukemia cell line for mechanistic in vitro and in vivo studies relevant to disease

Studies of chronic lymphocytic leukemia (CLL) have yielded substantial progress, however a lack of immortalized cell lines representative of the primary disease has hampered a full understanding of disease pathogenesis and development of new treatments. Here we describe a novel CLL cell line (OSU-CLL) generated by EBV transformation, which displays a similar cytogenetic and immunophenotype observed in the patient’s CLL (CD5 positive with trisomy 12 and 19). A companion cell line was also generated from the same patient (OSU-NB). This cell line lacked typical CLL characteristics, and is likely derived from the patient’s normal B cells. In vitro migration assays demonstrated that OSU-CLL exhibits migratory properties similar to primary CLL cells whereas OSU-NB has significantly reduced ability to migrate spontaneously or towards chemokine. Microarray analysis demonstrated distinct gene expression patterns in the two cell lines, including genes on chromosomes 12 and 19, which is consistent with the cytogenetic profile in this cell line. Finally, OSU-CLL was readily transplantable into NOG mice, producing uniform engraftment by three weeks with leukemic cells detectable in the peripheral blood spleen and bone marrow. These studies describe a new CLL cell line that extends currently available models to study gene function in this disease.

SCID mice model in vivo evaluation of autologous and allogeneic dendritic cells activity on B-cell chronic lymphocytic leukemia

In the present study we investigated in vivo therapeutic potential of DCs vaccines in B-cell chronic lymphocytic leukemia (B-CLL). On the day 0 the SCID mice were intraperitoneally inoculated with peripheral blood mononuclear cells (PBMC) of B-CLL patients at a dose of 10-30 x 10(6) and left untreated (controls) or i.p. injected on the day 7 with 0.2 - 14.0 x 10(6) dendritic cells. DCs were generated in vitro from peripheral blood monocytes of B-CLL donors (autologous DCs) or healthy donors (allogeneic cells) and pulsed with B-CLL antigens. On the day 14, the effect of implanted cells interactions was evaluated by a counting of CD19+CD5+ human leukemic cells and human T cells in the peritoneal fluid of mice. We found, that mean numbers of CD19+CD5+ leukemic cells as well as human T cells were lowered in peritoneal fluid of mice treated with allogeneic APCs. However, we did not observe similar effects with autologous DCs.

Multiplex Analysis of Intracellular Signaling Pathways in Lymphoid Cells by Microbead Suspension Arrays

Phosphorylation analysis of signaling proteins is key for examining intracellular signaling pathways. Conventional biochemical approaches, e.g. immunoprecipitation, Western blot, and ELISA, have played a major role in elucidation of individual signaling events. However, these methods are laborious, time-consuming, and difficult to adapt for high throughput analysis. A multiplex approach to measure phosphorylation state of multiple signaling proteins simultaneously would significantly enhance the efficiency and scope of signaling pathway analysis for mechanistic studies and clinical application. This report describes a novel multiplex microbead suspension array approach to examine phosphoproteomic profiles in lymphoid cells. In the Jurkat T-cell leukemia line, the multiplex assay enabled targeted investigation of phosphorylation kinetics of signal transduction from receptor proximal events (tyrosine phosphoproteins CD3, Lck, Zap-70, and linker for T-cell activation) to cytosolic events (serine/threonine phosphoproteins Erk and Akt) to transcription factors (serine/threonine phosphorylated Rsk, cyclic AMP-response element-binding protein, and STAT3). To broaden the application of the multiplex analysis, signaling pathways were also studied in B-cell lymphoid tumor lines that included chronic lymphocytic leukemia lines. In these cell lines, multiplex suspension array enabled phosphoproteomic analysis of signaling cascade mediated by Syk, a homolog of Zap-70. Results obtained by multiplex analysis were confirmed by immunoprecipitation and Western blot methods. The examples of T-cell and B-cell signaling pathway analyses in this report demonstrate the utility of the multiplex suspension arrays to investigate phosphorylation dynamics and kinetics of several signaling proteins simultaneously in signal transduction pathways.

Is targeted chemotherapy an alternative to immunotherapy in chronic lymphocytic leukemia?

Although molecular remission is now detected, it is still unknown whether we have the tools to cure B cell chronic lymphocytic leukemia (referred to as CLL). Nonetheless, several new therapeutic approaches have been introduced in cancer therapy during the last decade, including antiangiogenic therapy, apoptosis-inducing treatment and inhibition of heat shock proteins, farnesyl transferase, tyrosine kinases and proteasomes. These modalities may also be considered in CLL, but additional experimental characterization is required. Further characterization and development of CLL animal models should be a part of this preclinical work (especially xenografting in NOD/SCID animals, but also murine leukemia) to allow a more extensive evaluation prior to clinical trials. Animal models are particularly important for preclinical comparison of pharmacological effects between different disease compartments and for in vivo evaluation of antileukemic immune reactivity. However, T cell targeting therapy seems to have several advantages in comparison to other approaches: (1) based on the current clinical experience one would expect low toxicity for several of these strategies, especially vaccine treatment; (2) several studies have demonstrated that autologous T cells can recognize CLL cells; (3) experimental and clinical evidence suggests that immunotherapy can be combined with chemotherapy. Thus, T cell therapy has a relatively strong scientific basis that justifies further clinical studies of immunotherapy in CLL. Although several of the new pharmacological agents seem to have immunosuppressive effects, at least some of them (e.g. heat shock protein 90 inhibitors, proteasome inhibitors, inhibition of angiogenesis) appear to affect T cells only at relatively high concentrations and may thus be used in combination with immunotherapy.

Establishment of a novel human B-CLL-like xenograft model in nude mouse

We have developed a novel murine model for B-CLL by engrafting human prolymphocytic leukemia (PLL) or B-CLL cell line cells (JVM-3 and MEC-2 cell lines, respectively) into nude mice. Not only treatment of the mice was a prerequisite for the success of the graft, but also for the first time, females appeared to accept the cells more easily than males. Surprisingly, tumoral murine models for B-CLL could be established with PLL cells but not with B-CLL cells. JVM-3 cells were efficiently transplanted into nude mice through subcutaneous or intravenous routes. Irradiated female mice appeared to be the optimal recipients for tumor growth. Such murine models for human B-CLL may help the development of therapeutic agents.

MUM1/IRF4 expression is an unfavorable prognostic factor in B-cell chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL)

B-Cell chronic lymphocytic leukemia (B-CLL) / small lymphocytic lymphoma (SLL) consists of heterogeneous diseases that are distinguished by morphological, immunophenotypic and molecular features. MUM1 (multiple myeloma oncogene 1) is a protooncogene that is deregulated as a result of (6;14)(p25;q32) chromosomal translocation in multiple myeloma, and is also expressed in a variety of malignant lymphoma entities. We examined the expression of MUM1 in B-CLL / SLL, and found that 2 of 4 B-CLL-derived cell lines and 14 of 29 patients' specimens expressed MUM1 by immunohistochemical analysis. MUM1 expression was not associated with CD38 expression, somatic hypermutation of immunoglobulin heavy chain gene variable region (IgV(H)), or any other clinical characteristics of the patients. Interestingly, the patients who were positive for MUM1 showed shorter overall survival times than those who were negative for MUM1 (50% survival: 22 months vs. 82 months) (P = 0.0008, log-rank test). Multivariate analysis by Cox's proportional-hazards regression model showed that MUM1 expression and unmutated IgV(H) status were independent unfavorable prognostic factors in patients with B-CLL / SLL. These findings suggest that MUM1 expression is a useful prognostic factor in B-CLL / SLL. The biological role and mechanism of action of MUM1 in B-CLL / SLL need to be clarified for the development of therapies for patients with the poor prognostic subtype.

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.

Nucleotide sequence, transcription map, and mutation analysis of the 13q14 chromosomal region deleted in B-cell chronic lymphocytic leukemia

Deletions of the 13q14 chromosome region are associated with B-cell chronic lymphocytic leukemia (B-CLL) and several other types of cancer, suggesting the presence of a tumor suppressor gene. In previous studies the minimal region of deletion (MDR) was mapped to a less than 300-kilobase (kb) interval bordered by the markers 173a12-82 and 138G4/1.3R. For the identification of the putative tumor suppressor gene, the entire MDR (approximately 347 kb) has been sequenced, and transcribed regions have been identified by exon trapping, EST-based full-length complementary DNA cloning, database homology searches, and computer-assisted gene prediction analyses. The MDR contains 2 pseudogenes and 3 transcribed genes: CAR, encoding a putative RING-finger containing protein; 1B4/Leu2, generating noncoding transcripts; and EST70/Leu1, probably representing another noncoding gene (longest open reading frame of 78 codons). These genes have been sequenced in 20 B-CLL cases with 13q14 hemizygous deletion, and no mutations were found. Moreover, no somatic variants were found in the entire MDR analyzed for nucleotide substitutions by a combination of direct sequencing and fluorescence-assisted mismatch analysis in 5 B-CLL cases displaying 13q14-monoallelic deletion. The nondeleted allele of the CAR and EST70/Leu1 genes was expressed in B-CLL specimens, including those with monoallelic loss, whereas no expression of 1B4/Leu2 was detectable in B-CLL, regardless of the 13q14 status. These results indicate that allelic loss and mutation of a gene within the MDR is an unlikely pathogenetic mechanism for B-CLL. However, haplo-insufficiency of one of the identified genes may contribute to tumorigenesis. (Blood. 2001;97:2098-2104)

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.

A Model for Human B-Chronic Lymphocytic Leukemia in Human/Mouse Radiation Chimera: Evidence for Tumor-Mediated Suppression of Antibody Production in Low-Stage Disease

B-chronic lymphocytic leukemia (BCLL) is a lymphoproliferative disease that is characterized by clonal expansion of CD5+ B cells. BCLL is associated with secondary immunodeficiency and hypogammaglobulinemia. It has been suggested that T-cell dysregulation may play a role in the hypogammaglobulinemia and in the increased incidence of autoimmunity in BCLL patients. We attempted to transfer human peripheral blood mononuclear cells (PBMC) from BCLL patients in different stages of the disease into immunodeficient mice. PBMC from BCLL patients in stage 0, stages I to II, and stages III to IV were transplanted into the peritoneal cavity of lethally irradiated Balb/c or beige/nude/Xid (BNX) mice radioprotected with bone marrow (BM) from severe combined immunodeficiency (SCID) mice. Different engraftment profiles were found in the chimeric mice 2 weeks after transplantation of PBMC according to the disease stage of the BCLL donors. Infusion of PBMC from donors in stage 0 led to marked engraftment of human T cells, whereas the human tumor cells could hardly be detected. In contrast, chimeric mice receiving PBMC from patients in stage III to IV disease exhibited engraftment with a dominance of tumor cells, compared with a miniscule level of T cells. The ability of the engrafted cells to produce human Ig was also found to be correlated with the disease stage of the donor, although all donors had the same magnitude of hypogammaglobulinemia. Total human Ig production in the chimeric mice was normal in mice receiving PBMC from donors in stage 0, whereas in chimeric mice engrafted with PBMC from donors in stages III to IV almost no human Igs could be detected. This differential reconstitution of antibody production in the mouse model according to the stage of the patient's disease will allow further studies on possible cellular interactions between malignant and immune cells in BCLL.