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In a randomized trial of bortezomib, cyclophosphamide, and dexamethasone as compared with the same therapy plus daratumumab, patients with light-chain amyloidosis who received daratumumab had a higher frequency of hematologic complete response than those who did not (53.3% vs. 18.1%). Deaths were most commonly due to cardiac failure.

Systemic light chain amyloidosis (AL)  is a life-threatening disease caused by aggregation and deposition of monoclonal immunoglobulin light chains (LC) in target organs. Severity of heart involvement is the most important factor determining prognosis. Here, we report the 4.0 Å resolution cryo-electron microscopy map and molecular model of amyloid fibrils extracted from the heart of an AL amyloidosis patient with severe amyloid cardiomyopathy. The helical fibrils are composed of a single protofilament, showing typical 4.9 Å stacking and cross-β architecture. Two distinct polypeptide stretches (total of 77 residues) from the LC variable domain (V l ) fit the fibril density. Despite V l high sequence variability, residues stabilizing the fibril core are conserved through different cardiotoxic V l , highlighting structural motifs that may be common to misfolding-prone LCs. Our data shed light on the architecture of LC amyloids, correlate amino acid sequences with fibril assembly, providing the grounds for development of innovative medicines. Immunoglobulin Light Chain Amyloidosis (AL) is the most common systemic amyloidosis occurring in Western countries. Here the authors present the 4.0 Å cryo-EM structure of light chain AL55 fibrils that were isolated from the heart of an AL systemic amyloidosis patient.

Amyloid fibrils derived from antibody light chains are key pathogenic agents in systemic AL amyloidosis. They can be deposited in multiple organs but cardiac amyloid is the major risk factor of mortality. Here we report the structure of a λ1 AL amyloid fibril from an explanted human heart at a resolution of 3.3 Å which we determined using cryo-electron microscopy. The fibril core consists of a 91-residue segment presenting an all-beta fold with ten mutagenic changes compared to the germ line. The conformation differs substantially from natively folded light chains: a rotational switch around the intramolecular disulphide bond being the crucial structural rearrangement underlying fibril formation. Our structure provides insight into the mechanism of protein misfolding and the role of patient-specific mutations in pathogenicity. Systemic AL amyloidosis is caused by misfolding of immunoglobulin light chains and is one of the most frequently occurring forms of systemic amyloidosis. Here the authors present the 3.3 Å cryo-EM structure of a λ1 AL amyloid fibril that was isolated from an explanted human heart.

Amyloidosis, a systemic disease that manifests in various ways, should be in the differential diagnosis of unexplained proteinuria, restrictive cardiomyopathy, peripheral and autonomic neuropathy, and hepatomegaly. Treatments are improving.

Systemic AL amyloidosis is caused by deposition of monoclonal antibody light chains (LC) as insoluble amyloid fibrils in multiple tissues, leading to irreversible and eventually fatal organ damage. Each patient has a unique LC sequence that appears to define its propensity to aggregate. The complexity and diversity of LC sequences has impeded efforts to understand why some LCs aggregate to cause disease while others do not. We investigated residue changes, relative to the inferred precursor germline sequences, in monoclonal LCs associated with AL amyloidosis and multiple myeloma (MM), derived from the AL-Base resource. Consensus matrices, calculated using healthy polyclonal repertoire sequences from Observed Antibody Space (OAS), were used to determine the relative frequency of each residue in the monoclonal LC sequences. A subset of residues observed in AL-associated LCs was uncommon in the healthy repertoire, but these residues were highly diverse and were also observed in MM-associated LCs. We identified multiple positions that more frequently harbor uncommon residues in AL-associated LCs than OAS-derived LCs, including several positions that have previously been identified. However, each individual residue change occurs in only a small fraction of LCs, indicating that many types of residue change can contribute to disease. Furthermore, positions where residue changes occur most frequently were not enriched in amyloidosis-associated residues. These data provide a framework for future investigations into sequence determinants of amyloid propensity, supporting efforts towards earlier recognition and diagnosis of AL amyloidosis.

The light chain (AL) amyloidosis is caused by the aggregation of light chain of antibodies into amyloid fibrils. There are plenty of computational resources available for the prediction of short aggregation-prone regions within proteins. However, it is still a challenging task to predict the amyloidogenic nature of the whole protein using sequence/structure information. In the case of antibody light chains, common architecture and known binding sites can provide vital information for the prediction of amyloidogenicity at physiological conditions. Here, in this work, we have compared classical sequence-based, aggregation-related features (such as hydrophobicity, presence of gatekeeper residues, disorderness, β-propensity, etc.) calculated for the CDR, FR or V L regions of amyloidogenic and non-amyloidogenic antibody light chains and implemented the insights gained in a machine learning-based webserver called “V L AmY-Pred” ( https://web.iitm.ac.in/bioinfo2/vlamy-pred/ ). The model shows prediction accuracy of 79.7% (sensitivity: 78.7% and specificity: 79.9%) with a ROC value of 0.88 on a dataset of 1828 variable region sequences of the antibody light chains. This model will be helpful towards improved prognosis for patients that may likely suffer from diseases caused by light chain amyloidosis, understanding origins of aggregation in antibody-based biotherapeutics, large-scale in-silico analysis of antibody sequences generated by next generation sequencing, and finally towards rational engineering of aggregation resistant antibodies.

In systemic light chain amyloidosis (AL), pathogenic monoclonal immunoglobulin light chains (LC) form toxic aggregates and amyloid fibrils in target organs. Prompt diagnosis is crucial to avoid permanent organ damage, but delayed diagnosis is common because symptoms usually appear only after strong organ involvement. Here we present LICTOR, a machine learning approach predicting LC toxicity in AL, based on the distribution of somatic mutations acquired during clonal selection. LICTOR achieves a specificity and a sensitivity of 0.82 and 0.76, respectively, with an area under the receiver operating characteristic curve (AUC) of 0.87. Tested on an independent set of 12 LCs sequences with known clinical phenotypes, LICTOR achieves a prediction accuracy of 83%. Furthermore, we are able to abolish the toxic phenotype of an LC by in silico reverting two germline-specific somatic mutations identified by LICTOR, and by experimentally assessing the loss of in vivo toxicity in a Caenorhabditis elegans model. Therefore, LICTOR represents a promising strategy for AL diagnosis and reducing high mortality rates in AL. Systemic light chain amyloidosis (AL) is caused by the production of toxic light chains and can be fatal, yet effective treatments are often not possible due to delayed diagnosis. Here the authors show that a machine learning platform analyzing light chain somatic mutations allows the prediction of light chain toxicity to serve as a possible tool for early diagnosis of AL.

The vertebrate adaptive immune system modifies the genome of individual B cells to encode antibodies that bind particular antigens 1 . In most mammals, antibodies are composed of heavy and light chains that are generated sequentially by recombination of V, D (for heavy chains), J and C gene segments. Each chain contains three complementarity-determining regions (CDR1–CDR3), which contribute to antigen specificity. Certain heavy and light chains are preferred for particular antigens 2 – 22 . Here we consider pairs of B cells that share the same heavy chain V gene and CDRH3 amino acid sequence and were isolated from different donors, also known as public clonotypes 23 , 24 . We show that for naive antibodies (those not yet adapted to antigens), the probability that they use the same light chain V gene is around 10%, whereas for memory (functional) antibodies, it is around 80%, even if only one cell per clonotype is used. This property of functional antibodies is a phenomenon that we call light chain coherence. We also observe this phenomenon when similar heavy chains recur within a donor. Thus, although naive antibodies seem to recur by chance, the recurrence of functional antibodies reveals surprising constraint and determinism in the processes of V(D)J recombination and immune selection. For most functional antibodies, the heavy chain determines the light chain.  Among naturally occurring antibodies that have adapted to antigen, those with similar heavy chains usually have similar light chains.

Systemic AL amyloidosis is one of the most frequently diagnosed forms of systemic amyloidosis. It arises from mutational changes in immunoglobulin light chains. To explore whether these mutations may affect the structure of the formed fibrils, we determine and compare the fibril structures from several patients with cardiac AL amyloidosis. All patients are affected by light chains that contain an IGLV3-19 gene segment, and the deposited fibrils differ by the mutations within this common germ line background. Using cryo-electron microscopy, we here find different fibril structures in each patient. These data establish that the mutations of amyloidogenic light chains contribute to defining the fibril architecture and hence the structure of the pathogenic agent. Systemic AL amyloidosis is one of the most frequently diagnosed forms of systemic amyloidosis. Here the authors analyse the structures of AL amyloid fibrils with different light chain mutations and show that the mutations contribute to defining the fibril structure in different patients.

Systemic light-chain amyloidosis (AL) is characterized by the misfolding and aggregation of immunoglobulin light chains (LCs) into amyloid fibrils, leading to multiorgan deposition and dysfunction, with the kidneys being one of the most commonly involved organs. Here, we report high-resolution cryo-electron microscopy (cryo-EM) structures of AL amyloid fibrils from the kidney of a male patient with renal AL amyloidosis. Two distinct polymorphic fibril structures, polymorph A and polymorph B, were identified, both featuring ordered cores (Gln16-Ser95) with β-sheet-rich architectures stabilized by interchain hydrogen bonds and salt bridges. Notably, six mutations in the IGLV1-44*01 gene sequence, including Gln39His and Tyr37Phe, were identified within the fibril core. These mutations influence fibril stability and aggregation by altering intramolecular and intermolecular interactions, such as CH-π stacking and salt bridge formation. Comparative analysis with previously reported heart-derived IGLV1-44 fibrils reveals structural variations linked to light-chain sequence differences. Our findings provide critical insights into the molecular determinants of fibril assembly and organ tropism in AL amyloidosis. Authors report cryo-EM structures of AL amyloid fibrils from the kidney of a male patient with renal AL amyloidosis. Comparison to previous heart-derived fibrils reveals variations linked to sequence differences and insights into fibril assembly and organ tropism in AL amyloidosis.