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There is increasing recognition of monoclonal gammopathy as a cause of proliferative glomerulonephritis (GN), including cases in which glomerular deposition of monoclonal immunoglobulin is demonstrated. Recently, proliferative GN with monoclonal immunoglobulin deposits (PGNMID) has incorporated a light chain variant of the disease (termed PGNMID-LC). Intriguingly, glomerular co-deposition of C3 is found in addition to monotypic light chain, implying complement activation via the alternative pathway (AP). We present a unique case of proliferative GN in a 42-year-old man who presented with nephrotic syndrome and was found to have κ light chain multiple myeloma. Immune staining of the glomerulus was positive only for κ light chain and C3, with the striking appearance of nonamyloid fibrils on electron microscopy. Following clonally targeted therapy for myeloma, the renal clinical abnormalities resolved completely. We present detailed molecular studies for light chain and complement and consider local mechanisms whereby monoclonal κ light chain fibrils may have triggered AP activation within the glomerulus.

SATB1 (Special A-T rich Binding protein 1) is a cell type specific factor involved in chromatin remodelling events that participate in the regulation of the genetic network in developing T cells and neurons. In T cells, SATB1 is a key factor required for lineage commitment, VDJ recombination, development and maturation. In B cells, SATB1 is described as binding to the MARs-Eµ regions of the IgH locus. Considering that its expression varies during differentiation, the involvement of this factor needed to be clarified in B cells. Using a KO mouse model deleting SATB1 from the pro-B cell stage, we were able to examine the consequences of SATB1 deletion in naive and activated B cell subsets. Our model indicates firstly that SATB1 is not essential for B cell development and the establishment of a broad IgH repertoire. Second, we show that this factor exhibits an ambivalent function in mature B cells, acting sequentially as a positive and negative regulator of Ig gene transcription in naive and activated cells, respectively. Third, our study indicates that the negative regulatory function of SATB1 in B cells extends to the germinal center response in which this factor limits somatic hypermutation of Ig genes. This finding suggests that SATB1 may limit the introduction of unwanted mutations into B cells.

Two scaffold/matrix attachment regions (5’- and 3’-MARsEμ) flank the intronic core enhancer (cEμ) within the immunoglobulin heavy chain locus (IgH). Besides their conservation in mice and humans, the physiological role ofMARsEμis still unclear and their involvement in somatic hypermutation (SHM) has never been deeply evaluated. By analysing a mouse model devoid ofMARsEμ, we observed an inverted substitution pattern: SHM being decreased upstream fromcEμand increased downstream of it. Strikingly, the SHM defect induced byMARsEμ-deletion was accompanied by an increase of sense transcription of the IgH V region, excluding a direct transcription-coupled effect. Interestingly, by breeding to DNA repair-deficient backgrounds, we showed that the SHM defect, observed upstream fromcEμin this model, was not due to a decrease in AID deamination but rather the consequence of a defect in base excision repair-associated unfaithful repair process. Our study pointed out an unexpected “fence” function ofMARsEμregions in limiting the error-prone repair machinery to the variable region of Ig gene loci.

International audience; The diagnostic approach of monoclonal gammopathy of renal significance is based on the detection of a monoclonal immunoglobulin in the blood and urine, and the identification of the underlying clone through bone marrow and/or peripheral blood cytologic and flow cytometry analysis. However, the monoclonal component and its corresponding clone may be undetectable using these routine techniques. Since clone identification is the cornerstone for guiding therapy and assessing disease response, more sensitive methods are required. We recently developed a high-throughput sequencing assay from bone marrow mRNA encoding immunoglobulins (RACE-RepSeq). This technique provides both full-length V(D)J region (variable, diversity and joining genes that generate unique receptors as antigen receptors) of the monoclonal immunoglobulin and the dominant immunoglobulin repertoire. This allows analysis of mutational patterns, immunoglobulin variable gene frequencies and diversity due to somatic hypermutation. Here, we evaluated the diagnostic performance of RACE-RepSeq in 16 patients with monoclonal-associated kidney lesions, and low serum monoclonal immunoglobulin and free light chain levels at diagnosis. Bone marrow immunohistochemical analysis was negative in all 11 patients so tested and 7 of 12 patients had no detectable clone matching the kidney deposits using flow cytometry analysis. By contrast, RACE-RepSeq detected a dominant clonal light chain sequence of matched isotype with respect to kidney deposits in all patients. Thus, high throughput mRNA sequencing appears highly sensitive to detect subtle clonal disorders in monoclonal gammopathy of renal significance and suggest this novel approach could help improve the management of this kidney disease.

Heavy chain amyloidosis and heavy chain deposition disease are the only known kidney diseases caused by the deposition of truncated immunoglobulin heavy chains. Fibrillary glomerulonephritis typically results from deposition of DNAJB9 (DnaJ heat shock protein family [Hsp40] member B9) and polytypic immunoglobulin G (IgG). We describe a patient with monoclonal gammopathy (IgG with λ light chain) who developed DNAJB9-negative fibrillary glomerulonephritis leading to end-stage kidney disease, with recurrence in 2 kidney allografts. Pre- and postmortem examination showed glomerular deposition of Congo red-negative fibrillar material that was determined to be immunoglobulin heavy chain. We propose the term "heavy chain fibrillary glomerulonephritis" to describe this lesion, which appears to be a rare kidney complication of monoclonal gammopathy. The diagnosis should be suspected when the kidney biopsy shows fibrillary glomerulonephritis with negative staining for immunoglobulin light chains and DNAJB9; the diagnosis can be confirmed using immunochemical and molecular studies.

Kidney disease is common in patients with multiple myeloma. Patients often present with acute kidney failure most commonly the result of light chain cast nephropathy. Presentation can also be in the form of nephrotic syndrome associated with immunoglobulin light chain amyloidosis or monoclonal immunoglobulin deposition disease and tubulopathy as in acquired light chain Fanconi syndrome. We present a case of a 56-year-old male with multiple myeloma who presented with chronic kidney disease and uric acid stones. Chemical analysis of the nephrolithiasis showed it to be entirely composed of uric acid. Fractional excretion of uric acid was elevated at 35.9%. Kidney biopsy was consistent with light chain proximal tubulopathy. Bone marrow biopsy showed 30% kappa light chain–restricted plasma cells. Genetic sequencing identified the light chain to be from the Vk1-33 subgroup. The patient was treated with bortezomib, cyclophosphamide, and dexamethasone, with improvement of his kidney function. This case illustrates a rare presentation of multiple myeloma.

Research on AL amyloidosis suffers from the lack of a reliable animal model to better understand the pathophysiology of the disease and to design novel therapeutic strategies. Even if few mouse mod...

Plasma cells (PC) represent the last stage of B cell development and are mainly characterized by their capacity of secreting large quantities of antibodies. They can be implicated in a broad-spectrum of neoplastic disorders, including Multiple Myeloma, Waldenstrom macroglobulinemia or Monoclonal Gammopathy of Clinical Significance, all characterized by the abnormal proliferation of a PC clone. Up to date, there are only few reporter models to specifically follow PC development, migration and homing in mouse and none allowing the genetic manipulation of these cells. We created a transgenic mouse model in which a green fluorescent protein gene was placed under the control of the well-characterized regulatory elements of the murine immunoglobulin J (IgJ) chain locus. Thanks to this model, we demostrated that IgJ is an early and specific marker of antibody secreting cells (ASCs) and appears before the expression of CD138, making it a good candidate to targeted genetic modifications of plasma cells. Therefore, a conditional deletion model using a Tamoxifen-dependent Cre recombinase inserted into the IgJ locus was characterized. Using a reporter model, we showed that, in contrast with existing models of B cell lineage genetic modification, the activity of the CRE recombinase only affects ASCs after tamoxifen treatment. Additionally, we used this model in a functional in vitro assay, to show that Ig modifications directly affect plasma cell survival. These two new mouse models, IgJGFP and IgJCreERT2 represent exquisite tools to study PCs. In pathology, the IgJCreERT2model opens new frontiers for in vivo genetic modifications of PCs to better reflect the pathophysiology of PC-related diseases.

Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome is a rare multisystem disease resulting from an underlying plasma cell (PC) dyscrasia. The pathophysiology of the disease remains unclear, but the role of the monoclonal immunoglobulin (Ig) light chain (LC) is strongly suspected because of the highly restrictive usage of 2 λ variable (V) domains (IGLV1-40 and IGLV1-44) and the general improvement of clinical manifestations after PC clone-targeted treatment. However, the diagnostic value of Ig LC sequencing, especially in the case of incomplete forms of the disease, remains to be determined. Using a sensitive high-throughput Ig repertoire sequencing on RNA (rapid amplification of cDNA ends-based repertoire sequencing [RACE-RepSeq]), we detected a λ LC monoclonal expansion in the bone marrow (BM) of 83% of patients with POEMS syndrome, including some in whom BM tests routinely performed to diagnose plasma cell dyscrasia failed to detect λ+ monoclonal PCs. Twenty-four (83%) of the 29 LC clonal sequences found were derived from the IGLV1-40 and IGLV1-44 germline genes, as well as 2 from the closely related IGLV1-36 gene, and all were associated with an IGLJ3*02 junction (J) gene, confirming the high restriction of VJ region usage in POEMS syndrome. RACE-RepSeq VJ full-length sequencing additionally revealed original mutational patterns, the strong specificity of which might crucially help establish or eliminate the diagnosis of POEMS syndrome in uncertain cases. Thus, RACE-RepSeq appears as a sensitive, rapid, and specific tool to detect low-abundance PC clones in BM and assign them to POEMS syndrome, with all the consequences for therapeutic options.

Light chain deposition disease (LCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a monoclonal immunoglobulin (Ig) light chain (LC), leading to nodular glomerulosclerosis and nephrotic syndrome. We developed a transgenic model using site-directed insertion of the variable domain of a pathogenic human LC gene into the mouse Ig kappa locus, ensuring its production by all plasma cells (PCs). High free LC levels were achieved after backcrossing with mice presenting increased PC differentiation and no Ig heavy chain (HC) production. Our mouse model recapitulates the characteristic features of LCDD, including progressive glomerulosclerosis, nephrotic-range proteinuria and finally, kidney failure. The variable domain of the LC bears alone the structural properties involved in its pathogenicity. RNA sequencing conducted on PCs demonstrated that LCDD LC induces endoplasmic reticulum stress, likely accounting for the high efficiency of proteasome inhibitor-based therapy. Accordingly, reduction of circulating pathogenic LC was efficiently achieved and not only preserved renal function, but partially reversed kidney lesions. Finally, transcriptome analysis of pre-sclerotic glomeruli revealed that proliferation and extracellular matrix remodelling represented the first steps of glomerulosclerosis, paving the way for future therapeutic strategies in LCDD and other kidney diseases featuring diffuse glomerulosclerosis, particularly diabetic nephropathy.

We herein report the complete characterization of the monoclonal Ig fragments produced by the plasma cell clone in a 65-year-old patient with a typical heavy chain deposition disease (HCDD).[1][1]–[3][2] The patient was referred for nephrotic syndrome and the main biological parameters are

POEMS syndrome is a rare multisystem disease due to an underlying plasma cell (PC) dyscrasia. The pathophysiology of the disease remains unclear but the role of the monoclonal immunoglobulin (Ig) light chain (LC) is strongly suspected, due to the highly restrictive usage of two λ variable (V) domains (IGLV1-40 and IGLV1-44) and the general improvement of clinical manifestations following PC clone-targeted treatment. However, the diagnostic value of Ig LC sequencing, especially in case of incomplete forms of the disease, remains to be determined. Using a sensitive high-throughput Ig repertoire sequencing on RNA (RACE-RepSeq), we detected a λ LC monoclonal expansion in the bone marrow (BM) of 85% of patients with POEMS syndrome, including some in whom bone marrow tests routinely performed to diagnose plasma cell dyscrasia failed to detect λ+monoclonal PCs. Twenty-four of the 30 LC clonal sequences found (80%) were derived from the IGLV1-40 and IGLV1-44 germline genes, two from the closely related IGLV1-36 gene, and all were associated with an IGLJ3*02 junction (J) gene, confirming the high restriction of VJ region usage in POEMS syndrome. RACE-RepSeq VJ full-length sequencing additionally revealed original mutational patterns, the strong specificity of which might crucially help establish or eliminate the diagnosis of POEMS syndrome in uncertain cases. Thus, RACE-RepSeq appears as a sensitive, rapid and specific tool to detect low-abundance PC clones in BM, and assign them to POEMS syndrome, with all the consequences for therapeutic options hereby.

Background: AL amyloidosis is the most frequent type of amyloidosis caused by the deposition in tissues of fibrillar aggregates composed of an abnormal immunoglobulin (Ig) light chain (LC) and leading to organ dysfunction. The most frequent and severe forms involve kidney and heart. Research on this disease suffers from the lack of reliable animal models, that could allow a better understanding of the disease and the design of new therapeutic strategies. In the present study, we aimed at reproducing AL amyloidosis in a mouse model. Methods: We developed an original transgenic approach using an insertion of a human pathogenic LC gene in the endogenous mouse kappa locus, such as the LC is produced by the naturally Ig producing B and plasma cells. Then, to avoid the association of human LCs with endogenous murine HCs, we backcrossed this strain with the DH-LMP2A mice, characterized by a high number of plasma cells devoid of endogenous HC. This strategy leads to a production of the human free LC similar or higher than in patients and proved efficient to reproduce in mice several monoclonal gammopathies of clinical significance (MGCS) (Fig.1A). Results: Despite strong LC production (Fig.1B), mice did not naturally develop AL amyloidosis. In vitro, the full length LC was resistant to amyloid formation at physiological conditions but the variable domain (IGLV6) showed high propensity to form fibrils. A single injection of amyloid fibrils and/or seeds, obtained from the variable domain (VL) of the human LC gene, led to amyloid deposits starting at 1 month post-injection, especially in the heart, spleen, liver and, to a lesser extent, in the kidney (Fig.1C). We confirmed that the deposits contain the full-length human LCs, which elongate VL fibrils in vivo (Fig.1D). Conclusions: This is, to our knowledge, the first transgenic mouse model of AL amyloidosis closely reproducing human lesions, especially in heart. Further studies are needed to better understand the early biochemical events leading to AL amyloidosis in vivo, but this model already shows that a partial degradation of the LC is likely required to initiate amyloid fibrils and that once seeded, the full length LC can elongate these fibrils. This mouse model opens new perspectives to better understand the toxicity of amyloid LC, their involvements in different biological processes and organ dysfunction and of course, to test new therapeutic approaches. Figure 1 Figure 1. Disclosures Roussel: Takeda: Consultancy; Janssen: Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; BMS: Honoraria; Amgen: Consultancy. Jaccard: Janssen: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria; Abbvie: Honoraria. Bridoux: Janssen: Consultancy; AstraZeneca: Consultancy, Speakers Bureau. Sirac: Attralus, Inc: Patents & Royalties, Research Funding.

Background: Amyloidosis is characterized by extracellular deposition of protein fibrils that can involve any organ or tissue in the body. It is a severe, progressive and often lethal disorder. There are approximately seventeen different systemic amyloid diseases, each associated with the deposition of a specific precursor protein. Toxic amyloid deposits result in significant organ dysfunction and increased morbidity and mortality. Reduction and removal of tissue amyloid deposits could restore organ function, improve quality of life and increase life expectancy for patients. We have developed and characterized a fusion protein consisting of serum amyloid protein (SAP) linked to a single chain human IgG1 Fc domain, designated AT-03. SAP is a pentameric serum protein that is ubiquitously associated with amyloid deposits. The high affinity and specificity for amyloid resulted in the use of radio-iodinated SAP as an imaging agent for the non-invasive detection of systemic amyloid. The SAP domain of the fusion protein targets the amyloid deposits delivering Fc domains to stimulate amyloid removal via macrophage mediated phagocytosis. Methods: Binding of AT-03 to ATTR and AL fibrils and extracts was assessed by ELISA. Ex vivo phagocytosis of amyloid substrates was studied using activated human THP-1 cells. The biodistribution of AT-03 in murine models of AA, AApoA2 and AL amyloidosis was evaluated immunohistochemically or by SPECT imaging and microautoradiography. Clearance of AA amyloidosis in response to AT-03 therapy was accessed in a mouse model using histological scoring of amyloid burden. Results: AT-03 bound amyloid AL and ATTR substrates with sub nanomolar EC50 values. Systemic administration of AT-03 resulted in specific binding to diverse forms of amyloid in the heart, kidney, liver and/or spleen in multiple animal models. Opsonization of amyloid deposits with AT-03 in vitro resulted in a dose dependent phagocytosis by activated THP-1 cells. A single IV dose of AT-03 resulted in significant reduction of splenic AA amyloid within 14 days post-injection. Conclusions: We have developed a novel fusion protein with sub nanomolar pan amyloid reactivity that specifically binds diverse forms of amyloid in multiple organs and tissues in vivo and can effectuate amyloid removal. The data indicates that AT-03 may serve as a novel therapeutic for the removal of systemic amyloid deposits of diverse types. AT-03 is currently being developed for clinical evaluation. Disclosures Sirac: Attralus, Inc: Patents & Royalties, Research Funding. Jaccard: Janssen: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria; Abbvie: Honoraria. Bridoux: AstraZeneca: Consultancy, Speakers Bureau; Janssen: Consultancy. Bell: Attralus Inc: Current Employment. Guthrie: Attralus Inc: Current Employment. Selvarajah: Attralus Inc: Current Employment. Kennel: Attralus Inc: Current holder of stock options in a privately-held company, Patents & Royalties: Inventor and patent holder. Wall: Attralus Inc: Current holder of stock options in a privately-held company, Patents & Royalties: Inventor and patent holder, Research Funding.

Light chain deposition disease (LCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a monoclonal immunoglobulin (Ig) light chain (LC), leading to nodular glomerulosclerosis and nephrotic syndrome. We developed a transgenic model using site-directed insertion of the variable domain of a pathogenic human LC gene into the mouse Ig kappa locus, ensuring its production by all plasma cells. High free LC levels were achieved after backcrossing with mice presenting increased plasma cell differentiation and no Ig heavy chain (HC) production. Our mouse model recapitulates the characteristic features of LCDD, including progressive glomerulosclerosis, nephrotic-range proteinuria and finally, kidney failure. The variable domain of the LC bears alone the structural properties involved in its pathogenicity. RNA sequencing conducted on plasma cells demonstrated that LCDD LC induces endoplasmic reticulum stress, likely accounting for the high efficiency of proteasome inhibitor-based therapy. Accordingly, reduction of circulating pathogenic LC was efficiently achieved and not only preserved renal function, but partially reversed kidney lesions. Finally, transcriptome analysis of pre-sclerotic glomeruli revealed that proliferation and extracellular matrix remodelling represented the first steps of glomerulosclerosis, paving the way for future therapeutic strategies in LCDD and other kidney diseases featuring diffuse glomerulosclerosis, particularly diabetic nephropathy.

Monoclonal immunoglobulin deposition disease (MIDD) is a rare complication of B-cell clonal disorders, defined by Congo red negative–deposits of monoclonal light chain (LCDD), heavy chain (HCDD), or both (LHCDD). MIDD is a systemic disorder with prominent renal involvement, but little attention has been paid to the description of extrarenal manifestations. Moreover, mechanisms of pathogenic immunoglobulin deposition and factors associated with renal and patient survival are ill defined. We retrospectively studied a nationwide cohort of 255 patients, with biopsy-proven LCDD (n = 212) (including pure LCDD [n = 154], LCDD with cast nephropathy (CN) [n = 58]), HCDD (n = 23), or LHCDD (n = 20). Hematological diagnosis was monoclonal gammopathy of renal significance in 64% and symptomatic myeloma in 34%. Renal presentation was acute kidney injury in patients with LCCD and CN, and chronic glomerular disease in the other types, 35% of whom had symptomatic extrarenal (mostly hepatic and cardiac) involvement. Sequencing of 18 pathogenic LC showed high isoelectric point values of variable domain complementarity determining regions, possibly accounting for tissue deposition. Among 169 patients who received chemotherapy (bortezomib-based in 58%), 67% achieved serum free light chain (FLC) response, including very good partial response (VGPR) or above in 52%. Renal response occurred in 62 patients (36%), all of whom had achieved hematological response. FLC response ≥ VGPR and absence of severe interstitial fibrosis were independent predictors of renal response. This study highlights an unexpected frequency of extrarenal manifestations in MIDD. Rapid diagnosis and achievement of deep FLC response are key factors of prognosis.

The renal deposition of monoclonal immunoglobulins can cause severe renal complications in patients with B cell and plasma cell lymphoproliferative disorders. The overproduction of a structurally unique immunoglobulin can contribute to the abnormal propensity of monoclonal immunoglobulins to aggregate and deposit in specific organs. A wide range of renal diseases can occur in multiple myeloma or monoclonal gammopathy of renal significance, including tubular and glomerular disorders with organized or unorganized immunoglobulin deposits. The development of reliable experimental models is challenging owing to the inherent variability of immunoglobulins and the heterogeneity of the pathologies they produce. However, although imperfect, animal models are invaluable tools to understand the molecular pathogenesis of these diseases, and advances in creating genetically modified animals might provide novel approaches to evaluate innovative therapeutic interventions. We discuss the strategies employed to reproduce human monoclonal immunoglobulin-induced kidney lesions in animal models, and we highlight their advantages and shortcomings. We also discuss how these models have affected the management of these deposition diseases and might do so in the future. Finally, we discuss hypotheses that explain some limitations of the various models, and how these models might improve our understanding of other nephropathies without immunoglobulin involvement that have similar pathogenic mechanisms.

Introduction L’amylose a chaine lourde d’immunoglobulines (AH) est une complication exceptionnelle des gammapathies monoclonales, avec une dizaine de cas decrits. Methodes Nous rapportons retrospectivement les caracteristiques cliniques, immuno-hematologiques, histologiques et evolutives de 5 patients presentant une amylose AH. Resultats obtenus ou attendus Trois patients ont une atteinte extra-renale associee (neurologique predominante) mais aucun ne presente de cardiopathie amyloide. On retrouve trois cas de myelome multiple dont aucun n’est symptomatique, une MGUS et une maladie des chaines lourdes. L’etude des biopsies renales montre une atteinte glomerulaire constante et massive avec des lesions degeneratives tubulo-interstitielles et vasculaires importantes dans 2 cas. En immunofluorescence, les depots sont constitues de chaines lourdes monoclonales γ (n = 5) sans reactivite significative avec les anticorps anti-chaines legeres, et les sous-classes sont γ1 dans les 3 cas etudies. La deletion du domaine CH1 de la chaine γ est retrouvee dans 2 des 3 cas ou elle a ete recherchee. Dans un cas, c’est l’etude par proteomique qui a permis d’identifier la chaine lourde gamma 1. Le sequencage de la chaine lourde en biologie moleculaire met en evidence une chaine lourde gamma 1 tronquee du CH1 mais aussi d’une partie du domaine variable. Tous les patients ont ete traites par chimiotherapie, avec une reponse hematologique partielle dans 3 cas et une reponse renale partielle chez 3 patients. Apres un suivi median de 4 ans, deux patients ont evolue vers l’insuffisance renale terminale, trois autres patients gardent une insuffisance renale chronique et une patiente est decedee de neoplasie digestive ( Fig. 1 ). Conclusion En comparaison avec l’amylose AL, l’amylose AH semble etre associee a une meilleure survie globale. Nos donnees confirment que la deletion du CH1 est une caracteristique constante de cette maladie, en revanche la presence d’un domaine variable complet ne semble pas necessaire au depot tissulaire, suggerant des mecanismes physiopathologiques distincts de ceux des maladies de depot de chaine lourde.

Randall-type heavy chain deposition disease (HCDD) is a rare disorder characterized by tissue deposition of a truncated monoclonal immunoglobulin heavy chain lacking the first constant domain. Pathophysiological mechanisms are unclear and management remains to be defined. Here we retrospectively studied 15 patients with biopsy-proven HCDD of whom 14 presented with stage 3 or higher chronic kidney disease, with nephrotic syndrome in 9. Renal lesions were characterized by nodular glomerulosclerosis, with linear peritubular and glomerular deposits of γ-heavy chain in 12 patients or α-heavy chain in 3 patients, without concurrent light chain staining. Only 2 patients had symptomatic myeloma. By serum protein electrophoresis/immunofixation, 13 patients had detectable monoclonal gammopathy. However, none of these techniques allowed detection of the nephrotoxic truncated heavy chain, which was achieved by immunoblot and/or bone marrow heavy chain sequencing in 14 of 15 patients. Serum-free kappa to lambda light chain ratio was abnormal in 11 of 11 patients so examined. Immunofluorescence studies of bone marrow plasma cells showed coexpression of the pathogenic heavy chain with light chain matching the abnormal serum-free light chain in all 3 tested patients. Heavy chain sequencing showed first constant domain deletion in 11 of 11 patients, with high isoelectric point values of the variable domain in 10 of 11 patients. All patients received chemotherapy, including bortezomib in 10 cases. Renal parameters improved in 11 patients who achieved a hematological response, as assessed by normalization of the free light chain ratio in 8 cases. Tissue deposition in HCDD relates to physicochemical peculiarities of both variable and constant heavy chain domains. Early diagnosis and treatment with bortezomib-based combinations appear important to preserve renal prognosis. Thus, monitoring of serum-free light chain is an indirect but useful method to evaluate the hematological response.

Background:The measurement of circulating free light chain (FLC) is essential in the diagnosis, prognostic stratification and evaluation of response to therapy in light chain (AL) amyloidosis. For more than 10 years, this has been done with an immunonephelometric assay based on polyclonal antibodies (Freelite), and cutoffs for staging and response assessment have been validated with this method. Recently, a new assay based on monoclonal antibodies (N latex FLC) has been marketed in Europe.Methods:We evaluated and compared the clinical performance of the two assays in 426 patients with newly diagnosed AL amyloidosis.Results:We found suboptimal agreement between the two methods, with differences between values obtained with the Freelite and N latex FLC assays increasing with the concentration of clonal FLC. The diagnostic sensitivity of the Freelite (82%) and N latex FLC (84%) assays was similar, and both improved to 98% in combination with serum and urine immunofixation. The concentration of FLC measured with both methods had prognostic significance. Less pronounced decreases in FLC best predicted improved survival with the N latex FLC assay (33% vs. 50%), and there was poor concordance (84%) in discrimination of responders.Conclusions:The two assays have similar diagnostic and prognostic performance. However, they are not interchangeable, and follow-up should be done with either one. New response criteria are needed for the N latex FLC assay.

Significance The immunoglobulin heavy chain (IgH) 3′regulatory region ( 3′RR ) fine-tunes IgH gene expression during B cell development. One singularity of this region is its quasi-palindromic structure conserved in the 3′RR of other species. By comparing previous mouse knockout (KO) models ( 3′RR- and hs3b-4 KO) to a novel mutant devoid of the quasi-palindrome ( 3′PAL KO), we highlighted common features and differences that specify two distinct regulatory entities: ( i ) the distal module ( hs4 ) is sufficient for normal IgH expression up to the naïve B cell stage; ( ii ) during B-cell activation, the proximal module (quasi-palindrome) is important for both class switch recombination and somatic hypermutation; and ( iii ) in plasma cells, the quasi-palindrome is required for robust transcription of the IgH locus.

Introduction La maladie de depots de chaines lourdes monoclonales (= heavy chain deposition disease ou HCDD) est une gammapathie monoclonale rare de signification renale (= monoclonal gammopathy of renal significance ou MGRS). Elle se caracterise par la presence de depots amorphes de chaines lourdes d’immunoglobulines monoclonales tronquees le long des membranes basales glomerulaires et tubulaires du rein mais aussi d’autres organes. La principale caracteristique moleculaire de ces chaines lourdes pathogenes est l’absence recurrente du premier exon du domaine constant CH1 permettant leur secretion en l’absence d’une chaine legere d’immunoglobuline. Cependant, les mecanismes moleculaires menant a la production d’une chaine lourde tronquee sont encore inconnus. Patients/materiels et methodes Dans la presente etude, nous avons effectue une caracterisation moleculaire complete des fragments d’immunoglobulines produits par le clone plasmocytaire d’un patient. Resultats En plus de la deletion genomique du domaine CH1 de la chaine lourde, nous avons montre que le meme clone plasmocytaire produisait une chaine legere monoclonale tronquee. Lorsqu’elle est exprimee dans la lignee plasmocytaire murine sp2/0, cette chaine legere tronquee ne peut s’associer ni avec la chaine lourde pathogene ni avec la chaine lourde reconstituee avec un domaine CH1. Dans ce modele cellulaire experimental, nous montrons que la deletion du CH1 reduit le stress du reticulum endoplasmique induit par la retention intracellulaire de la chaine lourde complete isolee. Conclusion Nous emettons ainsi l’hypothese que l’alteration de la chaine legere est l’evenement inaugural menant a la production d’une chaine lourde tronquee et finalement a l’apparition de la maladie de depots de chaines lourdes monoclonales.

International audience; BACKGROUND:Kidney diseases associated with immunoglobulin M (IgM) monoclonal gammopathy are poorly described, with few data for patient outcomes and renal response.STUDY DESIGN:Case series.SETTING & PARTICIPANTS:35 patients from 8 French departments of nephrology were retrospectively studied. Inclusion criteria were: (1) detectable serum monoclonal IgM, (2) estimated glomerular filtration rate (eGFR) < 60mL/min/1.73m2 and/or proteinuria with protein excretion > 0.5g/d and/or microscopic hematuria, and (3) kidney biopsy showing monoclonal immunoglobulin deposits and/or lymphomatous B-cell renal infiltration. All patients received chemotherapy, including rituximab-based regimens in 8 cases.PREDICTORS:Patients were classified into 3 groups according to renal pathology: glomerular AL amyloidosis (group 1; n=11), nonamyloid glomerulopathies (group 2; n=15, including 9 patients with membranoproliferative glomerulonephritis), and tubulointerstitial nephropathies (group 3; n=9, including cast nephropathy in 5, light-chain Fanconi syndrome in 3, and isolated tumor infiltration in 1).OUTCOMES:Posttreatment hematologic response (≥50% reduction in serum monoclonal IgM and/or free light chain level) and renal response (≥50% reduction in 24-hour proteinuria or eGFR≥30mL/min/1.73m2 in patients with glomerular and tubulointerstitial disorders, respectively).RESULTS:Nephrotic syndrome was observed in 11 and 6 patients in groups 1 and 2, respectively. Patients in group 3 presented with acute kidney injury (n=7) and/or proximal tubular dysfunction (n=3). Waldenström macroglobulinemia was present in 26 patients (8, 12, and 6 in groups 1, 2, and 3, respectively). Significant lymphomatous interstitial infiltration was observed in 18 patients (4, 9, and 5 patients, respectively). Only 9 of 29 evaluable patients had systemic signs of symptomatic hematologic disease (2, 5, and 2, respectively). In groups 1, 2, and 3, respectively, hematologic response was achieved after first-line treatment in 3 of 9, 9 of 10, and 5 of 6 evaluable patients, while renal response occurred in 5 of 10, 9 of 15, and 5 of 8 evaluable patients.LIMITATIONS:Retrospective study; insufficient population to establish the impact of chemotherapy.CONCLUSIONS:IgM monoclonal gammopathy is associated with a wide spectrum of renal manifestations, with an under-recognized frequency of tubulointerstitial disorders.

International audience; Hepatocyte growth factor (HGF) is a pro-angiogenic cytokine activated by tissue-type plasminogen activator (tPA) that might play a role in the progression of multiple myeloma (MM). Preliminary studies indicated that serum HGF levels were higher in patients with AL amyloidosis (AL) compared to those with MM. The aim of the present study was to determine whether HGF is a relevant marker of diagnosis and prognosis in AL. HGF serum levels were measured at diagnosis in patients with monoclonal gammopathy (MG) without AL (76 controls), or with biopsy-proven systemic AL (69 patients). HGF serum levels were significantly higher in patients with AL compared to controls, respectively, 11.2 ng/mL [min: 0.95-max: 200.4] versus 1.4 ng/mL [min: 0.82-max: 6.2] (p

International audience; Randall-type heavy chain deposition disease (HCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a truncated monoclonal immunoglobulin heavy chain (HC) bearing a deletion of the first constant domain (CH1). We created a transgenic mouse model of HCDD using targeted insertion in the immunoglobulin κ locus of a human HC extracted from a HCDD patient. Our strategy allows the efficient expression of the human HC in mouse B and plasma cells, and conditional deletion of the CH1 domain reproduces the major event underlying HCDD. We show that the deletion of the CH1 domain dramatically reduced serum HC levels. Strikingly, even with very low serum level of truncated monoclonal HC, histologic studies revealed typical Randall-type renal lesions that were absent in mice expressing the complete human HC. Bortezomib-based treatment resulted in a strong decrease of renal deposits. We further demonstrated that this efficient response to proteasome inhibitors mostly relies on the presence of the isolated truncated HC that sensitizes plasma cells to bortezomib through an elevated unfolded protein response (UPR). This new transgenic model of HCDD efficiently recapitulates the pathophysiologic features of the disease and demonstrates that the renal damage in HCDD relies on the production of an isolated truncated HC, which, in the absence of a LC partner, displays a high propensity to aggregate even at very low concentration. It also brings new insights into the efficacy of proteasome inhibitor-based therapy in this pathology.

Introduction La maladie de depots de chaines legeres d’immunoglobulines (Ig) monoclonales (LCDD) est une complication rare des dyscrasies plasmocytaires caracterisee par des depots amorphes d’une Ig monoclonale le long des membranes basales tubulaires et glomerulaires. Elle se manifeste par une insuffisance renale progressive frequemment associees a un syndrome nephrotique et une glomerulosclerose nodulaire. Materiels et methodes Nous avons developpe un modele transgenique par insertion genique dirigee d’un domaine variable d’Ig humaine pathogene dans le locus des Ig kappa de souris. Un haut niveau de production seriques de chaines legeres est atteint (> 500 mg/L) grâce a un croisement avec des souris LMP2A qui presentent une hyperplasmocytose en absence de chaines lourdes d’Ig. Resultats Notre modele murin reproduit les principales caracteristiques de la LCDD, dont les depots peritubulaires et glomerulaires visibles des le 2e mois mais aussi a partir du 6e mois, la glomerulosclerose, le syndrome nephrotique et finalement l’insuffisance renale terminale avec une survie mediane des animaux de 8 mois. Un traitement hematologique a base d’inhibiteurs du proteasome permet de faire diminuer le taux d’Ig pathogenes et ainsi de preserver les fonctions renales et d’augmenter la survie des animaux. Discussion Nous demontrons que le domaine variable de l’Ig porte a lui-seul la pathogenicite de la proteine monoclonale. Contrairement a l’amylose AL qui reste difficile a modeliser chez la souris, le LCDD est parfaitement transposable aux rongeurs. Notre modele permet de reproduire l’ensemble des caracteristiques de la LCDD et va ainsi permettre de mieux comprendre la physiopathologie de cette maladie. Des etudes de transcriptomiques sont en cours afin de mettre en evidence les voies moleculaires impliquees dans la modification de la matrice extracellulaire au cours de la glomerulosclerose nodulaire. Conclusion Nous avons developpe le premier modele murin de LCDD recapitulant l’ensemble des caracteristiques de la maladie. Ce modele represente un outil important pour l’etude de la pathologie mais aussi pour mener des tests precliniques de nouvelles strategies therapeutiques.

Introduction La glomerulonephrite a depots non organises non Randall d’immunoglobuline monoclonale (PGNMID) est une entite maintenant bien individualisee au sein des gammapathies monoclonales de signification renale. Les depots sont le plus souvent constitues d’une immunoglobuline entiere, principalement IgG3 kappa. Nous rapportons une serie de 7 cas de PGNMID a chaine legere monoclonale. Patients et methodes Etude retrospective multicentrique incluant les patients presentant des depots granulaires, discontinus, de localisation glomerulaire exclusive, rouge Congo negatifs, marques en immunofluorescence par un seul isotype de chaine legere sans chaine lourde associee. Resultats L’âge median au diagnostic etait de 63 ans. Tous les patients presentaient une insuffisance renale chronique avec proteinurie et hematurie. Aucun cas n’avait de manifestations extrarenales. Un composant monoclonal circulant etait detectable dans 6/7 cas (myelome symptomatique, n = 1). L’aspect en microscopie optique etait une glomerulonephrite membrano-proliferative (n = 5), mesangiale (n = 1) ou extramembraneuse atypique (n = 1). En immunofluorescence, les depots etaient constitues de chaines legeres kappa (n = 5) ou lambda (n = 2), toujours associes a des depots de C3. Trois patients avaient un C3 serique bas sans anomalies des proteines regulatrices de la voie alterne. Dans 1 cas, nous avons montre que la chaine legere lambda purifiee activait la voie alterne du complement. Le sequencage de cette chaine legere Vλ3 a revele plusieurs mutations dans les regions hypervariables (principalement CDR1). Six patients ont recu une chimiotherapie a base d’alkylant ± bortezomib. Une reponse hematologique, suivie dans tous les cas d’une reponse renale, a ete obtenue chez les 3/3 patients traites par bortezomib. Tous les patients en bonne reponse hematologique ont normalise leur taux circulant de C3. Discussion Nous rapportons la premiere serie de PGNMID a chaine legere monoclonale. L’association constante avec des depots de C3 suggere une activation de la voie alterne du complement par la chaine legere monoclonale. Un traitement ciblant le clone B sous-jacent, parfois non detectable par les techniques usuelles, est indispensable pour preserver le pronostic renal. Conclusion Le sequencage des chaines legeres monoclonales pourrait permettre de mieux comprendre les mecanismes physiopathologiques impliques dans cette forme rare de PGNMID.

International audience; Monoclonal immunoglobulin (Ig) deposition in AL amyloidosis is a severe complication of lymphoproliferative disorders. Research on this disease suffers from the lack of animal models, as they could allow for the testing of new innovative therapeutic strategies. We are trying to develop a transgenic animal model for this disease by overexpressing Ig light chain (LC) sequences cloned from AL amyloidosis patients. After several unsuccessful attempts using additional transgenesis due to low LC expression, we currently are following a strategy of targeted insertion of human LC sequences in the mouse endogenous kappa LC locus. We describe here the first data from this ‘knock-in’ model and propose future prospects to increase the rates of free LC and mimic the human disease. Absence of amyloid deposits in such models would raise the possibility of a resistance to AL amyloidosis in mice and question the feasibility of a reliable animal model for this disease.

The IgH intronic enhancer region Eμ is a combination of both a 220-bp core enhancer element and two 310–350-bp flanking scaffold/matrix attachment regions named MARsEμ. In the mouse, deletion of the core-enhancer Eμ element mainly affects VDJ recombination with minor effects on class switch recombination. We carried out endogenous deletion of the full-length Eμ region (core plus MARsEμ) in the mouse genome to study VH gene repertoire and IgH expression in developing B-lineage cells. Despite a severe defect in VDJ recombination with partial blockade at the pro–B cell stage, Eμ deletion (core or full length) did not affect VH gene usage. Deletion of this regulatory region induced both a decrease of pre–B cell and newly formed B cell compartments and a strong orientation toward the marginal zone B cell subset. Because Igμ H chain expression was decreased in Eμ-deficient pre–B cells, we propose that modification of B cell homeostasis in deficient animals was caused by “weak” pre–B cell and BCR expression. Besides imbalances in B cell compartments, Ag-specific Ab responses were not impaired in animals carrying the Eμ deletion. In addition to its role in VDJ recombination, our study points out that the full-length Eμ region does not influence VH segment usage but ensures efficient Igμ-chain expression required for strong signaling through pre–B cells and newly formed BCRs and thus participates in B cell inflow and fate.

BACKGROUND Renal involvement in light chain (LC) deposition disease (LCDD) is typically characterized by nodular glomerulosclerosis and nephrotic range proteinuria. Rare cases of LCDD without glomerular symptoms have been reported, but clinical and pathological characteristics of this entity remain poorly described. METHODS This multi-centre retrospective study included 14 patients with biopsy-proven renal LCDD and proteinuria

Introduction Le syndrome de Fanconi (SF) correspond a une dysfonction du tube proximal. Dans sa forme acquise il est souvent secondaire a une gammapathie monoclonale. Il est classiquement lie a une chaine legere (CL) vkappa 1 resistante a la proteolyse. En ME, on observe une accumulation de la CL sous forme de cristaux au sein des lysosomes des TP. Le mecanisme de toxicite est inconnu. Nous avons voulu evaluer le spectre des SF : les aspects des CL en ME, l’atteinte mitochondriale, mais aussi evaluer l’impact des nouvelles therapeutiques (bortezomib) sur la fonction renale et la tubulopathie. Patients et methodes Nous avons analyse de facon prospective les donnees de 10 patients ayant eu une PBR entre 2010 et 2014 dans 5 centres de nephrologie pour une TP secondaire a une gammapathie monoclonale. Nous avons collige les donnees biologiques au moment du diagnostic et apres traitement. L’etude anatomopathologique comprenait une etude en MO, en IF standard et apres traitement par pronase en paraffine, en ME (± immunogold). La CL a pu etre sequencee dans 2/3 des cas et sa sensibilite aux cathepsines etudiee. Resultats Une hypouricemie etait presente chez tous les patients mais le SF etait le plus souvent incomplet. Des cristaux de CL ont pu etre vus dans les urines chez une patiente. Sur l’etude anatomopathologique, 4 patients avaient une histiocytose cristalline de surcharge associee. Les depots monotypiques n’ont pas pu etre prouves en IF standard dans la moitie des cas. La ME retrouvait une accumulation de CL intracytoplasmique sous forme de cristaux ou de depots pseudofibrillaires. Des anomalies mitochondriales ont souvent ete observees. Les CL legeres incriminees derivaient du segment de gene vkappa1 ou vkappa3. La resistance de la CL aux cathepsines n’a pas toujours etait observee. Le traitement a parfois permis une amelioration de la fonction renale et de la tubulopathie. Discussion Dans notre serie de SF secondaire a une gammapathie monoclonale, l’aspect en ME etait plus heterogene que celui initialement rapporte. La toxicite de la CL n’est pas univoque : par defaut de degradation, toxicite mitochondriale… Conclusion Les therapeutiques actuelles ameliorent notablement le pronostic renal.

International audience; A 62-year-old woman presented with crystalline keratopathy, crystal-storing histiocytosis, Fanconi syndrome, and a serum monoclonal IgG-κ and urinary κ light chain. Histology and electron microscopy studies revealed the presence of crystals within macrophages in multiple eye sites, in the kidney and in the bone marrow. The variable domain of the pathogenic κ light chain related to the Vk1-39 gene that was also involved in most previously reported cases of Fanconi syndrome. Owing to the severity of the damage to the eye and a potentially poor kidney prognosis, the patient underwent autologous stem cell transplantation. After 18 months follow-up, she is in complete hematological, ophthalmological, and renal remission.

Abstract 1783 Poster Board I-809 Purpose Hepatocyte Growth Factor (HGF) is a pro-angiogenic cytokine and a mitogenic, motogenic and morphogenic factor involved in tumor growth. Previous studies have shown that HGF is secreted by plasma cells in multiple myeloma and that HGF serum levels are higher in patients with multiple myeloma and correlate with disease activity. A previous study reported that serum HGF levels were significantly higher in patients with AL amyloidosis compared to patients with multiple myeloma (Iwasaki et al. Br J Haematol. 2002;116:796-802). A preliminary study of 18 AA and AL amyloidosis patients (Shikano et al, Intern Med. 2000;39:715-9) suggested that measurement of HGF might be useful for the diagnosis of amyloidosis. To determine whether HGF may be used as a relevant diagnosis marker and prognosis factor in AL amyloidosis, we have measured HGF serum levels in patients with AL amyloidosis and patients with plasma cell dyscrasia without amyloidosis. Patients and Methods Two groups of patients were included; patients with biopsy proven AL amyloidosis and patients with plasma cell dyscrasia (MGUS, multiple myeloma, POEMS) without amyloidosis as controls. Levels of HGF were measured by ELISA at diagnosis in the two groups, before any treatment (Quantikine® R&D Systems). Clinical features were recorded for AL patients. A Receiver Operating Characteristic curve (ROC) analysis was performed to assess the diagnostic accuracy of HGF for identification of amyloidosis cases among patients with monoclonal gammopathy. The area under the ROC curve (AUC) which can be interpreted as the probability that a randomly chosen amyloidosis patient has a test result greater than that of a randomly chosen non-amyloidosis patient, was calculated with its 95% confidence interval (95%CI). The ROC curve was also used to determine the best threshold for HGF. Using this threshold, sensitivity and specificity were calculated. Survival analyses were performed for patients suffering from AL amyloidosis. Baseline time was time from first HGF assessment to death or censoring date. Univariate analysis were done using Kaplan Meier and Cox proportional hazard models. Results Sixty-nine AL amyloidosis patients diagnosed between 2004 and 2008 and 76 controls (56 patients with MGUS, 17 with multiple myeloma, three with POEMS) were included. The median age was 61 (32-90) for AL patients and 60 (39-86) for controls. Median creatinine levels were respectively 86μmol/l (39-500) and 79μmol/l (44-317); 57 AL patients (82.6%) had renal involvement and 40 had (57.9%) cardiac disease. Monoclonal protein isotype was lambda in 69.6% of AL patients and kappa in 30.4%. HGF serum levels were significantly higher in patients with AL amyloidosis: 11.2ng/ml (0.5-200.4) compared with controls: 1.5ng/ml (0.8-8.2), p Conclusion This study confirms that HGF levels are elevated in patients with AL amyloidosis, significantly higher than in patients with other plasma cell disorders. A threshold value of 2.4ng/ml confers a good sensitivity (80%) and specificity (90%) to suggest AL amyloidosis. HGF measurement may be used in patients with plasma cell dyscrasia to determine which patient should be considered for a biopsy. We found a trend towards reduced survival in patients with the highest levels of HGF. This, and the usefulness of HGF measurement in predicting clinical responses should be confirmed on larger studies. Disclosures No relevant conflicts of interest to declare.