T cell/B cell collaboration in autoimmunity

10:30-10:35 Welcome and opening notices

10:35-11:00 Talk 1: A novel player in the regulation of B cells by T cells

Professor Carola Vinuesa, John Curtain School of Medical Research, The Australian National University

Abstract

Regulatory T cells prevent the emergence of autoantibodies and excessive IgE but the precise mechanisms are unclear. Here we show that BCL6-expressing Tregs, known as follicular regulatory T (Tfr) cells produce abundant amounts of a neuropeptide that targets B cells. Mice lacking Tfr cells or the Tfr-derived neuropeptide in Foxp3-expressing cells accumulated early plasma cells in germinal centers (GCs) and developed autoantibodies against histones and tissue-specific self-antigens. Upon immunization, these mice also produced increased serum IgE and IgG1. We show that the Tfr-derived neuropeptide is taken up by B cells, causes phosphorylation of numerous proteins and dampens IgE class switching. The Tfr-derived neuropeptide reduced differentiation of mouse and human GC B cells into plasma cells, downregulated BLIMP-1 and upregulated BCL6. Administration of the neuropeptide to Tfr-deficient mice prevented the accumulation of early plasma cells in GCs. Production of this neuropeptide by Tfr cells emerges as a central mechanism to suppress B cell-driven autoimmunity and IgE-mediated allergies. 

11:00-11:25 Talk 2: Dynamic T-B interactions in the germinal center

Dr Hai Qi, Tsinghua University, China

Abstract

Antibody affinity maturation depends on germinal center (GC) positive selection of rare clones that acquire higher-affinity B cell receptors via somatic hypermutation, present more antigen to follicular helper T (Tfh) cells and, consequently, receive more contact-dependent T-cell help. As Tfh and GC B cells do not maintain long-lasting contacts in the chaotic GC environment, it is unclear how sufficient T-cell help is cumulatively focused onto those rare clones. Here we show that, upon receipt of CD40 stimulation, GC B cells upregulate chemokine CCL22 and to a lesser extent CCL17. By engaging CCR4 on Tfh cells, CCL22 and CCL17 can attract attention to a B cell by multiple helper cells from a distance, thus increasing the chance of productive help. In a GC response, B cells that acquire higher antigen-binding affinities express higher levels of CCL22, and higher levels of CCL22 expression highlight GC B cells of higher affinities. Acute increase or blockade of Tfh help rapidly increase or decrease CCL22 expression by GC B cells. Therefore, a chemokine-based intercellular reaction circuit translates the amount of T-cell help individual B cells recently receive to their subsequent ability to attract more help. When CCL22 and CCL17 are ablated in B cells, GCs form but do not efficiently mature in affinity. When competing with wildtype B cells in the same reaction, those lacking CCL22 and CCL17 are disadvantaged in acquiring T-cell help to maintain GC participation or develop into bone-marrow plasma cells. Therefore, a chemokine-mediated mechanism highlights affinity-improved B cells for Tfh cells to focuses attention from a distance. This ensures efficient positive selection despite the chaotic crowding of competitors.

11:25-11:50 Talk 3: CD11c+ Tbet+ B cell get by with a little help from their friends, Tfh cells

Dr Jason Weinstein, Rutgers New Jersey Medical School, USA

Abstract

Follicular helper T cells (Tfh) cells shape the germinal center (GC) response by delivery of contact-dependent signals and cytokines, including IFN-γ and IL-21. The contribution of these discrete extrinsic signals to the dysregulation of GC B cells in lupus is unclear. In lupus, by contrast to acute viral challenge, GCs persist as disease progresses, and transcriptional analysis of lupus-Tfh cells at different stages of disease revealed an evolving gene expression profile that corresponded to disease progression. However, Tfh cells from early and chronic GCs continued to robustly co-produce both IL-21 and IFN-γ with ongoing genesis of IgG2 autoantibody production, necessary for immune complex-derived glomerulonephritis. Additionally, CD11c- and Tbet-expressing age-associated B cells (ABCs) comprise a distinct B-cell subset that contributes to autoantibody production. Unlike Tfh and GC B cells, we show that ABCs accumulate as disease progresses in lupus-prone mice. However, their developmental reliance upon T cell help and relationship to GC B cells are unclear. To this end, we examined ABCs in a murine acute LCMV infection model, finding that Tfh, not T helper 1, cells drove their differentiation prior to and independent of the GC response. ABCs rarely overlap with GC B cells in phenotype, transcriptional profile, and clonality, with their development often diverging from that of GC B cells. These data indicate that ABCs in response to viral infection are predominantly generated independent of the GC response, yet their development is dependent upon help delivered by Tfh cells.

11:50-12:00 Break

12:00-12:30 Additional Q&A for talks 1-3 and discussion

13:30-13:55 Talk 4: T peripheral helper cells in human autoimmunity

Dr Deepak Rao, Harvard University, USA

Abstract

T cell- B cell interactions often take place within target tissues in chronic autoimmune conditions, yet T cell populations that drive these peripheral T-B cell interactions remain difficult to define. Rheumatoid arthritis synovium provides a valuable test case, where the synovium is often studded with T cell-B cell aggregates. We found that rheumatoid synovium contains a highly expanded population of PD-1hi CXCR5- CD4+ T cells that express high levels of IL-21 and CXCL13 and resemble Tfh cells cytometrically and transcriptomically. However, this PD-1hi CXCR5- cell population differed from Tfh cells in particular in migratory programs, expressing a distinct set of chemokine receptors including CCR2 and CCR5. We called these cells T peripheral helper (Tph) cells to capture the idea that they would provide help to B cells in inflamed peripheral tissues rather than within lymphoid follicles. We found that Tph cells are also highly expanded in the circulation of patients with lupus and that they depend on expression of MAF to produce IL-21 and stimulate B cell responses in vitro. Current ongoing work aims to identify Tph cells in murine models of lupus and to evaluate their contribution to pathologic B cell responses in vivo.   

13:55-14:20 Talk 5: T follicular helper T cells in type 1 diabetes

Professor Tuure Kinnunen, University of Eastern Finland

Abstract

Type 1 diabetes (T1D) is an autoimmune disease that typically starts in childhood and results in the destruction of insulin-producing beta cells in the pancreas. Although type 1 diabetes is primarily considered to be a T-cell mediated disease, B cells clearly participate in the autoimmune process. For example, autoantibodies recognizing pancreatic islet antigens commonly appear in circulation before the onset of the disease. Using blood samples from a longitudinal follow-up cohort, we have analyzed the frequency of circulating T follicular helper (Tfh) and T peripheral helper (Tph) cells in children at different stages of T1D development. We have observed that both activated circulating Tfh cells (defined as CD4+CXCR5+PD-1+ICOS+) as well as Tph cells (CD4+CXCR5-PD1hi) are increased in the blood of children with newly diagnosed T1D, especially in those individuals positive for multiple autoantibodies. These cell subsets were also shown to be increased in frequency in autoantibody-positive at-risk individuals who later progressed to T1D. Our results suggest that an increase in circulating Tfh and Tph cells is associated with T1D onset and they could therefore potentially be used as biomarkers of disease progression. Moreover, our results lend support to the idea that Tfh/Tph activation pathways can be potential targets for the immunotherapy of T1D.

14:20-14:40 Additional Q&A for talks 4&5 and discussion

14:40-14:50 Break

14:50-15:15 Talk 6: T and B cell reactions in inflamed lung tissue

Professor Dr Andreas Hutloff, University of Kiel, Germany

Abstract

The lung is one of the largest barrier organs and not only involved in pulmonary infections but also different chronic inflammatory interstitial lung diseases. T and B cells are frequently found in inflammatory infiltrates. We recently showed in a mouse lung inflammation model that active T cell / B cell cooperation can take place directly in the lung tissue. A special population of T follicular helper- (Tfh-) like cells drives the differentiation of lung-infiltrating B cells into antibody-producing cells. Tfh-like cells (also known as peripheral T helper cells (Tph)) lack the classical Tfh markers CXCR5 and Bcl-6 but provide potent B cell help by production of IL-21 and high expression of CD40L. T/B cooperation in the lung takes places in unstructured, non-ectopic peribronchial infiltrates but nevertheless results in efficient B cell receptor hypermutation. 

We now identified a similar population of Tfh-like cells in inflamed lungs from sarcoidosis patients. This systemic inflammatory disease was previously thought to be a primarily Th1 and macrophage-driven disease. However, lung-infiltrating T cells also produce large amounts of IL-21 and provide potent B cell help in vitro. Large clusters of T and B cells can be found in the lung tissue and these infiltrates are typically surrounded by IgA-producing plasma blasts, indicating their local generation in the lung. These findings highlight the role of T cell / B cell cooperation as a novel pathomechanism for sarcoidosis.

15:15-15:40 Talk 7: New CD4 T cell helper populations in lupus

Dr Virginia Pascual, Weill Cornell Medicine, USA

15:40-16:05 Talk 8: The shaping of antibody responses by Tfh and non-Tfh populations during viral infection

Dr Stephanie Eisenbarth, Yale University School of Medicine, USA

Abstract

While the spectrum of coronavirus disease 2019 (COVID-19) ranges from asymptomatic infection to severe and sometimes fatal, it remains unknown what determines divergent clinical trajectories among patients. COVID-19 patients quickly develop antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but these antibodies may be protective or pathogenic. Protective antibodies neutralize virus or contribute to viral clearance by activating Fc receptor-expressing cells, while pathogenic antibodies can contribute to hyperinflammatory responses or even enhance infection by SARS-CoV-2. Studies of antibody responses in COVID-19 patients demonstrate that severe disease is associated with impaired T follicular helper (Tfh) cell and germinal center responses, suggesting that Tfh-independent pathways of antibody induction could contribute to COVID-19 severity. Using a murine model of SARS-CoV-2 infection, we defined the features of Tfh cell-dependent and Tfh cell-independent antibody responses. Tfh cell help was required for long-lived antibody responses to SARS-CoV-2. Tfh cell-dependent antibodies also demonstrated increased recognition of spike S2 fusion peptide-derived epitopes. Furthermore, antibodies that developed in the absence of Tfh cell help exhibited altered Fc isotype profiles. Ultimately, we aim to identify the cellular pathways and antibody features that mediate SARS-CoV-2-induced disease severity as well as define a new paradigm in which different CD4+ T cell subsets guide the production of protective versus pathogenic antibodies to viruses.

16:05-16:30 Additional Q&A for talks 6-8 and discussion

10:30-10:35 Introduction

10:35-11:00 Talk 1: Metabolic regulation of Tfh cells: monitoring and modulation 

Professor Di Yu, The University of Queensland Diamantina Institute, Australia

Abstract

CD4+ follicular helper T (Tfh) cells are instrumental in regulating germinal centre responses for antibody affinity maturation and memory formation. Despite the significant knowledge of Tfh cells in autoimmune diseases, the mechanisms underlying the regulation of Tfh function in healthy individuals in response to infections and vaccination are scarce. We identified metabolic hormone leptin as a natural regulator of Tfh cells by promoting both mouse and human Tfh differentiation and IL-21 production, which are mediated by STAT3 and mTOR pathways. We revealed that insufficient leptin was associated with reduced vaccine responses of the general population to influenza and hepatitis B virus (HBV) vaccines. We also discovered that Tfh cells show features of ferroptosis, a new type of programmed cell death that results from an iron-dependent accumulation of lipid ROS. Accordingly, the supplementation of selenium increased the synthesis of selenoprotein GPX4 to mitigate T cell ferroptosis, thus promoting Tfh function and antibody responses in immunised mice and young adults following influenza vaccination. Collectively, Tfh function is essentially controlled by metabolic pathways, which can be targeted to monitor and modulate Tfh function.

11:00-11:25 Talk 2: Tracking follicular helper T cells in type 1 diabetes: implications for immunotherapy

Professor Lucy Walker, University College London, UK

Abstract

T cells with a follicular helper (Tfh) phenotype are elevated in multiple autoimmune diseases, including type 1 diabetes. The propensity of T cells to become Tfh is tightly regulated by the inhibitory protein CTLA-4. CTLA-4 can limit CD28 engagement by binding to their shared ligands with higher affinity, and removing them from the surface of adjacent cells by a process of trans-endocytosis.

Soluble CTLA-4 (CTLA-4-Ig; Abatacept) can be used to suppress T cell responses in people with autoimmunity. We explored the impact of Abatacept on Tfh in a mouse model of autoimmune diabetes and in people with new onset type 1 diabetes.  Treatment with Abatacept induced profound changes to Tfh, and additional costimulation-sensitive populations were also identified. Using predictive modelling and data-driven analysis (CellCnn) we were able to identify patient Tfh profiles that were linked to the clinical response to Abatacept, as assessed by C-peptide retention at the 2 year time point. Our findings suggest that profiling Tfh cells may help identify the individuals most likely to benefit from this immunotherapy in the future.

11:25-11:50 Talk 3: Crosstalk of T cells and B cells in the pathogenesis of coeliac disease

Professor Ludvig Sollid, University of Oslo, Norway

Abstract

Adaptive immunity with involvement of antigen-specific T cells and B cells are likely essential in development of autoimmune diseases. Research on the involvement of autoimmune T and B cells is however in hampered by the lack of knowledge of the disease driving antigens, particularly in humans. Coeliac disease, a common disorder that has autoimmune features and this is caused by a maladapted immune response to cereal gluten proteins, is an exception in this regard. The disease is driven by activation of gluten-reactive CD4+ T cells and it is hallmarked by highly disease specific autoantibodies to the enzyme transglutaminase 2 (TG2) and to deamidated gluten peptides (DGP). I will discuss recent findings on the phenotype of gluten-reactive CD4+ T cells, the usage of disease-relevant T-cell receptors and B-cell receptors as well as the crosstalk between pathogenic T cells and B cells in this instructive human disorder.

11:50-12:00 Break

12:00-12:30 Additional Q&A for talks 1-3 and discussion

13:30-13:55 Talk 4: Follicular regulatory T cells in rheumatic diseases

Professor Luis Graca, Instituto de Medicina Molecular, Faculdade de Medicin, Universidade de Lisboa, Portugal

Abstract

Germinal centres (GC) are anatomic structures where B cells undergo affinity maturation leading to production of high-affinity antibodies. The balance between T follicular helper (Tfh) and regulatory (Tfr) cells is critical for adequate control of GC responses. The study of human Tfh and Tfr cells’ development has been hampered due to the lack of in vitro assays reproducing the in vivo biology, along with difficult access to healthy human lymphoid tissues. We investigated the maturation of human Tfh and Tfr cells isolated from different human tissues using single cell transcriptomics, as well as samples from patients with rheumatic diseases. This way, it became possible to reconstruct the normal maturation trajectory for human Tfh and Tfr cells, and to uncover differences in their differentiation that are associated with autoimmune rheumatic diseases.

13:55-14:20 Talk 5: Ageing and the response to vaccination

Dr Michelle Linterman, Babraham Institute Cambridge, UK

Abstract

Ageing dramatically affects the function of the immune system, resulting in increased susceptibility to infections and increased infection-related morbidity and mortality in older members of our communities. Notably, there is already an established intervention that can prevent a range of potentially life-threatening infections - vaccination. It has been observed, however, that older individuals often do not generate protective immunity after vaccination. The reasons for this are poorly understood, but it is clear that this leads to an increased prevalence of preventable disease in older people, even when good immunisation programmes are in place. At the heart of the immune response to vaccination is the germinal centre (GC) – a dynamic structure that forms in secondary lymphoid tissues after immunisation, and produces long-lived plasma cells, which secrete antibodies that block pathogens from establishing an infection, and memory B cells. A defining property of the GC is the collaboration of multiple cell types: proliferating B cells, T follicular helper cells (Tfh), T follicular regulatory cells (Tfr) and follicular dendritic cells to produce effector B cells of higher quality. With age, the magnitude of the GC response decreases resulting in impaired production of plasma cells, lower serum antibody levels and consequently, decreased protection against subsequent infection. Our research aims to understand how ageing affects the multiple cell types that participate in the GC response, and how we could mitigate the age-dependent changes with the goal of enhancing vaccine efficacy in older persons. 

14:20-14:40 Additional Q&A for talks 4&5 and discussion

14:40-14:50 Break

14:50-15:15 Talk 6: Regulation of CD11c+ T-bet+ B cells in autoimmunity

Professor Alessandra Pernis, Hospital for Special Surgery, Weill Cornell Medicine, USA

Abstract

Studies in aging mice have recently identified a B cell subset, termed ABCs (Age/Autoimmune-associated B cells), which exhibits a unique phenotype and preferentially expands in females with age. In addition to classical B cell markers, ABCs also express T-bet and myeloid markers like CD11c hence these cells are also known as CD11c+ T-bet+ B cells. Formation of ABCs is promoted by a combination of signals that include TLR7 engagement and cytokines like IFN- and IL-21. Both murine and human studies have shown a close association between aberrant accumulation of ABCs and the development of autoimmunity. In particular, ABCs expand prematurely in murine lupus and produce pathogenic autoantibodies. Furthermore, expansion of human ABC-like cells (also known as Double Negative=DN or DN2 B cells) has been observed in SLE patients where they have been shown to be major producers of autoAbs and to correlate with disease activity and clinical manifestations. Here I will discuss work from our lab on the molecular pathways that regulate the expansion, function, and differentiation of ABCs in autoimmune settings.

15:15-15:40 Talk 7: Maintenance of Tfh cell identity and its impact on GCs

Professor Dirk Baumjohann, University Hospital Bonn, Germany

Abstract

T follicular helper (Tfh) cells are crucial for the establishment of germinal centers (GCs) and potent antibody responses that are elicited during infection and vaccination. Despite their importance for humoral immunity, the T cell-intrinsic factors that are required for the maintenance of already established Tfh cells and GCs remain largely unknown.Temporally guided, tamoxifen-inducible CD4+ T cell-specific gene ablation was used to dissect the contributions of CXCR5, Bcl6, and mature miRNAs to the maintenance of Tfh cell function and identity. Induced ablation of Cxcr5 in CD4+ T cells had only minor effects on the identity and function of established Tfh cells. Phenotypical and transcriptional analyses revealed that Cxcr5-ablated cells still exhibited most features of CXCR5-positive Tfh cells. In contrast, continued Bcl6 expression was essential to maintain the GC Tfh cell phenotype and GC reaction. CD4+ T cell-specific Bcl6 ablation during acute viral infection resulted in transdifferentiation of established Tfh cells into Th1 cells. Finally, induced depletion of all mature miRNAs resulted in the loss of the Tfh cell phenotype and resolution of GCs. By highlighting the high degree of Tfh cell plasticity, these studies provide novel insights into the mechanisms underlying Tfh cell and GC maintenance.

15:40-16:05 Talk 8: Maintenance of GC Tfh Response in Humans

Professor Hideki Ueno, Graduate School of Medicine, Kyoto University, Japan

Abstract

Immunological memory is fundamental to protect the host from a re-infection of the pathogen.  The maintenance of humoral memory is mediated by long-lived plasma cells and memory B cells. Their development requires helper signals, including CD40, provided by T follicular helper (Tfh) cells in germinal centers (GCs).  GC-Tfh cells participate in the selection of high-affinity B cells and their differentiation into long-lived plasma cells and memory B cells and therefore are fundamental for the generation of durable humoral responses.

Memory Tfh cells play essential roles in the secondary Ab response and provide help to memory B cells and naïve B cells. Memory Tfh cells are present in blood circulation as well as lymphoid organs. The molecular mechanism required for the development of memory Tfh cells remains poorly defined. In my seminar, I will provide evidence that transcription factor Tox2 is important for the maintenance of GC Tfh cells both in humans and mice. I will also share our recent analysis on single cell RNAseq data of human tonsillar CD4+ T cells regarding the plasticity of human GC Tfh cells.

16:05-16:30 Additional Q&A for talks 6-8 and discussion

16:30-16:35 Closing remarks