Background: ANCA-associated vasculitis (AAV) with proteinase 3 (PR3) ANCA is genetically associated with HLA-DP [1], is often relapsing in nature, and has a predisposition for kidneys, lungs and ear-nose-throat involvement [2]. Despite the presence of PR3+ANCA, indicating CD4+T-cell help in the disease, the knowledge about autoreactive CD4+T cells is scarce. Activated T cells have been shown at site of inflammation [3] and involvement of proinflammatory cytokines in circulation is also reported [4, 5]. Objectives: Identification of autoreactive T cells may help to identify the drivers of the immune responses and chronicity. We therefore aimed to investigate PR3-specific CD4+T-cell responses in peripheral blood of AAV patients with a focus on both phenotype and T-cell receptor (TCR) repertoires. Methods: The study included sixty-six patients: 26 with active PR3 autoantibody+ AAV, 21 with inactive but PR3+ AAV and 19 with inactive PR3- AAV. In-vitro cultures with PR3 protein were established to assess antigen-specific cytokine responses in a 3-color fluorospot assay. Deep immunophenotyping was performed by flow cytometry. Antigen-responsive CD4+ T cells were isolated and single cell TCRαβ sequences were generated and analyzed from PR3+ AAV patients (n=5) using a previously published protocol [6]. Results: PBMCs from AAV patients demonstrated an HLA-DP associated cytokine responses to PR3 stimulation including IFN-γ and IL-10, but not IL-17A. This T-cell autoreactivity was found to be confined to a highly differentiated CD4+ T cell population characterized by perforin and GPR56 expression, implicating a cytotoxic feature of the response. Active disease involved a reduction in expression of several markers associated with cytotoxicity amongst the CD4+GPR56+ T cells. Their frequency was also negatively associated with the doses of prednisolone. A similar phenotype was shared with T cells activated by human cytomegalovirus (HCMV) peptides in the same patient cohort. Single cell sequencing of paired alpha beta T-cell receptors (TCRs) revealed different patterns of gene usage between PR3 and HCMV reactive T cells. Moreover, we could identify shared (public) PR3-reactive T-cell clones between different HLA-DPB1*04:01+ patients. Conclusion: PR3 is an autoantigen which provokes ANCA responses in AAV patients. Our study identified PR3-reactive CD4+ T cells at the level of their phenotype and TCR repertoire. The autoreactive CD4+ T cells, present in both active and inactive disease, implicate chronic antigen exposure and the persistence of long-lived T-cell clones. The presence of public autoreactive clones between HLA-DPB1*04:01+ patients suggests an active role for these cells in pathogenesis of AAV and validates the link with predisposed genotype. References: [1]Lyons PA, Rayner TF, Trivedi S, Holle JU, Watts RA, Jayne DR, et al. Genetically distinct subsets within ANCA-associated vasculitis. New England Journal of Medicine. 2012; 367(3):214-223. [2]Kumar Sharma R, Lövström B, Gunnarsson I, Malmström V. Proteinase 3 autoreactivity in Anti-Neutrophil Cytoplasmic Antibody-associated vasculitis–immunological versus clinical features. Scandinavian Journal of Immunology. 2020:e12958. [3]Wilde B, Thewissen M, Damoiseaux J, van Paassen P, Witzke O, Tervaert JWCJAr, et al. T cells in ANCA-associated vasculitis: what can we learn from lesional versus circulating T cells? 2010; 12(1):204. [4]Hoffmann JC, Patschan D, Dihazi H, Müller C, Schwarze K, Henze E, et al. Cytokine profiling in anti neutrophil cytoplasmic antibody-associated vasculitis: a cross-sectional cohort study. Rheumatology international. 2019; 39(11):1907-1917. [5]Berti A, Warner R, Johnson K, Cornec D, Schroeder D, Kabat B, et al. Circulating Cytokine Profiles and ANCA Specificity in Patients with ANCA-Associated Vasculitis. Arthritis & rheumatology (Hoboken, NJ). 2018; 70(7):1114. [6]Han A, Glanville J, Hansmann L, Davis MM. Linking T-cell receptor sequence to functional phenotype at the single-cell level. Nature biotechnology. 2014; 32(7):684-692. Disclosure of Interests: None declared

Advancing age is a risk factor for treatment-related side effects and mortality in AAV patients treated with cyclophosphamide (CYC) and glucocorticoids (GC) for remission induction. The efficacy and safety of rituximab (RTX) in elderly AAV patients has not been well described.We performed a single center retrospective review of 31 consecutive AAV patients aged 60 or more at the time of RTX use for remission induction. All patients received RTX with GC for remission induction. Four patients received concomitant CYC for a mean duration of 52 days. We evaluated clinical and laboratory variables at diagnosis, rates of complete remission defined as Birmingham Vasculitis Activity Score/Wegener's Granulomatosis (BVAS/WG) = 0 and patient survival, renal survival, infections requiring hospitalization, and vasculitis relapse 24 months following RTX use.Of the 31 patients, 77% were Caucasian, 68% female, mean age was 71 ± 6 years, 58% were MPO ANCA positive, and 42% had relapsing disease. The mean BVAS/WG score entry was 4.4 ± 1.5, 71% had glomerulonephritis (GN) and 10% had alveolar hemorrhage. The mean baseline e-GFR was 40 ± 28 ml/min/1.73 m2. Thirty patients achieved remission with a mean time to remission of 57 ± 27 days. The single patient with refractory vasculitis responded to CYC. The mean prednisone dose at 6 months was 5.6 ± 4 mg. Remission maintenance therapy was started within 12 months of RTX induction in 6 patients (4 with RTX, 1 with azathioprine, and 1 with mycophenolate mofetil). One patient suffered a limited relapse 10 months post RTX use. Among the 22 patients with GN at baseline, 1 developed ESRD. One-year patient survival among 25 patients with at least 1 year of follow-up was 100%. There were no episodes of infusion reaction or leukopenia. There were 3 episodes of bacterial pneumonia, 1 episode of candida pneumonia, and 1 episode of disseminated cutaneous zoster.This study demonstrates that rituximab is effective for remission induction in elderly patients with AAV. Furthermore, we observed a high incidence of infectious complications. Our experience was limited by its retrospective design, and further studies are needed to evaluate the efficacy and safety of RTX in elderly AAV patients.

Keratins (K) constitute the epithelial intermediate filaments. Among them, K7/K19 are widely used markers of the regenerative liver response termed ductular reaction (DR) that consists of activated biliary epithelial cells (BECs) and hepatic progenitor cells (HPCs) and correlates with liver disease severity. In the present study we aimed to characterize K23 in the liver.We analyzed the expression and localization of K23 in the digestive system under basal conditions as well as in various human and mouse liver diseases/stress models. Cell culture studies were used to study factors regulating K23 expression.In untreated mice, K23 was restricted to biliary epithelia. It was (together with K7/K19) markedly upregulated in three different DR/cholestatic injury models, i.e., multidrug resistance protein 2 (Mdr2) knockouts, animals treated with 3,5-diethoxycarbonyl-1,4-dihydrocollidine or subjected to bile duct ligation. K23 levels correlated with the DR marker Fn14 and immunofluorescence staining showed a distinct co-localization with K7/K19. In chronic human liver disease, K23 expression increased in patients with a more prominent inflammation/fibrosis. A dramatic upregulation (>200 times) was observed in patients with acute liver failure (ALF) and end-stage primary biliary cholangitis (PBC). Patients with alcoholic liver cirrhosis displayed increased K23 serum levels. In primary hepatocytes as well as hepatobiliary cell lines, treatment with TNF-related weak inducer of apoptosis (TWEAK), and the type I acute phase inducer interleukin (IL)-1β but not the type II inducer IL-6 elevated K23 expression.K23 represents a specific, stress-inducible DR marker, whose levels correlate with liver disease severity. K23 may represent a useful non-invasive DR marker.Ductular reaction represents a basic response to liver injury and correlates with liver disease severity. Our study identifies K23 as a novel ductular reaction marker in mice and humans.