Remote Activation of a Latent Epitope in an Autoantigen Decoded With Simulated B-Factors

Mutants of a catalytically inactive variant of Proteinase 3 (PR3)—iPR3-Val¹⁰³ possessing a Ser195Ala mutation relative to wild-type PR3-Val¹⁰³—offer insights into how autoantigen PR3 interacts with antineutrophil cytoplasmic antibodies (ANCAs) in granulomatosis with polyangiitis (GPA) and whether such interactions can be interrupted. Here we report that iHm5-Val¹⁰³, a triple mutant of iPR3-Val¹⁰³, bound a monoclonal antibody (moANCA518) from a GPA patient on an epitope remote from the mutation sites, whereas the corresponding epitope of iPR3-Val¹⁰³ was latent to moANCA518. Simulated B-factor analysis revealed that the binding of moANCA518 to iHm5-Val¹⁰³ was due to increased main-chain flexibility of the latent epitope caused by remote mutations, suggesting rigidification of epitopes with therapeutics to alter pathogenic PR3·ANCA interactions as new GPA treatments.

Immunomodulatory receptors are differentially expressed in B and T cell subsets relevant to autoimmune disease

Inhibitory cell-surface receptors on lymphocytes, often called immune checkpoints, are powerful targets for cancer therapy. Despite their direct involvement in autoimmune pathology, they are currently not exploited therapeutically for autoimmune diseases. Understanding the expression pattern of these receptors in health and disease is essential for targeted drug design. Here, we designed three 23-colour flow cytometry panels for peripheral-blood T cells, including 15 lineage-defining markers and 21 immunomodulatory cell-surface receptors, and a 22-marker panel for B cells. Blood samples from healthy individuals, multiple sclerosis (MS), and lupus (SLE) patients were included in the study. Several receptors show differential expression on regulatory T cells (Treg) compared to T helper (Th) 1 and Th17 cells, and functional relevance of this difference could be shown for BTLA and CD5. Unbiased multiparametric analysis revealed a subset of activated CD8⁺ T cells and a subset of unswitched memory B cells that are diminished in MS and SLE, respectively.

Dysregulated integrin αVβ3 and CD47 signaling promotes joint inflammation, cartilage breakdown, and progression of osteoarthritis

Osteoarthritis (OA) is the leading cause of joint failure, yet the underlying mechanisms remain elusive, and no approved therapies that slow progression exist. Dysregulated integrin function was previously implicated in OA pathogenesis. However, the roles of integrin αVβ3 and the integrin-associated receptor CD47 in OA remain largely unknown. Here, transcriptomic and proteomic analyses of human and murine osteoarthritic tissues revealed dysregulated expression of αVβ3, CD47, and their ligands. Using genetically deficient mice and pharmacologic inhibitors, we showed that αVβ3, CD47, and the downstream signaling molecules Fyn and FAK are crucial to OA pathogenesis. MicroPET/CT imaging of a mouse model showed elevated ligand-binding capacities of integrin αVβ3 and CD47 in osteoarthritic joints. Further, our in vitro studies demonstrated that chondrocyte breakdown products, derived from articular cartilage of individuals with OA, induced αVβ3/CD47-dependent expression of inflammatory and degradative mediators, and revealed the downstream signaling network. Our findings identify a central role for dysregulated αVβ3 and CD47 signaling in OA pathogenesis and suggest that activation of αVβ3 and CD47 signaling in many articular cell types contributes to inflammation and joint destruction in OA. Thus, the data presented here provide a rationale for targeting αVβ3, CD47, and their signaling pathways as a disease-modifying therapy.

Neutrophil extracellular traps, B cells, and type I interferons contribute to immune dysregulation in hidradenitis suppurativa

Hidradenitis suppurativa (HS), also known as acne inversa, is an incapacitating skin disorder of unknown etiology manifested as abscess-like nodules and boils resulting in fistulas and tissue scarring as it progresses. Given that neutrophils are the predominant leukocyte infiltrate in HS lesions, the role of neutrophil extracellular traps (NETs) in the induction of local and systemic immune dysregulation in this disease was examined. Immunofluorescence microscopy was performed in HS lesions and detected the prominent presence of NETs. NET complexes correlated with disease severity, as measured by Hurley staging. Neutrophils from the peripheral blood of patients with HS peripheral also displayed enhanced spontaneous NET formation when compared to healthy control neutrophils. Sera from patients recognized antigens present in NETs and harbored increased antibodies reactive to citrullinated peptides. B cell dysregulation, as evidenced by elevated plasma cells and IgG, was observed in the circulation and skin from patients with HS. Peptidylarginine deiminases (PADs) 1 to 4, enzymes involved in citrullination, were differentially expressed in HS skin, when compared to controls, in association with enhanced tissue citrullination. NETs in HS skin coexisted with plasmacytoid dendritic cells, in association with a type I interferon (IFN) gene signature. Enhanced NET formation and immune responses to neutrophil and NET-related antigens may promote immune dysregulation and contribute to inflammation. This, along with evidence of up-regulation of the type I IFN pathway in HS skin, suggests that the innate immune system may play important pathogenic roles in this disease.

Antigen-specific tolerance to self-antigens in protein replacement therapy, gene therapy and autoimmunity

Trials of antigen-specific tolerance have been undertaken in the clinic for over fifty years and the results of these antigen-specific clinical trials are described in this review. Antigen-specific tolerization of the immune system in protein replacement therapy for hemophilia A is an accepted treatment. Clinical trials are ongoing for autoimmune conditions such as type 1 diabetes, multiple sclerosis, neuromyelitis optica, and rheumatoid arthritis with various antigen-specific strategies. Trials for tolerization in celiac disease aim for antigen specific tolerance to gluten, an environmental trigger, which may then halt the progression to autoimmunity targeting a self-antigen, tissue transglutaminase. Although many promising approaches have been demonstrated in pre-clinical models, this review will focus primarily on clinical trials of antigen-specific tolerance that have been taken to the clinic and with initial results reported in the peer reviewed literature. A separate article on approaches with CAR-T cells appears in this volume.

Platelet-Rich Plasma (PRP) From Older Males With Knee Osteoarthritis Depresses Chondrocyte Metabolism and Upregulates Inflammation

There is intense clinical interest in the potential effects of platelet-rich plasma (PRP) for the treatment of osteoarthritis (OA). This study tested the hypotheses that (i) "lower" levels of the inflammatory mediators (IMs), interleukin-1β, and tumor necrosis factor α (TNF-α) and (ii) "higher" levels of the growth factors (GFs), insulin-like growth factor 1, and transforming growth factor β1 within leukocyte-poor PRP correlate with more favorable chondrocyte and macrophage responses in vitro. Samples were collected from 10 "healthy" young male (23-33 years old) human subjects (H-PRP) and nine older (62-85 years old) male patients with severe knee OA (OA-PRP). The samples were separated into groups of "high" or "low" levels of IM and GF based on multiplex cytokine and enzyme-linked immunosorbent assay data. Three-dimensional (3D) alginate bead chondrocyte cultures and monocyte-derived macrophage cultures were treated with 10% PRP from donors in different groups. Gene expression was analyzed by quantitative polymerase chain reaction. Contrary to our hypotheses, the effect of PRP on chondrocytes and macrophages was mainly influenced by the age and disease status of the PRP donor as opposed to the IM or GF groupings. While H-PRP showed similar effects on expression of chondrogenic markers (Col2a1 and Sox9) as the negative control group (p > 0.05), OA-PRP decreased chondrocyte expression of Col2a1 and Sox-9 messenger RNA by 40% and 30%, respectively (Col2a1, p = 0.015; Sox9, p = 0.037). OA-PRP also upregulated TNF-α and matrix metallopeptidase 9 (p < 0.001) gene expression in macrophages while H-PRP did not. This data suggests that PRP from older individuals with OA contain factors that may suppress chondrocyte matrix synthesis and promote macrophage inflammation in vitro. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1760-1770, 2019.

Histologic and Transcriptional Evidence of Subclinical Synovial Inflammation in Patients With Rheumatoid Arthritis in Clinical Remission

OBJECTIVE

Patients with rheumatoid arthritis (RA) in clinical remission may have subclinical synovial inflammation. This study was undertaken to determine the proportion of patients with RA in remission or with low disease activity at the time of arthroplasty who had histologic or transcriptional evidence of synovitis, and to identify clinical features that distinguished patients as having subclinical synovitis.

METHODS

We compared Disease Activity Score in 28 joints (DAS28) to synovial histologic features in 135 patients with RA undergoing arthroplasty. We also compared DAS28 scores to RNA-Seq data in a subset of 35 patients.

RESULTS

Fourteen percent of patients met DAS28 criteria for clinical remission (DAS28 <2.6), and another 15% met criteria for low disease activity (DAS28 <3.2). Histologic analysis of synovium revealed synovitis in 27% and 31% of samples from patients in remission and patients with low disease activity, respectively. Patients with low disease activity and synovitis also exhibited increased C-reactive protein (CRP) (P = 0.0006) and increased anti-cyclic citrullinated peptide (anti-CCP) antibody levels (P = 0.03) compared to patients without synovitis. Compared to patients with a "low inflammatory synovium" subtype, 183 genes were differentially expressed in the synovium of patients with subclinical synovitis. The majority of these genes (86%) were also differentially expressed in the synovium of patients with clinically active disease (DAS28 ≥3.2).

CONCLUSION

Thirty-one percent of patients with low clinical disease activity exhibited histologic evidence of subclinical synovitis, which was associated with increased CRP and anti-CCP levels. Our findings suggest that synovial gene expression signatures of clinical synovitis are present in patients with subclinical synovitis.

IgE-mediated mast cell activation promotes inflammation and cartilage destruction in osteoarthritis

Osteoarthritis is characterized by articular cartilage breakdown, and emerging evidence suggests that dysregulated innate immunity is likely involved. Here, we performed proteomic, transcriptomic, and electron microscopic analyses to demonstrate that mast cells are aberrantly activated in human and murine osteoarthritic joint tissues. Using genetic models of mast cell deficiency, we demonstrate that lack of mast cells attenuates osteoarthritis in mice. Using genetic and pharmacologic approaches, we show that the IgE/FcεRI/Syk signaling axis is critical for the development of osteoarthritis. We find that mast cell-derived tryptase induces inflammation, chondrocyte apoptosis, and cartilage breakdown. Our findings demonstrate a central role for IgE-dependent mast cell activation in the pathogenesis of osteoarthritis, suggesting that targeting mast cells could provide therapeutic benefit in human osteoarthritis.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Direct Diagnostic Tests for Lyme Disease

Borrelia burgdorferi was discovered to be the cause of Lyme disease in 1983, leading to seroassays. The 1994 serodiagnostic testing guidelines predated a full understanding of key B. burgdorferi antigens and have a number of shortcomings. These serologic tests cannot distinguish active infection, past infection, or reinfection. Reliable direct-detection methods for active B. burgdorferi infection have been lacking in the past but are needed and appear achievable. New approaches have effectively been applied to other emerging infections and show promise in direct detection of B. burgdorferi infections.

Exogenous micro-RNA and antagomir modulate osteogenic gene expression in tenocytes

Tendinopathy is a common and disabling condition that is difficult to treat. The pathomolecular events behind tendinopathy remain uncertain. Micro-RNAs (miRNAs, miRs) are short non-coding RNAs that regulate gene expression and may play a role in tendinopathy development. Tenocytes were obtained from human patellar tendons in patients undergoing anterior cruciate ligament (ACL) reconstruction. Micro-RNA mimics and antagomirs for miR-30d, 26a, and 29a were separately transfected into tenocyte culture. Gene expression for scleraxis, collagen 1 alpha 1 (COL1A1), collagen 3 alpha 1 (COL3A1), interleukin-1-beta (IL-1β), interleukin-6 (IL-6), bone morphogenic protein 2 (BMP2), bone morphogenic protein 12 (BMP12), and osteocalcin was determined for each miRNA mimic and antagomir transfection using real-time quantitative PCR (qPCR). The results showed that exogenous miR-29a downregulated BMP2 and BMP12, while miR-26a and miR-30d did not have a significant effect on tenocyte gene expression. These findings suggest miR-29a contributes to tendon homeostasis and can serve as a potential therapeutic target in treating tendinopathy.

Prefoldin 5 and Anti-prefoldin 5 Antibodies as Biomarkers for Uveitis in Ankylosing Spondylitis

Objective: Uveitis is the most common extra-articular manifestation of ankylosing spondylitis (AS), for which no diagnostic biomarkers have been identified. This study was conducted to identify biomarker for uveitis in AS.

Methods: To identify autoantibodies associated with uveitis in AS, we performed human protein microarray analysis using sera derived from various autoimmune diseases and ELISA analysis of sera derived from AS and rheumatoid arthritis patients. In the curdlan-induced SKG mice model, ophthalmic examination was performed at week 8 post-immunization and histologic examination of the ocular lesions performed at week 16 post-immunization. Serum levels of target antibodies were assessed at various time-points. To evaluate the functional role of specific autoantibodies, an in vitro apoptosis assay using ARPE-19 cells was performed.

Results: Reactivity against prefoldin subunit 5 (PFDN5) was identified in AS with uveitis. Levels of anti-PFDN5 antibodies and PFDN5 in sera from AS with uveitis patients were significantly higher than those in AS without uveitis. At week 8, half of curdlan-treated SKG mice developed anterior uveitis, while all of them developed histologically confirmed uveitis at week 16. The levels of anti-PFDN5 antibodies increased over time in the sera of curdlan-treated SKG mice along with increased expression of PFDN5 and apoptosis in the ocular lesions. Knockdown of PFDN5 in ARPE19 cells resulted in increased apoptosis, suggesting a protective role of PFDN5 against cell death in uveitis.

Conclusion: AS patients with uveitis have increased levels of anti-PFDN5 antibodies, and our findings suggest that anti-PFDN5 antibodies could provide a biomarker for uveitis in AS.

Affinity Maturation of the Anti-Citrullinated Protein Antibody Paratope Drives Epitope Spreading and Polyreactivity in Rheumatoid Arthritis

OBJECTIVE

Anti-citrullinated protein antibodies (ACPAs) are a hallmark of rheumatoid arthritis (RA). While epitope spreading of the serum ACPA response is believed to contribute to RA pathogenesis, little is understood regarding how this phenomenon occurs. This study was undertaken to analyze the antibody repertoires of individuals with RA to gain insight into the mechanisms leading to epitope spreading of the serum ACPA response in RA.

METHODS

Plasmablasts from the blood of 6 RA patients were stained with citrullinated peptide tetramers to identify ACPA-producing B cells by flow cytometry. Plasmablasts were single-cell sorted and sequenced to obtain antibody repertoires. Sixty-nine antibodies were recombinantly expressed, and their anticitrulline reactivities were characterized using a cyclic citrullinated peptide enzyme-linked immuosorbent assay and synovial antigen arrays. Thirty-six mutated antibodies designed either to represent ancestral antibodies or to test paratope residues critical for binding, as determined from molecular modeling studies, were also tested for anticitrulline reactivities.

RESULTS

Clonally related monoclonal ACPAs and their shared ancestral antibodies each exhibited differential reactivity against citrullinated antigens. Molecular modeling identified residues within the complementarity-determining region loops and framework regions predicted to be important for citrullinated antigen binding. Affinity maturation resulted in mutations of these key residues, which conferred binding to different citrullinated epitopes and/or increased polyreactivity to citrullinated epitopes.

CONCLUSION

These results demonstrate that the different somatic hypermutations accumulated by clonally related B cells during affinity maturation alter the antibody paratope to mediate epitope spreading and polyreactivity of the ACPA response in RA, suggesting that these may be key properties that likely contribute to the pathogenicity of ACPAs.

Response to comment on "Synovial fibroblast-neutrophil interactions promote pathogenic adaptive immunity in rheumatoid arthritis"

The citrullinome cargo in neutrophil extracellular traps varies according to disease condition and stimulation conditions.

Higher C6 enzyme immunoassay index values correlate with a diagnosis of noncutaneous Lyme disease

The correlation between the Food and Drug Administration-cleared C6 enzyme immunoassay (EIA) C6 index values and a diagnosis of Lyme disease has not been examined. We used pooled patient-level data from 5 studies of adults and children with Lyme disease and control subjects who were tested with the C6 EIA. We constructed a receiver operating characteristic curve using regression clustered by study and measured the area under the curve (AUC) to examine the accuracy of the C6 index values in differentiating between patients with noncutaneous Lyme disease and control subjects. In the 4821 included patients, the C6 index value had excellent ability to distinguish between patients with noncutaneous Lyme disease and control subjects [AUC 0.99; 95% confidence interval (CI) 0.99-1.00]. An index value cut point of ≥3.0 had a sensitivity of 90.9% (95% CI, 87.8-93.3) and specificity of 99.0% (95% CI, 98.6-99.2%) for Lyme disease.

Affinity Maturation Drives Epitope Spreading and Generation of Proinflammatory Anti-Citrullinated Protein Antibodies in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by the presence of anti-citrullinated protein antibodies (ACPAs); nevertheless, the origin, specificity, and functional properties of ACPAs remain poorly understood. The aim of this study was to characterize the evolution of ACPAs by sequencing the plasmablast antibody repertoire at serial time points in patients with established RA.

METHODS

Blood samples were obtained at up to 4 serial time points from 8 individuals with established RA who were positive for ACPAs by the anti-cyclic citrullinated peptide test. CD19+CD3-IgD-CD14-CD20-CD27+CD38++ plasmablasts were isolated by single-cell sorting and costained with citrullinated peptide tetramers to identify ACPA-expressing plasmablasts. Cell-specific oligonucleotide barcodes were utilized, followed by large-scale sequencing and bioinformatics analysis, to obtain error-corrected, paired heavy- and light-chain antibody gene sequences for each B cell.

RESULTS

Bioinformatics analysis revealed 170 persistent plasmablast lineages in the RA blood, of which 19% included multiple isotypes. Among IgG- and IgA-expressing plasmablasts, significantly more IgA-expressing than IgG-expressing persistent lineages were observed (P < 0.01). Shared complementarity-determining region 3 sequence motifs were identified across subjects. A subset of the plasmablast lineages included members derived from later time points with divergent somatic hypermutations that encoded antibodies that bind an expanded set of citrullinated antigens. Furthermore, these recombinant, differentially mutated plasmablast antibodies formed immune complexes that stimulated higher macrophage production of tumor necrosis factor (TNF) compared to antibodies representing earlier time point-derived lineage members that were less mutated.

CONCLUSION

These findings demonstrate that established RA is characterized by a persistent IgA ACPA response that exhibits ongoing affinity maturation. This observation suggests the presence of a persistent mucosal antigen that continually promotes the production of IgA plasmablasts and their affinity maturation and epitope spreading, thus leading to the generation of ACPAs that bind additional citrullinated antigens and more potently stimulate macrophage production of TNF.

T Cell-Dependent Affinity Maturation and Innate Immune Pathways Differentially Drive Autoreactive B Cell Responses in Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by the activation of B cells that produce anti-citrullinated protein antibodies (ACPAs) and rheumatoid factors (RFs), but the mechanisms by which tolerance is broken in these B cells remain incompletely understood. We undertook this study to investigate whether ACPA+ and RF+ B cells break tolerance through distinct molecular mechanisms.

METHODS

We developed antigen-tetramers to isolate ACPA+ and RF+ B cells and performed single-cell RNA sequencing on 2,349 B cells from 6 RA patients and 1 healthy donor to analyze their immunoglobulin repertoires and transcriptional programs. Prominent immunoglobulins were expressed as monoclonal antibodies and tested for autoantigen reactivity.

RESULTS

ACPA+ and RF+ B cells were enriched in the peripheral blood of RA patients relative to healthy controls. Characterization of patient-derived monoclonal antibodies confirmed ACPA and RF targeting of tetramer-specific B cells at both antigen-inexperienced and affinity-matured B cell stages. ACPA+ B cells used more class-switched isotypes and exhibited more somatic hypermutations relative to RF+ B cells, and these differences were accompanied by down-regulation of CD72 and up-regulation of genes that promote class-switching and T cell-dependent responses. In contrast, RF+ B cells expressed transcriptional programs that stimulate rapid memory reactivation through multiple innate immune pathways. Coexpression analysis revealed that ACPA+ and RF+ B cell-enriched genes belong to distinct transcriptional regulatory networks.

CONCLUSION

Our findings suggest that ACPA+ and RF+ B cells are imprinted with distinct transcriptional programs, which suggests that these autoantibodies associated with increased inflammation in RA arise from 2 different molecular mechanisms.

Rheumatoid arthritis and the mucosal origins hypothesis: protection turns to destruction

Individuals at high risk of developing seropositive rheumatoid arthritis (RA) can be identified for translational research and disease prevention studies through the presence of highly informative and predictive patterns of RA-related autoantibodies, especially anti-citrullinated protein antibodies (ACPAs), in the serum. In serologically positive individuals without arthritis, designated ACPA positive at risk, the presence of mucosal inflammatory processes associated with the presence of local ACPA production has been demonstrated. In other at-risk populations, local RA-related autoantibody production is present even in the absence of serum autoantibodies. Additionally, a proportion of at-risk individuals exhibit local mucosal ACPA production in the lung, as well as radiographic small-airway disease, sputum hypercellularity and increased neutrophil extracellular trap formation. Other mucosal sites in at-risk individuals also exhibit autoantibody production, inflammation and/or evidence of dysbiosis. As the proportion of individuals who exhibit such localized inflammation-associated ACPA production is substantially higher than the likelihood of an individual developing future RA, this finding raises the hypothesis that mucosal ACPAs have biologically relevant protective roles. Identifying the mechanisms that drive both the generation and loss of externally focused mucosal ACPA production and promote systemic autoantibody expression and ultimately arthritis development should provide insights into new therapeutic approaches to prevent RA.

Robust B Cell Responses Predict Rapid Resolution of Lyme Disease

Lyme disease (Borrelia burgdorferi infection) is increasingly recognized as a significant source of morbidity worldwide. Here, we show that blood plasmablasts and CD27⁻ memory B cells are elevated in untreated Lyme disease, with higher plasmablast levels associated with more rapid resolution of clinical symptoms. Stronger serum reactivity to surface proteins and peptides from B. burgdorferi was also associated with faster resolution of clinical symptoms. Through molecular identifier-enabled antibody heavy-chain sequencing of bulk B cells and single-cell paired-chain antibody sequencing of blood plasmablasts, we characterized immunoglobulin gene usage patterns specific to B. burgdorferi infection. Recombinantly expressed antibodies from expanded lineages bound B. burgdorferi antigens, confirming that these clones are driven by the infection. Furthermore, recombinant sequence-derived antibodies were functional, inhibiting growth of B. burgdorferi in vitro. Elevations and clonal expansion of blood plasmablasts were associated with rapid return to health, while poor plasmablast responses were associated with a longer duration of symptoms following treatment. Plasmablasts induced by B. burgdorferi infection showed preferential antibody gene segment usage, while bulk sequencing of total B cells revealed convergent CDR3 motifs specific to B. burgdorferi-infected patients. Our results show that robust plasmablast responses encoding Bb-static antibodies are associated with more rapid resolution of Lyme disease, and these antibodies could provide the basis for next-generation therapeutics for Lyme disease.

Methods for high-dimensional analysis of cells dissociated from cryopreserved synovial tissue

Background

Detailed molecular analyses of cells from rheumatoid arthritis (RA) synovium hold promise in identifying cellular phenotypes that drive tissue pathology and joint damage. The Accelerating Medicines Partnership RA/SLE Network aims to deconstruct autoimmune pathology by examining cells within target tissues through multiple high-dimensional assays. Robust standardized protocols need to be developed before cellular phenotypes at a single cell level can be effectively compared across patient samples.

Methods

Multiple clinical sites collected cryopreserved synovial tissue fragments from arthroplasty and synovial biopsy in a 10% DMSO solution. Mechanical and enzymatic dissociation parameters were optimized for viable cell extraction and surface protein preservation for cell sorting and mass cytometry, as well as for reproducibility in RNA sequencing (RNA-seq). Cryopreserved synovial samples were collectively analyzed at a central processing site by a custom-designed and validated 35-marker mass cytometry panel. In parallel, each sample was flow sorted into fibroblast, T-cell, B-cell, and macrophage suspensions for bulk population RNA-seq and plate-based single-cell CEL-Seq2 RNA-seq.

Results

Upon dissociation, cryopreserved synovial tissue fragments yielded a high frequency of viable cells, comparable to samples undergoing immediate processing. Optimization of synovial tissue dissociation across six clinical collection sites with ~ 30 arthroplasty and ~ 20 biopsy samples yielded a consensus digestion protocol using 100 μg/ml of Liberase™ TL enzyme preparation. This protocol yielded immune and stromal cell lineages with preserved surface markers and minimized variability across replicate RNA-seq transcriptomes. Mass cytometry analysis of cells from cryopreserved synovium distinguished diverse fibroblast phenotypes, distinct populations of memory B cells and antibody-secreting cells, and multiple CD4⁺ and CD8⁺ T-cell activation states. Bulk RNA-seq of sorted cell populations demonstrated robust separation of synovial lymphocytes, fibroblasts, and macrophages. Single-cell RNA-seq produced transcriptomes of over 1000 genes/cell, including transcripts encoding characteristic lineage markers identified.

Conclusions

We have established a robust protocol to acquire viable cells from cryopreserved synovial tissue with intact transcriptomes and cell surface phenotypes. A centralized pipeline to generate multiple high-dimensional analyses of synovial tissue samples collected across a collaborative network was developed. Integrated analysis of such datasets from large patient cohorts may help define molecular heterogeneity within RA pathology and identify new therapeutic targets and biomarkers.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1631-y) contains supplementary material, which is available to authorized users.

Chemerin 156F, generated by chymase cleavage of prochemerin, is elevated in joint fluids of arthritis patients

BACKGROUND

Chemerin is a chemoattractant involved in immunity that also functions as an adipokine. Chemerin is secreted as an inactive precursor (chem163S), and its activation requires proteolytic cleavages at its C-terminus, involving proteases in coagulation, fibrinolysis, and inflammation. Previously, we found chem158K was the dominant chemerin form in synovial fluids from patients with arthritis. In this study, we aimed to characterize a distinct cleaved chemerin form, chem156F, in osteoarthritis (OA) and rheumatoid arthritis (RA).

METHODS

Purified chem156F was produced in transfected CHO cells. To quantify chem156F in OA and RA samples, we developed a specific ELISA for chem156F using antibody raised against a peptide representing the C-terminus of chem156F.

RESULTS

Ca²⁺ mobilization assays showed that the EC₅₀ values for chem163S, chem156F, and chem157S were 252 ± 141 nM, 133 ± 41.5 nM, and 5.83 ± 2.48 nM, respectively. chem156F was more active than its precursor, chem163S, but very much less potent than chem157S, the most active chemerin form. Chymase was shown to be capable of cleaving chem163S at a relevant rate. Using the chem156F ELISA we found a substantial amount of chem156F present in synovial fluids from patients with OA and RA, 24.06 ± 5.51 ng/ml and 20.35 ± 5.19 ng/ml (mean ± SEM, n = 25) respectively, representing 20% of total chemerin in OA and 76.7% of chemerin in RA synovial fluids.

CONCLUSIONS

Our data show that chymase cleavage of chem163S to partially active chem156F can be found in synovial fluids where it can play a role in modulation of the inflammation in joints.

Abstract 3966: Mining the cancer immuno-responsome: The identification of functional antitumor antibodies from patients receiving checkpoint inhibitors

Background: The role of B cells and antibodies in anticancer immune responses may correlate with improved prognosis in several types of cancer. Indeed, tumor-reactive antibodies are detected in the blood of cancer patients, tumor-infiltrating B cells have been shown to produce tumor-reactive antibodies, and tumor-reactive antibodies can cause tumor regression in several mouse models. Taken together, these observations support further identification, isolation and characterization of antitumor antibodies from patients demonstrating effective anticancer responses and defining the cognate targets and mechanisms whereby they contribute to tumor control.

Methods: We identified cohorts of patients with nonprogressing metastatic cancer who had received checkpoint immunotherapy and isolated their circulating plasmablasts. Antibody heavy and light chain paired sequences were obtained from individual cells using Atreca's Immune Repertoire Capture (IRCTM) technology. The expressed antibodies were then analyzed for their ability to bind to tumor cells as well as tumor tissue and their ability to mediate antitumor activity was explored in syngeneic mouse tumor models.

Results: Elevated plasmablast levels were observed in individuals with nonprogressing metastatic cancer, and analysis of plasmablast antibody sequences revealed clonal families of B cells that persisted over time with hallmarks of affinity maturation and class switching. We also identified antibody sequences with features common to more than one patient, consistent with convergent antibody selection. In particular, one antibody (AB-213) isolated from a NSCLC patient was found to demonstrate binding to unrelated human tumors as well as the mouse EMT6 tumor. When AB-213 was expressed with a mouse IgG2a constant region the chimeric antibody showed efficacy in vivo by reducing tumor volume and increasing survival in Balb/c mice harboring the syngeneic EMT6 model. Antitumor activity of the chimeric antibody was observed to be dose-dependent when administered as monotherapy or in combination with checkpoint inhibitors. We feel, based on these data, AB-213 could become a very important clinical therapeutic.

Citation Format: Gilson Baia, Amy Manning-Bog, Alexander Scholz, Jeff DeFalco, Michael Harbell, Danhui Zhang, Felix Chu, Beatriz Millare, May Sumi, Patricia Zuno, Judevin Lugar Sapugay, Dongkyoon Kim, Yvonne Leung, Shuwei Jiang, Xiaobin Tang, Kevin Williamson, Xiaomu Chen, Sean Carroll, Christine Dowd, Ish Dhawan, Jonathan Benjamin, Gregg Espiritu Santo, Nicole Haaser, Ngan Nguyen, Eldar Giladi, David Minor, Yann Chong Tan, Jeremy B. Sokolove, Lawrence Steinman, Tito Serafini, Guy Cavet, Norman M. Greenberg, Jacob Glanville, Wayne Volkmuth, Daniel E. Emerling, William H. Robinson. Mining the cancer immuno-responsome: The identification of functional antitumor antibodies from patients receiving checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3966.

Abstract 615: Increased somatic hypermutation in the immunoglobulin sequences of melanoma patients who have durable response to checkpoint inhibitor therapy

Patient immune response to tumor can drive profound and durable clinical benefit, but the contribution of antibodies to this benefit is poorly understood. To further our understanding of the role of the humoral response, we compared antibody sequence repertoires of durable responder and non-responder melanoma patients before and during checkpoint inhibitor treatment.

We collected pre- and on-treatment peripheral blood from 26 melanoma patients treated with pembrolizumab (9), ipilimumab (8) or nivolumab+ipilimumab (9). Of the 26 patients, 14 were durable responders (RECIST stable disease, partial response, or complete response for at least 6 months) and 12 were non-responders. We generated natively paired heavy and light chain antibody sequences from individual IgG plasmablasts (CD19+CD20-CD38+CD3-CD14-IgA-IgM-IgD-). Sequences were obtained from a total of 26,725 plasmablasts. These sequences were used to reconstruct lineages (sets of plasmablasts likely derived from a common progenitor B cell) where each lineage shares heavy and light V genes, CDR3 length and 80% sequence similarity in CDR3s.

Durable responders exhibited an increase in somatic hypermutation (SHM) after initiation of treatment. In contrast, no significant change in SHM was observed in non-responders. Higher SHM was also observed in on-treatment repertoires of responders compared with those of non-responders suggesting that T cell checkpoint inhibitors promote activation of humoral immunity in clinical responders. Furthermore, persistent antibody lineages (observed both before and during treatment) showed higher SHM than lineages observed at only a single time point.

Comparison of lineages between patients identified antibodies with high sequence similarity suggesting these antibodies may have arisen from convergent selection, i.e., different patients raising antibodies against shared or similar epitopes. These putative convergent antibodies were enriched in IgG2. IgG2 usage was also higher overall in durable responders than non-responders, even in samples taken prior to treatment. The higher levels of IgG2 observed in responders and in the potentially convergent sets of antibodies suggest that IgG2 antibodies may play a role in effective anti-tumor responses.

In conclusion, our analysis of plasmablast repertoires from melanoma patients suggests that treatment with checkpoint inhibitors promotes SHM in durable responders, and that responder plasmablasts are enriched in IgG2. Moreover, patients make potentially convergent antibodies that are also enriched for the IgG2 subclass. Our observations demonstrate that the humoral immune response is remodeled in patients with anti-tumor responses and support a role for the humoral arm of the immune response in driving clinical benefit in patients treated with checkpoint inhibitors.

Citation Format: Ngan Nguyen, Alusha Mamchak, Mariano Severgnini, Kevin S. Williamson, Xinqi Wu, Elliott F. Drabek, Michael Manos, Xiaomu Chen, Xiaobin Tang, Zoe Amiri, Chantia Carroll, Yvonne Leung, Dongkyoon Kim, Wayne Volkmuth, Norman Greenberg, Daniel Emerling, William H. Robinson, Guy Cavet, F. Stephen Hodi. Increased somatic hypermutation in the immunoglobulin sequences of melanoma patients who have durable response to checkpoint inhibitor therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 615.

Plasma adiponectin levels are associated with circulating inflammatory cytokines in autoantibody positive first-degree relatives of rheumatoid arthritis patients

Background

Extra-articular manifestations of rheumatoid arthritis (RA), potentially due to systemic inflammation, include cardiovascular disease and sarcopenic obesity. Adiponectin, an adipose-derived cytokine, has been implicated in inflammatory processes in RA, but little is known regarding its association with inflammation in a pre-clinical period. Therefore, we investigated whether adiponectin was associated with inflammatory markers in individuals at risk for RA, and whether RA-related autoimmunity modifies these associations.

Methods

We analyzed samples from 144 first-degree relatives (FDRs) of RA probands, of whom 23 were positive for anti-cyclic citrullinated peptide antibody and/or ≥ 2 rheumatoid factor isotypes (IgM, IgG or IgA). We called this phenotype the ‘high risk autoantibody profile (HRP)’ as it has been shown in prior work to be >96% specific for future RA. We measured adiponectin, cytokines, and high-sensitivity C-reactive protein (hsCRP). Using linear mixed effects models, we evaluated interaction between HRP positivity and adiponectin on inflammatory markers, adjusting for age, sex, ethnicity, body mass index, pack-years smoking, and use of cholesterol-lowering medications.

Results

In everyone, adiponectin concentration was inversely associated with hsCRP and IL-1β in adjusted models, where a 1% higher adiponectin was associated with a 26% lower hsCRP (p = 0.04) and a 26% lower IL-1β (p = 0.04). Significant interactions between HRP and adiponectin for associations with GM-CSF, IL-6, and IL-9 were detected in fully adjusted models (p = 0.0006, p = 0.006, p = 0.01, respectively). In HRP positive FDRs but not HRP negative FDRs, a 1% higher adiponectin was associated with 97% higher GM-CSF, 73% higher IL-6, and 54% higher IL-9 concentrations.

Conclusions

Adiponectin associates with inflammatory markers, and these associations differ in individuals with a high-risk autoantibody profile compared with those without. The interaction between adiponectin and autoimmunity warrants further investigation into the potential systemic effects of RA-related autoantibodies and adiponectin on inflammation in the absence of clinically apparent RA.

Combination of anti-citrullinated protein antibodies and rheumatoid factor is associated with increased systemic inflammatory mediators and more rapid progression from preclinical to clinical rheumatoid arthritis

The development of rheumatoid factor (RF) and/or anti-citrullinated protein antibodies (ACPAs) can be observed years prior to clinical diagnosis of rheumatoid arthritis (RA). Nevertheless, the interaction between these two autoantibodies and their combined effect on development of RA is unclear. We measured RF, cytokines, and ACPA subtypes in serial pre-clinical serum samples collected from 83 US veterans who all developed RA. Levels of cytokines and ACPAs were compared between the following groups: anti-cyclic citrullinated peptide (anti-CCP)-/RF- (double negative), anti-CCP+/RF-, anti-CCP-/RF+, or anti-CCP+/RF+ (double-positive). The double-positive subgroup had significantly higher levels of 20 inflammatory cytokines and 29 ACPA reactivities, and the shortest interval, 1.3 years, between the preclinical sample timepoint and diagnosis of RA. Thus, the combined presence of ACPAs and RF is associated with a more rapid progression to RA, suggesting that anti-CCP+/RF+ individuals have a more advanced preclinical disease state and that the onset of RA may be imminent.