Highlights from the plenary session: cellular and molecular mechanisms of disease (I)

Abstract

The plenary session, ‘Cellular and Molecular Mechanisms of Disease (I)’ highlighted groundbreaking translational research in the field of autoimmune vasculitis, with a focus on ANCA-associated vasculitis (AAV). This research illuminates potential therapeutic avenues and advances our understanding of disease mechanisms. Additionally, the findings provide a basis for further mechanistic studies and may pave the way for potential human therapeutic options.

Beginning with the intriguing and currently highly regarded field of the gut microbiome, Kim Maree O’Sullivan presented their study exploring the effects of manipulating gut microbiota in an experimental MPO-AAV mouse model. A diet supplemented with 12.5% resistant starch (maize) compared with control diet significantly expanded the population of short-chain fatty acid (SCFA)-producing bacteria. The diets were calorie-, protein- and fat-matched. The mice receiving the high resistant starch diet exhibited notable reductions in clinical, histological and inflammatory parameters. Cecal content analysis revealed a substantial increase in acetate production in the resistant starch group compared with controls. Acetate is known to facilitate the induction of regulatory B cells, differentiation of CD4 T cells and inhibition of neutrophil extracellular trap (NET) formation, potentially affecting key pathophysiological mechanisms [1]. Oral administration of SCFA acetate (but not propionate or butyrate) replicated the effects of the high resistant starch diet, resulting in reduced kidney inflammation and injury. This study provides initial evidence of the therapeutic efficacy of a resistant starch or SCFA acetate-supplemented diet in experimental AAV, suggesting it could mitigate and potentially prevent disease flares. However, it is critical to acknowledge that differences in the gut microbiome between mice and humans may limit the direct applicability of these findings to human patients.

Transitioning to cellular biology, the award-winning abstract by Meghan Free highlighted the role of regulatory T cells (T_regs) in downregulating the autoimmune response in AAV using a mouse model of MPO-ANCA glomerulonephritis. The study demonstrated that transferring anti-MPO splenocytes into Rag2^–/– mice induced the development of anti-MPO titres and glomerulonephritis. Conversely, when these cells were transferred into wild-type (WT) mice, these titres were suppressed and glomerulonephritis was absent. Additionally, reconstituting WT splenocytes into Rag2^–/– mice prior to the transfer of anti-MPO splenocytes restored T cell populations and effectively prevented the development of anti-MPO titres and kidney disease, underscoring the pivotal role of T cells in modulating the autoimmune response. Furthermore, isolated WT T_regs dose-dependently inhibited anti-MPO antibody production and prevented renal involvement, emphasizing the critical role of T_regs in controlling the anti-MPO autoimmune response. This research lays a solid foundation for utilizing this model as a pre-clinical animal platform for future investigations into T_reg-based therapies in AAV, offering potential for significant therapeutic advances.

Shifting focus to B cell biology, Diane van der Woude presented their research on MPO-specific IgM B cells in MPO-AAV patients. Employing a flow cytometry-based approach, they identified MPO-specific B cells in the circulation of these patients. Notably, the MPO-specific B cell response was predominantly characterized by IgM-expressing B cells, while IgG⁺ MPO-specific cells were rare. In cultures, stimulated B cells from both patients and healthy controls (HCs) produced MPO-IgM. In HC, MPO-IgM B cells were primarily naive, whereas in patients, they also appeared in the memory (CD27⁺) and plasmablast compartments. Circulating anti-MPO IgM was exclusively detected in patients. These findings suggest a deficiency in early B cell tolerance to MPO and emphasize the role of activated IgM⁺ anti-MPO B cells in the pathogenesis of AAV, particularly through complement activation. It is noteworthy that a subset of the patients included in this study had previously undergone treatment with rituximab, resulting in repopulation of B cells. This research underscores the importance of understanding B cell subsets in AAV pathogenesis and opens new avenues for targeted therapies. Moving forward, the focus will be on correlating anti-MPO IgM levels with disease activity and flares.

Advancing towards innovative therapeutic approaches, Dörte Lodka presented their proof-of-principle study exploring the use of CD19 chimeric antigen receptor (CAR) T cells in a murine MPO-AAV model [2]. CD19 CAR-T cells exhibited effective migration and persistence in the bone marrow, spleen, peripheral blood and kidneys for up to 8 weeks. These cells specifically depleted CD19-expressing B cells in the aforementioned compartments. Consequently, anti-MPO-ANCA titres rapidly declined and the incidence of damaged glomeruli significantly decreased in CD19 CAR-T cell-treated mice. Notably, these mice exhibited no histological signs of crescentic or necrotic glomeruli. This study establishes a solid foundation for exploring CAR T cell therapy as a promising approach in the treatment of AAV. The ultimate goal of achieving drug-free remission is attainable. Future research will focus on developing anti-MPO specific CAR-T cells that target only the disease-specific B cells, enhancing specificity and potentially reducing side effects. The potential for human clinical trials represents an exciting next step in this line of research.

Maxime Samson’s research further elucidated disease mechanisms by investigating the role of IL-17 in GCA. To assess this role, temporal artery biopsies were cultured under various conditions. The study demonstrated that treatment with secukinumab (SCK), an anti-IL-17 monoclonal antibody, resulted in decreased expression of inflammatory genes, reduced T cell recruitment and diminished fibroblast proliferation in ex-vivo cultures. Conversely, the addition of IL-17 to the cultures significantly contributed to vascular inflammation and directly affected myofibroblasts, exhibiting a synergistic effect with IFN-γ. This synergy resulted in increased production of pro-inflammatory cytokines and chemokines leading to the recruitment of T cells and monocytes, as well as promoting factors involved in neoangiogenesis. These changes were reversed in the presence of SCK. Notably, IL-17 did not directly affect myofibroblast proliferation and migration. In conclusion, these findings reveal the potential mechanistic benefits of targeting the IL-17 signalling pathway in the treatment of GCA, suggesting that inhibiting this pathway could mitigate key immunological aspects of the disease’s pathology.

To further identify specific targetable pathways, Benoit Brilland analysed the kidney transcriptome of patients with microscopic polyangiitis (MPA) vs granulomatosis with polyangiitis (GPA). The study revealed that a group of seven genes associated with the type I interferon (IFN-I) signalling pathway were upregulated in MPA. To corroborate these findings, a more pronounced IFN-I signature was observed in peripheral blood mononuclear cells from patients with MPO-AAV compared with those with PR3-AAV. Additionally, an increase in serum IFNα levels was noted in patients with AAV relative to HCs. However, no differences were observed between MPA/MPO-AAV and GPA/PR3-AAV, nor was there a correlation between IFNα levels and clinical outcomes or histological severity. In summary, these results suggest a potential role for IFN-I in MPA/MPO-AAV and offer insights into the pathophysiological distinctions between MPA and GPA. Future research will focus on IFN inhibition in a murine model of renal MPO-AAV to explore its therapeutic potential.

Lastly, Kim Maree O’Sullivan investigated whether Deoxy Mab DX-1/DX-3 nuclear penetrating antibodies could inhibit NET formation by disrupting DNA damage repair responses and reduce inflammation in an experimental model of MPO-AAV. The study found that DX-1/DX-3 effectively inhibited NET formation in stimulated human neutrophils without affecting phagocytosis, triggering apoptosis, necrosis or MPO release. In DX-1 and DX-3 treated mice, a notable reduction in kidney injury, proteinuria and urinary leukocytes was observed. Additionally, the presence of pro-inflammatory cells in the kidneys was decreased, and both glomerular NET formation and MPO deposition were significantly reduced. This research marks the first demonstration of the beneficial effects of DX-1/DX-3 in a murine model of MPO-AAV, suggesting its potential as a novel therapeutic intervention that does not compromise host defence mechanisms.

In conclusion, the presentations effectively highlighted a series of transformative studies across various domains of autoimmune vasculitis, each presenting potential breakthroughs in therapeutic strategies. These studies collectively advance our understanding of disease mechanisms at both the molecular and cellular levels. Research presented on innovative approaches such as resistant starch or SCFA-supplemented diet, CAR-T cell therapies and novel antibody treatments pointed towards promising avenues for achieving drug-free remission and reducing the burden of disease. The potential of these therapies to specifically target disease mechanisms without compromising overall immune function could revolutionize treatment paradigms and significantly improve patient outcomes and survival. The insights gained from these studies not only enhance our comprehension of the pathophysiological differences and similarities among various forms of vasculitis but also underscore the importance of targeted therapeutic interventions. As these novel approaches continue to be explored and refined in preclinical and potential clinical settings, they hold the promise of developing more effective, personalized treatments that could substantially improve the quality of life and outcomes for patients with autoimmune vasculitis.

Data availability

The abstracts from the 21st International Vasculitis Workshop are available via 10.5281/zenodo.10932657.

Funding

No specific funding was received from any bodies in the public, commercial or not-for-profit sectors to carry out the work described in this article.

Disclosure statement: The authors have declared no conflicts of interest.

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