Waldenström Macroglobulinemia and Non-IgM-Type Lymphoplasmacytic Lymphoma Are Genetically Similar.

INTRODUCTION: Waldenström macroglobulinemia (WM) represents a subset of lymphoplasmacytic lymphoma (LPL) with the immunoglobulin (Ig)M paraprotein. MYD88 L265P and CXCR4 mutations are common mutations in WM patients, and mutations in ARID1A and KMT2D (MLL2) have also been reported. However, little information has been accumulated on genetic changes in LPL with other paraproteins like IgG. METHODS: We therefore aimed to evaluate genetic differences between WM and LPL with non-IgM paraprotein (non-IgM-type LPL) using targeted next-generation sequencing (NGS) in 20 Japanese patients (10 with WM, 10 with non-IgM-type LPL). RESULTS: Mutations were detected in ARID1A (10%), CXCR4 (20%), MYD88 (90%), and KMT2D (0%) for WM patients and in ARID1A (10%), CXCR4 (20%), MYD88 (70%), and KMT2D (10%) for non-IgM-type LPL patients. No significant differences were identified. No mutations were detected in NOTCH2, PRDM1, CD274 (PD-L1), PDCD1LG2 (PD-L2), RAG2, MYBBP1A, TP53, or CD79B. DISCUSSION: Mutant allele frequency in MYD88 L265P did not differ significantly between WM and non-IgM-type LPL. Most mutations detected by NGS were subclonal following MYD88 L265P, although one non-IgM-type LPL patient harbored only CXCR4 S338X mutation. Our NGS analyses reveal genetic characteristics in LPL patients and suggest genetic similarities between these two subsets of LPL, WM and non-IgM-type.

Lymphoplasmacytic lymphoma with IgG or IgA paraprotein: a study of 29 cases including cases that can mimic plasma cell neoplasms.

Lymphoplasmacytic lymphoma (LPL) with IgG or IgA paraprotein is rare and a subset of cases can mimic a plasma cell neoplasm (PCN). We studied 29 such cases to explore their clinicopathological features and the best diagnostic approaches with a focus on bone marrow findings. The cohort included 18 men and 11 women with a median age of 68 years. The median M protein was 3.1 g/dL, IgG in 19 patients (66%), IgA in 9 (31%), and dual IgG/IgA in 1 (3%). All patients had bone marrow involvement with CD138+ plasma cells (PCs) ranging from 1 to 35% (median, 10%). Two patients also had amyloidosis. Immunoglobulin light chain concordant monotypic PCs and monotypic B cells were identified in 96% of cases assessed by flow cytometry. Notably, the neoplastic PCs were consistently positive for CD45 (dim, 100%), CD19 (96%), CD81 (89%), CD27 (83%), rarely and only weakly or partially express CD56 (16%), whereas CD117 was consistently negative. Eleven cases analyzed by fluorescence in situ hybridization were negative for CCND1::IGH and myeloma-related aberrations. MYD88 mutation was detected in 17 of 24 cases (71%), and CXCR4 mutation was identified in 6 of 19 cases (32%), of which 4 had concurrent MYD88 mutation. In conclusion, the results highlight a potential diagnostic pitfall of LPL associated with marked plasmacytic differentiation and an IgG or IgA paraprotein that can resemble a PCN. Useful features in favor of LPL against PCN include the characteristic immunophenotypic profile of the PCs in LPL, absence of CCND1::IGH, and the presence of MYD88 and/or CXCR4 mutations.

Inactivation of protein-phosphatase 2A causing hyperphosphorylation of autoantigenic paraprotein targets in MGUS/MM is due to an exchange of its regulatory subunits.

Hyperphosphorylated paratarg-7 (pP-7) carrier state is the strongest molecularly defined risk factor for monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM). pP-7 is inherited as autosomal-dominant trait and depending on the ethnic background is found in over one-third of MGUS/MM patients. P-7, which is the antigenic paraprotein target in these patients, is hyperphosphorylated at serine17. P-7 hyperphosphorylation can be induced in wild-type P-7 (wtP-7) carriers by PKCζ and reverted by protein-phosphatase 2A (PP2A). Here we show that dephosphorylation of pP-7 is defective in pP-7 carriers due to inactivation of the PP2A by substitution of the regulatory B55δ subunit with B56γ3. In lymphoblastoid cell lines from pP-7 carriers, transfection of recombinant B55δ or treatment with ceramide led to a partial reconstitution of PP2A activity and dephosphorylation of pP-7 to wtP7. Similar results were observed with other previously reported autoantigenic paraproteins targets. In conclusion, the mechanisms responsible for the defective dephosphorylation and maintaining the hyperphosphorylated state of P-7 and other autoantigenic paraprotein targets have been elucidated, facilitating the identification of the genetic basis underlying this phenomenon which is obviously common in the pathogenesis of MGUS/MM/WM and not restricted to pP-7 cases.

Over one-third of African-American MGUS and multiple myeloma patients are carriers of hyperphosphorylated paratarg-7, an autosomal dominantly inherited risk factor for MGUS/MM.

As hyperphosphorylated paratarg-7 (pP-7) carrier state was shown to be the first molecularly defined autosomal dominantly inherited risk factor for monoclonal gammopathy of unknown significance (MGUS) and multiple myeloma (MM) in a European population, the prevalence of pP-7 carrier state among African-Americans who have a significantly higher incidence of MGUS/MM is of interest. We therefore determined pP-7 carrier state and paraproteins with specificity for P-7 in African-American, European and Japanese patients with MGUS/MM and healthy controls. By isoelectric focusing and ELISA, a paratarg-7-specific paraprotein and the associated pP-7 carrier state was observed in 30/81 (37.0%) African-American, 42/252 (16.7%) European and 7/176 (4.0%) Japanese MGUS/MM patients (p < 0.001). A pP-7 carrier state was found in 11/100 (11.0%) African-American, 8/550 (1.5%) European and 1/278 (0.4%) Japanese healthy controls (p < 0.001), resulting in an odds ratio for MGUS/MM of 4.8 (p < 0.001) among African-American, 13.6 among European (p < 0.001) and 11.5 (p = 0.023) among Japanese carriers of pP-7. We conclude that pP-7 carriers are most prevalent among African-Americans, but a pP-7 carrier state is the strongest molecularly defined single risk factor for MGUS/MM known to date in all three ethnic groups. The high prevalence of pP-7 carriers among African-American patients emphasizes a predominant role of this genetic factor in the pathogenesis of these diseases. The large number of pP7 African-American patients and controls should facilitate the identification of the SNP or mutation underlying the pP-7 carrier state.

Characterization of a novel mouse model of multiple myeloma and its use in preclinical therapeutic assessment.

To aid preclinical development of novel therapeutics for myeloma, an in vivo model which recapitulates the human condition is required. An important feature of such a model is the interaction of myeloma cells with the bone marrow microenvironment, as this interaction modulates tumour activity and protects against drug-induced apoptosis. Therefore NOD/SCIDγc(null) mice were injected intra-tibially with luciferase-tagged myeloma cells. Disease progression was monitored by weekly bioluminescent imaging (BLI) and measurement of paraprotein levels. Results were compared with magnetic resonance imaging (MRI) and histology. Assessment of model suitability for preclinical drug testing was investigated using bortezomib, melphalan and two novel agents. Cells engrafted at week 3, with a significant increase in BLI radiance occurring between weeks 5 and 7. This was accompanied by an increase in paraprotein secretion, MRI-derived tumour volume and CD138 positive cells within the bone marrow. Treatment with known anti-myeloma agents or novel agents significantly attenuated the increase in all disease markers. In addition, intra-tibial implantation of primary patient plasma cells resulted in development of myeloma within bone marrow. In conclusion, using both myeloma cell lines and primary patient cells, we have developed a model which recapitulates human myeloma by ensuring the key interaction of tumour cells with the microenvironment.

Hyperphosphorylation of autoantigenic targets of paraproteins is due to inactivation of PP2A.

Paratarg-7, a frequent autoantigenic target, and all other autoantigenic targets of human paraproteins molecularly defined to date are hyperphosphorylated in the respective patients compared with healthy controls, suggesting that hyperphosphorylation of autoantigenic paraprotein targets is a general mechanism underlying the pathogenesis of these paraproteins. We now show that hyperphosphorylation of paratarg-7 occurs because of an additional phosphorylation of Ser17, which is located within the paraprotein-binding epitope. Coimmunoprecipitation identified phosphokinase C ζ (PKCζ) as the kinase responsible for the phosphorylation of most, and phosphatase 2A (PP2A) as the phosphatase responsible for the dephosphorylation of all hyperphosphorylated autoantigenic targets of paraproteins. Single-nucleotide polymorphisms (SNPs) or mutations of PKCζ and PP2A were excluded. However, PP2A was inactivated by phosphorylation of its catalytic subunit at Y307. Stimulation of T cells from healthy carriers of wild-type paratarg-7 induced a partial and transient hyperphosphorylation between days 4 and 18, which was maintained by incubation with inhibitors of PP2A, again indicating that an inactivation of PP2A is responsible for the hyperphosphorylation of autoantigenic paraprotein targets. We conclude that the genetic defect underlying the dominantly inherited hyperphosphorylation of autoantigenic paraprotein targets is not in the PP2A itself, but in genes or proteins controlling PP2A activity by phosphorylation of its catalytic subunit.

Paraproteins of familial MGUS/multiple myeloma target family-typical antigens: hyperphosphorylation of autoantigens is a consistent finding in familial and sporadic MGUS/MM.

Paratarg-7 (P-7) is a frequent paraprotein target in monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM), and Waldenström macroglobulinemia. Patients with P-7-specific paraproteins carry a hyperphosphorylated paratarg-7 (pP-7). Because pP-7 carrier state is dominantly inherited, we determined the paraprotein targets in 4 families with familial MGUS/MM. No antigenic target was identified for the paraproteins from 2 members of one family. Paraproteins from affected members of 2 other families targeted P-7, and paraproteins from 4 affected members of a fourth family targeted P-8, which is encoded by the ATG13 gene. P-8 was hyperphosphorylated in the affected family members (pP-8) and pP-8 carrier state is inherited in a dominant fashion. Six additional autoantigenic nonfamilial paraprotein targets were also hyperphosphorylated in the respective patients compared with normal controls. We conclude that paraproteins of affected members with familial MGUS/MM share family-typical hyperphosphorylated antigens and hyperphosphorylation of paraprotein targets might be a general mechanism underlying the pathogenesis of MGUS/MM.

Familial monoclonal gammopathy: hyper-responsive B cells in unaffected family members.

BACKGROUND: In Iceland, eight families have been identified with multiple cases of monoclonal gammopathies (MG) and other lymphoproliferative diseases. In one of these families with several cases of monoclonal gammopathy of undetermined significance (MGUS) and Waldenströms macroglobulinemia, in vitro stimulation with poke-weed mitogen revealed hyper-responsive B cells showing increased immunoglobulin production in one-third of disease-free family members. DESIGN AND METHODS: In this study, the families were further traced and the list of names produced was compared with The Icelandic Cancer Registry (ICR) to find all recent cases of lymphoproliferative diseases. First-degree relatives and descendants older than 20yrs of age (n=350) were selected for screening for paraprotein. Selected family members were tested for B-cell hyper-responsiveness and the lymphocyte phenotype was analysed by flow cytometry. RESULTS: Comparison of the total list of 4370 family members with the ICR revealed 22 new cases and screening for serum paraprotein identified nine new cases of MG, eight being first-degree relatives of known probands. Sixty cases of lymphoproliferative diseases are currently known within the eight families, five of them containing both IgG/A and IgM disorders. Twelve hyper-responders (HR) were identified in four families, eight from one family, of whom four were known already. Stimulated B cells from HR had a significantly higher proportion of CD27(+) memory/plasma cells than controls. CONCLUSION: Identification of new affected family members by screening confirms a hereditary predisposition to B-cell proliferative diseases. Contrary to most studies, IgG/A and IgM disorders occurred together in five families. In four families, enhanced B-cell responsiveness was found in healthy subjects clustered around cases.

Induction of cellular immune responses in patients with stage-I multiple myeloma after vaccination with autologous idiotype-pulsed dendritic cells.

Idiotype vaccines have shown both biological efficacy and clinical benefit in lymphoma. Circulating idiotype proteins (Id) in multiple myeloma patients offer a suitable target for immunotherapy. So far, specific immune responses after vaccination with Ids have been evaluated mostly in advanced myeloma. We explored the potential of dendritic-cell (DC)-based immunotherapy in 9 patients with stage-I disease. Mature monocyte-derived Id-pulsed DCs and keyhole limpet hemocyanin (KLH) were administered at dose levels between 2 and 20×106 cells. Patients received 5 immunizations every 4 weeks. A median number of 6.8×106 DCs were administered per vaccination. Five out of 9 patients (56%) developed Id-specific T cells as showed in proliferation assays and 8 out of 9 patients (89%) showed specific T-cell-mediated cytokine release after Id stimulation. The cytokine-secretion did not show a distinct Th1-type or Th2-type pattern. The M protein dropped slightly in 3 out of 9 patients. We could show that DC-based Id vaccination is a feasible way of inducing specific T-cell responses in stage-I myeloma patients. Further trials are needed to increase the rate of responses and to define the role of DC-based vaccination in the era of new pharmacologic therapies.

Mechanisms underlying acquired von Willebrand syndrome associated with an IgM paraprotein.

Acquired von Willebrand (vW) syndrome is a rare bleeding disorder which is frequently associated with immunological, malignant or cardiovascular disorders. The underlying pathomechanisms, particularly in patients with IgM monoclonal gammopathies, often remain unknown. We report a patient with indolent small B-cell lymphoma (immunocytoma) and plasmacytic differentiation with an IgM kappa paraprotein who was admitted with retroperitoneal haematoma. Medical history and coagulation testing were consistent with acquired vW syndrome. vW immunohistochemistry showed normal cytoplasmic labelling of endothelial cells and megakaryocytes, whereas the lymphomatous infiltrate was negative. Acquired vW syndrome due to adsorption of vW factor on malignant cells was thus excluded. In the multimeric analysis, all multimers were present similar to that in type 1 vW syndrome, but the triplet structures were blurred. The bands on serum immunofixation electrophoresis were also atypically broadened, which suggested complex formation between the IgM and vW factor. Immunoprecipitation studies showed that the 176-kDa proteolytic fragment of vW factor co-precipitated with the IgM paraprotein in the patient but not in the controls, suggesting a specific interaction between vW factor and the paraprotein in the patient. The patient required surgery and was successfully managed by chemotherapy consisting of rituximab and fludarabin as well as plasma exchange.

Accurate identification of paraprotein antigen targets by epitope reconstruction.

We describe the first successful clinical application of a new discovery technology, epitope-mediated antigen prediction (E-MAP), to the investigation of multiple myeloma. Until now, there has been no reliable, systematic method to identify the cognate antigens of paraproteins. E-MAP is a variation of previous efforts to reconstruct the epitopes of paraproteins, with the significant difference that it provides enough epitope sequence data so as to enable successful protein database searches. We first reconstruct the paraprotein's epitope by analyzing the peptides that strongly bind. Then, we compile the data and interrogate the nonredundant protein database, searching for a close match. As a clinical proof-of-concept, we apply this technology to uncovering the protein targets of para-proteins in multiple myeloma (MM). E-MAP analysis of 2 MM paraproteins identified human cytomegalovirus (HCMV) as a target in both. E-MAP sequence analysis determined that one para-protein binds to the AD-2S1 epitope of HCMV glycoprotein B. The other binds to the amino terminus of the HCMV UL-48 gene product. We confirmed these predictions using immunoassays and immunoblot analyses. E-MAP represents a new investigative tool for analyzing the role of chronic antigenic stimulation in B-lymphoproliferative disorders.

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 heel" 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 biased Gm haplotype and Gm paraprotein allotype in multiple myeloma suggests a role for the Gm system in myeloma development.

The association between a particular Gm haplotype and susceptibility to multiple myeloma (MM) is not clear. The reason is probably because no investigations have so far been carried out on the relationship between the Gm haplotype, which represents the inherited combination of IgG Gm allotypes, and the Gm allotype expressed at the IgG paraprotein (M-component), which reflects the enhanced gene expression within the haplotype in MM. We studied the incidence of Gm allotypic markers present in IgG subclasses in the serum from 52 patients with MM and in parallel with the isolated IgG paraproteins. The results showed that 84.6% of the patients were heterozygous for haplotypes Gm(a; z; n-; g;)/Gm(f; n+/n-; b1; b0; b5) and 15.3% were homozygous for Gm(f; n/n-; b1; b0; b5), while no homozygous Gm(a; z; n-; g) individuals were found among the studied patients. The incidence of these combinations in the healthy population in Serbia is 34%, 66% and < 1%, respectively. Subjects with Gm(a; z; n-; g)/Gm(f; n+/n-; b1; b0; b5) combination are over 10 times [odds ratio (OR) = 10.69; 95% confidence interval 1.67-68] as likely to be affected by the disease as the subjects with homozygous Gm(f; n+/n-; b1; b0; b5) combination (OR = 0.35, 95% confidence interval 0.06-2.23). However, despite the Gm heterozygosity, most of the Gm(a; z; n-; g;)/Gm(f; n+/n-; b1; b0; b5) positive patients with MM (86.3%) had IgG paraprotein with the allotypic marker from the Gm(f; n+/n-; b1; b0; b5) haplotype. Together with patients homozygous for this haplotype, the relative number of patients with serum IgG paraprotein carrying allotypic marker from the Gm(f; n/n-; b1; b0; b5) haplotype was 88.5%. These results suggest that the development of an M-component could be related to a disturbance on chromosome 14q32 carrying the Gm (f; n+/n-; b1; b0; b5) set of genes.

Chronic lymphocytic leukemia preceded by cold agglutinin disease: intraclonal immunoglobulin light-chain diversity in V(H)4-34 expressing single leukemic B cells.

Autoimmune phenomena may precede or accompany lymphoid malignancies, especially B-chronic lymphocytic leukemia (B-CLL). We report a patient with a 7-year history of primary (idiopathic) cold agglutinin (CA) disease in whom B-CLL subsequently developed. Immunophenotyping and single-cell reverse transcription-polymerase chain reaction (RT-PCR) were applied to investigate the origin and diversification of leukemic B cells. The obtained data indicate a memory cell-type origin of the B-CLL cells. Remarkably, the IgV(kappa) genes of the B-CLL cells showed intraclonal diversity, whereas the mutational pattern of their paired IgV(H) genes were invariant. Thus, the light-chain-restricted intraclonal diversity in individual leukemic B cells in this patient strongly indicates a differential regulation or selection of the ongoing mutational process. Of note, our findings suggest that this B-CLL had developed from the patient's CA-producing B-cell population.

Contribution of cytogenetics and in situ hybridization to the study of monoclonal gammopathies of undetermined significance.

Monoclonal gammopathies of undetermined significance (MGUS) are characterized by the presence of a monoclonal protein in serum in quite asymptomatic patients. Ten to 33% of MGUS patients eventually will develop overt multiple myeloma, but no single laboratory test exists that can predict changes toward a malignant evolution. The aim of the present study was to apply conventional cytogenetics, the MAC (morphology, antibody, chromosome) method and fluorescence in situ hybridization (FISH) techniques in a series of 50 MGUS patients and 4 "smoldering" multiple myeloma patients to test the usefulness of their approaches as predictive methodologies. All patients studied by conventional cytogenetics presented a normal karyotype independent of the culture conditions used. The MAC method revealed that all mitotic cells showing a normal karyotype were positive for anti-MOP7 or anti-CD3 in 12 patients studied. In addition, two of them presented a numerical abnormality detected by FISH. Using a FISH technique with direct labeled centromeric probes for chromosomes 3, 7, 11, and 18 we showed a numerical abnormality in eight of 35 patients (23%) with a normal karyotype. The common occurrence of MGUS and the fact that they may evolve toward lymphoproliferative disorders displays the importance of being able to identify laboratory results that are capable of predicting the evolution of these patients. In the literature, patients who presented an IgA peak of immunoglobulin type have been associated with a higher risk of evolving to a malignant condition. Our study shows the correlation of MGUS patients who presented monosomy 18 with the presence of an immunoglobulin peak of the IgA type. Prospective follow-up is needed to evaluate the clinical value of monosomy 18 as a predictive factor for defining a high risk of malignant transformation in MGUS patients.

Molecular monitoring of the tumor load predicts progressive disease in patients with multiple myeloma after high-dose therapy with autologous peripheral blood stem cell transplantation.

The clinical relevance of the assessment of minimal residual disease (MRD) in patients with multiple myeloma (MM) to predict disease recurrence has not been proven. In the present study, we retrospectively analyzed the tumor load in peripheral blood (PB) and bone marrow (BM) samples of 13 patients with MM both in remission after high-dose therapy (HDT) with autologous PBSC transplantation (PBSCT) and at the time of progressive disease (PD). For six patients, subsequent samples obtained in remission could be included in the study. Tumor cells were assessed by means of quantitative PCR with allele-specific oligonucleotides (ASO-qPCR) based on the method of limiting dilutions. PD was documented with ASO-qPCR in BM samples (median concentration of tumor cells in remission vs at PD: 0.18% vs 4.6%) representing a significant increase by a median factor of 8.7. In PB, the median tumor load was 799 cells/ml in remission and 23 400 cells/ml at PD. With a median factor of 45, the increase was much more pronounced. Comparing the results of the molecular monitoring in PB with those of the determination of the monoclonal protein, routinely applied as parameter for the course of the disease, revealed a superiority of the molecular monitoring because of the significantly higher increase in the tumor load. Analyzing the subsequent remission samples showed an increase of the malignant cells in four out of six PB samples and in all four BM samples available, indicating the potential of ASO-qPCR for an early PD recognition.

Systematic search and molecular characterization of the antigenic targets of myeloma immunoglobulins: a monoclonal IgA from a female patient targeting sperm-specific cylicin II.

The identification of the antigenic stimuli of B-cell neoplasms might be of considerable importance since a causal relationship between these neoplasms and antigenic stimulation has been suggested. To date the identification of such antigens has been erratic and accidental. For a systematic search and molecular characterization of human proteins that are antigenic target structures of myeloma-associated immunoglobulins, we applied SEREX (serological analysis of antigens by recombinant cDNA expression cloning) using a testis cDNA expression library and myeloma proteins from 42 patients. A monoclonal IgA from a female patient was shown to target sperm-specific cylicin II. The specificity of the reaction was confirmed by the characteristic staining of the equatorial belt of human sperm heads by the patient's myeloma protein. Serological analysis of recombinantly expressed cDNAs is a straightforward and high throughput approach for the molecular characterization of the targets of myeloma-associated immunoglobulins. The analysis of the antigenic spectrum of immunoglobulins associated with B-cell neoplasms will provide valuable information for the understanding of the pathogenesis of these diseases.

Phenotypic and genotypic alterations characterize patients bearing plasma cell dyscrasias with a high M-component.

As at present only a long-term follow-up can fully determine whether monoclonal gammapathies of undetermined significance (MGUS) will evolve into multiple myeloma (MM), this study attempted to identify other variables connected with the amount of monoclonal component (MC), generally considered as the most reliable marker of malignant evolution. Thirty-four MGUS subjects showing a high MC (> or = 15.0 g/l) but without clinical evidence of MM (MGUS group b), were characterized for their phenotypic and genotypic profile by comparing them either with 40 MM patients or with 24 subjects affected by a benign form of monoclonal gammapathy (MGUS group a) according to the standard criteria. In addition to the usual laboratory markers, the levels of expression of a panel of CD membrane subsets were measured on B and T lymphocytes. Also, the serum level of the p53 mutant protein and the structural alterations of the c-myc oncogene were evaluated. The results show that for MGUS group b patients, an increased M-protein was accompanied by significantly increased levels of peripheral blood CD3+ T cells and oncogenetic aberrations in c-myc. Since a high serum MC level seems to indicate a greater likelihood of malignant transformation for MGUS patients, these findings suggest that this relationship may be a result of the concomitant alterations observed at a phenotypic and genotypic level. Such alterations may be potentially useful as surrogate markers for the transition of benign to malignant (MM) plasma cell dyscrasia.

VH gene analysis of clonally related IgM and IgG from human lymphoplasmacytoid B-cell tumors with chronic lymphocytic leukemia features and high serum monoclonal IgG.

An unusual group of human B-cell tumors with cellular features of chronic lymphocytic leukemia or lymphoplasmacytoid leukemia, together with high levels of a monoclonal IgG serum protein, has been investigated. Analysis of tumor-derived VH genes of neoplastic B lymphocytes was used to determine the clonal relationship between the IgM expressed or secreted by the tumor cells and the IgG serum paraprotein. In all five cases, VH gene sequences showed transcripts of IgM and IgG of common clonal origin. Sequences were derived from VH3 (4 of 5) and VH1 (1 of 5) families and were all highly somatically mutated with strong evidence for antigen selection. There was no intraclonal variation detectable in either IgM or IgG sequences. In 3 of 5 cases, in which monoclonal IgM and IgG were found in serum, the VH genes combined to Cmu or Cgamma showed identical mutational patterns. However, in 2 of 5 cases, in which IgM was confined to cell expression with only monoclonal IgG in serum, sequences of the VH transcripts of IgM and IgG showed many shared mutations but also numerous differences. In these cases, the level of mutation was similar in IgM and IgG and both appeared to be antigen selected. In summary, the final neoplastic event in this group of tumors has apparently occurred at the point of isotype switch from IgM to IgG, leading to dual isotype synthesis. In the group that secreted both isotypes, the mutation pattern was identical, indicating either synthesis by a single cell, or silencing of mutational activity before switching. In the group that did not secrete IgM, cells of each isotype were distinct and reflected a divergent mutational history.