Lymphoma Driver Mutations in the Pathogenic Evolution of an Iconic Human Autoantibody.

Pathogenic autoantibodies arise in many autoimmune diseases, but it is not understood how the cells making them evade immune checkpoints. Here, single-cell multi-omics analysis demonstrates a shared mechanism with lymphoid malignancy in the formation of public rheumatoid factor autoantibodies responsible for mixed cryoglobulinemic vasculitis. By combining single-cell DNA and RNA sequencing with serum antibody peptide sequencing and antibody synthesis, rare circulating B lymphocytes making pathogenic autoantibodies were found to comprise clonal trees accumulating mutations. Lymphoma driver mutations in genes regulating B cell proliferation and V(D)J mutation (CARD11, TNFAIP3, CCND3, ID3, BTG2, and KLHL6) were present in rogue B cells producing the pathogenic autoantibody. Antibody V(D)J mutations conferred pathogenicity by causing the antigen-bound autoantibodies to undergo phase transition to insoluble aggregates at lower temperatures. These results reveal a pre-neoplastic stage in human lymphomagenesis and a cascade of somatic mutations leading to an iconic pathogenic autoantibody.

Immunoglobulin repertoire restriction characterizes the serological responses of patients with predominantly antibody deficiency.

BACKGROUND: Predominantly antibody deficiency (PAD) is the most common category of inborn errors of immunity and is underpinned by impaired generation of appropriate antibody diversity and quantity. In the clinic, responses are interrogated by assessment of vaccination responses, which is central to many PAD diagnoses. However, the composition of the generated antibody repertoire is concealed from traditional quantitative measures of serological responses. Leveraging modern mass spectrometry-based proteomics (MS-proteomics), it is possible to elaborate the molecular features of specific antibody repertoires, which may address current limitations of diagnostic vaccinology. OBJECTIVES: We sought to evaluate serum antibody responses in patients with PAD following vaccination with a neo-antigen (severe acute respiratory syndrome coronavirus-2 vaccination) using MS-proteomics. METHODS: Following severe acute respiratory syndrome coronavirus-2 vaccination, serological responses in individuals with PAD and healthy controls (HCs) were assessed by anti-S1 subunit ELISA and neutralization assays. Purified anti-S1 subunit IgG and IgM was profiled by MS-proteomics for IGHV subfamily usage and somatic hypermutation analysis. RESULTS: Twelve patients with PAD who were vaccine-responsive were recruited with 11 matched vaccinated HCs. Neutralization and end point anti-S1 titers were lower in PAD. All subjects with PAD demonstrated restricted anti-S1 IgG antibody repertoires, with usage of <5 IGHV subfamilies (median: 3; range 2-4), compared to ≥5 for the 11 HC subjects (P < .001). IGHV3-7 utilization was far less common in patients with PAD than in HCs (2 of 12 vs 10 of 11; P = .001). Amino acid substitutions due to somatic hypermutation per subfamily did not differ between groups. Anti-S1 IgM was present in 64% and 50% of HC and PAD cohorts, respectively, and did not differ significantly between HCs and patients with PAD. CONCLUSIONS: This study demonstrates the breadth of anti-S1 antibodies elicited by vaccination at the proteome level and identifies stereotypical restriction of IGHV utilization in the IgG repertoire in patients with PAD compared with HC subjects. Despite uniformly pauci-clonal antibody repertoires some patients with PAD generated potent serological responses, highlighting a possible limitation of traditional serological techniques. These findings suggest that IgG repertoire restriction is a key feature of antibody repertoires in PAD.

Anti-Ro60 and anti-Ro52/TRIM21: Two distinct autoantibodies in systemic autoimmune diseases.

As iconic and important diagnostic autoantibodies, anti-Ro60 and anti-Ro52/tri-partite motif-containing 21 (TRIM21) make a common appearance in a number of systemic autoimmune disorders such as systemic lupus erythematosus (SLE). These autoantibodies often co-exist together; yet despite their close relationship, there is no evidence that they are physically linked and probably reflect a convergence of separate processes of failed immunological tolerance. Confusingly, they are sometimes classed together as the "SSA" or "Ro" autoantibody system without clear distinction between the two. In this Short Communication, we discuss the diagnostic merits for separate detection and reporting of these two autoantibodies, and discuss avenues for future research. Indeed, further insight into their fascinating origins and pathogenic roles in autoimmunity will surely shed light on how we can prevent and treat devastating autoimmune disorders.

Primary Sjögren's syndrome in South Australia.

OBJECTIVES: To describe clinical and serological characteristics of a South Australian primary Sjögren's syndrome (pSS) cohort. METHODS: The South Australian Sjögren's Syndrome Research Clinic and Database is a clinical cohort of patients with pSS at a single site. Baseline clinical and laboratory data from 172 patients were retrospectively examined to determine their prevalence and clinical associations. Results were compared to findings from 10,500 patients from The Big Data Sjogren Project Consortium; an international, multicentre registry established in 2014, which included the South Australian data. RESULTS: Of 172 South Australian patients with pSS, 90.1% were female with a mean age at diagnosis of 57 years. Ocular and oral sicca symptoms were common, affecting 97.1% and 99.4% respectively. Anti-Ro ± La positivity was detected in 82.6%, ANA positivity in 77%, and in 9% of patients both ANA and ENA were negative. Mean ESSDAI was 6.8 at baseline, slightly higher than the international cohort at 6.1; the most commonly positive domains being biological, articular and glandular. Pulmonary manifestations represented the most significant morbidity over time. Lymphoma was recorded in 5.2% of patients and congenital heart block in 4 offspring of 52 patients with longitudinal follow-up (7.7%), although incomplete data likely resulted in underestimation of both. CONCLUSIONS: Despite the relatively small sample size of the South Australian cohort, clinical and serological characteristics correspond closely with international descriptions.

IgV peptide mapping of native Ro60 autoantibody proteomes in primary Sjögren's syndrome reveals molecular markers of Ro/La diversification.

We have used high-resolution mass spectrometry to sequence precipitating anti-Ro60 proteomes from sera of patients with primary Sjögren's syndrome and compare immunoglobulin variable-region (IgV) peptide signatures in Ro/La autoantibody subsets. Anti-Ro60 were purified by elution from native Ro60-coated ELISA plates and subjected to combined de novo amino acid sequencing and database matching. Monospecific anti-Ro60 Igs comprised dominant public and minor private sets of IgG1 kappa and lambda restricted heavy and light chains. Specific IgV amino acid substitutions stratified anti-Ro60 from anti-Ro60/La responses, providing a molecular fingerprint of Ro60/La determinant spreading and suggesting that different forms of Ro60 antigen drive these responses. Sequencing of linked anti-Ro52 proteomes from individual patients and comparison with their anti-Ro60 partners revealed sharing of a dominant IGHV3-23/IGKV3-20 paired clonotype but with divergent IgV mutational signatures. In summary, anti-Ro60 IgV peptide mapping provides insights into Ro/La autoantibody diversification and reveals serum-based molecular markers of humoral Ro60 autoimmunity.

Serum SmD autoantibody proteomes are clonally restricted and share variable-region peptides.

Recent advances in mass spectrometry-based proteomic methods have allowed variable (V)-region peptide signatures to be derived from human autoantibodies present in complex serum mixtures. Here, we analysed the clonality and V-region composition of immunoglobulin (Ig) proteomes specific for the immunodominant SmD protein subunit of the lupus-specific Sm autoantigen. Precipitating SmD-specific IgGs were eluted from native SmD-coated ELISA plates preincubated with sera from six patients with systemic lupus erythematosus (SLE) positive for anti-Sm/RNP. Heavy (H)- and light (L)-chain clonality and V-region sequences were analysed by 2-dimensional gel electrophoresis and combined de novo database mass spectrometric sequencing. SmD autoantibody proteomes from all six patients with SLE expressed IgG1 kappa restricted clonotypes specified by IGHV3-7 and IGHV1-69 H-chains and IGKV3-20 and IGKV2-28 L-chains, with shared and individual V-region amino acid replacement mutations. Clonotypic sharing and restricted V-region diversity of systemic autoimmunity can now be extended from the Ro/La cluster to Sm autoantigen and implies a common pathway of anti-Sm autoantibody production in unrelated patients with SLE.

Long-term Ro60 humoral autoimmunity in primary Sjögren's syndrome is maintained by rapid clonal turnover.

Long-term humoral autoimmunity to RNA-protein autoantigens is considered a hallmark of systemic autoimmune diseases. We use high resolution Orbitrap mass spectrometric autoantibody sequencing to track the evolution of a Ro60-specific public clonotypic autoantibody in 4 patients with primary Sjögren's syndrome. This clonotype is specified by a VH3-23/VK3-20 heavy and light chain pairing. Despite apparent stability by conventional immunoassay, analysis of V-region molecular signatures of clonotypes purified from serum samples collected retrospectively over 7years revealed sequential clonal replacement. Prospective longitudinal studies confirmed clonotype loss and replacement at approximately three-monthly intervals. Levels of secreted anti-Ro60 clonotypes fluctuated markedly over time, despite minimal changes in clonal affinity. Our novel findings indicate a relentless turnover of short-lived clonotypic variants, masquerading as long-lived Ro60 humoral autoimmunity.

ß2-glycoprotein I and protection from anti-SSA/Ro60-associated cardiac manifestations of neonatal lupus.

One mechanism to molecularly explain the strong association of maternal anti-Ro60 Abs with cardiac disease in neonatal lupus (NL) is that these Abs initiate injury by binding to apoptotic cardiomyocytes in the fetal heart. Previous studies have demonstrated that ß(2)-glycoprotein I (ß(2)GPI) interacts with Ro60 on the surface of apoptotic Jurkat cells and prevents binding of anti-Ro60 IgG. Accordingly, the current study was initiated to test two complementary hypotheses, as follows: 1) competition between ß(2)GPI and maternal anti-Ro60 Abs for binding apoptotic induced surface-translocated Ro60 occurs on human fetal cardiomyocytes; and 2) circulating levels of ß(2)GPI influence injury in anti-Ro60-exposed fetuses. Initial flow cytometry experiments conducted on apoptotic human fetal cardiomyocytes demonstrated dose-dependent binding of ß(2)GPI. In competitive inhibition experiments, ß(2)GPI prevented opsonization of apoptotic cardiomyocytes by maternal anti-Ro60 IgG. ELISA was used to quantify ß(2)GPI in umbilical cord blood from 97 neonates exposed to anti-Ro60 Abs, 53 with cardiac NL and 44 with no cardiac disease. ß(2)GPI levels were significantly lower in neonates with cardiac NL. Plasmin-mediated cleavage of ß(2)GPI prevented binding to Ro60 and promoted the formation of pathogenic anti-Ro60 IgG-apoptotic cardiomyocyte complexes. In aggregate these data suggest that intact ß(2)GPI in the fetal circulation may be a novel cardioprotective factor in anti-Ro60-exposed pregnancies.

Phases and Natural History of Sjögren's Disease: A New Model for an Old Disease?

Sjögren's disease (SjD) is an archetypal and heterogenous autoimmune disorder that is characterized by exocrine glandular dysfunction. A proportion of patients develop severe extraglandular manifestations, such as cryoglobulinemia, and have an increased risk of lymphoma, both of which can adversely affect quality of life and occasionally mortality. As with most autoimmune disorders, the pathogenesis is poorly understood and difficult to predict, and, frustratingly, there is a lack of targeted therapies to cure this disease. We review the disease manifestations of SjD and propose a staged model for understanding the evolution of pathology. In longitudinal studies, most patients remain relatively stable in terms of their laboratory and clinical parameters. However, in the setting of various risk factors, a proportion of patients develop severe symptoms and/or lymphoma. We discuss potential underlying mechanisms for disease progression and the strengths and limitations of using a staged model to correlate the pathogenesis and spectrum of manifestations in SjD. Ultimately, understanding how and why some patients remain relatively stable, whereas others progress and develop florid systemic disease and a fraction develop lymphoma, is key to developing preventative and therapeutic treatments.

Isolated anti-Ro52 identifies a severe subset of Sjögren's syndrome patients.

Introduction: Serum autoantibodies targeting the SSA/Ro proteins are a key component of the classification criteria for the diagnosis of Sjögren's syndrome (SS). Most patients' serum reacts with both Ro60 and Ro52 proteins. Here we compare the molecular and clinical characteristics of patients diagnosed with SS with anti-Ro52 in the presence or absence of anti-Ro60/La autoantibodies. Methods: A cross-sectional study was performed. Patients in the SS biobank at Westmead Hospital (Sydney, Australia) that were positive for anti-Ro52 were included and stratified based on the absence (isolated) or presence (combined) of anti-Ro60/La, measured by line immunoassay. We examined clinical associations and the serological and molecular characteristics of anti-Ro52 using ELISA and mass spectrometry in serological groups. Results: A total of 123 SS patients were included for study. SS patients with isolated anti-Ro52 (12%) identified a severe serological subset characterised by higher disease activity, vasculitis, pulmonary involvement, rheumatoid factor (RhF) and cryoglobulinaemia. Serum antibodies reacting with Ro52 in the isolated anti-Ro52 subset displayed less isotype switching, less immunoglobulin variable region subfamily usage and a lower degree of somatic hypermutation than the combined anti-Ro52 subset. Conclusions: In our cohort of SS patients, isolated anti-Ro52 represents a severe subset of SS, and is associated with the presence of cryoglobulinaemia. We therefore provide clinical relevance to the stratification of SS patients by their sero-reactivities. It is possible that the autoantibody patterns may be immunological epiphenomena of the underlying disease process, and further work is required to unearth the mechanisms of the differential clinical phenotypes.

Broad immunity to SARS-CoV-2 variants of concern mediated by a SARS-CoV-2 receptor-binding domain protein vaccine.

BACKGROUND: The SARS-CoV-2 global pandemic has fuelled the generation of vaccines at an unprecedented pace and scale. However, many challenges remain, including: the emergence of vaccine-resistant mutant viruses, vaccine stability during storage and transport, waning vaccine-induced immunity, and concerns about infrequent adverse events associated with existing vaccines. METHODS: We report on a protein subunit vaccine comprising the receptor-binding domain (RBD) of the ancestral SARS-CoV-2 spike protein, dimerised with an immunoglobulin IgG1 Fc domain. These were tested in conjunction with three different adjuvants: a TLR2 agonist R4-Pam2Cys, an NKT cell agonist glycolipid α-Galactosylceramide, or MF59® squalene oil-in-water adjuvant, using mice, rats and hamsters. We also developed an RBD-human IgG1 Fc vaccine with an RBD sequence of the immuno-evasive beta variant (N501Y, E484K, K417N). These vaccines were also tested as a heterologous third dose booster in mice, following priming with whole spike vaccine. FINDINGS: Each formulation of the RBD-Fc vaccines drove strong neutralising antibody (nAb) responses and provided durable and highly protective immunity against lower and upper airway infection in mouse models of COVID-19. The 'beta variant' RBD vaccine, combined with MF59® adjuvant, induced strong protection in mice against the beta strain as well as the ancestral strain. Furthermore, when used as a heterologous third dose booster, the RBD-Fc vaccines combined with MF59® increased titres of nAb against other variants including alpha, delta, delta+, gamma, lambda, mu, and omicron BA.1, BA.2 and BA.5. INTERPRETATION: These results demonstrated that an RBD-Fc protein subunit/MF59® adjuvanted vaccine can induce high levels of broadly reactive nAbs, including when used as a booster following prior immunisation of mice with whole ancestral-strain spike vaccines. This vaccine platform offers a potential approach to augment some of the currently approved vaccines in the face of emerging variants of concern, and it has now entered a phase I clinical trial. FUNDING: This work was supported by grants from the Medical Research Future Fund (MRFF) (2005846), The Jack Ma Foundation, National Health and Medical Research Council of Australia (NHMRC; 1113293) and Singapore National Medical Research Council (MOH-COVID19RF-003). Individual researchers were supported by an NHMRC Senior Principal Research Fellowship (1117766), NHMRC Investigator Awards (2008913 and 1173871), Australian Research Council Discovery Early Career Research Award (ARC DECRA; DE210100705) and philanthropic awards from IFM investors and the A2 Milk Company.

Interim results from a phase I randomized, placebo-controlled trial of novel SARS-CoV-2 beta variant receptor-binding domain recombinant protein and mRNA vaccines as a 4th dose booster.

BACKGROUND: SARS-CoV-2 booster vaccination should ideally enhance protection against variants and minimise immune imprinting. This Phase I trial evaluated two vaccines targeting SARS-CoV-2 beta-variant receptor-binding domain (RBD): a recombinant dimeric RBD-human IgG1 Fc-fusion protein, and an mRNA encoding a membrane-anchored RBD. METHODS: 76 healthy adults aged 18-64 y, previously triple vaccinated with licensed SARS-CoV-2 vaccines, were randomised to receive a 4th dose of either an adjuvanted (MF59®, CSL Seqirus) protein vaccine (5, 15 or 45 µg, N = 32), mRNA vaccine (10, 20, or 50 µg, N = 32), or placebo (saline, N = 12) at least 90 days after a 3rd boost vaccination or SARS-CoV-2 infection. Bleeds occurred on days 1 (prior to vaccination), 8, and 29. CLINICALTRIALS: govNCT05272605. FINDINGS: No vaccine-related serious or medically-attended adverse events occurred. The protein vaccine reactogenicity was mild, whereas the mRNA vaccine was moderately reactogenic at higher dose levels. Best anti-RBD antibody responses resulted from the higher doses of each vaccine. A similar pattern was seen with live virus neutralisation and surrogate, and pseudovirus neutralisation assays. Breadth of immune response was demonstrated against BA.5 and more recent omicron subvariants (XBB, XBB.1.5 and BQ.1.1). Binding antibody titres for both vaccines were comparable to those of a licensed bivalent mRNA vaccine. Both vaccines enhanced CD4+ and CD8+ T cell activation. INTERPRETATION: There were no safety concerns and the reactogenicity profile was mild and similar to licensed SARS-CoV-2 vaccines. Both vaccines showed strong immune boosting against beta, ancestral and omicron strains. FUNDING: Australian Government Medical Research Future Fund, and philanthropies Jack Ma Foundation and IFM investors.

Pathogenicity and proteomic signatures of autoantibodies to Ro and La.

Ro/SSA and La/SSB comprise a linked set of autoantigens that are clinically important members of the extractable nuclear antigen family and key translational biomarkers for lupus and primary Sjögren's syndrome. Autoantibodies directed against the Ro60 and La polypeptide components of the Ro/La ribonucleoprotein complex, and the structurally unrelated Ro52 protein, mediate tissue damage in the neonatal lupus syndrome, a model of passively acquired autoimmunity in humans in which the most serious manifestation is congenital heart block (CHB). Recent studies have concentrated on two distinct pathogenic mechanisms by which maternal anti-Ro/La autoantibodies can cause CHB: by forming immune complexes with apoptotic cells in developing fetal heart; and/or by acting as functional autoantibodies that cross-react with and inhibit calcium channels. Although the precise role of the individual autoantibodies is yet to be settled, maternal anti-Ro60 and anti-Ro52 remain the most likely culprits. This article will discuss the molecular pathways that culminate in the development of CHB, including the recent discovery of ß2 glycoprotein I as a protective factor, and present a proteomic approach based on direct mass spectrometric sequencing, which may give a more representative snapshot of the idiotype repertoire of these autoantibodies than genomic-based technologies.

Secreted human Ro52 autoantibody proteomes express a restricted set of public clonotypes.

Long-lived secreted autoantibody responses in systemic autoimmunity are generally regarded to be polyclonal and to express a diverse B-cell repertoire. Here, we have used a proteomic approach based on de novo sequencing to determine the clonality and V region structures of human autoantibodies directed against a prototypic systemic autoantigen, Ro52 (TRIM21). Remarkably, anti-Ro52 autoantibodies from patients with primary Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis or polymyositis were restricted to two IgG1 kappa clonotypes that migrated as a single species on isoelectric focusing; shared a common light chain paired with one of two closely-related heavy chains; and were public in unrelated patients. Targeted mass spectrometry using these uniquely mutated V region peptides as surrogates detected anti-Ro52 autoantibodies in human sera with high sensitivity and specificity compared with traditional ELISA. Mass spectrometry-based detection of specific autoantibody motifs provides a powerful new tool for analysis of humoral autoimmunity.

Antibodies interfering with the type 3 muscarinic receptor pathway inhibit gastrointestinal motility and cholinergic neurotransmission in Sjögren's syndrome.

OBJECTIVE: In primary Sjögren's syndrome (SS), impairment of the gastrointestinal (GI) tract is common, and includes reduced esophageal motor function, delayed gastric emptying, and abnormalities in colonic motility; the pathogenesis is as yet unknown. We undertook this study to investigate the role of functional antibodies to the type 3 muscarinic receptor (M3R) in GI dysfunction associated with primary SS. METHODS: Muscle strip and whole-organ functional assays were used to determine whether IgG with anti-M3R activity from patients with primary SS disrupted neurotransmission in tissue from throughout the mouse GI tract. Specificity of the autoantibody for the M3R was determined using knockout mice that were deficient in the expression of muscarinic receptor subtypes. RESULTS: Functional antibodies to the M3R inhibited neuronally mediated contraction of smooth muscle from throughout the GI tract and disrupted complex contractile motility patterns in the colon. The autoantibodies were not active on tissue from mice that lacked the M3R, providing compelling evidence of the direct interaction of patient autoantibodies with the M3R. CONCLUSION: Our results indicate that anti-M3R autoantibodies have the potential to mediate multiple dysfunctions of the GI tract in primary SS, ranging from reduced esophageal motor activity to altered colonic motility. We hypothesize that altered GI motility forms part of a broader autonomic dysfunction mediated by pathogenic anti-M3R autoantibodies in primary SS.

Molecular signature of a public clonotypic autoantibody in primary Sjögren's syndrome: a "forbidden" clone in systemic autoimmunity.

OBJECTIVE: This study was undertaken to determine the molecular characteristics of clonotypic autoantibodies in the sera of patients with primary Sjögren's syndrome (SS). This characterization is hampered by the presence of mixed anti-Ro/La specificities that may conceal clonotypic species. In order to narrow clonotypic diversity, a positive selection step was performed on a peg-like determinant of Ro 60 (termed Ro 60-peg) prior to analysis of the autoantibody proteome. METHODS: Monospecific anti-Ro 60-peg IgG were isolated by affinity purification from the sera of 7 patients with primary SS and anti-Ro/La and subjected to 2-dimensional gel electrophoresis and high-resolution orbitrap mass spectrometric sequencing. V regions of heavy and light chains were analyzed by combined database and de novo amino acid sequencing. RESULTS: Proteomic analysis revealed a Ro 60-peg-specific IgG1κ-restricted monoclonal autoantibody that was present in the sera of all patients and specified by a V(H) 3-23 heavy chain paired with a V(κ) 3-20 light chain. The public anti-Ro 60-peg clonotype was specified further by common mutations in the heavy-chain and light-chain complementarity-determining regions. Titers and relative affinities of clonotypic IgG did not vary over the course of the disease. CONCLUSION: The expression of a Ro 60-reactive public B cell clonotype in a subset of patients with primary SS as a long-lived, class-switched circulating autoantibody implies a common breach of B cell tolerance checkpoints in these patients. The unique heavy chain/light chain signature opens the possibility of tracking the development of a "forbidden" clone against a bona fide systemic autoantigen in human disease.

Validation of a commercial line blot for the detection of serum anti-Ro60 autoantibodies.

Serum anti-Ro60 is one the most frequently encountered autoantibodies in the diagnostic immunopathology laboratory and in clinical practice. A large variety of assays are available to detect this including the popular multiplex line immunoblot (IB) assay. We evaluated the analytical performance of the IB for anti-Ro60 detection, using the counterimmunoelectrophoresis (CIEP) method as the 'gold standard'. We also undertook a survey of international laboratories, who use the IB, about their reporting practices for anti-Ro60. Using the manufacturer's reported cut-off of 15 units, the IB has an analytical sensitivity of 90.9% and specificity of 99.3% for anti-Ro60 detection. The optimal cut-off to balance sensitivity and specificity was determined to be 5 units with a sensitivity of 100% and specificity of 97.4%. Most laboratories use the manufacturer's specified cut-off (15 units) when determining a positive anti-Ro60 result. Whilst the commercial IB generally performs well, laboratorians need to be mindful of the limitations of IB in detecting antibodies that recognise conformational epitopes and what cut-offs they use. A vast majority of laboratories could potentially miss detection of this clinically important autoantibody.