Tumor cells in light-chain amyloidosis and myeloma show distinct transcriptional rewiring of normal plasma cell development.

Although light-chain amyloidosis (AL) and multiple myeloma (MM) are characterized by tumor plasma cell (PC) expansion in bone marrow (BM), their clinical presentation differs. Previous attempts to identify unique pathogenic mechanisms behind such differences were unsuccessful, and no studies have investigated the differentiation stage of tumor PCs in patients with AL and MM. We sought to define a transcriptional atlas of normal PC development in secondary lymphoid organs (SLOs), peripheral blood (PB), and BM for comparison with the transcriptional programs (TPs) of tumor PCs in AL, MM, and monoclonal gammopathy of undetermined significance (MGUS). Based on bulk and single-cell RNA sequencing, we observed 13 TPs during transition of normal PCs throughout SLOs, PB, and BM. We further noted the following: CD39 outperforms CD19 to discriminate newborn from long-lived BM-PCs; tumor PCs expressed the most advantageous TPs of normal PC differentiation; AL shares greater similarity to SLO-PCs whereas MM is transcriptionally closer to PB-PCs and newborn BM-PCs; patients with AL and MM enriched in immature TPs had inferior survival; and protein N-linked glycosylation-related TPs are upregulated in AL. Collectively, we provide a novel resource to understand normal PC development and the transcriptional reorganization of AL and other monoclonal gammopathies.

A Strategy for the Selection of RT-qPCR Reference Genes Based on Publicly Available Transcriptomic Datasets.

In the next-generation sequencing era, RT-qPCR is still widely employed to quantify levels of nucleic acids of interest due to its popularity, versatility, and limited costs. The measurement of transcriptional levels through RT-qPCR critically depends on reference genes used for normalization. Here, we devised a strategy to select appropriate reference genes for a specific clinical/experimental setting based on publicly available transcriptomic datasets and a pipeline for RT-qPCR assay design and validation. As a proof-of-principle, we applied this strategy to identify and validate reference genes for transcriptional studies of bone-marrow plasma cells from patients with AL amyloidosis. We performed a systematic review of published literature to compile a list of 163 candidate reference genes for RT-qPCR experiments employing human samples. Next, we interrogated the Gene Expression Omnibus to assess expression levels of these genes in published transcriptomic studies on bone-marrow plasma cells from patients with different plasma cell dyscrasias and identified the most stably expressed genes as candidate normalizing genes. Experimental validation on bone-marrow plasma cells showed the superiority of candidate reference genes identified through this strategy over commonly employed "housekeeping" genes. The strategy presented here may apply to other clinical and experimental settings for which publicly available transcriptomic datasets are available.

Targeting Amyloid Fibrils by Passive Immunotherapy in Systemic Amyloidosis.

Systemic amyloidoses are characterized by the unrelenting deposition of autologous proteins as highly ordered fibrils in target organs. The ensuing, potentially fatal organ dysfunction is the result of the combined damage caused by the proteotoxic effect of prefibrillar species and by the cytotoxicity and the structural alterations produced by the amyloid fibrils. Current therapy is focused on eliminating the amyloid protein, thus extinguishing the amyloid cascade at its origin. While this approach may end the cell damage caused by prefibrillar aggregates and prevent further amyloid accumulation, the noxious effects of the amyloid fibrils persist and may hamper the recovery of organ function, which is the ultimate goal of therapy as it is necessary to improve the quality of life and extend survival. Preclinical studies indicate that the clearance of amyloid deposits can be accelerated by specific antibodies targeting amyloid fibrils that activate complement-mediated macrophages and giant cell phagocytosis, possibly promoting the recovery of organ function. Measuring the therapeutic effect of anti-amyloid agents is still a matter of research. In recent years, several monoclonal antibodies targeting amyloid deposits have been tested in clinical trials with mixed outcomes. Recent encouraging results from phase I/II trials, new anti-amyloid agents, and new antibody engineering offer hope that effective amyloid removal will be accomplished in the near future, accelerating organ recovery and improving quality of life and survival.

An N-glycosylation hotspot in immunoglobulin κ light chains is associated with AL amyloidosis.

Immunoglobulin light chain (AL) amyloidosis is caused by a small, minimally proliferating B-cell/plasma-cell clone secreting a patient-unique, aggregation-prone, toxic light chain (LC). The pathogenicity of LCs is encrypted in their sequence, yet molecular determinants of amyloidogenesis are poorly understood. Higher rates of N-glycosylation among clonal κ LCs from patients with AL amyloidosis compared to other monoclonal gammopathies indicate that this post-translational modification is associated with a higher risk of developing AL amyloidosis. Here, we exploited LC sequence information from previously published amyloidogenic and control clonal LCs and from a series of 220 patients with AL amyloidosis or multiple myeloma followed at our Institutions to define sequence and spatial features of N-glycosylation, combining bioinformatics, biochemical, proteomics, structural and genetic analyses. We found peculiar sequence and spatial pattern of N-glycosylation in amyloidogenic κ LCs, with most of the N-glycosylation sites laying in the framework region 3, particularly within the E strand, and consisting mainly of the NFT sequon, setting them apart with respect to non-amyloidogenic clonal LCs. Our data further support a potential role of N-glycosylation in determining the pathogenic behavior of a subset of amyloidogenic LCs and may help refine current N-glycosylation-based prognostic assessments for patients with monoclonal gammopathies.

Bone Marrow Microenvironment in Light-Chain Amyloidosis: In Vitro Expansion and Characterization of Mesenchymal Stromal Cells.

Immunoglobulin light-chain amyloidosis (AL) is caused by misfolded light chains produced by a small B cell clone. Mesenchymal stromal cells (MSCs) have been reported to affect plasma cell behavior. We aimed to characterize bone marrow (BM)-MSCs from AL patients, considering functional aspects, such as proliferation, differentiation, and immunomodulatory capacities. MSCs were in vitro expanded from the BM of 57 AL patients and 14 healthy donors (HDs). MSC surface markers were analyzed by flow cytometry, osteogenic and adipogenic differentiation capacities were in vitro evaluated, and co-culture experiments were performed in order to investigate MSC immunomodulatory properties towards the ALMC-2 cell line and HD peripheral blood mononuclear cells (PBMCs). AL-MSCs were comparable to HD-MSCs for morphology, immune-phenotype, and differentiation capacities. AL-MSCs showed a reduced proliferation rate, entering senescence at earlier passages than HD-MSCs. The AL-MSC modulatory effect on the plasma-cell line or circulating plasma cells was comparable to that of HD-MSCs. To our knowledge, this is the first study providing a comprehensive characterization of AL-MSCs. It remains to be defined if the observed abnormalities are the consequence of or are involved in the disease pathogenesis. BM microenvironment components in AL may represent the targets for the prevention/treatment of the disease in personalized therapies.

Minimal residual disease negativity by next-generation flow cytometry is associated with improved organ response in AL amyloidosis.

Light chain (AL) amyloidosis is caused by a small B-cell clone producing light chains that form amyloid deposits and cause organ dysfunction. Chemotherapy aims at suppressing the production of the toxic light chain (LC) and restore organ function. However, even complete hematologic response (CR), defined as negative serum and urine immunofixation and normalized free LC ratio, does not always translate into organ response. Next-generation flow (NGF) cytometry is used to detect minimal residual disease (MRD) in multiple myeloma. We evaluated MRD by NGF in 92 AL amyloidosis patients in CR. Fifty-four percent had persistent MRD (median 0.03% abnormal plasma cells). There were no differences in baseline clinical variables in patients with or without detectable MRD. Undetectable MRD was associated with higher rates of renal (90% vs 62%, p = 0.006) and cardiac response (95% vs 75%, p = 0.023). Hematologic progression was more frequent in MRD positive (0 vs 25% at 1 year, p = 0.001). Altogether, NGF can detect MRD in approximately half the AL amyloidosis patients in CR, and persistent MRD can explain persistent organ dysfunction. Thus, this study supports testing MRD in CR patients, especially if not accompanied by organ response. In case MRD persists, further treatment could be considered, carefully balancing residual organ damage, patient frailty, and possible toxicity.

Treating Protein Misfolding Diseases: Therapeutic Successes Against Systemic Amyloidoses.

Misfolding and extracellular deposition of proteins is the hallmark of a heterogeneous group of conditions collectively termed protein misfolding and deposition diseases or amyloidoses. These include both localized (e.g. Alzheimer's disease, prion diseases, type 2 diabetes mellitus) and systemic amyloidoses. Historically regarded as a group of maladies with limited, even inexistent, therapeutic options, some forms of systemic amyloidoses have recently witnessed a series of unparalleled therapeutic successes, positively impacting on their natural history and sometimes even on their incidence. In this review article we will revisit the most relevant of these accomplishments. Collectively, current evidence converges towards a crucial role of an early and conspicuous reduction or stabilization of the amyloid-forming protein in its native conformation. Such an approach can reduce disease incidence in at risk individuals, limit organ function deterioration, promote organ function recovery, improve quality of life and extend survival in diseased subjects. Therapeutic success achieved in these forms of systemic amyloidoses may guide the research on other protein misfolding and deposition diseases for which effective etiologic therapeutic options are still absent.