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Therapeutic targeting of immune checkpoints has garnered significant attention in the area of cancer immunotherapy, in which efforts have focused in particular on cytotoxic T lymphocyte antigen 4 (CTLA4) and PD1, both of which are members of the CD28 family. In autoimmunity, these same pathways can be targeted to opposite effect: to curb the over-exuberant immune response. The CTLA4 checkpoint serves as an exemplar, whereby CTLA4 activity is blocked by antibodies in cancer immunotherapy and augmented by the provision of soluble CTLA4 in autoimmunity. Here, we review the targeting of co-stimulatory molecules in autoimmune diseases, focusing in particular on agents directed at members of the CD28 or tumour necrosis factor receptor families. We present the state of the art in co-stimulatory blockade approaches, including rational combinations of immune inhibitory agents, and discuss the future opportunities and challenges in this field. Immune activating antibodies that target co-stimulatory molecules have altered the cancer therapy landscape. Here, Walker and colleagues discuss therapies — particularly those that target molecules in the same families as CTLA4 and PD1 or TNF receptor — that inhibit the immune system and are being investigated for the treatment of autoimmune diseases. They describe the future opportunities and challenges for the field, including combination approaches.

Context The CD40-CD154 co-stimulatory pathway plays an important role in the pathogenesis of Graves disease (GD) by promoting autoreactive B-cell activation. Objective Evaluate efficacy and safety of a human, blocking, nondepleting anti-CD40 monoclonal antibody, iscalimab, in hyperthyroid patients with GD. Design Open-label, phase II proof-of-concept study. Setting Multicenter. Patients Fifteen with GD. Intervention Patients received 5 doses of iscalimab at 10 mg/kg intravenously over 12 weeks. Main outcome measures Thyroid-related hormones and autoantibodies, plasma soluble CD40, free CD40 on B cells, soluble CXCL13, pharmacokinetics, and safety were assessed. Results The iscalimab intervention resulted in complete CD40 engagement for up to 20 weeks. A clinical response and biochemical euthyroidism was observed in 7 of 15 (47%) patients. Free and total triiodothyronine and thyroxine normalized in 7 patients who did not receive any rescue medication with antithyroid drugs (ATD), and 2/15 (13.3%) showed normal thyrotropin. Six (40%) patients required ATD. Four of 7 responders relapsed after treatment completion. Serum concentrations of thyrotropin receptor autoantibodies (TSH-R-Ab) significantly declined in all patients (mean 15.3 IU/L vs 4.0 IU/L, 66% reduction; P < 0.001) and TSH-R-Ab levels normalized in 4 (27%). Thyroperoxidase and thyroglobulin autoantibodies significantly decreased in responders. Iscalimab rapidly reduced serum CXCL13 concentrations (P < 0.001). Twelve (80.0%) patients reported at least 1 adverse event (AE). All treatment-related AE were mild or moderate and resolved by end of the study. Conclusion Iscalimab was generally safe and clinically effective in a subgroup of hyperthyroid GD patients. The potential therapeutic benefit of iscalimab should be further tested.

ObjectiveTo examine the role of CD40–CD154 costimulation and effects of therapeutic pathway blockade in the non-obese diabetic (NOD/ShiLtJ) model of Sjögren’s syndrome (SS).MethodsWe assessed leucocyte infiltration in salivary glands (SGs) from NOD/ShiLtJ mice by immunohistochemistry and examined transcriptomics data of SG tissue from these animals for evidence of a CD40 pathway gene signature. Additionally, we dosed MR1 (anti-CD154 antibody) in NOD mice after the onset of SS-like disease and examined the effects of MR1 treatment on sialadenitis, autoantibody production, SG leucocyte infiltration, gene expression downstream of CD40 and acquaporin 5 (AQP5) expression.ResultsWe could detect evidence of CD40 expression and pathway activation in SG tissue from NOD mice. Additionally, therapeutic treatment with MR1 suppressed CD40 pathway genes and sialadenitis, inhibited ectopic lymphoid structure formation and autoantibody production, as well as decreased the frequency of antibody-secreting cells in SGs but had minimal effects on AQP5 expression in NOD/ShiLtJ SGs.ConclusionCD40–CD154 interactions play an important role in key pathological processes in a mouse model of SS, suggesting that blockade of this costimulatory pathway in the clinic may have beneficial therapeutic effects in patients suffering from this autoimmune exocrinopathy.

Iscalimab is a fully human, CD40 pathway blocking, nondepleting monoclonal antibody being developed as an immunosuppressive agent. We describe a first-in-human, randomized, double-blind, placebo-controlled study investigating the safety, tolerability, pharmacokinetics, and pharmacodynamics of iscalimab in healthy subjects and rheumatoid arthritis patients. Healthy subjects (n = 56) received single doses of intravenous iscalimab (0.03, 0.1, 0.3, 1, or 3 mg/kg), or subcutaneous iscalimab (3 mg/kg), or placebo. Rheumatoid arthritis patients (n = 20) received single doses of intravenous iscalimab (10 or 30 mg/kg) or placebo. Iscalimab exhibited target-mediated drug disposition resulting in dose-dependent and nonlinear pharmacokinetics. Complete (≥90%) CD40 receptor occupancy on whole blood B cells was observed at plasma concentrations >0.3-0.4 µg/mL. In subjects receiving 3 mg/kg iscalimab, antibody responses to keyhole limpet hemocyanin were transiently suppressed. CD40 occupancy by iscalimab prevented ex vivo human rCD154-induced expression of CD69 on B cells in whole blood. All doses were generally safe and well tolerated, with no clinically relevant changes in any safety parameters, including no evidence of thromboembolic events. Iscalimab appears to be a promising blocker of the CD40-CD154 costimulatory pathway with potential use in transplantation and other autoimmune diseases.

Background: Primary Sjogren’s syndrome (pSS) is a systemic progressive autoimmune disease characterised by formation of lymphoid structures and germinal centres within glandular tissue. Iscalimab (CFZ533) is a novel monoclonal antibody that potently and selectively blocks CD40, a co-stimulatory pathway receptor important for germinal centre reactions and B cell activation. Iscalimab showed clinical efficacy in a Proof of Concept randomised controlled trial at a dose of 10 mg/kg intravenously (IV), whereas subcutaneous (SC) dosing at 3 mg/kg was associated with unexpectedly low plasma concentrations and reduced efficacy, likely due to efficient pre-systemic target-mediated clearance. Objectives: To test IV versus SC loading doses of iscalimab followed by SC maintenance dosing, as a means of achieving target drug exposure and clinical efficacy. Methods: Patients with clinically active pSS [EULAR Sjogren’s Syndrome Disease Activity Index (ESSDAI) ≥6] were randomised to receive either 600 mg SC iscalimab weekly on 4 occasions, followed by 300 mg SC weekly until week 12, or a single IV dose of 10 mg/kg iscalimab on study Day 1, followed by 300 mg SC weekly until week 12. Subjects and investigator staff remained blinded to study treatment allocation until first dosing. Results: Twenty-five patients were randomised; 13 in the SC loading and 12 in the IV loading arms. Baseline characteristics were similar to the previous phase IIa cohorts with mean ESSDAI scores of 12.7 (SD 6.1) and 10.4 (5.9) in the SC and IV loading arms respectively. In Arm 1 (SC) and Arm 2 (IV), the mean trough plasma concentrations were 169 μg/mL (SD 64.1, CV 38%) and 135 μg/mL (SD 70.9, CV 53%) on Day 85, respectively. Both values were well above levels previously reported to be sufficient for suppression of germinal centre development and T dependent antigen responses in cynomolgus monkeys. Consistent with this finding, clinically important improvements were seen in both arms with a mean decrease in ESSDAI scores of -5.5 (+/- SD: 5.5) and -7.6 (+/- 7.1) points from baseline to Day 85 in the SC and IV dosing arms. Improvements were also seen in EULAR Sjogren’s Syndrome Patient Reported Index (ESSPRI) scores: -1.67 (+/- 1.8) and -1.17 (+/- 2.3), respectively. Other secondary efficacy outcomes showed similar patterns of improvement. Treatment with iscalimab was associated with a reduction in the germinal centre-related serum biomarker CXCL13 in both groups. Overall, iscalimab was safe and well-tolerated with no new safety signal emerging. One subject experienced three SAEs (hemarthrosis, worsening of right knee pain and swelling requiring arthroscopy) in the safety follow-up period, all unrelated to study drug. Conclusion: These results further support the safety and efficacy of iscalimab in pSS and the suitability of SC dosing for future development. Disclosure of Interests: Benjamin Fisher Consultant for: Novartis, Roche, MedImmune, Bristol-Myers Squibb, Antonia Szanto: None declared, Wan Fai Ng: None declared, Michele Bombardieri Grant/research support from: Celgene, Consultant for: Medimmune, Maximilian Posch: None declared, Athena Papas Grant/research support from: Novartis, Consultant for: Novartis, Arwa Farag: None declared, Thomas Daikeler: None declared, Bettina Bannert: None declared, Alan Kivitz Shareholder of: Novartis, Consultant for: Abbvie, Janssen, Pfizer, UCB, Genzyme, Sanofi, Regeneron, Boehringer Ingelheim, Sun Pharma Advanced Research, Flexion., Paid instructor for: Celgene, Horizon, Merck, Novartis, Pfizer, Genzyme, Sanofi, Regeneron, Speakers bureau: Celgene, Horizon, Merck and Genetech, Flexion, Steven Carsons Grant/research support from: Novartis, David Isenberg: None declared, Francesca Barone Grant/research support from: GlaxoSmithKline, Roche, UCB Pharma, Actelion, ONO Pharmaceutical, Consultant for: GlaxoSmithKline, Roche, Actelion, ONO Pharmaceutical, Simon J. Bowman Grant/research support from: Previously UCB Pharma (to University of Birmingham) and Roche, Consultant for: 2016-7: Novartis, Mitsubishi Tanabe Pharma 2017-8: AstraZeneca, MedImmune, GFK, Xtlbio, ONO Pharmaceutical 2018-9: Novartis, AstraZeneca, UCB Pharma, Pascal Espie Employee of: Novartis, Grazyna Wieczorek Employee of: Novartis, Pierre Moulin Employee of: Novartis, David Floch Employee of: Novartis, Cyrielle Dupuy Employee of: Novartis, Amanda Nguyen Employee of: Novartis, Andrew Wright Shareholder of: Novartis, Employee of: Novartis, Michael Rotte Employee of: Novartis, James Rush Employee of: Novartis, Peter Gergely Employee of: Novartis

Background Identification of non-invasive differentially regulated markers in SLE are valuable to improve diagnosis, prediction of response to treatment(s) or classification of disease subpopulations. Our goal was to assess a broad range of serum protein markers in a large cohort of SLE patients and further characterize the role of autoantibodies in serum of these patients for their functional capacity as specific immune complexes to activate the IFN axis. Methods In this multicenter study, we have characterised a large cohort of mostly pediatric SLE patients (n=150) with longitudinal sera samples (total n=269). Serum cytokines/chemokines levels and their extractable nuclear antigen antibody (ENA) and antinuclear antibody (ANA) profiles measured from SLE patients and healthy subjects using a 30-panel Multiplex and individual enzyme-linked immunosorbent assays. Patient sera containing autoantibodies and specific antigens activating the IFN pathway quantified on human primary cells using AlphaLisa technology. Statistics for significance Mann-Whitney (*p Results Differentially regulated cytokines/chemokines were elevated in sera of SLE patients compared to healthy individuals. Notably, IFN-related proteins (IFNalpha*, IFNgamma* and IP10****), B-cell and monocytes chemokines including CXCL13**** and MCP-1***, as well as Th1/17 activating cytokines (IL-12****, IL-17**) and those involved in antibody production by B lymphocytes (IL-10**, IL-13**, IL-6*) being more significant. Collectively, these peripheral markers may serve to help inform diagnosis and support the choice treatment in the clinic. We established a miniaturized functional assay and show that the vast majority of SLE patient sera containing common ENAs (against RNP/Sm, SS-A) and ANAs (dsDNA) could specifically activate the type I IFN pathway as an immune-complex on healthy peripheral blood mononuclear cells (PBMCs) (figure 1). We demonstrate that SLE containing immune-complexes (with specific antigens) can trigger IFN release potentially via nucleic-acid RNA/DNA sensors. Clustering patient autoantibody ENAs profiles reveal that most of the SLE patients in this cohort display a stronger IFN functional activation profile. Conclusions Given the high incidence of elevated IFN signatures in SLE patients, it is not surprising that increased IFN-related proteins and ENA/ANAs that trigger IFN responses are more evident in SLE patient serum. The prevalence of ENA/ANAs in patient sera that have the functional capacity to activate IFN downstream of nucleic acid sensors may help to define subpopulations of SLE. Funding Source(s): National Council for Scientific and Technological Development (CNPq 157534/2015–4) PBMCs were prepared from fresh healthy human blood, stimulated with individual patient SLE serum in combination with defined antigens corresponding to their ENA or ANA titer profile. After 20 hour, IFNalpha protein levels were quantified and expressed relative to agonist ssRNA40. Data shown are from 2 more independent donors with total SLE patients numbers indicated in parenthesis. ****p

CFZ533 is a pathway blocking, nondepleting anti-CD40 antibody that is in clinical development for inhibition of transplant organ rejection and therapy for autoimmune diseases. A 26-week GLP toxicity study in sexually mature Cynomolgus monkeys was conducted in order to support chronic application of CFZ533. CFZ533 was subcutaneously administered at doses up to 150 mg/kg/week and was safe and generally well tolerated. CFZ533 showed no adverse effects for cardiovascular, respiratory, and neurobehavioral endpoints, and no changes were observed for blood lymphocyte and platelet counts or blood coagulation markers. In line with the nondepleting nature of CFZ533, CD20+ B cells in the blood were only marginally reduced. A complete suppression of germinal center (GC) development in lymph nodes and spleen was the most prominent result of post-mortem histological investigations. This was corroborated by an abrogated T-dependent antibody response (TDAR) to the antigen Keyhole Limpet Hemocyanin (KLH) as well as an absence of anti-drug antibodies (ADAs) in the absence of B cell depletion as seen with immunophenotyping and histology. When serum levels of CFZ533 in recovery animals dropped levels necessary for full CD40 occupancy on B cells, all animals were able to mount a TDAR to KLH. All histological changes also reverted to normal appearance after recovery. In summary, CFZ533 was shown to be well tolerated and safe in the 26-week toxicity study with a distinct pharmacodynamic profile in histology and immune function.

The CD40-CD154 costimulatory pathway is essential for T cell-dependent immune responses, development of humoral memory, and antigen presenting cell function. These immune functions have been implicated in the pathology of multiple autoimmune diseases as well as allograft rejection. We have generated CFZ533, a fully human, pathway blocking anti-CD40 monoclonal antibody that has been modified with a N297A mutation to render it unable to mediate Fcγ-dependent effector functions. CFZ533 inhibited CD154-induced activation of human leukocytes in vitro, but failed to induce human leukocyte activation. Additionally, CFZ533 was unable to mediate depletion of human CD40 expressing B cells. In vivo, CFZ533 blocked primary and recall T cell-dependent antibody responses in nonhuman primates and abrogated germinal formation without depleting peripheral blood B cells. We also established a relationship between plasma concentrations of CFZ533 and CD40 pathway-relevant pharmacodynamic effects in tissue. Collectively these data support the scientific rationale and posology for clinical utility of this antibody in select autoimmune diseases and solid organ transplantation.

Cross-presentation is the process by which professional APCs load peptides from an extracellularly derived protein onto class I MHC molecules to trigger a CD8(+) T cell response. The ability to enhance this process is therefore relevant for the development of antitumor and antiviral vaccines. We investigated a new TLR2-based adjuvant, Small Molecule Immune Potentiator (SMIP) 2.1, for its ability to stimulate cross-presentation. Using OVA as model antigen, we demonstrated that a SMIP2.1-adjuvanted vaccine formulation induced a greater CD8(+) T cell response, in terms of proliferation, cytokine production and cytolytic activity, than a non-adjuvanted vaccine. Moreover, using an OVA-expressing tumor model, we showed that the CTLs induced by the SMIP2.1 formulated vaccine inhibits tumor growth in vivo. Using a BCR transgenic mouse model we found that B cells could cross-present the OVA antigen when stimulated with SMIP2.1. We also used a flow cytometry assay to detect activation of human CD8(+) T cells isolated from human PBMCs of cytomegalovirus-seropositive donors. Stimulation with SMIP2.1 increased the capacity of human APCs, pulsed in vitro with the pp65 CMV protein, to activate CMV-specific CD8(+) T cells. Therefore, vaccination with an exogenous antigen formulated with SMIP2.1 is a successful strategy for the induction of a cytotoxic T cell response along with antibody production.

CD40-CD154 pathway blockade prolongs renal allograft survival in nonhuman primates (NHPs). However, antibodies targeting CD154 were associated with an increased incidence of thromboembolic complications. Antibodies targeting CD40 prolong renal allograft survival in NHPs without thromboembolic events but with accompanying B cell depletion, raising the question of the relative contribution of B cell depletion to the efficacy of anti-CD40 blockade. Here, we investigated whether fully silencing Fc effector functions of an anti-CD40 antibody can still promote graft survival. The parent anti-CD40 monoclonal antibody HCD122 prolonged allograft survival in MHC-mismatched cynomolgus monkey renal allograft transplantation (52, 22, and 24 days) with accompanying B cell depletion. Fc-silencing yielded CFZ533, an antibody incapable of B cell depletion but still able to potently inhibit CD40 pathway activation. CFZ533 prolonged allograft survival and function up to a defined protocol endpoint of 98-100 days (100, 100, 100, 98, and 76 days) in the absence of B cell depletion and preservation of good histological graft morphology. CFZ533 was well-tolerated, with no evidence of thromboembolic events or CD40 pathway activation and suppressed a gene signature associated with acute rejection. Thus, use of the Fc-silent anti-CD40 antibody CFZ533 appears to be an attractive approach for preventing solid organ transplant rejection.

The paracaspase MALT1 plays an important role in immune receptor-driven signaling pathways leading to NF-κB activation. MALT1 promotes signaling by acting as a scaffold, recruiting downstream signaling proteins, as well as by proteolytic cleavage of multiple substrates. However, the relative contributions of these two different activities to T and B cell function are not well understood. To investigate how MALT1 proteolytic activity contributes to overall immune cell regulation, we generated MALT1 protease-deficient mice (Malt1PD/PD) and compared their phenotype with that of MALT1 knockout animals (Malt1−/−). Malt1PD/PD mice displayed defects in multiple cell types including marginal zone B cells, B1 B cells, IL-10–producing B cells, regulatory T cells, and mature T and B cells. In general, immune defects were more pronounced in Malt1−/− animals. Both mouse lines showed abrogated B cell responses upon immunization with T-dependent and T-independent Ags. In vitro, inactivation of MALT1 protease activity caused reduced stimulation-induced T cell proliferation, impaired IL-2 and TNF-α production, as well as defective Th17 differentiation. Consequently, Malt1PD/PD mice were protected in a Th17-dependent experimental autoimmune encephalomyelitis model. Surprisingly, Malt1PD/PD animals developed a multiorgan inflammatory pathology, characterized by Th1 and Th2/0 responses and enhanced IgG1 and IgE levels, which was delayed by wild-type regulatory T cell reconstitution. We therefore propose that the pathology characterizing Malt1PD/PD animals arises from an immune imbalance featuring pathogenic Th1- and Th2/0-skewed effector responses and reduced immunosuppressive compartments. These data uncover a previously unappreciated key function of MALT1 protease activity in immune homeostasis and underline its relevance in human health and disease.

Class switch recombination (CSR) is the process by which B cells alter the effector function properties of their Ig molecules. The decision to switch to a particular Ig isotype is determined primarily by the mode of B cell activation and cytokine exposure. More recent work indicates that the likelihood or probability of switching increases with successive cell divisions and is largely independent of time. We have analyzed different molecular features of CSR using cell division as a reference point in an attempt to gain insight into the mechanism of division-linked switching. Our results indicated that the accessibility of Ig heavy chain constant regions targeted for CSR was established after the cells had undergone a single cell division and did not vary significantly with subsequent cell divisions. In contrast, expression of activation-induced cytidine deaminase (AID) mRNA was found to increase with successive divisions, exhibiting a striking correlation with the frequency of CSR. Levels of AID in a given division remained constant at different time points, strongly suggesting that the regulation of AID expression was division-linked and independent of time. In addition, constitutive AID expression from a transgene accelerated division-linked CSR. Thus, we propose that the division-linked increase in AID expression provides an underlying molecular explanation for division-linked CSR.

T cell stimulation of B cell proliferation during T-B collaboration requires membrane-bound stimulatory ligands, such as CD40 ligand and the secretion of soluble cytokines, such as IL-4. Nevertheless, it remains unclear whether T cell contact is required to provoke each consecutive B cell division, or whether B cells divide in a T cell-free burst following the initial stimulation. To test this, naive B cells were cultured with anti-CD40 monoclonal antibody (mAb) and IL-4 and, after various times, these stimuli were removed and the cells re-cultured with or without further stimulation. Following stimulus removal, B cells were able to continue proliferating, with the size of the B cell burst dependent on the strength of the initial anti-CD40 mAb stimulus. Furthermore, in the absence of activating signals from anti-CD40 and/or IL-4, re-cultured B cells died rapidly. In addition, B cells undergoing a stimulus-free division burst could switch to IgG1. Thus, maximal B cell proliferation, differentiation and survival may require continued, although not necessarily consecutive, cognate interactions with T cells. These results suggest that antigen persistence and T cell help are necessary to sustain B cell proliferation and differentiation in vivo.

Background Aberrant CD40-CD154 pathway signaling has been linked to pathology in autoimmune disease. Blocking the CD40-CD154 pathway prevents T cell-dependent antibody responses, germinal center formation and prolongs renal allograft survival in non-human primates. CFZ533 is a novel, fully human, non-agonistic Fc-silent, anti-CD40 monoclonal antibody being developed for treatment of autoimmune diseases and prevention of rejection in solid-organ transplantation. Objectives To assess the safety, pharmacokinetics (PK) and pharmacodynamics activity (PD) of CFZ533 in humans. Methods A double-blind, placebo controlled, ascending, single-dose study was conducted in 48 healthy volunteers (HV) receiving 0.03, 0.1, 0.3, 1.0, 3.0 mg/kg i.v., 3.0 mg/kg s.c. CFZ533 or matching placebo (3:1) as well as in 12 rheumatoid arthritis (RA) patients receiving 10.0 mg/kg i.v. CFZ533 or placebo (1:1). HVs were immunized with a single intramuscular dose of a T-cell dependent neo-antigen, Keyhole Limpet Hemocyanin (KLH) with alum adjuvant on Day 3 and again between Day 29–85 depending on predicted loss of CD40 receptor occupancy (RO) as a function of CFZ533 dose. Blood samples for PK, CD40 RO and anti-KLH IgG and IgM profiling were collected at multiple time points during the study. Anti-KLH antibodies were assessed using a validated human ELISA system with an LOQ of 0.7 (IgG) and 2.1 (IgM) μg/mL. RA patients were evaluated for safety, PK and RO. Results All doses of CFZ533 and KLH were safe and well tolerated. CFZ533 PK concentrations were quantifiable at all dose levels tested. Complete (≥90%) peripheral CD40 RO by 3 mg/kg i.v. CFZ533 in HVs was maintained for 28 days. During this period of full RO, full suppression of the primary humoral response to KLH was evident in all treated subjects (KLH administered 2 days after CFZ533 dosing). After complete CFZ533 washout in 3 mg/kg cohort, all subjects mounted a robust anti-KLH response following a re-challenge on Day 85. Full RO in RA patients who received 10 mg/kg i.v. CFZ533 was maintained for at least 6 weeks and up to 10 weeks. Conclusions The favorable safety and tolerability profile of CFZ533 coupled with a predictable concentration-CD40 receptor occupancy relationship and suppression of a primary T cell-dependent antibody response supports future clinical trials of CFZ533 in select autoimmune diseases and transplantation. Disclosure of Interest A. Slade Employee of: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA, P. Koo Employee of: Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA, Y. He Employee of: Novartis Pharmaceuticals Corporation, Cambridge, MA, USA, P. Espie Employee of: Novartis Pharmaceuticals Corporation, Basel, Switzerland, A. Auger-Sarrazin Employee of: Novartis Pharmaceuticals Corporation, Basel, Switzerland, J. Rush Employee of: Novartis Pharmaceuticals Corporation, Basel, Switzerland, P. Gergely Employee of: Novartis Pharmaceuticals Corporation, Basel, Switzerland

Background T cell-dependent activation of B lymphocytes is a key effector arm of the adaptive immune system, resulting in protective antibody responses and long-lived humoral immunity. Such B cell responses often occur in germinal centres (GCs); specialized anatomical locations within secondary lymphoid organs. Similar GC-like structures can also be found in involved tissue in various autoimmune diseases, including the salivary glands of primary Sjogren9s syndrome (pSS) patients. Objectives Previous work has implicated CD40-CD154 pathway-dependent processes in regulating B cell survival and function in GCs, and we were wanted to investigate whether this costimulatory pathway might be linked to ELS formation and function in pSS. Methods Histological analysis of minor salivary gland biopsies from pSS patients revealed evidence of CD40 and CD154 expression on ELS-resident B and T cells respectively, co-locating receptor and ligand positive cells in affected tissue. These results suggested that there might be ongoing T-B cell collaboration in these ELS and we therefore wanted to examine whether there was evidence of CD40 pathway activation in situ . To do this we first generated a CD40-pathway gene signature in primary human B cells following recombinant CD154 stimulation in vitro . Results Using a published microarray dataset generated using parotid gland biopsies we could demonstrate upregulation of a portion of the B cell CD40 gene signature in biopsies from pSS patients but not from healthy donors or individuals with Sicca symptoms, suggesting that CD40 pathway activation was occurring within disease-relevant tissue in lymphocytes implicated in disease pathology. To better understand the role of CD40-CD154 interactions in ELS, we examined salivary glands in CD40 knockout NOD mice. Wild-type NOD mice develop sialadenitis, anti-SSA/SSB autoantibodies, and display evidence of ELS in salivary glands. In contrast, there was no evidence of ELS, sialadenitis or autoantibodies in CD40 deficient NOD mice up to one year of age. Further, anti-CD154 treatment resulted in disaggregation in splenic GCs as well as established ELS in NOD mice and resulted in decreased levels of IgG secreting cells in salivary glands. Conclusions Collectively our data indicate that CD40 pathway signalling is essential for formation and maintenance of salivary gland ELS and suggest that CD40 pathway signalling is active in established ELS from pSS patients, supporting the notion that blockade of CD40-CD154 interactions may provide therapeutic benefit in patients suffering from this autoimmune exocrinopathy. Disclosure of Interest G. Wieczorek Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, M. Bigaud Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, S. Pfister Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, S. Hoersch Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, K. McMichael Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, C. Afatsawo Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, M. Hamburger Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, C. Texier Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, C. Cojean Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland, M. Henry Employee of: Ex employee of Novartis Institutes for Biomedical Research, Basel, Switzerland, J. Rush Employee of: Novartis Institutes for Biomedical Research, Basel, Switzerland

Class switch recombination (CSR) is the process whereby B cells alter the effector properties of their Ig molecules. Whilst much is known about the cellular regulation of this process, many of the molecular details remain elusive. Recent evidence suggests that CSR involves blunt DNA double strand breaks (dsbs), and that formation of these dsbs requires the function of the activation-induced cytidine deaminase (AID). We sought to characterize the structural properties and kinetics of induction of the DNA lesions associated with CSR. Using ligation-mediated PCR, we found that AID-dependent DNA dsbs were specifically induced in the S mu region of murine B cells stimulated to undergo CSR. While blunt dsbs were detected, they were only a minor species, with staggered breaks being more than an order of magnitude more abundant. In addition, these breaks could be detected at equal frequency at upstream and downstream portions of S mu, and were induced prior to expression of newly switched isotypes. Collectively, these results provide direct evidence that staggered, S mu-targeted AID-dependent dsbs are the predominant DNA lesion associated with CSR, with important implications for the mechanisms by which CSR DNA lesions are made and processed.

Class switch recombination (CSR), somatic hypermutation, and gene conversion are immunoglobulin diversification mechanisms that are strictly dependent on the activity of the activation-induced cytidine deaminase (AID). The precise role and substrate(s) of AID in these processes remain to be well defined. The closest homologue of AID is APOBEC-1, a bona fide mRNA-editing enzyme, which shares with AID the ability to deaminate cytidines within single-stranded DNA in vitro and in prokaryotic cells. To determine whether APOBEC-1 can therefore substitute for AID in activated B cells, we expressed human AID, a catalytic mutant thereof, and rat APOBEC-1 in AID-deficient murine B cells. Whereas AID rescued CSR, neither the inactive mutant nor APOBEC-1 could complement AID deficiency. This indicates that cytidine deaminase activity is necessary but not sufficient to initiate CSR, and suggests that AID is specifically targeted to its cognate substrate, the immunoglobulin genes or a distinct mRNA, by an as-yet-unknown mechanism.

T cells stimulate B cells to divide and differentiate by providing activating signals in the form of inducible membrane-bound molecules and secreted cytokines. Provision of these signals in vitro reproduces many of the consequences of T-B collaboration in the absence of any form of Ag stimulation. Although clearly not obligatory, Ag signals appear to play an important regulatory role in numerous aspects of the B cell response. To examine directly the effect of an Ag signal, naive B cells were stimulated in the presence of rCD40 ligand, with or without IL-4 in the presence or absence of different anti-Ig mAbs. Anti-Ig mAbs exerted variable effects on the B cell division rate, from enhancement to no effect to inhibition. In contrast, all anti-Ig mAbs tested inhibited division-linked isotype switching to IgG1 and IgE. Thus, B cell Ag receptor ligands could modify the rates of B cell expansion and class switching independently. The ability of anti-Ig reagents to modify class switching suggests the B cell Ag receptor may play an important role in the selection of Ig isotypes during T cell-dependent humoral immune responses to Ags of different physical structure.

Mature T and B lymphocytes respond to receptor-delivered signals received during and following activation. These signals regulate the rates of cell death, growth, differentiation and migration that ultimately establish the behaviour patterns collectively referred to as immune regulation. We have been pursuing the philosophy that in vitro systems of lymphocyte stimulation, when analysed quantitatively, help reveal the logical attributes of lymphocyte behaviour. The development of carboxyfluorescein diacetate succinimidyl ester (CFSE) to track division has enabled the variable of division number to be incorporated into these quantitative analyses. Our studies with CFSE have established a fundamental link between differentiation and division number. Isotype switching, expression of T cell cytokines, surface receptor alterations and changes to intracellular signalling components all display independent patterns of change with division number. The stochastic aspects of these changes and the ability of external signals to independently regulate them argue for a probabilistic modelling framework for describing and understanding immune regulation.

Top of pageAbstract The collaboration between T and B lymphocytes is used as an example to illustrate how the key features of immune regulation (cell interaction, reciprocal exchange of signals by cell contact, and dependence on soluble cytokines) serve as amplifying reactions. By linking cell-based amplifiers in sequence, the resulting immune response is made highly sensitive to small changes in the environment. Thus, intercellular communication in the immune system can be viewed as a higher level analogue to the kinase cascades that amplify intracellular signalling mechanisms. Keywords: CD40, cell communication, cytokines, immune regulation, T–B collaboration, T-dependent antibody