Immunologic basis for the rare occurrence of true nonsecretory plasma cell dyscrasias

Functions of IgM fc receptor (FcµR) related to autoimmunity

Unlike Fc receptors for switched immunoglobulin (Ig) isotypes, Fc receptor for IgM (FcµR) is selectively expressed by lymphocytes. The ablation of the FcµR gene in mice impairs B cell tolerance as evidenced by concomitant production of autoantibodies of IgM and IgG isotypes. In this essay, we reiterate the autoimmune phenotypes observed in mutant mice, ie IgM homeostasis, dysregulated humoral immune responses including autoantibodies, and Mott cell formation. We also propose the potential phenotypes in individuals with FCMR deficiency and the model for FcµR-mediated regulation of self-reactive B cells.

Periodic Acid Schiff Staining to Detect Mott Cells, Aberrant Plasma Cells Containing Immunoglobulin Inclusions Called Russell Bodies

Hematoxylin and eosin staining is widely used for routine histopathological analysis under light microscopic examination to determine alterations of tissue architecture and cellular components in animal studies. Aside from hematoxylin/eosin staining, periodic acid Schiff (PAS) staining is used to detect polysaccharides and carbohydrate-rich macromolecules, and is essential in immunological fields for evaluation of glomerular lesions of kidneys in autoimmune animals. Since erythrocytes are not stained by PAS, this stain is also helpful for identifying changes in immune cells in the red pulp of the spleen, which is filled with erythrocytes. This article describes a protocol to detect Mott cells, bizarre plasma cells containing immunoglobulin inclusion bodies (Russell bodies) in the cytoplasm. The protocol can be used for formalin-fixed, paraffin-embedded tissue sections, frozen tissue sections, tissue-touch preparations, blood films, and cytocentrifuged cell smears. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Detection of Mott cells by PAS staining in formalin-fixed, paraffin-embedded tissue sections Basic Protocol 2: Detection of Mott cells by PAS staining in frozen tissue sections, touch preparations, blood films, and cytocentrifuged cell smears.

The presence of Mott cells in the lymph nodes of rats with experimental autoimmune encephalomyelitis

Mott cells are plasma cells that have multiple spherical Russell bodies packed in their cytoplasm. Russell bodies are dilated endoplasmic reticulum cisternae filled with aggregates of immunoglobulins that are neither secreted nor degraded. Mott cells were observed in our study by light and electron microscope in the lymph nodes of rats with experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Mott cells were detected on hematoxylin and eosin (HE)-stained lymph node sections as vacuolated cells with eccentrically positioned nuclei and large number of faint blue spherical inclusions in the cytoplasm. Electron microscopic investigation revealed the presence of Russell bodies of the "medusa" form inside Mott cells in lymph node ultra-thin sections of EAE animals. Mott cells expressed the plasma cell marker CD138 and either kappa or lambda immunoglobulin light chains, indicating their origin from polyclonally activated B cells. Finally, Mott cells were associated with active EAE, as they were not found in the lymph nodes of EAE-resistant Albino Oxford rats. The presence of Russell bodies implies an excessive production of immunoglobulins in EAE, thus further emphasizing the role of B cells, and among them Mott cells, in the pathogenesis of this animal model of multiple sclerosis.

Enhanced Mott cell formation linked with IgM Fc receptor (FcμR) deficiency

In previous studies, Mott cells, an unusual form of plasma cells containing Ig-inclusion bodies, were frequently observed in peripheral lymphoid tissues in our IgM Fc receptor (FcμR)-deficient (KO) mouse strain. Because of discrepancies in the reported phenotypes of different Fcmr KO mouse strains, we here examined two additional available mutant strains and confirmed that such enhanced Mott-cell formation was a general phenomenon associated with FcμR deficiency. Splenic B cells from Fcmr KO mice clearly generated more Mott cells than those from WT mice when stimulated in vitro with LPS alone or a B-1, but not B-2, activation cocktail. Nucleotide sequence analysis of the Ig variable regions of a single IgMλ+ Mott-hybridoma clone developed from splenic B-1 B cells of Fcmr KO mice revealed the near (VH) or complete (Vλ) identity with the corresponding germline gene segments and the addition of six or five nucleotides at the VH/DH and DH/JH junctions, respectively. Transduction of an FcμR cDNA into the Mott hybridoma significantly reduced cells containing IgM-inclusion bodies with a concomitant increase in IgM secretion, leading to secreted IgM binding to FcμR expressed on Mott transductants. These findings suggest a regulatory role of FcμR in the formation of Mott cells and IgM-inclusion bodies.

Soluble B-cell maturation antigen as a monitoring marker for multiple myeloma

Objective: Response to treatment in multiple myeloma (MM) is routinely measured by serum and urine M-protein and free light chain (FLC), as described by the International Myeloma Working Group (IMWG) consensus statement. A non-negligible subgroup of patients however present without measurable biomarkers, others become oligo or non-secretory during recurrent relapses. The aim of our research was to evaluate soluble B-cell maturation antigen (sBCMA) as a monitoring marker measured concurrent with the standard monitoring in MM patients at diagnosis, at relapse and during follow up, in order to establish its potential usefulness in oligo and non-secretory disease. Method: sBCMA levels were measured in 149 patients treated for plasma cell dyscrasia (3 monoclonal gammopathy of unknown significance, 5 smoldering myeloma, 7 plasmacytoma, 8 AL amyloidosis and 126 MM) and 16 control subjects using a commercial ELISA kit. In 43 newly diagnosed patients sBCMA levels were measured at multiple timepoints during treatment, and compared to conventional IMWG response and progression free survival (PFS). Results: sBCMA levels among control subjects were significantly lower than among newly diagnosed or relapsed MM patients [20.8 (14.7-38.7) ng/mL vs. 676 (89.5-1,650) and 264 (20.7-1,603) ng/mL, respectively]. Significant correlations were found between sBCMA and the degree of bone marrow plasma cell infiltration. Out of the 37 newly diagnosed patients who have reached partial response or better per IMWG criteria, 33 (89%) have had at least a 50% drop in sBCMA level by therapy week 4. Cohorts made similarly to IMWG response criteria-achieving a 50% or 90% drop in sBCMA levels compared to level at diagnosis-had statistically significant differences in PFS. Conclusion: Our results confirmed that sBCMA levels are prognostic at important decision points in myeloma, and the percentage of BCMA change is predictive for PFS. This highlights the great potential use of sBCMA in oligo- and non-secretory myeloma.

Hypoglobulinemia in a dog with disseminated plasma cell neoplasia: Case report and review of the diagnostic criteria

This is the first reported case of hypoglobulinemia in a dog with disseminated plasma cell neoplasia. A 6-year-old male intact Rottweiler was referred to the U-Vet Animal Hospital (Werribee, Vic, Australia) for weight loss, hyporexia, lethargy, vomiting, and soft stools. Examination of a buffy coat preparation and splenic and liver aspirates revealed a monomorphic population of plasmacytoid cells, and the same cells comprised approximately 90% of bone marrow samples submitted for cytologic and histologic evaluation. Biochemistry revealed a hypoglobulinemia, and the presence of an M-protein was not supported by serum and urine protein electrophoresis or serum immunofixation. Immunohistochemistry demonstrated strong nuclear labeling for MUM-1.

Non-secretory multiple myeloma with unusual TFG-ALK fusion showed dramatic response to ALK inhibition

Non-secretory multiple myeloma (NSMM) constitutes a distinct entity of multiple myeloma characterized by the absence of detectable monoclonal protein and rarely an absence of free light chains in the serum and urine. Given its rarity, the genomic landscape, clinical course, and prognosis of NSSM are not well characterized. Here, we report a case of a patient with relapsed and refractory NSMM with brain metastasis harboring a TFG-ALK fusion showing a dramatic and durable (over two years) response to commercially available anaplastic lymphoma kinase (ALK) inhibitors. The case emphasizes the beneficial role of molecular profiling in this target-poor disease.

Cytogenetic Features and Clinical Outcomes of Patients With Non-secretory Multiple Myeloma in the Era of Novel Agent Induction Therapy

BACKGROUND

Non-secretory multiple myeloma (NSMM) is a rare subtype of multiple myeloma (MM) characterized by the absence of monoclonal protein in the serum and/or urine. We look at the clinical and cytogenetic features of NSMM in this study.

PATIENTS AND METHODS

This study evaluates a cohort of 30 patients with newly diagnosed NSMM seen at the Mayo Clinic, Rochester, MN, between 2008 and 2018 and treated with novel agent induction therapies. Survival outcomes were estimated using the Kaplan-Meier method and compared using the log-rank test.

RESULTS

These patients with NSMM appear to have a large disease burden at diagnosis with a median bone marrow plasma cell percentage of 70% and more than one-half of all patients having Multiple Myeloma International Staging System Stage III disease. There was a higher preponderance for t(11;14) primary cytogenetic abnormality in this NSMM cohort, accounting for more than 50% of the cohort. Finally, the overall survival of this cohort appears to be slightly worse than a matched-control group of newly diagnosed patients with MM with secretory disease.

CONCLUSIONS

Future multi-institution studies confirming these above findings on this rare entity are warranted.

Non-Secretory Myeloma: Ready for a new Definition?

Non-secretory myeloma is a rare myeloma subtype whose diagnosis, until a few years ago, was established by demonstration of monoclonal plasma cells ≥10% in the bone marrow and by negative results on serum and urine electrophoresis and immunofixation studies. However, this type of myeloma could be misdiagnosed if the workup does not include an accurate study of serum free light chain test since some of the patients diagnosed as non-secretory could be light chain only with small amounts monoclonal proteinuria. Due to this limit in classification, all the information available today, generally coming from retrospective studies including patients studied completely and incompletely, could be misleading. A new definition is, thus, needed to distinguish between the true non-secretory, with a possible better prognosis, and the other forms of oligo-secretory myeloma with a prognosis more similar to the secretory form of myeloma. With all the data of the literature, the availability of laboratory and radiological tools, times are mature to depict a new definition of nonsecretory myeloma that deserves a peculiar work up and different response evaluation and, may be, a different therapeutic approach.

In vitro co-expression of human amyloidogenic immunoglobulin light and heavy chain proteins: a relevant cell-based model of AL amyloidosis

Immunoglobulin (Ig) light chain (LC) amyloidosis (AL) is characterized by the overproduction and tissue deposition of monoclonal LC in various organs and tissues. The plasma circulating monoclonal LC is believed to be the precursor of the deposited protein and in vitro studies aimed at understanding AL pathobiology have mainly focused on LC and its variable domain. While 33% of patients have free circulating monoclonal LC, ∼40% feature LC complexed to heavy chain (HC) forming a monoclonal intact Ig; the significance of free vs. bound LC in the amyloid forming pathway is unknown. To address this issue, we developed a cell-based model using stable mouse plasmacytoma Sp2/0 cells that co-express patient-derived amyloidogenic LC and HC proteins. The system was designed using amyloidogenic kappa and lambda LC, and gamma HC sequences; stable production and secretion of either free LC and/or intact Ig were accomplished by varying the LC to HC ratios. This novel cell-based system provides a relevant tool to systematically investigate LC and HC interactions, and the molecular events leading to the development of AL amyloidosis.

Non-secretory multiple myeloma: from biology to clinical management

Multiple myeloma (MM) is the second most common hematologic malignancy in the US. It is typically characterized by production of large amounts of defective immunoglobulin (Ig). Diagnosing MM and monitoring treatment response, including eventual relapse, are largely based on sequential measurements of Ig. However, a small subset of MM called non-secretory multiple myeloma (NSMM) produces no detectable Ig. This subset of true NSMM has become even smaller over time, as the advent of the serum free light chain assay has resulted in the majority of NSMM patients being recategorized as light-chain MM – that is, MM cells that produce only the light-chain component of Ig. True forms of NSMM, meaning MM that secretes no monoclonal proteins whatsoever, constitute a distinct entity that is reviewed; definition of NSMM using current detection methods, discuss the biology underpinning NSMM development, and share recommendations for how NSMM should be managed clinically with respect to detection, treatment, and monitoring.

Is it solitary plasmacytoma or nonsecretory myeloma? A must-be-solved dilemma?

Presentation of multiple myeloma with bone lesions is common. It is vital that differentiation between nonsecretory multiple myeloma and plasmocytoma be done and that each disorder be treated accordingly. In this paper, we present a patient with nonsecretory multiple myeloma, who suffered from distal humerus fracture with severe bone destruction, renal failure, hypercalcemia and anemia.

A plasma cell differentiation quality control ablates B cell clones with biallelic Ig rearrangements and truncated Ig production

Aberrantly rearranged immunoglobulin (Ig) alleles are frequent. They are usually considered sterile and innocuous as a result of nonsense-mediated mRNA decay. However, alternative splicing can yield internally deleted proteins from such nonproductively V(D)J-rearranged loci. We show that nonsense codons from variable (V) Igκ exons promote exon-skipping and synthesis of V domain-less κ light chains (ΔV-κLCs). Unexpectedly, such ΔV-κLCs inhibit plasma cell (PC) differentiation. Accordingly, in wild-type mice, rearrangements encoding ΔV-κLCs are rare in PCs, but frequent in B cells. Likewise, enforcing expression of ΔV-κLCs impaired PC differentiation and antibody responses without disturbing germinal center reactions. In addition, PCs expressing ΔV-κLCs synthesize low levels of Ig and are mostly found among short-lived plasmablasts. ΔV-κLCs have intrinsic toxic effects in PCs unrelated to Ig assembly, but mediated by ER stress-associated apoptosis, making PCs producing ΔV-κLCs highly sensitive to proteasome inhibitors. Altogether, these findings demonstrate a quality control checkpoint blunting terminal PC differentiation by eliminating those cells expressing nonfunctionally rearranged Igκ alleles. This truncated Ig exclusion (TIE) checkpoint ablates PC clones with ΔV-κLCs production and exacerbated ER stress response. The TIE checkpoint thus mediates selection of long-lived PCs with limited ER stress supporting high Ig secretion, but with a cost in terms of antigen-independent narrowing of the repertoire.

The class-specific BCR tonic signal modulates lymphomagenesis in a c-myc deregulation transgenic model

Deregulation of c-myc by translocation onto immunoglobulin (Ig) loci can promote B cell malignant proliferations with phenotypes as diverse as acute lymphoid leukemia, Burkitt lymphoma, diffuse large B cell lymphoma, myeloma… The B cell receptor (BCR) normally providing tonic signals for cell survival and mitogenic responses to antigens, can also contribute to lymphomagenesis upon sustained ligand binding or activating mutations. BCR signaling varies among cell compartments and BCR classes. For unknown reasons, some malignancies associate with expression of either IgM or class-switched Ig. We explored whether an IgA BCR, with strong tonic signaling, would affect lymphomagenesis in c-myc IgH 3′RR transgenic mice prone to lymphoproliferations. Breeding c-myc transgenics in a background where IgM expression was replaced with IgA delayed lymphomagenesis. By comparison to single c-myc transgenics, lymphomas from double mutant animals were more differentiated and less aggressive, with an altered transcriptional program. Larger tumor cells more often expressed CD43 and CD138, which culminated in a plasma cell phenotype in 10% of cases. BCR class-specific signals thus appear to modulate lymphomagenesis and may partly explain the observed association of specific Ig classes with human B cell malignancies of differential phenotype, progression and prognosis.

Clinical course and prognosis of non-secretory multiple myeloma

OBJECTIVE

To determine the prognosis of patients with non-secretory myeloma.

METHODS

We studied 124 patients diagnosed with multiple myeloma who had no monoclonal protein detected on serum and urine immunofixation at diagnosis and on all subsequent follow-up testing (non-secretory myeloma). The overall survival (OS) of patients with non-secretory myeloma was compared with 6953 patients with typical myeloma seen during the same time period in whom a monoclonal protein was detected at the time of diagnosis.

RESULTS

One hundred and twenty-four patients met criteria for non-secretory multiple myeloma. The median follow-up was 102 months (range, 1-204 months). The median progression-free survival with initial therapy was 28.6 months, and the median OS was 49.3 months. There was a significant improvement in OS since 2001; median survival 43.8 months (prior to 2001) vs. 99.2 months (2001-2012), P < 0.001. OS was superior in patients with a normal baseline FLC ratio (n = 10) compared to patients with an abnormal ratio (n = 19), medians not reached in both groups. Prior to 2001, OS was similar in non-secretory myeloma (n = 86) and secretory myeloma (n = 4011), median 3.6 vs. 3.5 yr, respectively, P = 0.63. However, among patients diagnosed between 2001 and 2012, OS was superior in non-secretory myeloma (n = 36) compared to secretory myeloma (n = 2942), median 8.3 vs. 5.4 yr, respectively, P = 0.03.

CONCLUSIONS

Non-secretory myeloma is an uncommon subtype of multiple myeloma. In the last decade, there has been an improvement in the survival of non-secretory myeloma and appears superior to secretory myeloma.

Non-secretory immunoglobulin E myeloma associated with immunoglobulin G monoclonal gammopathy of undetermined significance

A 68-year old woman came to our hospital with a severe case of anemia. Serum immunoelectropheresis identified a monoclonal immunoglobulin (Ig) G and κ protein. The serum IgE level was within the nomal range and the amounts of remaining immunogloblins were low. On bone marrow aspirate, plasma cells made up 55.5% of nucleated cells and the plasma cells showed positive readings for IgE κ and IgG by immunohistochemistry. Serum immunofixation did not reveal the IgE monoclonal band. She was diagnosed as having non-secretory IgE myeloma with IgG monoclonal gammopathy of undetermined significance. The nature of this rare myeloma will be discussed.

Relationship between elevated immunoglobulin free light chain and the presence of IgH translocations in multiple myeloma

Elevated immunoglobulin free light chain (FLC) level and abnormal FLC ratio are commonly seen in multiple myeloma (MM) and have prognostic implications. We hypothesized that presence of immunoglobin heavy chain (IgH) translocations leads to unbalanced production of light chains and more extreme abnormalities of FLC, and may explain the prognostic value of FLC. We studied 314 patients with newly diagnosed MM enrolled in a phase III trial, in whom results of fluorescence in situ hybridization testing and data on serum FLC levels were available. Cytogenetic analyses and FLC estimates were performed on stored samples and results were correlated with clinical data. The median ratio (FLC ratio) and the absolute difference (FLC diff) between the involved and uninvolved FLC were higher among those with IgH translocations, especially t(14;16). In multivariate analysis, the prognostic value of FLC estimates on progression-free and overall survival were independent of high-risk IgH translocations t(4;14) and t(14;16). A combination of the risk factors; either abnormal FLC estimate and/or the presence of high-risk IgH translocation, achieved better prognostic stratification. We conclude that patients with IgH translocations have higher FLC levels and abnormal ratios, but the prognostic effect of FLC is only partially explained by translocation status. A system including both these risk factors allows better prediction of outcome.

Immunoglobulin aggregation leading to Russell body formation is prevented by the antibody light chain

Russell bodies (RBs) are intracellular inclusions filled with protein aggregates. In diverse lymphoid disorders these occur as immunoglobulin (Ig) deposits, accumulating in abnormal plasma or Mott cells. In heavy-chain deposition disease truncated antibody heavy-chains (HCs) are found, which bear a resemblance to diverse polypeptides produced in Ig light-chain (LC)-deficient (L(-/-)) mice. In L(-/-) animals, the known functions of LC, providing part of the antigen-binding site of an antibody and securing progression of B-cell development, may not be required. Here, we show a novel function of LC in preventing antibody aggregation. L(-/-) mice produce truncated HC naturally, constant region (C)gamma and Calpha lack C(H)1, and Cmicro is without C(H)1 or C(H)1 and C(H)2. Most plasma cells found in these mice are CD138(+) Mott cells, filled with RBs, formed by aggregation of HCs of different isotypes. The importance of LC in preventing HC aggregation is evident in knock-in mice, expressing Cmicro without C(H)1 and C(H)2, which only develop an abundance of RBs when LC is absent. These results reveal that preventing antibody aggregation is a major function of LC, important for understanding the physiology of heavy-chain deposition disease, and in general recognizing the mechanisms, which initiate protein conformational diseases.

Primary non-secretory plasma cell leukemia with atypical morphology - a case report

Only one case of primary non-secretory plasma cell leukemia with atypical morphology has been reported thus far. Here we report another such case of plasma cell leukemia diagnosed on fl ow cytometry, as morphological heterogeneity and lack of monoclonal immunoglobulins in both serum and urine, made it difficult to come to a conclusive diagnosis based purely on morphology.

t(11;14) Plasma cell disorder presents as a true nonsecretory, nonproducer multiple myeloma

We describe an extremely rare case of so-called nonsecretory, nonproducer myeloma in an 80-year-old man who presented with weight loss and anemia. The patient's serum protein electrophoresis was negative for M protein spike, and quantitation of his immunoglobulin level was far below the normal range. The bone marrow biopsy showed a sheet-like diffuse plasmacytic infiltrate with essential absence of trilineage hematopoiesis. Flow cytometry analysis and immunohistochemical study demonstrated a strong CD38/CD138/immunoglobulin G heavy chain-positive plasma cell population but failed to detect either cytoplasmic kappa or lambda light chain expression. Chromosomal analysis and dual fluorescence in situ hybridization studies clearly demonstrated the presence of t(11;14)(q13;q32) translocation in the neoplastic plasma cells.