Oligosecretory biclonal multiple myeloma

Among the plasma cell dyscrasias, non-secretory myeloma is one of the rarest. This diagnosis is based on the absence of monoclonal proteins in the serum and urine. When serum free light chains are trace and the kappa: lambda ratio normal, clonality may however be established by PCR. We present a case of an oligosecretory myeloma confirmed by PCR, which would have hitherto been classified as non-secretory.

Prediction of High Affinity Class I-restricted Multiple Myeloma Idiotype Peptide Epitopes

Idiotypic determinants are potential patient-specific tumor antigens in multiple myeloma (MM). In this study, we have determined the DNA sequence of the variable region of the tumor immunoglobulin (Ig) in 6 patients with MM. We then selected high affinity class I-restricted T-cell peptide epitopes in tumor Ig using two different internet-based epitope prediction programs. High affinity binding peptides were identified by at least one program in 4 out of 6 patients. Of these 35 peptides, only 3 scored high by both analyses. Given that all 6 patients had expanded T-cell clones with a cytotoxic (CD57+CD8+CD28-perforin+) phenotype, known to be associated with a longer survival and postulated to recognise tumor epitopes, this analysis indicates that such clones are unlikely to be exclusively directed towards tumor immuoglobulin, and suggests the need to expand the scope of the search for tumor epitopes with the ability to stimulate cytotoxic T cells in vivo.

Function and pathology of the sugar chains of human immunoglobulin G

Human immunoglobulin G (IgG) is unique among serum glycoproteins because it contains more than 30 different biantennary complex-type asparagine-linked oligosaccharides. This extremely high microheterogeneity is probably produced because human individuals have a series of B cell clones equipped with different sets of glycosyltransferases. Despite this complex composition, IgG samples purified from whole human sera have the same mole ratios of oligosaccharides, indicating that the ratio of B cell clones synthesizing IgGs with different sugar chains is constant in healthy individuals. We found that the glycosylation patterns of whole serum IgGs obtained from patients with rheumatoid arthritis (RA) are quite different from those of whole serum from healthy individuals. Structural studies of the oligosaccharides revealed that the sugar chains of the IgGs obtained from patients with RA are depleted of the beta-galactose residues. The sugar chains of transferrin from patients with RA are fully galactosylated. Therefore the galactose deletion from IgG is probably brought about by a decrease in galactosyltransferase activity in B cells rather than by degradation by galactosidase during circulation. Enzymic study revealed that human B cells contain various beta-galactosyltransferases which form the Gal(beta 1-4)GlcNAc groups in the sugar chains of different glycoproteins. Among these enzymes, abnormality in patients with RA was found only in the one that transfers beta-galactose residues specifically to degalactosylated IgG. This enzyme showed lower affinity toward UDP-Gal in B cells of patients with RA than that in healthy individuals.

Molecular portrait of high productivity in recombinant NS0 cells

Many important therapeutic proteins are produced in recombinant mammalian cells. Upon the introduction of the product gene, the isolated clones typically exhibit a wide range of productivity and high producers are subsequently selected for use in production. Using DNA microarray, two-dimensional gel electrophoresis (2DE), and iTRAQ as global surveying tools, we examined the transcriptome and proteome profiles of 11 lines of NS0 cells producing the same antibody molecule. Genes that are significantly differentially expressed between high and low producer groups statistically fall into a number of functional classes. Their distribution among the functional classes differs somewhat between transcriptomic and proteomic results. Overall, a high degree of consistency between transcriptome and proteome analysis are seen, although some genes exhibiting inconsistent trends between transcript and protein levels were observed as expected. In a novel approach, functional gene networks were retrieved using computational pathway analysis tools and their association with productivity was tested by physiological comprehension of the possible pathways involved in high recombinant protein production. Network analysis indicates that protein synthesis pathways were altered in high producers at both transcriptome and proteome levels, whereas the effect on cell growth/death pathways was more prominent only at the transcript level. The results suggest a common mechanism entailing the alteration of protein synthesis and cell growth control networks leading to high productivity. However, alternate routes with different sets of genes may be invoked to give rise to the same mechanistic outcomes. Such systematic approaches, combining transcriptomic and proteomic tools to examine high and low producers of recombinant mammalian cells will greatly enhance our capability to rationally design high producer cells. This work is a first step towards shedding a new light on the global physiological landscape of hyper productivity of recombinant cells.

A VH4-34+ myeloma protein with weak autoreactivity

It has been suggested that VH4-34 gene segment expression is counter-selected in multiple myeloma (MM) due to a self-tolerance mechanism. We cloned and sequenced a VH4-34 gene segment from bone marrow mononuclear cells of a stage III MM patient. We show that VH4-34 was expressed by the serum IgA myeloma (M)-protein, as demonstrated by reactivity with the VH4-34 specific 9G4 mAb and mass spectrometry (MS). The M-protein had weak reactivity with nuclei. These results demonstrate that VH4-34 may be expressed in secreted IgA M-protein with weak autoreactivity. Thus, counter-selection of VH4-34 is pronounced but not absolute in MM. Mechanisms of how VH4-34 can occasionally be expressed in MM and clinical implications are discussed.

Specific targeting to murine myeloma cells of Cyt1Aa toxin from Bacillus thuringiensis subspecies israelensis

Multiple myeloma is currently an incurable cancer of plasma B cells often characterized by overproduction of abnormally high quantities of a patient-specific, clonotypic immunoglobulin "M-protein." The M-protein is expressed on the cell membrane and secreted into the blood. We previously showed that ligand-toxin conjugates (LTC) incorporating the ribosome-inactivating Ricin-A toxin were very effective in specific cytolysis of the anti-ligand antibody-bearing target cells used as models for multiple myeloma. Here, we report on the incorporation of the membrane-disruptive Cyt1Aa toxin from Bacillus thuringiensis subsp. israelensis into LTCs targeted to murine myeloma cells. Proteolytically activated Cyt1Aa was conjugated chemically or genetically through either its amino or carboxyl termini to the major peptidic epitope VHFFKNIVTPRTP (p87-99) of the myelin basic protein. The recombinant fusion-encoding genes were cloned and expressed in acrystalliferous B. thuringiensis subsp. israelensis through the shuttle vector pHT315. Both chemically conjugated and genetically fused LTCs were toxic to anti-myelin basic protein-expressing murine hybridoma cells, but the recombinant conjugates were more active. LTCs comprising the Cyt1Aa toxin might be useful anticancer agents. As a membrane-acting toxin, Cyt1Aa is not likely to induce development of resistant cell lines.

A genome-wide transcriptional analysis of producer and non-producer NS0 myeloma cell lines

'Genome-wide' or 'global' gene expression profiling provides a powerful approach to the characterization of a cell's transcriptional state. Such technology has been used in animal cell culture to create genome-wide snapshots of transcriptional activity in response to environmental factors or cellular triggers under bioprocessing conditions. Furthermore, it allows us to have a fundamental understanding of genetic mechanisms involved in recombinant protein production. One such mechanism adversely affecting the growth of recombinant bacteria is the increased metabolic burden resulting from the maintenance of plasmid copy number and heterologous protein expression. There have also been some reports on the effect of metabolic burden in mammalian cell systems. In the present study, we have used a mouse array representing 6400 genes to assess the expression profile of a WT (wild-type) mouse plasmacytoma cell line, NS0 WT, and a GS (glutamine synthetase)-NS0 6A1-100 cell line expressing chimaeric monoclonal antibody. The producer cells did not exhibit a slower growth as the result of any metabolic burden, but showed differences in metabolic activity. Gene expression profiling revealed that the producer cell line was selected for a higher expression of chromosomal genes, genes for zinc-finger proteins as well as cell-cycle-related events. On the other hand, protein synthesis is greater and ribosomal genes were more expressed in the WT cells. A possible shift from expressing antigen presenting proteins to recombinant protein could also be seen. Hence, gene expression profiling suggests that the effect of the metabolic burden in slowing growth can be mostly negated in producer cell lines by careful clonal selection, where stable transfected cells are selected for both high productivity as well as high growth rates.

Rapid specific amplification of rat antibody cDNA from nine hybridomas in the presence of myeloma light chains

Most monoclonal antibodies to mouse antigens have been derived from rat spleen-mouse myeloma fusions. Many resultant hybridomas express one of several myeloma kappa chain transcripts, even though the parent myeloma may have been ascribed as not expressing light chain protein. Previous reports have only differentiated against one of these mouse light chains. We have found at least three different myeloma kappa transcripts in the panel of nine hybridomas that were derived from four different myeloma parents. We have designed an amplification strategy that differentiates the rearranged rat kappa chain from all mouse light chains. Moreover, this method is expedient as it requires minimal downstream manipulation.

A potential role for centrosomal deregulation within IgH translocation-positive myeloma

Multiple myeloma is a late stage B-cell malignancy that is characterized by recurrent translocations into the immunoglobulin heavy chain locus as well as multiple and complex chromosomal abnormalities. Multiple myeloma is not characterized by a defining IgH translocation partner locus; rather, the frequency of individual translocations ranges from 5% to 15% of the patient population. The current hypothesis that IgH translocations contribute to chromosomal instability through the augmented expression of cyclin D family members and upstream regulatory gene products has led to the development of clinical therapies targeting these potentially oncogenic gene products. Here, we postulate that IgH translocations affect both cyclin D family members and spindle assembly pathways. In forming the hypothesis, this manuscript provides a mechanistic connectivity between IgH translocations and associated chromosome 13 deletions and highlights a number of additional gene products that, along with already defined target genes, may be deregulated in myeloma and represent potential therapeutic targets.

Comparative genomic hybridisation identifies two variants of smoldering multiple myeloma

Two variants of smoldering multiple myeloma (SMM) have been recognised: (i) an evolving type, characterised by a progressive increase in the M-protein size and short time to progression to overt multiple myeloma (MM) and (ii) a non-evolving type, with a long-lasting, stable M-protein and longer time to progression. Comparative genomic hybridisation (CGH) analyses in both subtypes of SMM (seven evolving and eight non-evolving SMM) were performed. Evolving SMM showed cytogenetic changes consistent with those found in de novo symptomatic MM (1q gains, chromosome 13 deletions) while the non-evolving variant showed no 1q gains and deletions were uncommon.

Molecular definition of predictive indicators of stable protein expression in recombinant NS0 myeloma cells

We have generated a molecular description of the loci at which stability/instability of expression of a monoclonal antibody (MAb) (anti-CD38) occurs within the GS-NS0 expression system. Critically, these data show that, in the absence of changes to copy number for the recombinant gene sequences, all cell lines examined exhibit a progressive loss (instability) in expression of mRNA during prolonged culture. However, not all cell lines express instability at the level of MAb protein production. The molecular distinction between stable and unstable production at the protein level is a reflection of the cellular amount of recombinant mRNA encoding MAb. Our data indicate a threshold level, a putative saturation point for utilisation of mRNA in translational/secretory events, that defines stability or instability of protein production. Above this level of recombinant mRNA expression, cell lines are stable, whereas below this level cell lines will show instability of protein production. Our studies indicate that absolute levels of expression of recombinant mRNA encoding for MAb in the GS-NS0 expression system offer a potential predictive indicator for the selection of stable cell lines for scale-up. These studies identify molecular facets of host cell biology of generic interest for gene regulation and expression and define techniques and approaches for enhancement of recombinant protein expression and process development.

V(L)IgMM transgene expression in DC via a GPI-anchor using a novel retroviral vector induces an in vitro autologous T-cell proliferation restricted to MHC class I molecules

INTRODUCTION

In order to improve the treatment and cure rate of multiple myeloma (MM), immunotherapy is a novel therapeutic approach. Since neoplastic plasma cells do not undergo further hypermutation, the variable region of the immunoglobulin light chain obtained from MM patients (V(L)IgMM) could serve as a tumor-specific antigen. In addition, dendritic cells (DC) have been identified as potent stimulators of an antigen-specific immune response. Here, we analyze in vitro autologous T-cell proliferation against the V(L)IgMM on presentation by retrovirally transduced dendritic cells.

MATERIALS AND METHODS

Expression of the tumor antigen in DC has been achieved using a novel retroviral vector containing NH(2)(34a.a)DAF-FLAG-V(L)IgMM-DAF(37a.a)COOH transgene. After cleavage of the amino- and carboxy-terminal hydrophobic domains of DAF, the FLAG-V(L)IgMM fusion gene is attached to the membrane via a GPI-anchor molecule. Thus, transduced cells can be detected using monoclonal anti-FLAG antibodies.

RESULTS

PI-PLC releases cell surface FLAG-antigen from transduced CD34(+) cells indicating that the vector directs the fusion protein to the cell surface via GPI-anchor. V(L)IgMM transgene expression in DC using our retroviral vector elicited an autologous T-cell proliferation restricted to MHC class I molecules. The proliferative response is more prominent in PMA-derived DC compared to cytokine-derived DC indicating that PMA-derived DC are more potent in activating autologous T-cell proliferation.

CONCLUSION

V(L)IgMM is an immunogenic peptide, which under certain conditions could provide a basis for a V(L)Ig-based immunotherapy in MM.

Melphalan-mobilized blood stem cell components contain minimal clonotypic myeloma cell contamination

Optimal methods of stem cell mobilization in multiple myeloma are undefined, and contaminating clonotypic cells could contribute to disease recurrence. A phase 2 trial of intravenous melphalan (60 mg/m2) and granulocyte colony-stimulating factor (G-CSF) (10 microg/kg/d) for mobilization was performed. To enhance reliability, contamination was assessed with 2 sensitive methods, immunoglobulin light and heavy chain variable region patient-specific limiting-dilution polymerase chain reaction (PCR). We evaluated 29 stem cell components (SCCs) from 15 patients; for 9 SCCs, only VL PCR was used because of light chain disease or technical problems with VH primers. For 20 SCCs, VL and VH PCR results were highly correlated (r2 = 0.93, P <.01), with 35% (7 of 20) having identical estimates. VH PCR gave significantly higher estimates for 8-and VL PCR for 5-SCCs, supporting the utility of using 2 methods. Estimated clonotypic contamination per SCC was 0.0009% (range, 0%-0.1%) or 0.5 x 10(4) clonotypic cells per kilogram (range, 0-41.2 x 10(4)/kg), and contamination correlated with CD34+ cells collected (r2 = 0.42, P <.01). Melphalan-mobilized SCCs contain minimal clonotypic contamination.

Genetically targeted radiotherapy for multiple myeloma

Multiple myeloma is a disseminated neoplasm of terminally differentiated plasma cells that is incurable with currently available therapies. Although the disease is radiosensitive, external beam radiation leads to significant toxicity due to sensitive end-organ damage. Thus, genetic approaches for therapy are required. We hypothesized that the incorporation of immunoglobulin promoter and enhancer elements in a self-inactivating (SIN) lentiviral vector should lead to specific and high-level transgene expression in myeloma cells. A SIN lentivector with enhanced green fluorescent protein (EGFP) expression under the control of a minimal immunoglobulin promoter as well as the Kappa light chain intronic and 3' enhancers transduced myeloma cell lines with high efficiency (30%-90%). EGFP was expressed at a high level in myeloma cells but silent in all nonmyeloma cell lines tested compared with the cytomegalovirus (CMV) promoter/enhancer. Transduction of myeloma cells with the targeted vector coding for the human sodiumiodide symporter (hNIS) led to hNIS expression by these cells allowing them to concentrate radioiodine up to 18-fold compared with controls. Tumor xenografts in severe combined immunodeficiency mice expressing hNIS could be imaged using iodine-123 (123I) and shown to retain iodide for up to 48 hours. These tumor xenografts were completely eradicated by a single dose of the therapeutic isotope iodine-131 (131I) without evidence of recurrence up to 5 months after therapy. We conclude that lentivectors can be transcriptionally targeted for myeloma cells and the use of hNIS as a therapeutic gene for myeloma in combination with 131I needs further exploration.

Probing the specificity of human myeloma proteins with a random peptide phage library

Human myeloma proteins (HMPs) from 10 patients with multiple myeloma (MM) were used to affinity-select peptides from a random phage-display peptide library. Binding peptides were identified for the 10 analysed antibodies (eight, immunoglobulin G (IgG), and two, immunoglobulin A (IgA)). The specificity of the binding was confirmed by competitive experiments using phages and chemically synthesized peptides. Interestingly, some phage-displayed peptides were immuno-selected with HMPs isolated from different patients. Sequence alignments and homology searches revealed a significant homology with human proteins (e.g. neural cell adhesion proteins) and pathogen-derived proteins (e.g. herpes simplex virus capsid proteins). The selected peptides could be useful as targeting agents for myeloma cells expressing surface immunoglobulins.

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.

Flow cytometric disease monitoring in multiple myeloma: the relationship between normal and neoplastic plasma cells predicts outcome after transplantation

Conventional monitoring strategies for myeloma are not sufficiently sensitive to identify patients likely to benefit from further therapy immediately after transplantation. We have used a sensitive flow cytometry assay that quantitates normal and neoplastic plasma cells to monitor the bone marrow of 45 patients undergoing high-dose chemotherapy. Neoplastic plasma cells were detectable at 3 months after transplantation in 42% of patients. Once detected, neoplastic cell levels increased steadily until clinical progression: these patients had a significantly shorter progression-free survival (PFS) (median, 20 months) than those with no detectable disease (median, longer than 35 months; P =.003). Neoplastic plasma cells were detectable in 27% (9 of 33) of immunofixation-negative complete-remission patients. These patients had a significantly shorter PFS than immunofixation-negative patients with no detectable neoplastic plasma cells (P =.04). Normal plasma cells were present in 89% of patients immediately after transplantation, but were not sustained in most cases. Patients with only normal phenotype plasma cells present at 3 months after transplantation and also at second assessment had a low risk of disease progression. Patients with neoplastic plasma cells present at 3 months after transplantation, or with only normal plasma cells present at first assessment and only neoplastic plasma cells at second assessment, had a significantly higher risk of early disease progression (P <.0001) with a 5-year survival of 54% for the high-risk group, compared with 100% in the low-risk group (P =.036). Analysis of normal and neoplastic plasma cell levels is more sensitive than immunofixation and can identify which patients may benefit from additional treatment strategies at an early stage after transplantation.

Dealing with intractable protein cores: protein sequencing of the Mcg IgG and the Yvo IgM heavy chain variable domains

The VH domains of two human monoclonal antibodies, designated Mcg IgG1(lambda) and Yvo IgM(kappa), were particularly intractable to standard protein sequencing protocols. Peptides liberated from the VH domains of these proteins, using standard enzymatic or chemical cleavages, invariably precipitated during the procedures. Boiling in SDS containing buffers dissolved precipitates and the peptides were separated using SDS-PAGE. Fully overlapped VH sequences were obtained with a series of 'in-gel' cleavages, followed by passive/differential transfers of peptides onto PVDF membranes. Both the in-gel cleavages and passive transfers could be applied to 'wet' or 'dry' gels so that gels could be archived and used at a later date to obtain additional sequence information from a fragment of interest. Repetitive yields of even the most insoluble peptides were such that the sequences of various peptides from relatively complex mixtures of peptides could be assigned with confidence. Despite the overall success of the sequencing, we occasionally referred to electron density maps, calculated for crystals of the Fab of Yvo IgM, to resolve particular sequences and confirm ambiguous amino acid assignments. Methods we describe in this report should be generally useful for obtaining sequences of proteins with intractable cores and may find many applications in the 'post genomic era'.

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.

Gene scanning of VDJH-amplified segments is a clinically relevant technique to detect contaminating tumor cells in the apheresis products of multiple myeloma patients undergoing autologous peripheral blood stem cell transplantation

Contaminating tumour cells in apheresis products have proved to influence the outcome of patients with multiple myeloma (MM) undergoing autologous stem cell transplantation (APBSCT). The gene scanning of clonally rearranged VDJ segments of the heavy chain immunoglobulin gene (VDJH) is a reproducible and easy to perform technique that can be optimised for clinical laboratories. We used it to analyse the aphereses of 27 MM patients undergoing APBSCT with clonally detectable VDJH segments, and 14 of them yielded monoclonal peaks in at least one apheresis product. The presence of positive results was not related to any pre-transplant characteristics, except the age at diagnosis (lower in patients with negative products, P = 0.04). Moreover, a better pre-transplant response trended to associate with a negative result (P = 0.069). Patients with clonally free products were more likely to obtain a better response to transplant (complete remission, 54% vs 28%; >90% reduction in the M-component, 93% vs 43% P = 0.028). In addition, patients transplanted with polyclonal products had longer progression-free survival, (39 vs 19 months, P = 0.037) and overall survival (81% vs 28% at 5 years, P = 0.045) than those transplanted with monoclonal apheresis. In summary, the gene scanning of apheresis products is a useful and clinically relevant technique in MM transplanted patients.

A new model for intermediate molecular weight recombinant bispecific and trispecific antibodies by efficient heterodimerization of single chain variable domains through fusion to a Fab-chain

Due to their specificity and versatility in use, bispecific antibodies (BsAbs) are promising therapeutic tools in tomorrow's medicine, provided sufficient BsAb can be produced. Expression systems favoring efficient heterodimerization of intermediate-sized bispecific antibodies will significantly improve existing production methods. Recombinant BsAb can be made by fusing single chain variable fragments (scFv) to a heterodimerization domain. We compare the efficiency of the isolated CL and CH1 constant domains with complete Fab chains to drive heterodimerization of BsAbs in mammalian cells. We found that the isolated CL:CH1 domain interaction was inefficient for secretion of heterodimers. However, when the complete Fab chains were used, secretion of a heterodimerized bispecific antibody was successful. Since the Fab chain encodes a binding specificity on its own, bispecific (BsAb) or trispecific (TsAb) antibodies can be made by C-terminal fusion of scFv molecules to the L or Fd Fab chains. This gave rise to disulphide stabilized Fab-scFv BsAb (Bibody)or Fab-(scFv)2 TsAb (Tribody) of intermediate molecular size. Heterodimerization of the L and Fd-containing fusion proteins was very efficient, and up to 90% of all secreted antibody fragments was in the desired heterodimerized format. All building blocks remained functional in the fusion product, and the bispecific character of the molecules as well as the immunological functionality was demonstrated.

Analysis of clonal relationship using single-cell polymerase chain reaction in a patient with concomitant mantle cell lymphoma and multiple myeloma

We report a case of concomitant mantle cell lymphoma (MCL) and multiple myeloma (MM) in which we investigated the possibility of a clonal relationship. A 76-year-old man was diagnosed with MCL [immunoglobulin (Ig)M,D-kappa; stage IVB] and MM (IgG-kappa; stage I). Ig heavy chain (IgH) gene complementarity-determining region 3 in DNA from both the MCL tumor and from single MM cells from bone marrow smears was amplified to investigate whether there was a clonal relationship between MCL and MM. Sequence analysis revealed no clonal relationship between MCL and MM in our patient.

IRTA1 and IRTA2, novel immunoglobulin superfamily receptors expressed in B cells and involved in chromosome 1q21 abnormalities in B cell malignancy

Abnormalities of chromosome 1q21 are common in B cell malignancies, but their target genes are largely unknown. By cloning the breakpoints of a (1;14) (q21;q32) chromosomal translocation in a myeloma cell line, we have identified two novel genes, IRTA1 and IRTA2, encoding cell surface receptors homologous to the Fc and inhibitory receptor families. Both genes are selectively expressed in mature B cells: IRTA1 in marginal zone B cells and IRTA2 in centrocytes, marginal zone B cells, and immunoblasts. As a result of the t(1;14), IRTA1 is fused to the immunoglobulin Calpha domain to produce a chimeric IRTA1/Calpha fusion protein. In tumor cell lines with 1q21 abnormalities, IRTA2 expression is deregulated. Thus, IRTA1 and IRTA2 are novel immunoreceptors implicated in B cell development and lymphomagenesis.

Frequency and kinetics of polyclonal and clonal B cells in the peripheral blood of patients being treated for multiple myeloma

Recent studies concerning the numbers of circulating clonal B cells in patients with multiple myeloma (MM) have reported conflicting data regarding the exact level and phenotype of clonal B cells and their response to treatment. In this report we document that the peripheral blood tumor burden at presentation was reduced by induction therapy to a low level, regardless of the initial tumor burden. However, the residual clonal compartment persisted before and after transplant. The level of clonal cells showed no correlation with CD19(+) cell levels. In a single patient with MM, high numbers of phenotypically aberrant clonal cells with altered CD19 expression were identified. (Blood. 2000;96:4357-4359)

Four structural risk factors identify most fibril-forming kappa light chains

Antibody light chains (LCs) comprise the most structurally diverse family of proteins involved in amyloidosis. Many antibody LCs incorporate structural features that impair their stability and solubility, leading to their assembly into fibrils and to their subsequent pathological deposition when produced in excess during multiple myeloma and primary amyloidosis. The particular amino acid variations in antibody LCs that account for fibril formation and amyloidogenesis have not been identified. This study focuses on amyloidogenesis within the kappa1 family of human LCs. Reanalysis of the current database of primary structures of proteins from more than 100 patients who produced kappa1 LCs, 37 of which were amyloidogenic, reveals apparent structural features that may contribute to amyloidosis. These features include loss of conserved residues or the gain of particular residues through mutation at sites involving a repertoire of approximately 20% of the amino acid positions in the light chain variable domain (V(L)). Moreover 80% of all kappa1 amyloidogenic V(L)s are identifiable by the presence of at least one of three single-site substitutions or the acquisition of an N-linked glycosylation site through mutations. These findings suggest that it is feasible to predict fibril propensity by analysis of primary structure.

Ectopic expression of fibroblast growth factor receptor 3 promotes myeloma cell proliferation and prevents apoptosis

The t(4;14) translocation occurs in 25% of multiple myeloma (MM) and results in both the ectopic expression of fibroblast growth factor receptor 3 (FGFR3) from der4 and immunoglobulin heavy chain-MMSET hybrid messenger RNA transcripts from der14. The subsequent selection of activating mutations of the translocated FGFR3 by MM cells indicates an important role for this signaling pathway in tumor development and progression. To investigate the mechanism by which FGFR3 overexpression promotes MM development, interleukin-6 (IL-6)-dependent murine B9 cells were transduced with retroviruses expressing functional wild-type or constitutively activated mutant FGFR3. Overexpression of mutant FGFR3 resulted in IL-6 independence, decreased apoptosis, and an enhanced proliferative response to IL-6. In the presence of ligand, wild-type FGFR3-expressing cells also exhibited enhanced proliferation and survival in comparison to controls. B9 clones expressing either wild-type FGFR3 at high levels or mutant FGFR3 displayed increased phosphorylation of STAT3 and higher levels of bcl-x(L) expression than did parental B9 cells after cytokine withdrawal. The mechanism of the enhanced cell responsiveness to IL-6 is unknown at this time, but does not appear to be mediated by the mitogen-activated protein kinases SAPK, p38, or ERK. These findings provide a rational explanation for the mechanism by which FGFR3 contributes to both the viability and propagation of the myeloma clone and provide a basis for the development of therapies targeting this pathway.

Acute promyelocytic leukaemia complicating multiple myeloma: evidence of different cell lineages

The association of leukemia and multiple myeloma is well described usually as a complication of chemotherapy but also in the absence of chemotherapy or at diagnosis. Such leukemias are typically acute myeloid leukemia (AML), particularly myelomonocytic subtype, and cases of acute promyelocytic leuke (APL) are rarely reported. Controversy exists as to whether myeloma and AML originate from a single haematopoietic progenitor or arise from different cell lineages. We report a case of a 58 year old female who developed APL 10 months following diagnosis of nonsecretory light chain (kappa) myeloma which had been treated with local spinal irradiation and low dose oral melphalan and prednisone. Clonality had originally been demonstrated by light chain restriction (kappa) of her bone marrow plasma cells whilst immunoglobulin heavy chain and T cell receptor genes were germ line. At development of APL cytogenetics revealed t(15;17) and PML-RAR fusion gene was detected by RT-PCR. The patient was treated with all-trans retinoic acid (ATRA) and received 2 cycles of consolidation chemotherapy with Idarubicin. Following this therapy the t(15;17) and PML-RAR were both undetectable whilst the clonal population of kappa staining plasma cells persisted. This particular patient represents a rare case of APL complicating multiple myeloma with persistence of the myeloma clone but disappearance of PML-RAR alpha RNA following therapy. This case study appears to support the argument that the APL and myeloma originated from distinct cell lineages.

Detection of t(4;14)(p16.3;q32) chromosomal translocation in multiple myeloma by double-color fluorescent in situ hybridization

Chromosomal translocations involving the immunoglobulin heavy chain (IGH) locus at chromosome 14q32 represent a common mechanism of oncogene activation in lymphoid malignancies. In multiple myeloma (MM), variable chromosome partners have been identified by conventional cytogenetics, including the 11q13, 8q24, 18q21, and 6p21 loci. We and others have recently reported a novel, karyotypically undetectable chromosomal translocation t(4;14)(p16. 3;q32) in MM-derived cell lines, as well as in primary tumors. The 4p16.3 breakpoints are relatively scattered and located less than 100 kb centromeric of the fibroblast growth factor receptor 3 (FGFR3) gene or within the recently identified WHSC1 gene, both of which are apparently deregulated by the translocation. To assess the frequency of the t(4;14)(p16.3;q32) translocation in MM, we performed a double-color fluorescent in situ hybridization (FISH) analysis of interphase nuclei with differently labeled probes specific for the IGH locus (a pool of plasmid clones specific for the IGH constant regions) or 4p16.3 (yeast artificial chromosome (YAC) 764-H1 spanning the region involved in breakpoints). Thirty MM patients, the MM-derived cell lines KMS-11 and OPM2, and six normal controls were examined. The identification of a t(4;14) translocation, evaluated as the presence of a der(14) chromosome, was based on the colocalization of signals specific for the two probes; a cutoff value of 15% (mean + 3 standard deviation [SD]) derived from the interphase FISH of the normal controls (range, 5% to 11%; mean +/- SD, 8.16 +/- 2.2) was used for the quantification analysis. In interphase FISH, five patients (one in clinical stage I, two in stage II, one in stage III, and a plasma cell leukemia) were found to be positive (approximately 15%). FISH metaphases with split or colocalized signals were detected in only two of the translocated cases and confirmed the pattern found in the interphase nuclei. Furthermore, in three of the five cases with the translocation, FISH analysis with the IGH joining probe (JH) showed the presence of the reciprocal product of the translocation [der(4) chromosome]. Overall, our study indicates that the t(4;14)(p16. 3;q32) chromosomal translocation is a recurrent event in MM tumors and may contribute towards the detection of this lesion and our understanding of its pathogenetic and clinical implications in MM.

A new multiple myeloma cell line, MEF-1, possesses cyclin D1 overexpression and the p53 mutation

BACKGROUND

The t(11;14)(q13;q32) translocation with cyclin D1 overexpression commonly is found in multiple myeloma (MM) and in mantle cell lymphoma (MCL). Several reports have shown that p53 mutations in MCL lead to blastoid transformation and a worse prognosis; however, the role of p53 mutations in MM with t(11;14) is unclear.

METHODS

In this study the authors describe a patient with MM with t(11;14) and a p53 mutation at presentation and characterized a cell line, MEF-1, established from this patient. Immunohistochemical analysis of p53 and cyclin D1 proteins was performed. The p53 gene was analyzed by polymerase chain reaction-single strand conformation polymorphism and direct sequencing. The expression of cyclin D1 mRNA was examined by Northern blot analysis.

RESULTS

MEF-1 had t(11;14) with overexpression of cyclin D1 mRNA and produced immunoglobulin kappa-light chain. MEF-1 had a mutation in exon 7 (codon 255-257) of the p53 gene, which was noted in the patient's myeloma cells.

CONCLUSIONS

p53 mutations may be important genetic events in disease progression of MM with t(11;14). The MEF-1 cell line may be a useful tool to study mechanisms of progression in MM based on abnormalities of the cyclin D1 gene.

[Multiple myeloma in siblings]

We encountered 2 patients with multiple myeloma in a family with 11 siblings, suggesting that the occurrence of the disease may be associated with genetic factors. Patient 1: The second daughter (age 79) was given a diagnosis of multiple myeloma and admitted to our hospital in December 1997 for treatment. IgG-lambda type M protein was detected by serum immunoelectrophoresis, punched out lesions (+) by X ray examination, and atypical plasma cells (14% of total) by bone marrow examination. Patient 2: The fifth daughter (age 68) received a diagnosis of multiple myeloma and was admitted to our hospital in May 1997 for treatment. Bence Jones-kappa type and IgA-kappa type M protein were detected by serum immunoelectrophoresis, punched out lesions (+) by X ray examination, and atypical plasma cells (90% of total) by bone marrow examination. It was noted that the sixth daughter had leukemia; hence, 3 of the 11 siblings had blood disorders. For this reason, HLA studies were performed and detected A31, B39, B51, and Cw7 in patient 1 and A31, B51, B62, and Cw4 in patient 2. Further case studies will hopefully reveal more details concerning the relationship between myeloma and HLA.

Replacements in the exposed loop of the T15 antibody VH CDR2 affect carrier recognition of PC-containing pathogens

A panel of mutant antibodies of the phosphocholine (PC)-binding antibody, T15, was tested for binding to PC-protein, Streptococcus pneumoniae, Trichinella spiralis and Ascaris suum. Relative to wildtype T15, all the mutant antibodies showed differential recognition of the panel of PC-associated antigens. These mutant antibodies contain amino acid replacements in the CDR2 region of the heavy chain variable region, indicating the importance of CDR2 in recognition of carrier determinants. A model of T15 is shown that illustrates the strategic placement of mutations that could allow interaction with determinants associated with PC. A direct implication of this finding is that the T15 antibody combining site accommodates structures larger than phosphocholine and that recognition of associated carrier determinants could be a significant force in shaping the immune response to PC-containing pathogens.

A high frequency of circulating B cells share clonotypic Ig heavy-chain VDJ rearrangements with autologous bone marrow plasma cells in multiple myeloma, as measured by single-cell and in situ reverse transcriptase-polymerase chain reaction

In multiple myeloma (MM), the VDJ rearrangement of the immunoglobulin heavy chain expressed by MM plasma cells provides a unique clonotypic marker. Although clonotypic MM cells have been found in the circulation, their number has been controversial. Our objective was to provide direct evidence, using single-cell assays, for the frequency of clonotypic cells in blood of 18 MM patients, and to confirm their identity as B cells. The clonotypic Ig heavy-chain (IgH) VDJ was determined from single plasma cells using consensus reverse transcriptase-polymerase chain reaction (RT-PCR), subcloning, and sequencing. For all patients, using patient-specific primers, clonotypic transcripts were amplified from 10 or more individual plasma cells. Using in situ RT-PCR, for all patients greater than 80% of plasma cells were found to be clonotypic. Three separate methods, RT-PCR, single-cell RT-PCR, and in situ RT-PCR, were used to analyze clonotypic cells in peripheral blood mononuclear cells (PBMC) from MM patients. Sequencing of the IgH transcripts expressed by individual cells obtained by limiting dilution of freshly isolated PBMC from a MM patient showed that all B cells expressed an identical CDR3. This intraclonal homogeneity indicates an escape from antigenic-selection, characteristic of malignant B cells. For this patient, the frequency of clonotypic PBMC, about 25%, was comparable to the number of PBMC B cells (34%). Because the PBMC included less than 1% plasma cells, virtually all clonotypic PBMC must be B cells. Using single-cell RT-PCR, clonotypic IgH transcripts were identified in individual sorted B cells from blood. To accurately quantify the number of clonotypic B cells, sorted B cells derived from 18 MM patients (36 samples) and 18 healthy donors (53 samples) were analyzed using in situ RT-PCR with patient-specific primers. Clonotypic transcripts were not detectable among normal B cells. For the 18 MM patients, a mean of 66% +/- 4% (SE) of blood B cells were clonotypic (range, 9% to 95%), with mean absolute number of 0.15 +/- .02 x 10(9)/L blood. Over time in individual patients, conventional chemotherapy transiently decreased circulating clonotypic B cells. Their numbers were increased in granulocyte colony-stimulating factor (G-CSF)- mobilized blood of one patient. However, clonotypic B cells of a one patient became undetectable after allogeneic transplant, correlating with complete remission. Although contributions to MM spread and progression is likely, their malignant status and impact has yet to be clarified. Their high frequency in the blood, and their resistence to conventional chemotherapy suggests that the number of circulating clonotypic cells should be clinically monitored, and that therapeutic targeting of these B cells may benefit myeloma patients.

Disseminated growth of murine plasmacytoma: similarities to multiple myeloma

Murine plasma cell tumors share a number of common features with human multiple myeloma, suggesting their possible use as a model for this disease. However, one major difference between the two is the peritoneal localization of murine tumors as opposed to bone marrow residence of malignant plasma cells in early stages of multiple myeloma. We have thus examined the ability of murine plasmacytoma to produce disseminated growth similar to that seen in myeloma or other lymphoid neoplasias. Of four murine cell lines evaluated, all were demonstrated to effect highly metastatic disease involving multiple organs, although variation was observed between lines. A temporal analysis was accordingly performed with the S107 line to assess the pattern of cellular localization. Both light microscopy and PCR analysis revealed that engraftment of plasma cells occurs first in the bone marrow, followed by dissemination to other sites including the spleen, lung, and liver. Cells passaged in vivo through the bone marrow display an entirely different metastatic pattern with no homing preference to bone marrow or any other organ, suggesting the occurrence of a phenotypic change. Microscopic osteolytic lesions were observed adjacent to plasma cell tumor masses in the bone marrow, indicating early stages of bone disease. These findings demonstrate previously unrecognized similarities between the murine and human diseases and suggest the use of this in vivo model for experimental approaches to the treatment of human disease.

Somatic mutation in VH complementarity-determining region 2 and framework region 2: differential effects on antigen binding and Ig secretion

The extent to which somatic mutation impairs the Ig complementarity-determining region (CDR) and framework region (FRW) structure/function is not clear. Previously, we found that the VH CDR2 of the murine T15 Ab is highly sensitive to mutation; 56% (26 of 46) of Abs mutated in vitro had reduced or no Ag binding capability, and 9% were secretion impaired. Here we test whether the T15 VH CDR2 structure is unique by mutating the VH CDR2 of the anti-PC-protein murine Ab, PCG1-1. PCG1-1 VH is encoded by the M141 gene and is unrelated in sequence or structure to that of T15 VH1. The majority (54%, 20 of 37) of PCG1-1 mutants carrying one to five mutations in VH CDR2 had reduced or abolished Ag binding, while 10% were secretion impaired. Taken together, mutational analysis of the VH1 and VH M141 genes demonstrates that impaired binding and secretion may be common outcomes of CDR2 somatic mutation. We also tested the tolerance of the VH FRW2 of T15 to mutation, expecting this sequence-conserved region to be highly sensitive to alterations. However, FRW2 accommodated many nonconservative changes, and only 12% (3 of 25) of secreted mutants had impaired Ag binding. Moreover, mutations in FRW2 caused secretion defects in 24% (8 of 33), a frequency twice that of VH CDR2 mutants. A total of 16 unique secretion mutants have now been identified. These findings suggest that B cell losses from somatic mutation may be extensive and due to varied causes not all related to Ag binding.

A natural antibody missing a cysteine in VH: consequences for thermodynamic stability and folding

While the disulfide bridge is highly conserved within the immunoglobulin fold, a few antibody variable domains lack one of the essential cysteine residues. In the levan binding antibody ABPC48 one of the essential cysteine residues (Cys H92) of the heavy chain variable domain is replaced by tyrosine. We expressed scFv fragments with the ABPC48 sequence and a mutant in which the VH disulfide bond has been restored in Escherichia coli, purified both proteins by antigen affinity chromatography and characterized them by equilibrium denaturation. While the ABPC48 protein was found to be significantly less stable than an average scFv molecule, the restored disulfide increased its stability above that of other, unrelated scFv fragments, explaining why it tolerates the disulfide loss. Surprisingly, we observed that under some refolding conditions, the unpaired cysteine residue of functional scFv of ABPC48 is derivatized by glutathione. It is easily accessible to other reagents and thus appears to be solvent-exposed, in contrast to the deeply buried disulfide of ordinary variable domains. This implies a very unusual conformation of stand b containing the unpaired Cys H22, which might be stabilized by interactions with the tyrosine residue in position H92.

Myeloma VL and VH gene sequences reveal a complementary imprint of antigen selection in tumor cells

In multiple myeloma, sequence studies of VH genes used to encode clonal Ig in neoplastic plasma cells have shown a common pattern of extensive somatic hypermutation. A further consistent feature of these VH sequences is a complete lack of intraclonal variation. These findings indicate that the malignant cell arises at a mature, postfollicular stage of B-cell development. However, only a minority of cases have a distribution of somatic mutations in VH consistent with a prior role for antigen in selecting the B cell of origin. To complement these studies, and to take further the investigation of a role for antigen in the clonal history of myeloma, we have investigated tumor-derived VL sequences from bone marrows of 15 patients. All sequences (9V kappa and 6V lambda A) were potentially functional and 5 of 15 had evidence for N-region additions. All had undergone extensive somatic hypermutation, and showed no intraclonal variation. In 4 of 15 cases, the distribution of mutations revealed a significant (P < .05) clustering of replacement mutations in the CDR sequences, indicating a role for VL in selection by antigen. Comparison with the VH sequences used by the same tumor cells showed that, if significant clustering was present, it was in either VH or VL but not both. Altogether, 10 of 15 V-regions showed evidence for antigen selection, suggesting that the B cell of origin has behaved as a normal germinal center B cell. Deductions concerning a role for antigen selection may require both VH and VL sequences for validation.

Dysregulation of cyclin D1 by translocation into an IgH gamma switch region in two multiple myeloma cell lines

Translocations involving the IgH locus at chromosomal locus 14q32.3 are a common event in many B-cell malignancies. The translocations, which generally occur into JH and switch regions, are mediated by errors in the two developmentally regulated, lymphocyte-specific pathways: VDJ-and switch-mediated recombination. Dysregulation of cyclin D1 by a t(11;14)(q13;q32) translocation occurs in most cases of mantle-cell lymphoma and in approximately 30% of multiple myeloma (MM) tumors in which a 14q32 translocation can be detected. We show here that in two of three myeloma lines that overexpress cyclin D1, there is an 11;14 translocation into a gamma switch region, suggesting an error in switch recombination. By contrast, 11;14 translocations in mantlecell lymphoma are invariably into or near a JH segment, suggesting an error in VDJ recombination. This is consistent with the fact that myeloma cells have undergone lgH switch recombination, whereas mantle-cell lymphoma cells generally have not.

Tumor-specific aneuploidy not detected in CD19+ B-lymphoid cells from myeloma patients in a multidimensional flow cytometric analysis

Aneuploidy and lg light chain restriction were used as separate, independent tumor specific markers to study 26 patients with multiple myeloma to determine whether bone marrow B cells, as defined by CD19 expression, are clonally related to myeloma plasma cells. Specimens were characterized using multidimensional flow cytometry to identify the presence of clonality in both the B lymphoid and plasma cell populations using both surface and cytoplasmic staining with antibodies specific for kappa or lambda lg light chain In none of the patients with multiple myeloma were CD19+ cells found to be clonally restricted to kappa or lambda. The monoclonal plasma cells (MPC) were found to be uniformly negative for CD10, CD19, and CD34, while the CD19+ B lymphoid cells present within the samples expressed normal intensities and relationships of these antigens, which allowed them to serve as internal positive controls. Combined analysis of call surface antigen expression and DNA content allowed plasma cell populations to be characterized for aneuploidy without interference from normal bone marrow cells. The MPC, detected on the basis of bright CD38 expression (CD38+2), demonstrated DNA aneuploidy in 65% of cases (DNA index range of 0.9 to 1.3). These aneuploid DNA distributions had typical cell cycle profiles (including G1,S and G2+M) expected of a proliferating population. In all cases, DNA aneuploidy was confined almost entirely to the CD38+2, CD19- malignant plasma cells, while cells expressing CD19 were diploid. These results support the concept that myeloma is a disease process mediated by self-replicating, late compartments of B-cell ontogeny.

Clonal circulating cells are common in plasma cell proliferative disorders: a comparison of monoclonal gammopathy of undetermined significance, smoldering multiple myeloma, and active myeloma

The blood of most patients with active multiple myeloma (MM) contains cells related to the bone marrow tumor. However, identifying clonal cells in the blood of patients with monoclonal gammopathy of undetermined significance (MGUS) has been difficult. In this study, we analyzed blood mononuclear cells (BMNCs) from 16 patients with MGUS, 2 with amyloidosis, 8 with smoldering MM (SMM), 2 with indolent MM (IMM), and 15 with active MM using three different methods to detect and quantitate clonal cells, ie, immunofluorescence microscopy (IM) for monoclonal plasma cells, three-color flow cytometry (FC) for CD38(+)CD45- CD45(dim) cells, and the allele-specific oligonucleotide polymerase chain reaction (ASO-PCR). Using ASO-PCR, we were able to detect clonal cells in the blood in 13 of 16 patients with MGUS, 2 of 2 with amyloid, 6 of 8 with SMM, 2 of 2 with IMM, and 13 of 15 with MM. In 9 of the 13 patients with MGUS with blood involvement, the number of clonal cells was very small ( < 0.04% of the BMNCs). The median percentage of clonal cells as determined by ASO-PCR was 0.02 for MGUS, 0.02 for SMM, and 0.24 for MM. Clonal plasma cells or CD38+CD45-CD45(dim) cells were identified by IM or FC in 6 of 16 MGUS patients, 4 of 8 with SMM, and 11 of 15 with MM. In all cases in which IM or FC detected clonal cells, the ASO-PCR was positive. This study shows that, by using ASO-PCR, clonal cells can be found at very low levels in the blood in most patients with MGUS. However, the number of clonal cells in the blood of MGUS patients is less than those with overt MM (P = .006). In contrast to MGUS, patients with active MM are more likely to have identifiable clonal circulating plasma cells (P = .05).

Quantitative comparison of multiple myeloma tumor contamination in bone marrow harvest and leukapheresis autografts

Autologous transplantation is increasingly being used to treat patients with multiple myeloma (MM). Recently, peripheral blood progenitor cell (PBPC) harvest have been preferred over autologous bone marrow (BM) harvests due to reduced engraftment time, ease of attainment, and presumptive reduction of occult tumor involvement. To resolve this latter assumption quantitatively, we have used the unique immunoglobulin (Ig) heavy chain variable region sequence of the patient's myeloma cell as a marker of clonality. Samples from PBPC collections and 'back-up' BM harvests were obtained from 13 patients with MM and analyzed for tumor contamination using patient-specific oligonucleotide primers and the polymerase chain reaction. As expected, the percentage of tumor cells contaminating the BM harvest (median, 0.74%) was higher than in the PBPC specimens (median, 0.0024%). Because of the increased total number of cells required for PBPC transplantation, the increase in total number of contaminating cells in the BM vs PBPC autografts was less pronounced, (BM:PBPC tumor contamination ratios ranging from 0.9 to > 4500; median, 14). This confirms that in most but not all cases unmanipulated PBPC products are preferable over BM harvests as a method of reducing myeloma autograft tumor contamination.

Tolerance of single, but not multiple, amino acid replacements in antibody VH CDR 2: a means of minimizing B cell wastage from somatic hypermutation?

Mutations in the heavy chain complementarity determining region 2 (CDR2) of the phosphocholine-specific T15 Ab can have a dramatic effect on the ability of the Ab to bind Ag. A panel of multisite mutants that had lost detectable binding to phosphocholine-containing Ags was previously created by saturation mutagenesis of the CDR2 region of T15. Based on the predicted importance of amino acid changes represented in the multisite mutants, we have created single-site mutations, yielding a panel of Abs with which to test 17 of the 19 CDR2 residues. Of the 17 positions examined, only one, Arg52, is intolerant to change, yielding a nonbinder phenotype even with conservative amino acid replacement. Mutation at two other sites, Ala50 and Tyr55, can yield a nonbinder phenotype depending on the amino acid replacement. Single-site mutations of the remaining 14 positions allowed retention of binding ability. Thus, except for positions 50, 52, and 55, multiple mutations must be introduced into the CDR2 region to create a nonbinder phenotype. We provide a newly refined model of T15, illustrating the structure and the interactions of the CDR2 region. Our results imply that introduction of point mutations would not normally delete Ag-binding ability until two or more mutations had accumulated. This would minimize potentially harmful effects of somatic mutation on Ig V region genes and improve the chance of survival for an Ab such as T15, which in its unmutated form is already well suited to bind Ag.

Circulating clonal lymphocytes in myeloma constitute a minor subpopulation of B cells

The mononuclear cells in the blood of myeloma patients have been reported to contain a high proportion of phenotypically abnormal myeloma B lymphocytes. These cells have been proposed to constitute the drug-resistant proliferative myeloma cell compartment. To determine the extent of B lymphocyte involvement, the proportion of clonotypic cells among the CD19-expressing cells from myeloma patients was estimated by quantitative polymerase chain reaction analysis of the third complementarity determining region (CDR3). The results indicate that the B lymphocytes constitute, on average, 6% of blood mononuclear cells, and that only a minor fraction of these are clonally related to the myeloma cells. While the small number of circulating clonal cells is not incompatible with their proposed role as a reservoir of proliferating myeloma progenitors, the majority of the B cells appear not to be clonally related to the myeloma cells.

Ig VH gene mutational patterns indicate different tumor cell status in human myeloma and monoclonal gammopathy of undetermined significance

Plasma cell tumors display a wide spectrum of clinical progression, ranging from aggressive multiple myeloma to a benign form known as monoclonal gammopathy of undetermined significance (MGUS), which requires no treatment. Because both diseases involve mature Ig-secreting plasma cells, the reason for this variation in malignant behavior is unclear. However, assessment of malignant potential is desirable for choice of treatment protocols. Ig variable (VH) gene sequences analysis has previously shown the tumor cell of multiple myeloma to be postfollicular, with mutated homogeneous clonal sequences indicating no continuing exposure to the somatic hypermutation mechanism, and this was confirmed in 7 of 7 patients. Comparison of the VH gene sequences in the monoclonal cells in MGUS yielded a different result, with 3 of 7 patients demonstrating mutated heterogeneous sequences consistent with the tumor cells remaining under the influence of the mutator. In 1 of 3 of these patients, an IgM-positive precursor cell was identified that expressed heterogeneous VH sequences similar to those of the isotype-switched plasma cell. These results indicate that the clonal cells in MGUS differ from those in myeloma and suggest that the difference may reflect malignant potential.

Partial activation of CD8+ T cells by a self-derived peptide

T cells are normally activated when the peptide for which they are specific is presented to them in the context of the appropriate major histocompatibility complex (MHC) (class I and Class II for CD8+ and CD4+ T cells, respectively). An increasing body of evidence indicates that structural homologues of the immunogenic peptide can partially activate or antagonize CD4+ T cells. CD8+ T cells may also be partially antagonized by such peptides, and self-derived peptides of this type may play a role in CD8+ T cell selection in the thymus. Activated CD8+ T cells lyse their targets by perforin-dependent granule exocytosis and by inducing apoptosis mediated by CD95 (also known as Fas or APO1) with its ligand (CD95L). Here we show that a clone of Kd-restricted CD8+ T cells specific for influenza haemagglutinin, which can also be activated in a crossreactive manner by a peptide derived from a myeloma tumour immunoglobulin heavy-chain variable region (IgVH) to kill by both routes, kills only by the CD95-CD95L pathway when stimulated by the corresponding germline IgVH peptide. As this germline IgVH peptide differs from the tumour peptide only at a single position buried in the MHC-binding groove, this indicates that CD95-CD95L-mediated killing can be triggered independently of the perforin-mediated pathway, and can be selectively affected by changes in MHC conformation.

Role of light chain variable region in myeloma with light chain deposition disease: evidence from an experimental model

Light chain deposition disease (LCDD) results from a propensity of some human monoclonal L chains to form tissue deposits. We designed an experimental model for in vivo expression of human kappa L chain sequences in mice and compared a somatically mutated LCDD chain with a closely related control kappa chain, both encoded by the unique V kappa IV gene. Mice secreting the LCDD chain but not those producing the control chain showed deposits with a distribution similar to that observed in patients. These data show that discrete changes in V region sequences can play a major role in tissue deposition of human L chains.