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The 15th edition of the Workshop on Recent Issues in Bioanalysis (15th WRIB) was held on 27 September to 1 October 2021. Even with a last-minute move from in-person to virtual, an overwhelmingly high number of nearly 900 professionals representing pharma and biotech companies, contract research organizations (CROs), and multiple regulatory agencies still eagerly convened to actively discuss the most current topics of interest in bioanalysis. The 15th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on biomarker assay development and validation (BAV) (focused on clarifying the confusion created by the increased use of the term “Context of Use – COU”); mass spectrometry of proteins (therapeutic, biomarker and transgene); state-of-the-art cytometry innovation and validation; and, critical reagent and positive control generation were the special features of the 15th edition. This 2021 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2021 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on TAb/NAb, Viral Vector CDx, Shedding Assays; CRISPR/Cas9 & CAR-T Immunogenicity; PCR & Vaccine Assay Performance; ADA Assay Comparability & Cut Point Appropriateness. Part 1A (Endogenous Compounds, Small Molecules, Complex Methods, Regulated Mass Spec of Large Molecules, Small Molecule, PoC), Part 1B (Regulatory Agencies' Inputs on Bioanalysis, Biomarkers, Immunogenicity, Gene & Cell Therapy and Vaccine) and Part 2 (ISR for Biomarkers, Liquid Biopsies, Spectral Cytometry, Inhalation/Oral & Multispecific Biotherapeutics, Accuracy/LLOQ for Flow Cytometry) are published in volume 14 of Bioanalysis, issues 9 and 10 (2022), respectively.

The 14th edition of the Workshop on Recent Issues in Bioanalysis (14th WRIB) was held virtually on June 15-29, 2020 with an attendance of over 1000 representatives from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations, and regulatory agencies worldwide. The 14th WRIB included three Main Workshops, seven Specialized Workshops that together spanned 11 days in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy and vaccine. Moreover, a comprehensive vaccine assays track; an enhanced cytometry track and updated Industry/Regulators consensus on BMV of biotherapeutics by LCMS were special features in 2020. As in previous years, this year's WRIB continued to gather a wide diversity of international industry opinion leaders and regulatory authority experts working on both small and large molecules to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance and achieving scientific excellence on bioanalytical issues. This 2020 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the Global Bioanalytical Community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2020 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on Vaccine, Gene/Cell Therapy, NAb Harmonization and Immunogenicity). Part 1 (Innovation in Small Molecules, Hybrid LBA/LCMS & Regulated Bioanalysis), Part 2A (BAV, PK LBA, Flow Cytometry Validation and Cytometry Innovation) and Part 2B (Regulatory Input) are published in volume 13 of Bioanalysis, issues 4 and 5 (2020), respectively.

The 15th edition of the Workshop on Recent Issues in Bioanalysis (15th WRIB) was held on 27 September to 1 October 2021. Even with a last-minute move from in-person to virtual, an overwhelmingly high number of nearly 900 professionals representing pharma and biotech companies, contract research organizations (CROs), and multiple regulatory agencies still eagerly convened to actively discuss the most current topics of interest in bioanalysis. The 15th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on biomarker assay development and validation (BAV) (focused on clarifying the confusion created by the increased use of the term "Context of Use - COU"); mass spectrometry of proteins (therapeutic, biomarker and transgene); state-of-the-art cytometry innovation and validation; and, critical reagent and positive control generation were the special features of the 15th edition. This 2021 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2021 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on TAb/NAb, Viral Vector CDx, Shedding Assays; CRISPR/Cas9CAR-T Immunogenicity; PCRVaccine Assay Performance; ADA Assay ComparabilityCut Point Appropriateness. Part 1A (Endogenous Compounds, Small Molecules, Complex Methods, Regulated Mass Spec of Large Molecules, Small Molecule, PoC), Part 1B (Regulatory Agencies' Inputs on Bioanalysis, Biomarkers, Immunogenicity, GeneCell Therapy and Vaccine) and Part 2 (ISR for Biomarkers, Liquid Biopsies, Spectral Cytometry, Inhalation/OralMultispecific Biotherapeutics, Accuracy/LLOQ for Flow Cytometry) are published in volume 14 of Bioanalysis, issues 9 and 10 (2022), respectively.

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BI 695501 has shown similar efficacy, safety, and immunogenicity to the adalimumab reference product, Humira®. We present two phase 1 studies comparing the pharmacokinetics, safety, and immunogenicity of BI 695501 delivered via autoinjector (AI) vs. prefilled syringe (PFS). Both trials were randomized, open-label, parallel-group studies undertaken in subjects aged ≥ 18–65 years. VOLTAIRE®-AI (NCT02606903) recruited healthy, Caucasian, male, non-athletic volunteers with BMI ≥ 18 to ≤ 30 kg/m2. VOLTAIRE®-TAI (NCT02899338) recruited healthy men and women with BMI > 17.5 to

This Phase I study (VOLTAIRE®-PK) aimed to evaluate three-way pharmacokinetic similarity (bioequivalence), safety, and immunogenicity of BI 695501 (a Humira® [adalimumab] biosimilar candidate) compared with US- and EU-approved Humira in healthy male subjects.Subjects (N = 327) were randomized 1:1:1 to receive one 40-mg subcutaneous dose of BI 695501, US- or EU-approved Humira; safety was assessed for 70 days. Bioequivalence was evaluated using the average bioequivalence method to test if the 90% confidence intervals (CIs) of the geometric means (BI 695501 vs US- and EU-approved Humira) for the primary end points were within prespecified acceptance ranges (80-125%). Immunogenicity was assessed using a sensitive bridging method.Bioequivalence between BI 695501 and US- and EU-approved Humira was demonstrated with the 90% CIs of the ratios of all primary end points: CThree-way bioequivalence of BI 695501 to US- and EU-approved Humira was demonstrated; safety and immunogenicity results of the three study drugs were also similar.2013-003722-84 (EudraCT) and NCT02045979.

Introduction BI 695501 has shown similar efficacy, safety, and immunogenicity to the adalimumab reference product, Humira®. We present two phase 1 studies comparing the pharmacokinetics, safety, and immunogenicity of BI 695501 delivered via autoinjector (AI) vs. prefilled syringe (PFS). Methods Both trials were randomized, open-label, parallel-group studies undertaken in subjects aged ≥ 18–65 years. VOLTAIRE®-AI (NCT02606903) recruited healthy, Caucasian, male, non-athletic volunteers with BMI ≥ 18 to ≤ 30 kg/m2. VOLTAIRE®-TAI (NCT02899338) recruited healthy men and women with BMI > 17.5 to

Background PK bioequivalence of BI 695501, an adalimumab biosimilar candidate, and the adalimumab originator was demonstrated previously (VOLTAIRE®-PK: Wynne et al., Expert Opin Investig Drugs 2016;25:1361–70). Administration in chronic inflammatory diseases benefits from patient-friendly PFSs or AIs, the development of which requires assessment of PK, safety, immunogenicity, and local tolerability. Objectives To compare PK, safety, immunogenicity, and tolerability of BI 695501 after subcutaneous (SC) injection using either a PFS or an AI. Methods In this 16-week randomised, single-dose, open-label, parallel-group study (NCT02606903), 40mg BI 695501 was administered either via PFS or AI in healthy, Caucasian, male, non-athletic volunteers aged 18–65 years with body mass index (BMI) of ≥18 to ≤30 kg/m 2 . The study end points included AUC 0–1032 , C max , and AUC 0–∞ , analysed using an ANOVA model with fixed effects for treatment and BMI group. Safety assessment included the proportion of subjects with drug-related adverse events (AEs). Immunogenicity parameters were: proportion of subjects with binding/neutralising anti-drug antibodies (ADAs), and ADA titers. Results Seventy-one volunteers were randomised: PFS, n=36; AI, n=35. Key demographic and baseline characteristics were well balanced between the treatment groups. PK end point results are shown in Table 1. Estimates for AI/PFS geometric mean (gMean) ratios were within the standard bioequivalence acceptance range (80–125%). Mean plasma concentration-time profiles and total exposure for BI 695501 administered via PFS or AI were similar over the observation period; treatment-emergent AEs (TEAEs) and administration site conditions (ASC) are shown in Table 2. Similar frequencies of patients tested positive for ADAs (57.6% in the PFS group and 51.5% in the AI group), and for neutralising antibodies (33.3%% in the PFS group and 30.3% in the AI group) at the end of the study. Conclusions PK, safety, tolerability, and immunogenicity of BI 695501 after SC injection with a PFS or an AI were comparable. Disclosure of Interest : S. Ramael: None declared, V. Moschetti Employee of: Boehringer Ingelheim, N. Peter Employee of: Boehringer Ingelheim, I. Sonderegger Employee of: Boehringer Ingelheim, S. Wiebe Employee of: Boehringer Ingelheim, B. Liedert Employee of: Boehringer Ingelheim

Background PK bioequivalence of BI 695501, a biosimilar candidate, and the adalimumab originator was demonstrated previously (VOLTAIRE®-PK: Wynne et al., Expert Opin Investig Drugs 2016;25:1361–70) and led to further clinical development. Objectives To demonstrate clinical equivalence of BI 695501 with the adalimumab originator by comparing efficacy, safety and immunogenicity using a clinical model sensitive to detect potential differences between the two biologics. Methods In this 58-week, multi-national, multicentre, randomised, double-blind, parallel arm Phase III study (NCT02137226), 645 pts (18–80 years) with moderate to severe active RA on stable treatment with methotrexate were randomised to receive US-licensed SC adalimumab originator or BI 695501 40mg Q2W for 24 weeks. At Wk 24, pts on adalimumab originator were re-randomised to continue the adalimumab originator or switch to BI 695501 until Wk 48. Pts on BI 695501 were dummy re-randomised. Co-primary end points were proportion of pts achieving ACR20 at Wks 12 and 24. Equivalence between BI 695501 and the adalimumab originator was demonstrated if the relevant confidence intervals (CI) for differences in ACR20 response rate at Wks 12 and 24 were within the predefined margins (Wk 12: 90% CI –12%, 15%; Wk 24: 95% CI –15%, 15%). The secondary efficacy end point was change from baseline in DAS28-ESR at Wks 12 and 24. Safety and immunogenicity were exploratory objectives. Wk 48/58 data will be reported later. Results The co-primary end points of ACR20 response at Wks 12 and 24 were within the pre-defined criteria for equivalence, demonstrating clinical equivalence between BI 695501 and the adalimumab originator (Table 1). The proportion of pts with treatment-emergent adverse events (TEAE) was similar between the BI 695501 and the adalimumab originator treatment groups (Table 2). Rates of serious AEs and discontinuation due to TEAEs were similar across the groups. No deaths were reported during the study. Similar frequencies of pts tested positive for anti-drug antibodies (BI 695501 43.2%; adalimumab originator 47.8%), and neutralising antibodies (BI 695501 16.0%; adalimumab originator 20.6%) in both groups at Week 24. Conclusions This study in pts with RA demonstrated that BI 695501 and the adalimumab originator are highly similar in terms of efficacy, safety and immunogenicity. Disclosure of Interest : S. Cohen Grant/research support from: Amgen, Boehringher Ingelheim, Coherus, Pfizer, Consultant for: Amgen, Boehringher Ingelheim, Celltrion, Merck, Pfizer, Sandoz, A. Alonso-Ruiz: None declared, P. Klimiuk: None declared, E. Lee: None declared, N. Peter Employee of: Boehringer Ingelheim, I. Sonderegger Employee of: Boehringer Ingelheim, D. Assudani Employee of: Boehringer Ingelheim

A long systemic half-life is key for therapeutic proteins. To that end we have generated serum albumin-binding designed ankyrin repeat domains. These domains bind serum albumin of different species with nanomolar affinities, and have significantly improved pharmacokinetic properties both in mouse and cynomolgus monkey compared to non-serum albumin-binding DARPin® domains. In addition, they exhibit high thermal stability and long storage stability, which is an essential feature for their use in drug development. Covalently linking a serum albumin-binding DARPin® domain to domains with other target specificities results in improvements of multiple orders of magnitude in exposure and terminal half-life, both in mouse and cynomolgus monkey. Pharmacokinetic assessment of such constructs revealed terminal half-life values ranging from 27 h to 80 h in mouse, and from 2.6 days to 20 days in cynomolgus monkey. Extrapolation by allometric scaling on these findings suggests terminal half-life values of 5-50 days in human, indicating that pharmacokinetic properties in the range of monoclonal antibodies can be achieved with DARPin® drug candidates. Such serum albumin-binding DARPin® domains are thus valuable tools for the generation of multi-functional drugs with an extended in vivo half-life.

Objective To demonstrate clinical equivalence of adalimumab biosimilar candidate BI 695501 with Humira. Methods Patients with active rheumatoid arthritis on stable methotrexate were randomised to BI 695501 or Humira in a double-blind, parallel-group, equivalence study. At week 24, patients were rerandomised to continue BI 695501 or Humira, or switch from Humira to BI 695501. The coprimary endpoints were the percentage of patients achieving the American College of Rheumatology 20% response criteria (ACR20) at weeks 12 and 24. Further efficacy and safety endpoints and immunogenicity were assessed up to week 58. Results 645 patients were randomised. At week 12, 67.0% and 61.1% (90% CI –0.9 to 12.7) of patients receiving BI 695501 (n=324) and Humira (n=321), respectively, achieved ACR20; at week 24 the corresponding values were 69.0% and 64.5% (95% CI –3.4 to 12.5). These differences were within prespecified margins (week 12: 90% CI (–12% to 15%); week 24: 95% CI (−15% to 15%)), demonstrating therapeutic bioequivalence. 593 patients were rerandomised at week 24. Up to week 48, mean change from baseline in Disease Activity Score 28-erythrocyte sedimentation rate and ACR20/ACR50/ACR70 response rates were similar across the switched (n=147), continuous BI 695501 (n=298) and continuous Humira (n=148) groups. Similar immunogenicity (antidrug antibodies (ADAs), ADA titres and neutralising antibodies) was seen between BI 695501 and Humira (to week 24) and across rerandomised groups (to week 48). Safety and tolerability profiles were similar between groups. Conclusions BI 695501 demonstrated similar efficacy, safety and immunogenicity to Humira; switch from Humira to BI 695501 had no impact on efficacy, safety and immunogenicity. Trial registration number NCT02137226, Results.

IL-17-producing CD4 + T cells have been recognized as key players in organ-related autoimmune disease; however, the parameters that govern their development are yet to be elucidated fully. By using both in vivo and in vitro systems, we have investigated the role of antigen dose, pathogen-associated molecular patterns, and CD40–CD40 ligand (CD40L) cross-talk in Th17 differentiation. We found that the strength of antigenic stimulation critically influenced the extent of Th17 differentiation, because high, but not low or intermediate, antigen concentrations led to IL-17 production. Strong antigenic stimulation of T cells up-regulated CD40L expression, which in concert with certain microbial stimuli (i.e., cytosine phosphate guanine, curdlan, and zymosan) synergistically increased dendritic cell (DC) IL-6 production and Th17 polarization. CD40-deficient DCs exhibited reduced cytokine release and failed to drive Th17 development in vitro. These results were confirmed in vivo where the absence of CD40–CD40L cross-talk was found to prevent the expansion of IL-17-producing cells and accordingly the development of experimental autoimmune encephalitis. Our data demonstrate that CD40–CD40L cross-talk is important for Th17 development by translating strong T cell receptor and microbial stimuli into IL-6 production.

Th17 cells have been recognized as the central effectors in organ-related autoimmune diseases. IL-6 is a key factor that reciprocally regulates Th17 and Foxp3(+) Treg differentiation by inhibition of TGF-beta induced Foxp3 and induction of RORgammat, a Th17 lineage-specific transcription factor. Recently IL-21 has been suggested to induce RORgammat and Th17 development in the absence of IL-6. However, the relevance of IL-21 for Th17-dependent inflammatory responses in vivo remains unclear. In this study, we demonstrate that differentiation of IL-17-producing CD4 T cells, their recruitment to inflamed organs, and the development of autoimmune disease was not affected in il21R(-/-) and il21(-/-) mice in models of myelin oligodendrocyte glycoprotein-induced autoimmune encephalitis and autoimmune myocarditis. IL-6 induced Th17 differentiation independent of and much more potently than IL-21 in vitro. These data suggest that IL-6 is sufficient to drive Th17 development and associated autoimmunity in vivo in the absence of IL-21 or IL-21R.

Interleukin 21 (IL-21) is a member of the common γ-chain family of cytokines, which influence a broad spectrum of immunologic responses. A number of studies have examined the function of IL-21, but its specific role in Th1/Th2-cell differentiation and related effector responses remains to be clarified. Thus, we generated IL-21R–deficient mice and have investigated the role of IL-21R signaling using a series of in vivo experimentally induced disease models. We first addressed the role of IL-21R signaling in Th2 immune responses by examining allergic airway inflammation, and Nippostrongylus brasiliensis and Heligmosomoides polygyrus antihelminth responses. In each of these systems, IL-21R signaling played a clear role in the development of Th2 responses. Comparatively, IL-21R signaling was not required for the containment of Leishmania major infection or the development of experimental autoimmune myocarditis, indicative of competent Th1 and Th17 responses, respectively. Adoptive transfer of T cells and analysis of IL-21R+/+/IL-21R−/− chimera mice revealed that IL-21R–signaling was central to Th2-cell survival or migration to peripheral tissues. Overall, our data show IL-21 plays a crucial role in supporting polarized Th2 responses in vivo, while appearing superfluous for Th1 and Th17 responses.

Genetic susceptibility and autoimmunity triggered by microbial infections are factors implicated in the pathogenesis of dilated cardiomyopathy, the most common cause of heart failure in young patients. Here we show that dendritic cells (DCs) loaded with a heart-specific self peptide induce CD4+ T-cell-mediated myocarditis in nontransgenic mice. Toll-like receptor (TLR) stimulation, in concert with CD40 triggering of self peptide-loaded dendritic cells, was shown to be required for disease induction. After resolution of acute myocarditis, DC-immunized mice developed heart failure, and TLR stimulation of these mice resulted in relapse of inflammatory infiltrates. Injection of damaged, syngeneic cardiomyocytes also induced myocarditis in mice if TLRs were activated in vivo. DC-induced myocarditis provides a unifying theory as to how tissue damage and activation of TLRs during infection can induce autoimmunity, relapses and cardiomyopathy.

Dilated cardiomyopathy, resulting from myocarditis, is the most common cause of heart failure in young patients. We here show that interleukin (IL)-1 receptor type 1-deficient (IL-1R1(-/-)) mice are protected from development of autoimmune myocarditis after immunization with alpha-myosin-peptide(614-629). CD4(+) T cells from immunized IL-1R1(-/-) mice proliferated poorly and failed to transfer disease after injection into naive severe combined immunodeficiency (SCID) mice. In vitro stimulation experiments suggested that the function of IL-1R1(-/-)CD4(+) T cells was not intrinsically defect, but their activation by dendritic cells was impaired in IL-1R1(-/-) mice. Accordingly, production of tumor necrosis factor (TNF)-alpha, IL-1, IL-6, and IL-12p70 was reduced in dendritic cells lacking the IL-1 receptor type 1. In fact, injection of immature, antigen-loaded IL-1R1(+/+) but not IL-1R1(-/-) dendritic cells into IL-1R1(-/-) mice fully restored disease susceptibility by rendering IL-1R1(-/-) CD4(+) T cells pathogenic. Thus, IL-1R1 triggering is required for efficient activation of dendritic cells, which is in turn a prerequisite for induction of autoreactive CD4(+) T cells and autoimmunity.

Interleukin-5 (IL-5) is a cytokine which is essential for the maturation of eosinophils in bone marrow and for their release into the blood. Eotaxin is a CC type chemokine implicated in the recruitment of eosinophils in a variety of inflammatory disorders. Since eosinophil-activity is governed by these two pathways, we targeted both IL-5 and eotaxin by active vaccination to block eosinophilia. We produced two vaccines by chemically cross-linking IL-5 or eotaxin to a virus-like particle (VLP) derived from the bacteriophage Qbeta, yielding highly repetitive arrays of these cytokines on the VLP surface. Both vaccines overcame self-tolerance and induced high antibody titers against the corresponding self-molecules in mice. Immunization with either of the two vaccines reduced eosinophilic inflammation of the lung in an ovalbumin (OVA) based mouse model of allergic airway inflammation. Animals immunized with the two vaccines at the same time developed high antibody titers against both cytokines and also reduced eosinophil-infiltration of the lung. These data demonstrate that targeting either IL-5 or eotaxin may lower eosinophilia. Simultaneous immunization against IL-5 and eotaxin demonstrates that such a therapeutic approach may be used to treat complex disorders in which multiple mediators are involved.

Granulocyte macrophage–colony stimulating factor (GM-CSF) is critically involved in development of organ-related autoimmune inflammatory diseases including experimental allergic encephalitis and collagen-induced arthritis. Roles of GM-CSF in the initiation and in the effector phase of the autoimmune response have been proposed. Our study was designed to investigate the mechanisms of GM-CSF in autoimmunity using a model of autoimmune heart inflammatory disease (myocarditis). The pathological sequel after immunization with heart myosin has been shown previously to depend on IL-1, IL-6, IL-23, and IL-17. We found that innate GM-CSF was critical for IL-6 and IL-23 responses by dendritic cells and generation of pathological Th17 cells in vivo. Moreover, GM-CSF promoted autoimmunity by enhancing IL-6–dependent survival of antigen specific CD4+ T cells. These results suggest a novel role for GM-CSF in promoting generation and maintenance of Th17 cells by regulation of IL-6 and IL-23 in vivo.

Autoimmune responses directed against heart-specific antigens most likely play a key role in the pathogenesis of myocarditis. Although autoantibodies against cardiac determinants are frequently detected both in human patients and mice suffering from myocarditis, the immunological mechanisms for their induction have not yet been fully explored. We used here the SEREX approach (serological identification of recombinantly expressed proteins) to molecularly dissect heart-specific autoimmune B cell responses that develop in the course of experimentally induced myocarditis. Screening of a heart cDNA library with sera of cardiac myosin heavy chain alpha (myhcalpha) peptide-immunized BALB/c mice revealed a strong focusing of the B cell response on the myhcalpha protein. The vast majority of the myhcalpha transcripts coded for regions other than the sequence of the immunogenic myhcalpha peptide, indicating extensive intramolecular epitope spreading. Importantly, we found that the infection with cardiotropic viruses such as MCMV and Coxsackievirus B3 elicited specific autoantibody pattern with a particular skewing to the myhcalpha protein. The induction of myhcalpha peptide-specific Th cells in the course of both infections suggests that infection-associated determinant spreading on the Th cell level paves the way for a focused and dominant anti-myhcalpha B cell response.

The most common reason for heart failure in young adults is dilated cardiomyopathy often resulting from myocarditis. Clinical studies and animal models provide evidence that an autoimmune response against heart myosin is the underlying reason for the disease. IL-12 has been suggested to play a key role in development of experimental autoimmune myocarditis (EAM), as IL-12p40 and IL-12Rbeta1 knockouts are protected from disease. In this study, we have compared IL-12p40-/- mice, IL-12p35-/- mice and mice treated with a neutralizing IL-23 antibody in EAM and found that in fact IL-23, not IL-12, is responsible for inflammatory heart disease. However, these cytokines appear to have redundant activity for priming and expansion of autoreactive CD4 T cells, as specific T cell proliferation was only defective in the absence of both cytokines. IL-23 has been suggested to promote a pathogenic IL-17-producing T cell population. We targeted IL-17 by capitalizing on an active vaccination approach that effectively breaks B cell tolerance. Neutralization of IL-17 reduced myocarditis and heart autoantibody responses, suggesting that IL-17 is the critical effector cytokine responsible for EAM. Thus, targeting of IL-23 and IL-17 by passive and active vaccination strategies holds promise as a therapeutic approach to treat patients at risk for development of dilated cardiomyopathy.

The activation of lymphocytes and development of adaptive immune responses is initiated by the engagement of TCRs by antigenic peptide–MHC complexes and shaped at the clonal level by both positive and negative costimulatory signals. The B7 family members are involved at several stages in this process. In this issue of the JCI, Vogt et al. show that the B7 family–related protein V-set and Ig domain–containing 4 (VSIG4) can act as an inhibitor of T cell activation (see the related article beginning on page 2817). Intriguingly, the same molecule was recently independently identified as a complement receptor of the Ig superfamily (CRIg) and was convincingly demonstrated to be a receptor for complement component 3 fragments. These findings raise interesting questions regarding the physiological roles and mechanisms of action of this molecule. Identification of dual functions of this molecule provides an additional level of complexity in T cell costimulation.

Members of a subfamily of the type 1 four-helix-bundle cytokines with receptors sharing the common gamma (cγ) chain including IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 have distinct activities on the differentiation of effector, memory, and regulatory T cells [1,2]. Furthermore, IL-2, IL-4, and IL-21 serve distinct roles in control of B cell development and differentiation to antibody producing cells. We and others recently reported that both IL-2 and IL-21 are essential for maintenance of CD8 T cells and control of chronic viral infection, while both cytokines are dispensable for expansion and contraction of CD8 T cells during acute and resolved viral infection [3-7]. While IL-21 has been implicated in cross-regulation of Th17 cells and inducible regulatory T cells (Treg) in vitro, development of Th17 and Treg cells and consequently organ-related autoimmune disease remain unaffected in IL-21R-deficient mice in vivo [8,9]. In contrast, we now found that IL-21 can potently inhibit proliferation and function of inducible and natural Treg cells in models of T cell transfer colitis, viral infection, and asthma. Increased numbers of Tregs in IL-21R-deficient mice offer an explanation for suppression of Th2-mediated asthma and susceptibility to chronic viral infection described in the knockout mice [5,10]. Furthermore, the importance of IL-21 for B cell and antibody responses has been well established. Recently, it has been suggested that IL-21 is crucial for development of T follicular helper cells (Tfh) and defective B cell responses in IL-21R-deficient mice are due to the absence of Tfh cells. However, we found that germinal center development and antibody responses were severely impaired in mice that lack IL-21R specifically on B cells suggesting that IL-21 regulates germinal center responses in a B cell intrinsic manner [11]. In addition, we have shown that requirement of IL-21 for a B cell response is overcome by immunization with particulate antigens containing TLR7/8 ligands (such as viral RNS). These data demonstrate that innate pathogen patterns (PAMPs) and Th cell derived signals co-operate in the induction of optimal IgG responses. Interestingly, in contrast to follicular B cell responses, IL-21 has been shown to negatively regulate marginal zone (MZ) B-cell survival and antibody production to Streptococous pneumonia [12].

Corrigendum: Dendritic cell–induced autoimmune heart failure requires cooperation between adaptive and innate immunity