Trans-homophilic interaction of CADM1 activates PI3K by forming a complex with MAGuK-family proteins MPP3 and Dlg

CADM1 (Cell adhesion molecule 1), a cell adhesion molecule belonging to the immunoglobulin superfamily, is involved in cell-cell interaction and the formation and maintenance of epithelial structure. Expression of CADM1 is frequently down-regulated in various tumors derived from epithelial cells. However, the intracellular signaling pathways activated by CADM1-mediated cell adhesion remain unknown. Here, we established a cell-based spreading assay to analyze the signaling pathway specifically activated by the trans-homophilic interaction of CADM1. In the assay, MDCK cells expressing exogenous CADM1 were incubated on the glass coated with a recombinant extracellular fragment of CADM1, and the degree of cell spreading was quantified by measuring their surface area. Assay screening of 104 chemical inhibitors with known functions revealed that LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), efficiently suppressed cell spreading in a dose-dependent manner. Inhibitors of Akt and Rac1, downstream effectors of PI3K, also partially suppressed cell spreading, while the addition of both inhibitors blocked cell spreading to the same extent as did LY294002. Furthermore, MPP3 and Dlg, membrane-associated guanylate kinase homologs (MAGuK) proteins, connect CADM1 with p85 of PI3K by forming a multi-protein complex at the periphery of cells. These results suggest that trans-homophilic interaction mediated by CADM1 activates the PI3K pathway to reorganize the actin cytoskeleton and form epithelial cell structure.

Distearoyl anchor-painted erythrocytes with prolonged ligand retention and circulation properties in vivo

Red blood cells (RBCs) attract significant interest as carriers of biomolecules, drugs, and nanoparticles. In this regard, versatile technologies to attach molecules and ligands to the RBC surface are of great importance. Reported here is a fast and efficient surface painting strategy to attach ligands to the surface of RBCs, and the factors that control the stability and circulation properties of the modified RBCs in vivo. Distearoyl phosphatidylethanolamine anchor-conjugated immunoglobulin (IgG) efficiently incorporates in the RBC membrane following 15-30 min incubation. The optimized RBCs show prolonged circulation in vivo (70% of the injected dose after 48 h) and efficient retention of IgG in the membrane with terminal half-life of 73 h. The IgG construct is gradually lost from the RBCs mainly due to the transfer to plasma components, liver endothelial cells, and Kupffer cells. The ligand retention efficiency is partially dictated by ligand type, anchor type, and ligand concentration in the membrane, while RBC half-life is determined by initial concentration of the ligand in the membrane and presence of PEG linker between the ligand and the anchor. This work provides important guidance for non-covalent surface painting of RBCs as well as other types of blood borne cells for in vivo therapeutic and targeting applications.

Advances in chimeric antigen receptor immunotherapy for chronic lymphocytic leukemia

Despite the recent advances with targeted therapies in chronic lymphocytic leukemia (CLL), allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative option. However, this procedure is associated with significant morbidity and mortality due to high rates of infection and the toxicity of graft versus host disease (GVHD). One of the principle aims of cellular immunotherapy is to target the malignant cells without damaging the other tissues of the body. T lymphocytes offer the opportunity to do this, due to the exquisite specificity that they exhibit as part of the adaptive immune response. Chimeric antigen receptor (CAR) T cells are lymphocytes that have been genetically modified to express the antigen binding component of an immunoglobulin molecule coupled to T-cell signaling domains. The use of an immunoglobulin molecule eliminates MHC restriction, enabling the same CAR to be used for several different patients and increasing the feasibility of widespread clinical use. They can be constructed to target a huge range of antigens, allowing the targeting of cancer cells with unprecedented levels of specificity. The addition of co-stimulatory domains to the CAR construct has enhanced the efficacy and durability of these T cells, which are under investigation in several clinical trials. The early results from these trials have been very encouraging with dramatic responses being observed in heavily pre-treated patients with otherwise poor risk disease.

[Circular dichroism chromatography of secondary structures of anti-HBV IgY in eggs from hens immunized with recombinant yeast HBV vaccine]

OBJECTIVE

To study the generation and structure of anti-HBV IgY in eggs from hens immunized with recombinant yeast HBV vaccine.

METHODS

From the hens immunized three times with the recombinant yeast HBV vaccine, the eggs were collected to extract anti-HBV IgY. After purified, the anti- HBV IgY was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and reverse phase high-performance liquid chromatography (RP-HPLC), and its secondary structure was examined by circular dichroism (CD) chromatography.

RESULTS

The relative molecular mass (Mr;) of anti-HBV IgY expressed by the recombinant yeast HBV vaccine on hens was 178 000. CD chromatography showed that the α-helix, β-fold, β-turn and random coil of anti-HBV IgY had 38, 0, 44 and 17 amino acids, respectively.

CONCLUSION

The anti-HBV IgY can be expressed in eggs from hens immunized with recombinant yeast HBV vaccine. The α-helix and β-turn are major secondary structures of anti-HBV IgY.

[Identification of some proteins of blood and tissue fluid in fish with undeciphered genome]

In blood and tissue fluid of squamulose redeye, rock perches, starlet, and two species of electric rays, with aid of methods of proteomics, there were identified ependemines, vitellogenins, immunoglobulins, and albumin-like proteins (ALP). For all proteins except for ALP, identification was successful with use of MALDI mass-spectroscopy in the tandem regime. Reconstruction of fragments of amino acid sequences was performed with databases of fish with the sequenced genome and mammals. Problems at the ALP identification are connected with a high level of their structural diversity and the absence of similarity with mammalian proteins.

IgY antibodies anti-Tityus caripitensis venom: purification and neutralization efficacy

Tityus caripitensis is responsible for most of scorpion stings related to human incidents in Northeastern Venezuela. The only treatment for scorpion envenomation is immunotherapy based on administration of scorpion anti-venom produced in horses. Avian antibodies (IgY) isolated from chicken egg yolks represent a new alternative to be applied as anti-venom therapy. For this reason, we produced IgY antibodies against T. caripitensis scorpion venom and evaluated its neutralizing capacity. The anti-scorpion venom antibodies were purified by precipitation techniques with polyethylene glycol and evaluated by Multiple Antigen Blot Assay (MABA), an indirect ELISA, and Western blot assays. The lethality neutralization was evaluated by preincubating the venom together with the anti-venom prior to testing. The IgY immunoreactivity was demonstrated by a dose-dependent inhibition in Western blot assays where antibodies pre-absorbed with the venom did not recognize the venom proteins from T. caripitensis. The anti-venom was effective in neutralizing 2LD50 doses of T. caripitensis venom (97.8 mg of IgY neutralized 1 mg of T. caripitensis venom). Our results support the future use of avian anti-scorpion venom as an alternative to conventional equine anti-venom therapy in our country.

Feasibility study of the optical imaging of a breast cancer lesion labeled with upconversion nanoparticle biocomplexes

Innovative luminescent nanomaterials, termed upconversion nanoparticles (UCNPs), have demonstrated considerable promise as molecular probes for high-contrast optical imaging in cells and small animals. The feasibility study of optical diagnostics in humans is reported here based on experimental and theoretical modeling of optical imaging of an UCNP-labeled breast cancer lesion. UCNPs synthesized in-house were surface-capped with an amphiphilic polymer to achieve good colloidal stability in aqueous buffer solutions. The scFv4D5 mini-antibodies were grafted onto the UCNPs via a high-affinity molecular linker barstar:barnase (Bs:Bn) to allow their specific binding to the human epidermal growth factor receptor HER2/neu, which is overexpressed in human breast adenocarcinoma cells SK-BR-3. UCNP-Bs:Bn-scFv4D5 biocomplexes exhibited high-specific immobilization on the SK-BR-3 cells with the optical contrast as high as 10:1 benchmarked against a negative control cell line. Breast cancer optical diagnostics was experimentally modeled by means of epi-luminescence imaging of a monolayer of the UCNP-labeled SK-BR-3 cells buried under a breast tissue mimicking optical phantom. The experimental results were analyzed theoretically and projected to in vivo detection of early-stage breast cancer. The model predicts that the UCNP-assisted cancer detection is feasible up to 4 mm in tissue depth, showing considerable potential for diagnostic and image-guided surgery applications.

Functional classification of immune regulatory proteins

The members of the immunoglobulin superfamily (IgSF) control innate and adaptive immunity and are prime targets for the treatment of autoimmune diseases, infectious diseases, and malignancies. We describe a computational method, termed the Brotherhood algorithm, which utilizes intermediate sequence information to classify proteins into functionally related families. This approach identifies functional relationships within the IgSF and predicts additional receptor-ligand interactions. As a specific example, we examine the nectin/nectin-like family of cell adhesion and signaling proteins and propose receptor-ligand interactions within this family. Guided by the Brotherhood approach, we present the high-resolution structural characterization of a homophilic interaction involving the class-I MHC-restricted T-cell-associated molecule, which we now classify as a nectin-like family member. The Brotherhood algorithm is likely to have a significant impact on structural immunology by identifying those proteins and complexes for which structural characterization will be particularly informative.

The glycosylated IgII extracellular domain of EMMPRIN is implicated in the induction of MMP-2

EMMPRIN is a widely expressed transmembrane glycoprotein that plays important roles in many physiological and pathological processes, such as tumor invasion and metastasis. It stimulates the production of matrix metalloproteinase (MMPs) by tumor-associated fibroblasts. In the present study, our aim was to (a) to investigate if the IgII loop domain of the extracellular domain (ECD) of EMMPRIN contributes to the MMP production by fibroblasts and (b) to evaluate the significance of glycosylation in this process. For this purpose, we expressed the ECD, IgI, or IgII domains of EMMPRIN, in their glycosylated and non-glycosylated forms, in the heterologous expression systems of P. pastoris and E. coli, respectively. Dermal fibroblasts were treated with purified recombinant domains and proteins from cell extracts and supernatants were analyzed by Western blot and zymography assays. Fibroblasts treated with ECD-, IgI-, and IgII-glycosylated domains of EMMPRIN significantly stimulated the gelatinolytic activity of MMP-2, compared to untreated fibroblasts, whereas no significant effect was observed after treatment with the non-glycosylated ECD, IgI, and IgII domains. Western blot analysis from cell extracts and supernatants revealed that only the glycosylated forms were able to stimulate MMP-2 production and secretion, respectively. Quantitative PCR revealed that this effect was not attributed to transcriptional alterations. This study showed that N-glycosylation was a prerequisite for efficient MMP-2 production, with the IgII loop domain contributing significantly to this process. Perturbation of the function of IgII-EMMPRIN loop could have potential therapeutic value in the inhibition of MMP-2-dependent cancer cell invasion and metastasis.

IgH loci of American alligator and saltwater crocodile shed light on IgA evolution

Immunoglobulin loci of two representatives of the order Crocodylia were studied from full genome sequences. Both Alligator mississippiensis and Crocodylus porosus have 13 genes for the heavy chain constant regions of immunoglobulins. The IGHC locus contains genes encoding four immunoglobulins M (IgM), one immunoglobulin D (IgD), three immunoglobulins A (IgA), three immunoglobulins Y (IgY), and two immunoglobulins D2 (IgD2). IgA and IgD2 genes were found in reverse transcriptional orientation compared to the other Ig genes. The IGHD gene contains 11 exons, four of which containing stop codons or sequence alterations. As described in other reptiles, the IgD2 is a chimeric Ig with IgA- and IgD-related domains. This work clarifies the origin of bird IgA and its evolutionary relationship with amphibian immunoglobulin X (IgX) as well as their links with mammalian IgA.

(1)H, (13)C, and (15)N resonance assignments of the second immunoglobulin domain of neurolin from Carassius auratus

Neurolin is a member of the superfamily of immunoglobulin-like cell surface receptors. It is essential during neuronal development in the model organism Carassius auratus (goldfish) and involved in the guidance of the growing axon. Among the five extracellular immunoglobulin (Ig) domains, the second Ig domain is crucial for axon pathfinding. In the present study, we report the NMR assignment and secondary structure prediction of the second Ig domain of neurolin.

Reduction of low-density lipoprotein cholesterol, plasma viscosity, and whole blood viscosity by the application of pulsed corona discharges and filtration

The present study investigated the feasibility of applying pulsed corona discharges to blood plasma to reduce the viscosity of blood plasma and whole blood. Blood plasma was separated from blood cells, treated with corona discharges, and filtered before it was re-mixed with blood cells. Plasma viscosity (PV), whole blood viscosity (WBV), and low-density lipoprotein (LDL)-c concentration were measured before and after the corona treatment and filtration. Both PV and WBV increased in the case of the corona treatment only, whereas both of them decreased in the case of the corona treatment plus filtration. In particular, the LDL-c decreased in the case of the corona treatment plus filtration by 31.5% from the baseline value. The effect of the corona treatment on the reduction of the WBV was significant at low shear rates, but not at high shear rates, suggesting that the precipitation of the molecules in blood plasma by the corona treatment and subsequent removal may suppress the aggregation of erythrocytes and improve rheological properties of blood.

[The development of polymer immunoglobulin preparations to identify different serovars legionella pneumophilia in reaction of slide-agglutination]

The article deals with the results of study targeted to develop polymer diagnostic preparation to identify epidemically significant serogroups Legionella pneumophilia. The preparation combines rate of record (1-5 min) of reaction of paragglutinining preparations with color visualization and demonstrative of reaction of volume agglomeration with polymer diagnosticums. The specially synthesized polymer microspheres were sensibilized with serums enriched with antibodies to lipopolysaccharide of corresponding serovar L. pneumophilia. The derived immunoglobulin diagnostic preparations detect agent of legionellesis in the reaction of slide-agglutination on glass during 1-5 min. The polymer diagnostic preparations provide positive reaction with culture of corresponding serovar and no reaction with other gomologic and geterologic agents of infectious diseases.

A novel mutation of IGSF1 in a Japanese patient of congenital central hypothyroidism without macroorchidism

Congenital central hypothyroidism (C-CH) is a rare disease known to be caused by mutations of the genes encoding TSH β or the TRH receptor gene, although the cause of the disease in a number of patients has not yet been clarified. Recently, mutations and deletions of the immunoglobulin superfamily member 1 (IGSF1) gene have been reported to be the cause of C-CH. Here we report a Japanese male patient with C-CH due to a novel IGSF1 mutation. He was detected by neonatal mass screening of simultaneous TSH and free T4 measurements and levothyroxine was initiated. At 6 years of age he underwent ¹²³I scintigraphy after levothyroxine treatment had been discontinued for one month and his thyroid and pituitary function were evaluated. Since TSH and PRL responses after TRH stimulation were low, his diagnosis of C-CH was confirmed. During follow up, whereas onset of his puberty was delayed, his secondary sex characterization completed at 17 years old. In this patient we analyzed IGSF1 and TRHR. As results, we identified a novel insertion mutation in IGSF1 (c.3528-3529insC), resulting in a premature stop codon (p.Pro1082Trpfs39X). In conclusion, we identified a novel mutation of IGSF1 in a Japanese male patient with C-CH.

Use of mutated self-cleaving 2A peptides as a molecular rheostat to direct simultaneous formation of membrane and secreted anti-HIV immunoglobulins

In nature, B cells produce surface immunoglobulin and secreted antibody from the same immunoglobulin gene via alternative splicing of the pre-messenger RNA. Here we present a novel system for genetically programming B cells to direct the simultaneous formation of membrane-bound and secreted immunoglobulins that we term a "Molecular Rheostat", based on the use of mutated "self-cleaving" 2A peptides. The Molecular Rheostat is designed so that the ratio of secreted to membrane-bound immunoglobulins can be controlled by selecting appropriate mutations in the 2A peptide. Lentiviral transgenesis of Molecular Rheostat constructs into B cell lines enables the simultaneous expression of functional b12-based IgM-like BCRs that signal to the cells and mediate the secretion of b12 IgG broadly neutralizing antibodies that can bind and neutralize HIV-1 pseudovirus. We show that these b12-based Molecular Rheostat constructs promote the maturation of EU12 B cells in an in vitro model of B lymphopoiesis. The Molecular Rheostat offers a novel tool for genetically manipulating B cell specificity for B-cell based gene therapy.

Human anti-Aβ IgGs target conformational epitopes on synthetic dimer assemblies and the AD brain-derived peptide

Soluble non-fibrillar assemblies of amyloid-beta (Aβ) and aggregated tau protein are the proximate synaptotoxic species associated with Alzheimer's disease (AD). Anti-Aβ immunotherapy is a promising and advanced therapeutic strategy, but the precise Aβ species to target is not yet known. Previously, we and others have shown that natural human IgGs (NAbs) target diverse Aβ conformers and have therapeutic potential. We now demonstrate that these antibodies bound with nM avidity to conformational epitopes on plate-immobilized synthetic Aβ dimer assemblies, including synaptotoxic protofibrils, and targeted these conformers in solution. Importantly, NAbs also recognized Aβ extracted from the water-soluble phase of human AD brain, including species that migrated on denaturing PAGE as SDS-stable dimers. The critical reliance on Aβ's conformational state for NAb binding, and not a linear sequence epitope, was confirmed by the antibody's nM reactivity with plate-immobilized protofibrills, and weak uM binding to synthetic Aβ monomers and peptide fragments. The antibody's lack of reactivity against a linear sequence epitope was confirmed by our ability to isolate anti-Aβ NAbs from intravenous immunoglobulin using affinity matrices, immunoglobulin light chain fibrils and Cibacron blue, which had no sequence similarity with the peptide. These findings suggest that further investigations on the molecular basis and the therapeutic/diagnostic potential of anti-Aβ NAbs are warranted.

[Study on the stability of chicken egg yolk immunoglobulin (IgY) modified with mPEG]

The objective of the present paper was to study the effect of monomethoxypolyethlene glycol (mPEG) modification on the stability of chicken IgY and compare the stability of the modification products by Fourier transform infrared spectroscopy (FTIR), CD spectrooscopy and fluorescence spectroscopy. NHS-mPEG was used to modify IgY after mPEG was activated with N-hydroxysuccinimide (NHS). The optimal reaction condition for modification was 1:10 molar rate of IgY to mPEG at pH 7, reaction for 1 h, and the product was obtained with modification rate of 20.56% and activity reservation of 87. 62%. In addition, the thermal and pH stability of IgY and mPEG-IgY was compared by spectroscopic methods. The results showed that the alpha-helix, beta-sheet, beta-turn, and random content of IgY changed from 14.5%, 42.1%, 6.2% and 37.2% to 1.6%, 55.25%, 5.8% and 37.5%, while mPEG changed from 12.9%, 42.7%, 6.3% and 38. 1% to 3.1%, 50.5%, 7.2% and 39.2%, respectively, after incubating for 120 min at 70 degrees C. For the treatment with acid-base, similarly, the structure changes of mPEG-IgY were smaller than IgY. Thus, it is indicated that IgY modified by mPEG had greater stable properties.

L1CAM binds ErbB receptors through Ig-like domains coupling cell adhesion and neuregulin signalling

During nervous system development different cell-to-cell communication mechanisms operate in parallel guiding migrating neurons and growing axons to generate complex arrays of neural circuits. How such a system works in coordination is not well understood. Cross-regulatory interactions between different signalling pathways and redundancy between them can increase precision and fidelity of guidance systems. Immunoglobulin superfamily proteins of the NCAM and L1 families couple specific substrate recognition and cell adhesion with the activation of receptor tyrosine kinases. Thus it has been shown that L1CAM-mediated cell adhesion promotes the activation of the EGFR (erbB1) from Drosophila to humans. Here we explore the specificity of the molecular interaction between L1CAM and the erbB receptor family. We show that L1CAM binds physically erbB receptors in both heterologous systems and the mammalian developing brain. Different Ig-like domains located in the extracellular part of L1CAM can support this interaction. Interestingly, binding of L1CAM to erbB enhances its response to neuregulins. During development this may synergize with the activation of erbB receptors through L1CAM homophilic interactions, conferring diffusible neuregulins specificity for cells or axons that interact with the substrate through L1CAM.

[Avidity and competitive inhibition of binding native and chaotropically modified immunoglobulins with protein and glycolipid antigens]

It is established, that native and chaotropically modified immunoglobulins essentially differ by avidity and character of competitive inhibition of binding with protein (ovalbumin), glycolipid (lipopolysaccharides) antigens and native double-strand DNA. Apparently, it is connected with structural and functional distinctions of their antigen-binding centres.

Delayed toxicity associated with soluble anthrax toxin receptor decoy-Ig fusion protein treatment

Soluble receptor decoy inhibitors, including receptor-immunogloubulin (Ig) fusion proteins, have shown promise as candidate anthrax toxin therapeutics. These agents act by binding to the receptor-interaction site on the protective antigen (PA) toxin subunit, thereby blocking toxin binding to cell surface receptors. Here we have made the surprising observation that co-administration of receptor decoy-Ig fusion proteins significantly delayed, but did not protect, rats challenged with anthrax lethal toxin. The delayed toxicity was associated with the in vivo assembly of a long-lived complex comprised of anthrax lethal toxin and the receptor decoy-Ig inhibitor. Intoxication in this system presumably results from the slow dissociation of the toxin complex from the inhibitor following their prolonged circulation. We conclude that while receptor decoy-Ig proteins represent promising candidates for the early treatment of B. anthracis infection, they may not be suitable for therapeutic use at later stages when fatal levels of toxin have already accumulated in the bloodstream.

Passive adsorption of human antirrabic immunoglobulin onto a polystyrene surface

The latex agglutination immunoassay technique uses polymer colloids as carriers of adsorbed proteins to enhance the antigen-antibody reaction. The aim of the present work is to study the adsorption of Human Antirrabic Immunoglobulin (HA-IgG) on polystyrene latex (PS). The physical adsorption of HA-IgG on PS latex was investigated as a function of pH at 2 mM ionic strength. The amount of HA-IgG adsorbed onto PS latex greatly depends on pH; its value showed a maximum in the neighborhood of the IEP of HA-IgG. The electrophoretic method was applied to characterize latex particles. The influence of the amount of HA-IgG adsorbed (J(ads)) on the electrophoretic mobility and zeta-potential values was also studied.

Characterization of the immunoglobulin repertoire of the spiny dogfish (Squalus acanthias)

The cartilaginous fish (chimeras, sharks, skates and rays) are the oldest group relative to mammals in which an adaptive immune system founded upon immunoglobulins has been found. In this manuscript we characterize the immunoglobulins of the spiny dogfish (Squalus acanthias) at both the molecular and expressed protein levels. Despite the presence of hundreds of IgM clusters in this species the serum levels of this isotype are comparatively low. However, analysis of cDNA sequences and serum protein suggests microheterogeneity in the IgM heavy chains and supports the proposal that different clusters are preferentially used in the two forms (monomer or pentamer) of this isotype. We also found that the IgNAR isotype in this species exists in a previously unknown multimeric format in serum. Finally, we identified a new form of the IgW isotype (the shark IgD orthologue), in which the leader is spliced directly to the first constant domain, resulting in a molecule lacking an antigen-binding domain.

Ex-vivo clonally expanded B lymphocytes infiltrating colorectal carcinoma are of mature immunophenotype and produce functional IgG

Background

Tumor infiltrating B cells (TiBc) have not yet been investigated in detail. This may at least in part be due to technical difficulties. Here we describe a straightforward and reproducible method to isolate and culture TiBc from primary colorectal carcinomas (CRC).

Methods/Results

TiBc cultures were generated by Epstein-Barr virus (EBV) immortalization. With this method, monoclonal TiBc cultures were obtained for 14/19 CRCs. As assessed by flow cytometry and ELISA, TiBc showed an activated immunophenotype (CD23⁺, CD80⁺) and produced immunoglobulin (Ig; IgG secretion in 55% of the cultures). In functional in vitro analysis, most of the IgGs specifically bound to allogeneic CRC target cells. These data suggest that TiBc are antigen-experienced and thus may exhibit functionality in situ. Additionally, mini-cultures generated from 12 further CRCs revealed TiBc outgrowth exclusively in the presence of EBV.

Conclusion

In summary, this simple method provides a cellular tool and our data set the stage for analysing the bivalent role of TiBc; being antigen-presenting cells on the one hand and tumor-specific antibody producers on the other. Additionally, the generation of long-term TiBc cultures and their monoclonal Ig may serve to identify novel tumor-specific antigens.

Phenotypic detection of clonotypic B cells in multiple myeloma by specific immunoglobulin ligands reveals their rarity in multiple myeloma

In multiple myeloma, circulating “clonotypic” B cells, that express the immunoglobulin rearrangement of the malignant plasma cell clone, can be indirectly detected by PCR. Their role as potential “feeder” cells for the malignant plasma cell pool remains controversial. Here we established for the first time an approach that allows direct tracking of such clonotypic cells by labeling with patient-specific immunoglobulin ligands in 15 patients with myeloma. Fifty percent of patients showed evidence of clonotypic B cells in blood or bone marrow by PCR. Epitope-mimicking peptides from random libraries were selected on each patient's individual immunoglobulin and used as ligands to trace cells expressing the idiotypic immunoglobulin on their surface. We established a flow cytometry and immunofluorescence protocol to track clonotypic B cells and validated it in two independent monoclonal B cell systems. Using this method, we found clonotypic B cells in only one out of 15 myeloma patients. In view of the assay's validated sensitivity level of 10⁻³, this surprising data suggests that the abundance of such cells has been vastly overestimated in the past and that they apparently represent a very rare population in myeloma. Our novel tracing approach may open perspectives to isolate and analyze clonotypic B cells and determine their role in myeloma pathobiology.