Fluorescence in situ hybridization analysis shows the frequent occurrence of 14q32.3 rearrangements with involvement of immunoglobulin switch regions in myeloma cell lines

Localized Peritumoral AL Amyloidosis Associated With Mantle Cell Lymphoma With Plasmacytic Differentiation

Immunoglobulin light chain (AL) amyloidosis is characterized by the deposition of amyloid fibers derived from pathologic immunoglobulin light chains. Although systemic plasma cell neoplasms are the most common cause of AL amyloidosis, a subset of cases is caused by B-cell lymphoproliferative disorders such as lymphoplasmacytic lymphoma or extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue. Recently, SOX11-negative IGH hypermutated mantle cell lymphoma (MCL) is recognized to show frequent plasmacytic differentiation and indolent clinical course. Here, we report 3 cases of peritumoral AL amyloidosis associated with SOX11-negative MCL. All 3 cases showed cyclin D1 expression by immunohistochemistry and CCND1 translocation as detected by fluorescence in situ hybridization analysis. Peritumoral AL amyloidosis was observed at the biopsy sites in the gastrointestinal tract, a supraclavicular lymph node, and a cervical lymph node, and all presented with marked plasmacytic differentiation of lymphoma cells. None of the cases showed evidence of bone marrow involvement by morphology and immunophenotyping. None of the patients had distant organ involvement with systemic amyloidosis. All 3 patients had an indolent clinical course and are alive with disease at the time of the last follow-up (range: 48 to 74 mo). Our findings show that MCL with plasmacytic differentiation can cause amyloid deposition and CCND1 abnormalities should be performed in all cases of extramedullary AL amyloidosis. Recognition of indolent MCL as a cause of peritumoral AL amyloidosis may have important clinical management implications.

Novel anti-CD38 humanized mAb SG003 possessed enhanced cytotoxicity in lymphoma than Daratumumab via antibody-dependent cell-mediated cytotoxicity

Background

In vivo use of monoclonal antibodies has become routine clinical practice in the treatment of human cancer. CD38 is an attractive target, because it has double roles, as a receptor and an ectoenzyme. Daratumumab, an anti-CD38 antibody, is currently in the clinical trials for multiple myeloma.

Results

Here we obtained a humanized anti-CD38 antibody, SG003, using SDR-grafting method. SG003 possessed stronger antigen binding activity than Daratumumab, and its epitope was far from that of Daratumumab, an anti-CD38 antibody currently in the clinical trials for multiple myeloma; besides, SG003 showed enhanced antibody-dependent cell-mediated cytotoxicity function and in vivo inhibitory efficacy of tumor growth in xenograft mice model.

Conclusion

SG003 seemed to be a good option to improve the curative effect of CD38-related cancers.

Overexpression of the proneural transcription factor ASCL1 in chronic lymphocytic leukemia with a t(12;14)(q23.2;q32.3)

Background

Translocations of the IGH locus on 14q32.3 are present in about 8% of patients with chronic lymphocytic leukemia (CLL) and contribute to leukemogenesis by deregulating the expression of the IGH-partner genes. Identification of these genes and investigation of the downstream effects of their deregulation can reveal disease-causing mechanisms.

Case presentation

We report on the molecular characterization of a novel t(12;14)(q23.2;q32.3) in CLL. As a consequence of the rearrangement ASCL1 was brought into proximity of the IGHJ-Cμ enhancer and was highly overexpressed in the aberrant B-cells of the patient, as shown by qPCR and immunohistochemistry. ASCL1 encodes for a transcription factor acting as a master regulator of neurogenesis, is overexpressed in neuroendocrine tumors and a promising therapeutic target in small cell lung cancer (SCLC). Its overexpression has also been recently reported in acute adult T-cell leukemia/lymphoma.To examine possible downstream effects of the ASCL1 upregulation in CLL, we compared the gene expression of sorted CD5⁺ cells of the translocation patient to that of CD19⁺ B-cells from seven healthy donors and detected 176 significantly deregulated genes (Fold Change ≥2, FDR p ≤ 0.01). Deregulation of 55 genes in our gene set was concordant with at least two studies comparing gene expression of normal and CLL B-lymphocytes. INSM1, a well-established ASCL1 target in the nervous system and SCLC, was the gene with the strongest upregulation (Fold Change = 209.4, FDR p = 1.37E-4).INSM1 encodes for a transcriptional repressor with extranuclear functions, implicated in neuroendocrine differentiation and overexpressed in the majority of neuroendocrine tumors. It was previously shown to be induced in CLL cells but not in normal B-cells upon treatment with IL-4 and to be overexpressed in CLL cells with unmutated versus mutated IGHV genes. Its role in CLL is still unexplored.

Conclusion

We identified ASCL1 as a novel IGH-partner gene in CLL. The neural transcription factor was strongly overexpressed in the patient's CLL cells. Microarray gene expression analysis revealed the strong upregulation of INSM1, a prominent ASCL1 target, which was previously shown to be induced in CLL cells upon IL-4 treatment. We propose further investigation of the expression and potential role of INSM1 in CLL.

Dysregulated Class I histone deacetylases are indicators of poor prognosis in multiple myeloma

Histone deacetylases (HDAC) control gene expression through their ability to acetylate proteins, thereby influencing a diverse range of cellular functions. Class I HDAC (HDAC1-3 and 8) and HDAC6 are predominantly upregulated in malignancies and their altered expression in some cancers has a significant prognostic implication. The expression and prognostic consequence of dysregulated Class I HDAC and HDAC6, key players in multiple myeloma (MM), are unknown. This study hypothesized that HDAC are dysregulated in MM and patients with high expression have significantly poorer prognostic outcomes. Quantitative PCR for 11 HDAC (Class I, II, and IV) was performed in genetically heterogeneous human myeloma cell lines (HMCL) and primary MM and compared to normal plasma cells (PC). In HMCL, HDAC1-3 and 8 (Class I), and HDAC5 and HDAC10 (Class II) were significantly upregulated compared to normal PC. In primary MM, the median expression level of all of the HDAC, except HDAC1 and HDAC11, were elevated when compared to normal PC. Patients with higher levels of HDAC1-3, HDAC4, HDAC6, and HDAC11 transcripts demonstrated a significantly shorter progression-free survival (PFS). Immunohistochemical staining for HDAC1 and HDAC6 on bone marrow trephines from a uniformly treated cohort of transplant eligible MM patients revealed that HDAC1 protein was detectable in most patients and that higher levels of MM cell HDAC1 protein expression (≥90 % versus ≤20 % MM cell positivity) correlated with both shorter PFS (P = 0 .07) and shorter overall survival (P = 0 .003). Conversely, while the majority of patients expressed HDAC6, there was no correlation between HDAC6 levels and patient outcome. Together, these results indicate that overexpression of Class I HDAC, particularly HDAC1, is associated with poor prognosis in MM.

Antibody-mediated phagocytosis contributes to the anti-tumor activity of the therapeutic antibody daratumumab in lymphoma and multiple myeloma

Daratumumab (DARA) is a human CD38-specific IgG1 antibody that is in clinical development for the treatment of multiple myeloma (MM). The potential for IgG1 antibodies to induce macrophage-mediated phagocytosis, in combination with the known presence of macrophages in the tumor microenvironment in MM and other hematological tumors, led us to investigate the contribution of antibody-dependent, macrophage-mediated phagocytosis to DARA's mechanism of action. Live cell imaging revealed that DARA efficiently induced macrophage-mediated phagocytosis, in which individual macrophages rapidly and sequentially engulfed multiple tumor cells. DARA-dependent phagocytosis by mouse and human macrophages was also observed in an in vitro flow cytometry assay, using a range of MM and Burkitt's lymphoma cell lines. Phagocytosis contributed to DARA's anti-tumor activity in vivo, in both a subcutaneous and an intravenous leukemic xenograft mouse model. Finally, DARA was shown to induce macrophage-mediated phagocytosis of MM cells isolated from 11 of 12 MM patients that showed variable levels of CD38 expression. In summary, we demonstrate that phagocytosis is a fast, potent and clinically relevant mechanism of action that may contribute to the therapeutic activity of DARA in multiple myeloma and potentially other hematological tumors.

Identification of primary MAFB target genes in multiple myeloma

OBJECTIVE

In multiple myeloma (MM), seven primary recurrent translocations involving the immunoglobulin heavy chain locus have been identified. One of the partner loci maps to 20q12 and involves the MAFB gene resulting in its ectopic expression. We attempt here to identify MAFB target genes in MM.

MATERIALS AND METHODS

We used an inducible system to upregulate MAFB in MM cell lines not carrying the t(14;20). Microarray expression analysis was used to detect gene expression changes upon MAFB expression. These genes were further evaluated comparatively with gene expression profiles obtained from MM or plasma cell leukemia tumors carrying an activated MAFB gene. Functional implications of these upregulated genes were studied by testing their promoter activity in reporter assays. C-MAF was included comparatively as well.

RESULTS

The inducible cell lines identified a total of 284 modulated transcripts. After further evaluation using ex vivo data 14 common upregulated genes were found, common to the C-MAF pathway as well. The promoter activity of some of these secondary genes proved a functional relationship with MAFB. In connection with one of these secondary genes (NOTCH2), even tertiary upregulated genes were found. Functional studies indicated that inducible MAFB expression conferred antiapoptotic effects.

CONCLUSION

We identified 14 upregulated genes, and their downstream consequences in the combined MAFB/C-MAF pathway. Eleven of these genes are novel in the C-MAF pathway as well. These direct target genes may be responsible for the oncogenic transformation of MAF expressing myeloma cells.

'Light-chain escape-multiple myeloma'-an escape phenomenon from plateau phase: report of the largest patient series using LC-monitoring

PURPOSE

More intensive and novel therapy options in multiple myeloma (MM) hold the promise to improve treatment outcome. However, disease evolution, induced with long disease duration and extensive pretreatment, has resulted in changes in the biological behaviour of MM and unusual relapse emergence, such as of extramedullary (EM) disease or a shift in secretion from intact immunoglobulin (Ig) to free-light chains (FLCs) only.

METHODS

We studied ten patients since 2004, thoroughly assessed relevant patient characteristics, prominent similarities, SFLC-changes, therapy response, mode and speed of progression, and the incidence of light-chain escape (LCE)-MM within our entire myeloma patient cohort. Serum FLCs (SFLCs) were determined via Freelite-assay (Dade-Behringer Nephelometer).

RESULTS

This report summarizes the to date largest series of ten patients, whose MM appeared stable, as judged by conventional monitoring of intact Ig levels, but developed severe organ dysfunction as a consequence of initially undetected LC-progression. Median number of anti-MM cycles before LCE occurrence was six, including autologous and/or allogeneic stem cell transplants and novel drugs, predominantly thalidomide, in 4/10. Classic diagnostics, such as electrophoresis and quantitative Ig measurement proved futile to detect LC-progression, whereas SFLCs were reliable markers. The LCE-MM prevalence within 407 MM patients treated in our institution between 2004 and 2007 was 2.46%.

CONCLUSIONS

Our report suggests that early detection of LCE-MM by means of serial SFLC measurements may prevent unnecessary complications, allows to detect unusual relapse manifestations in the era of intensive and biological therapy options and possibly also permits to improve treatment results in LCE-MM.

Immunoglobulin gene rearrangements and the pathogenesis of multiple myeloma

The ability to rearrange the germ-line DNA to generate antibody diversity is an essential prerequisite for the production of a functional repertoire. While this is essential to prevent infections, it also represents the “Achilles heal” of the B-cell lineage, occasionally leading to malignant transformation of these cells by translocation of protooncogenes into the immunoglobulin (Ig) loci. However, in evolutionary terms this is a small price to pay for a functional immune system. The study of the configuration and rearrangements of the Ig gene loci has contributed extensively to our understanding of the natural history of development of myeloma. In addition to this, the analysis of Ig gene rearrangements in B-cell neoplasms provides information about the clonal origin of the disease, prognosis, as well as providing a clinical useful tool for clonality detection and minimal residual disease monitoring. Herein, we review the data currently available on both Ig gene rearrangements and protein patterns seen in myeloma with the aim of illustrating how this knowledge has contributed to our understanding of the pathobiology of myeloma.

A class II-restricted cytotoxic T-cell clone recognizes a human minor histocompatibility antigen with a restricted tissue distribution

Following a human leucocyte antigen (HLA)-identical allogeneic stem cell transplantation (allo-SCT), minor histocompatibility antigens (mHags) play an important role in the induction of graft-versus-leukaemia (GvL) and graft-versus-myeloma (GvM). Many mHags show ubiquitous tissue expression and are associated with GvL and graft-versus-host disease. Here we describe a cytotoxic CD4(+) T lymphocyte line and a cytotoxic, CD4(+) T cell clone (CTC), 3AB11, which recognized a tissue-restricted mHag. This CTC was isolated from a multiple myeloma patient with clinical GvM following an HLA-matched allo-SCT. CTC 3AB11 was activated in a HLA-DP*0401 restricted fashion and the antigen was expressed by 27% of HLA-DP*0401 positive Epstein-Barr virus (EBV)-transformed B-cell lines (EBV-B). Tissue distribution analysis of antigen 3AB11 showed it to be expressed by patient-derived EBV-transformed B cell lines (EBVp), the myeloma plasma cell-line UM9 and monocytes. It was weakly expressed by peripheral blood-derived phytohaemagglutinin-induced T-cell blasts and absent on CD40L stimulated peripheral B (CD40L B) cells and stromal cells. The relatively high prevalence of the HLA class II-restricted 3AB11 antigen, together with its apparent haematopoietic-restricted expression, makes it an antigen of interest for cellular immunotherapy.

The recurrent translocation t(14;20)(q32;q12) in multiple myeloma results in aberrant expression of MAFB: a molecular and genetic analysis of the chromosomal breakpoint

Chromosomal translocations of the immunoglobulin heavy chain (IgH) gene region at 14q32 are regularly involved in B lymphoid malignancies; they may initiate transformation either by deregulation of existing (proto) oncogenes or creation of new hybrid genes with transforming properties. Previously, we reported a reciprocal novel translocation, t(14;20)(q32;q12), found in the myeloma cell line UM3. In this cell line, the t(14;20) is the only translocation involving the IgH locus. Using double colour immunofluorescence in situ hybridization, the t(14;20) was also found in the diagnostic bone marrow sample, excluding a possible in vitro artefact. We also have found this recurrent t(14;20) in four other cell lines and in additional patient material. We cloned the regions containing the breakpoints in the der(14) and der(20) chromosomes from UM3, and analysed ectopic mRNA expression of genes in the breakpoint regions of both derivative chromosomes. Ectopic gene expression was observed for the transcription factor MAFB in der(14). The breakpoint scatter in the five cell lines with a t(14;20)--all expressing MAFB--is comprised within a region of 0.8 Mb. Provisional data indicate that this t(14;20) is associated with an adverse prognosis. Aberrant expression of MAFB may be involved in the oncogenic transformation of myeloma cells that harbour the t(14;20).

Light-chain only multiple myeloma is due to the absence of functional (productive) rearrangement of the IgH gene at the DNA level

Although most multiple myeloma (MM) cases are characterized by the detection of a monoclonal immunoglobulin in the serum, about 15% of the patients present only immunoglobulin light chains, detected either in the urine or serum or both. These patients are designated as having light-chain (LC) MM. Using fiber-fluorescent in situ hybridization, and in contrast to patients and myeloma cell lines secreting heavy chains (who presented a legitimate functional IgH rearrangement in every case), LC MM never displayed a functional IgH recombination. Interestingly, most LC MM cases presented one IgH allele with a germline configuration (including the DJ region), the second allele being usually involved in an illegitimate recombination. Of note, most of these translocations occurred close to (or at) switch regions, even though in some cases, breakpoints involving nonswitch regions were observed. Thus, this study clearly showed that LC MM is due to the absence of legitimate IgH rearrangement at the DNA level, reflecting possible abnormalities in the IgH gene recombinations during B-cell maturation. Furthermore, it showed that this defect did not prevent the activation of the switch process because most of 14q32 translocations observed in LC MM occurred at switch regions.

Illegitimate WNT signaling promotes proliferation of multiple myeloma cells

The unrestrained growth of tumor cells is generally attributed to mutations in essential growth control genes, but tumor cells are also influenced by signals from the environment. In multiple myeloma (MM), the factors and signals coming from the bone marrow microenvironment are possibly even essential for the growth of the tumor cells. As targets for intervention, these signals may be equally important as mutated oncogenes. Given their oncogenic potential, WNT signals form a class of paracrine growth factors that could act to influence MM cell growth. In this paper, we report that MM cells have hallmarks of active WNT signaling, whereas the cells have not undergone detectable mutations in WNT signaling genes such as adenomatous polyposis coli and beta-catenin (CTNNB1). We show that the malignant MM plasma cells overexpress beta-catenin, including its N-terminally unphosphorylated form, suggesting active beta-catenin/T cell factor-mediated transcription. Further accumulation and nuclear localization of beta-catenin, and/or increased cell proliferation, was achieved by stimulation of WNT signaling with either Wnt3a, LiCl, or the constitutively active S33Y mutant of beta-catenin. In contrast, by blocking WNT signaling by dominant-negative T cell factor, we can interfere with the growth of MM cells. We therefore suggest that MM cells are dependent on an active WNT signal, which may have important implications for the management of this incurable form of cancer.

The hepatocyte growth factor/Met pathway controls proliferation and apoptosis in multiple myeloma

The evolution of multiple myeloma (MM) depends on complex signals from the bone marrow (BM) microenvironment, supporting the proliferation and survival of malignant plasma cells. An interesting candidate signal is hepatocyte growth factor/scatter factor (HGF), since its receptor Met is expressed on MM cells, while HGF is produced by BM stromal cells and by some MM cell lines, enabling para- or autocrine interaction. To explore this hypothesis, we studied the biological effects of HGF stimulation on MM cell lines and on primary MMs. We observed that Met is expressed by the majority of MM cell lines and by approximately half of the primary plasma cell neoplasms tested. Stimulation of MM cells with HGF led to the activation of the RAS/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/protein kinase B (PI3K/PKB) pathways, signaling routes that have been implicated in the regulation of cell proliferation and survival. Indeed, functional studies demonstrated that HGF has strong proliferative and anti-apoptotic effects on both MM cell lines and primary MM cells. Furthermore, by applying specific signal-transduction inhibitors, we demonstrated that MEK is required for HGF-induced proliferation, whereas activation of PI3K is required for both HGF-induced proliferation and for rescue of MM cells from apoptosis. Taken together, our data indicate that HGF is a potent myeloma growth and survival factor and suggest that the HGF/Met pathway is a potential therapeutic target in MM.

Overexpression of the myeloma-associated oncogene fibroblast growth factor receptor 3 confers dexamethasone resistance

Translocations involving the immunoglobulin heavy-chain switch region and fibroblast growth factor receptor 3 (FGFR3) are identified in 10% to 15% of patients with myeloma. In previous research we overexpressed FGFR3 or the constitutively active FGFR3-TD mutant in an interleukin-6 (IL-6)-dependent murine myeloma cell line, B9. FGFR3-enhanced IL-6 responsiveness increased phosphorylation of STAT3 and up-regulated Bcl-x(L). Since Bcl-x(L) was up-regulated, we have tested FGFR3-expressing B9 cells for chemotherapy sensitivity. FGFR3 expression did not alter sensitivity to melphalan or doxorubicin. In contrast, B9 cells overexpressing FGFR3 were resistant to treatment with dexamethasone, a phenomenon successfully reversed using a Bcl-x(L) antisense oligonucleotide. These data demonstrate that the overexpression of FGFR3 in B9 cells confers resistance to dexamethasone but not to anthracyclines or alkylating agents, at least in part through the up-regulation of Bcl-x(L). This finding has potential implications for the use of chemotherapy in t(4;14)-positive myeloma.

Isotype switch-mediated CH deletions are a recurrent feature of Myc/CH translocations in peritoneal plasmacytomas in mice

Oncogene activating chromosomal translocations that interrupt IGH switch (S) regions at 14q32 are thought to be caused by misguided IGH isotype switching in postgerminal center B-cell lymphomas and plasma cell myelomas in humans. Aberrant switching also seems to be involved in altering the fine structure of the translocation in some of these tumors, but the significance of these changes is not known. Here we report on 3 cases of IL-6 transgenic mouse plasmacytomas (PCT) that harbor T(12;15) translocations that had been modified by frustrated switch attempts that result in C(H) deletions. When considered together with 6 similar cases of PCT described previously, our observations suggest that secondary deletions in C(H) are a regular feature in the molecular evolution of T(12;15) translocations and, thereby, in the progression of PCT. We propose that the T(12;15)(+) mouse PCT offers a uniquely valuable model system for elucidating the dual role of abnormal isotype switching in causation and 'remodeling' of chromosomal translocations.

Detection of illegitimate rearrangement within the immunoglobulin locus on 14q32.3 in B-cell malignancies using end-sequenced probes

Translocation involving the immunoglobulin heavy chain (IGH) locus is a recurring event in B-cell oncogenesis. The aim of this study was to characterize clones from bacterial artificial chromosome (BAC) libraries and/or bacteriophage P1 artificial chromosome libraries spanning the IGH locus for detection of illegitimate rearrangement within the region by fluorescence in situ hybridization (FISH). In silico analysis of the IGH variable (IGHV) DNA sequence (NT_001716.v1) was performed to identify BAC probes located within the IGHV cluster. Clones of the constant (IGHC) cluster were found in the literature or at http://www.biologia.uniba.it/rmc/. Validation, orientation, and overlap of these probes were confirmed using interphase-, metaphase-, and fiber-FISH. We have identified seven BAC end-sequenced probes (3087C18, 47P23, 76N15, 12F16, 101G24, 112H5, and 151B17) covering 612 kb of the distal IGHV cluster, which, together with probes covering the IGHC cluster (11771 and 998D24), could be used in interphase nuclei and metaphase chromosome analysis. A visual split of the IGHV and IGHC clusters indicating a translocation was analyzed by dual-color FISH in a series of 21 cell lines of different origins. Translocations were found, as expected, in eight of eight myelomas, four of four lymphomas, none of five leukemias, and none of four Epstein-Barr virus-transformed B-lymphoblastoid cell lines. To summarize, we have established a set of IGHV and IGHC probes that can be used for universal screening of illegitimate rearrangement within the IGH locus in B-cell malignancies. These probes allow for routine FISH analysis to detect this early central oncogenic event.

Molecular aspects of multiple myeloma

Multiple myeloma (MM) is a B-cell neoplasm characterized by bone marrow infiltration with malignant plasma cells, which synthesize and secrete monoclonal immunoglobulin (Ig) fragments. Despite the considerable progress in the understanding of MM biology, the molecular basis of the disease remains elusive. The initial transformation is thought to occur in a postgerminal center B-lineage cell, carrying a somatically hypermutated Ig heavy chain (IGH) gene. This plasmablastic precursor cell colonizes the bone marrow, propagates clonally and differentiates into a slowly proliferating myeloma cell population, all under the influence of specific cell adhesion molecules and cytokines. Production of interleukin-6 by stromal cells, osteoblasts and, in some cases, neoplastic cells is an essential element of myeloma cell growth, with the cytokine stimulus being delivered intracellularly via the Jack-STAT and ras signaling pathways. While karyotypic changes have been identified in up to 50% of MM patients, recent molecular cytogenetic techniques have revealed chromosomal abnormalities in the vast majority of examined cases. Translocations mostly involve illegal switch rearrangements of the IGH locus with various partner genes (CCND1, FGFR3, c-maf). Such events have been assigned a critical role in MM development. Mutations in coding and regulatory regions, as well as aberrant expression patterns of several oncogenes (c-myc, ras) and tumor suppressor genes (p16, p15) have been reported. Key regulators of programmed cell death (BCL-2, Fas), tumor expansion (metalloproteinases) and drug responsiveness (topoisomerase II alpha) have also been implicated in the pathogenesis of this hematologic malignancy. A tumorigenic role for human herpesvirus 8 (HHV8) was postulated recently, following the detection of viral sequences in bone marrow dendritic cells of MM patients. However, since several research groups were unable to confirm this observation, the role of HHV8 remains unclear. Translation of the advances in MM molecular biology into novel therapeutic strategies is essential in order to improve disease prognosis.

Molecular features responsible for the absence of immunoglobulin heavy chain protein synthesis in an IgH− subgroup of multiple myeloma

This study involved 12 patients with multiple myeloma (MM), in whom malignant plasma cells did not contain immunoglobulin heavy chain (IgH) protein chains. Southern blot analysis revealed monoallelic Jh gene rearrangements in 10 patients, biallelic rearrangement in 1 patient, and biallelic deletion of the Jh and Cμ regions in 1 patient. Heteroduplex polymerase chain reaction analysis enabled the identification and sequencing of 9 clonal Jhgene rearrangements. Only 4 of the joinings were complete Vh-(D)-Jhrearrangements, including 3 in-frame rearrangements with evidence of somatic hypermutation. Five rearrangements concerned incomplete Dh-Jh joinings, mainly associated with deletion of the other allele. Curiously, in at least 1 of these 5 cases the second allele seemed to be in germline configuration, whereas the in-frame Vκ-Jκgene rearrangements contained somatic mutations. The configuration of the IGH genes was further investigated by use of Ch probes. In 5 patients the rearrangements in the Jh and Ch regions were not concordant, probably caused by illegitimate IGH class switch recombination (chromosomal translocations to 14q32.3). These data indicate that in many IgH− MM patients illegitimateIGH class switch rearrangement or illegitimate deletion of the functional Vh-(Dh)-Jhallele are responsible for IgH negativity. For example, the exclusive presence ofDh-Jhrearrangements in combination with mutated IGK genes can only be explained in terms of normal B-cell development, if the second (functional) IGH allele is deleted, which was probably the case in most patients. Therefore, defects at the DNA level are responsible for the lack of IgH protein production in most IgH− MM patients.

Malignant hematopoietic cell lines: in vitro models for the study of multiple myeloma and plasma cell leukemia

Multiple myeloma (MM) is a neoplasm of a terminally differentiated B-cell. The disease is progressive and always lethal characterized by the slow proliferation of malignant plasma cells in the bone marrow. Much of our current understanding of the biology of MM has been obtained by studying MM-derived cell lines. Human myeloma cell lines were shown to be suitable model systems for use in various fields of the biological sciences. However, it has proved very difficult to establish cell lines from plasma cell dyscrasias. Most reported MM cell lines have been derived from patients with advanced disease and from extramedullary sites. Nevertheless, within the last 20 years more than 100 cell lines have been established. A significant portion of this panel is partially or well characterized with regard to their cell culture, clinical, immunophenotypic, cytogenetic and functional features. Distinct immunoprofiles could be assigned to MM cell lines. All MM cell lines display chromosomal aberrations; in more than 80% of the cell lines analyzed, chromosome 14 band q32 (immunoglobulin heavy chain locus) is affected; the various types of 14q+ chromosomes showed different distributions among the MM cell lines. A large percentage of MM cell lines is constitutively interleukin-6-dependent or responsive to various cytokines. It is important to realize that not every cell line established from a patient with myeloma is a neoplastic cell line. So-called 'myeloma cell lines' have been previously reported and are still widely used which are in reality Epstein-Barr virus (EBV)-positive B-lymphoblastoid cell lines. The presence of the EBV-genome in residual normal B-cells provides them with a selective growth advantage after explantation. In summary, a significant number of authentic and well-characterized MM cell lines has been established and described. The availability of these bona fide MM cell lines is of great importance for the study of the biology, etiology and treatment of the disease.

Molecular features responsible for the absence of immunoglobulin heavy chain protein synthesis in an IgH− subgroup of multiple myeloma

This study involved 12 patients with multiple myeloma (MM), in whom malignant plasma cells did not contain immunoglobulin heavy chain (IgH) protein chains. Southern blot analysis revealed monoallelic Jh gene rearrangements in 10 patients, biallelic rearrangement in 1 patient, and biallelic deletion of the Jh and Cμ regions in 1 patient. Heteroduplex polymerase chain reaction analysis enabled the identification and sequencing of 9 clonal Jhgene rearrangements. Only 4 of the joinings were complete Vh-(D)-Jhrearrangements, including 3 in-frame rearrangements with evidence of somatic hypermutation. Five rearrangements concerned incomplete Dh-Jh joinings, mainly associated with deletion of the other allele. Curiously, in at least 1 of these 5 cases the second allele seemed to be in germline configuration, whereas the in-frame Vκ-Jκgene rearrangements contained somatic mutations. The configuration of the IGH genes was further investigated by use of Ch probes. In 5 patients the rearrangements in the Jh and Ch regions were not concordant, probably caused by illegitimate IGH class switch recombination (chromosomal translocations to 14q32.3). These data indicate that in many IgH− MM patients illegitimateIGH class switch rearrangement or illegitimate deletion of the functional Vh-(Dh)-Jhallele are responsible for IgH negativity. For example, the exclusive presence ofDh-Jhrearrangements in combination with mutated IGK genes can only be explained in terms of normal B-cell development, if the second (functional) IGH allele is deleted, which was probably the case in most patients. Therefore, defects at the DNA level are responsible for the lack of IgH protein production in most IgH− MM patients.