Christophe M. Filippi

Resolution of a chronic viral infection after interleukin-10 receptor blockade

A defining characteristic of persistent viral infections is the loss and functional inactivation of antiviral effector T cells, which prevents viral clearance. Interleukin-10 (IL-10) suppresses cellular immune responses by modulating the function of T cells and antigen-presenting cells. In this paper, we report that IL-10 production is drastically increased in mice persistently infected with lymphocytic choriomeningitis virus. In vivo blockade of the IL-10 receptor (IL-10R) with a neutralizing antibody resulted in rapid resolution of the persistent infection. IL-10 secretion was diminished and interferon γ production by antiviral CD8+ T cells was enhanced. In persistently infected mice, CD8α+ dendritic cell (DC) numbers declined early after infection, whereas CD8α− DC numbers were not affected. CD8α− DCs supported IL-10 production and subsequent dampening of antiviral T cell responses. Therapeutic IL-10R blockade broke the cycle of IL-10–mediated immune suppression, preventing IL-10 priming by CD8α− DCs and enhancing antiviral responses and thereby resolving infection without causing immunopathology.

Viral Trigger for Type 1 Diabetes: Pros and Cons

The most popular hypothesis circulating within and beyond the scientific community is that viral infections enhance or elicit autoimmune disorders such as type 1 diabetes. Indeed, viruses can injure β-cells and have been isolated in pancreatic tissues from diabetic patients. However, accumulating evidence suggests that the opposite scenario, which is prevention or amelioration of type 1 diabetes, might be at least as common an outcome of viral infection. Here, we discuss epidemiological and experimental evidence for the main mechanisms accounting for the role of viruses in type 1 diabetes to better understand the complex relationship between viral infections and autoimmune diabetes. ### The influence of the environment. Type 1 diabetes is a genetic autoimmune disorder caused by autoreactive CD4+ and CD8+ T-cells that recognize pancreatic antigens such as insulin or GAD and subsequently destroy insulin-producing β-cells. The subject of very active research is the question of how endogenous β-cell antigens become immunogenic. Infiltration of the islets of Langerhans, where β-cells reside, by activated autoreactive T-cells is considered to be the major driving force in type 1 diabetes progression. The islet infiltrate in humans consists primarily of CD8+ T-cells and B-cells, followed by macrophages and dendritic cells of different subtypes (1). Interestingly, significantly fewer T-cells are found in human islets compared with islets from nonobese diabetic (NOD) mice. The reduced numbers of T-cells, and in this way a limited autoreactive component in human islets, leads one to consider whether other contributing factors may be involved in disease development. Otherwise, sufficient insulitic infiltrate to destroy islet β-cells might not be easily maintained in humans. Further supporting a role for nongenetic factors in the control of type 1 diabetes is the observation that disease concordance among monozygotic twins is below 50% (2). Migrant studies also suggest the involvement of an environmental factor in type 1 diabetes, …

Immunoregulatory mechanisms triggered by viral infections protect from type 1 diabetes in mice

Type 1 diabetes (T1D) is an autoimmune disease that is caused by the destruction of insulin-producing beta cells. Viral infections induce immune responses that can damage beta cells and promote T1D or on the other hand prevent the development of the disease. However, the opposing roles of viral infections in T1D are not understood mechanistically. We report here that viruses that do not inflict damage on beta cells provided protection from T1D by triggering immunoregulatory mechanisms. Infection of prediabetic NOD mice with Coxsackie virus B3 or lymphocytic choriomeningitis virus (LCMV) delayed diabetes onset and reduced disease incidence. Delayed T1D onset was due to transient upregulation of programmed cell death-1 ligand 1 (PD-L1) on lymphoid cells, which prevented the expansion of diabetogenic CD8+ T cells expressing programmed cell death-1 (PD-1). Reduced T1D incidence was caused by increased numbers of invigorated CD4+CD25+ Tregs, which produced TGF-beta and maintained long-term tolerance. Full protection from T1D resulted from synergy between PD-L1 and CD4+CD25+ Tregs. Our results provide what we believe to be novel mechanistic insight into the role of viruses in T1D and should be valuable for prospective studies in humans.

IL-10 and the resolution of infections.

Chronic viral infections pose serious health concerns, as secondary complications such as immunodeficiencies and cancers are common. Treating such infections with conventional vaccine approaches has proved to be difficult. Studies in animals and humans suggest that vaccine failure is probably due to exhaustion of antiviral T cell responses, which occurs in a number of chronic infections. Attempts to elucidate the causes of impairment of antiviral immunity have pointed to a role for the immunomodulatory cytokine IL‐10 in the ability of viruses to establish persistence. Induction of IL‐10 production by the host during chronic infection appears to be one of the viral means to alter the class of the antiviral immune response and induce generalized immune suppression. Recent work by us and others suggests that it is possible to resuscitate antiviral immunity by interfering with the IL‐10 signalling pathway. Targeting IL‐10 thus constitutes a promising alternative to conventional vaccine strategies which have not proved to be successful in treating chronic infections. In addition, sterile cure may be achieved with minimal side‐effects by combining agents that alter the IL‐10 signalling pathway with other compounds, such as antiviral drugs or interferon, but also agents neutralizing other crucial elements of T cell exhaustion, such as PD‐1. Copyright

Transforming Growth Factor-β Suppresses the Activation of CD8+ T-Cells When Naïve but Promotes Their Survival and Function Once Antigen Experienced : A Two-Faced Impact on Autoimmunity

OBJECTIVE—Transforming growth factor-β (TGF-β) can exhibit strong immune suppression but has also been shown to promote T-cell growth. We investigated the differential effect of this cytokine on CD8+ T-cells in autoimmunity and antiviral immunity. RESEARCH DESIGN AND METHODS—We used mouse models for virally induced type 1 diabetes in conjunction with transgenic systems enabling manipulation of TGF-β expression or signaling in vivo. RESULTS—Surprisingly, when expressed selectively in the pancreas, TGF-β reduced apoptosis of differentiated autoreactive CD8+ T-cells, favoring their expansion and infiltration of the islets. These results pointed to drastically opposite roles of TGF-β on naïve compared with antigen-experienced/memory CD8+ T-cells. Indeed, in the absence of functional TGF-β signaling in T-cells, fast-onset type 1 diabetes caused by activation of naïve CD8+ T-cells occurred faster, whereas slow-onset disease depending on accumulation and activation of antigen-experienced/memory CD8+ T-cells was decreased. TGF-β receptor–deficient CD8+ T-cells showed enhanced activation and expansion after lymphocytic choriomeningitis virus infection in vivo but were more prone to apoptosis once antigen experienced and failed to survive as functional memory cells. In vitro, TGF-β suppressed naïve CD8+ T-cell activation and γ-interferon production, whereas memory CD8+ T-cells stimulated in the presence of TGF-β showed enhanced survival and increased production of interleukin-17 in conjunction with γ-interferon. CONCLUSIONS—The effect of TGF-β on CD8+ T-cells is dependent on their differentiation status and activation history. These results highlight a novel aspect of the pleiotropic nature of TGF-β and have implications for the design of immune therapies involving this cytokine.

TLR2 signaling improves immunoregulation to prevent type 1 diabetes

Signaling through TLR2 promotes inflammation and modulates CD4+CD25+ Tregs. We assessed mechanistically how this molecule would alter immunoregulation in type 1 diabetes (T1D). We also asked whether TLR2 may be involved in our recent discovery that viral infection can protect from autoimmune diabetes by expanding and invigorating Tregs. Treatment of prediabetic mice with a synthetic TLR2 agonist diminished T1D and increased the number and function of CD4+CD25+ Tregs, also conferring DCs with tolerogenic properties. TLR2 ligation also promoted the expansion of Tregs upon culture with DCs and ameliorated their capacity to prevent the disease. Protection from T1D by lymphocytic choriomeningitis virus (LCMV) infection depended on TLR2. LCMV increased the frequency of CD4+CD25+ Tregs and their production of TGF‐β more significantly in WT than TLR2‐deficient mice. Furthermore, LCMV infection in vivo or LCMV‐infected DCs in vitro rendered, via TLR2, CD4+CD25+ Tregs capable of diminishing T1D. We identify novel mechanisms by which TLR2 promotes immunoregulation and controls autoimmune diabetes in naïve or infected hosts. This work should help understand T1D etiology and develop novel immune‐based therapeutic interventions.

Essential Role for TLR9 in Prime but Not Prime-Boost Plasmid DNA Vaccination To Activate Dendritic Cells and Protect from Lethal Viral Infection

One of the requirements for efficient vaccination against infection is to achieve the best combination of an adequate adjuvant with the antigenic information to deliver. Although plasmid DNA is a promising tool bearing the unique potential to activate humoral and cellular immunity, an actual challenge is to increase plasmid immunogenicity in human vaccination protocols in which efficacy has proven rather limited. Previous work showed that the bacterial DNA backbone of the plasmid has potent adjuvant properties because it contains CpG motifs that are particular activating nucleotidic sequences. Among TLRs, which are key sensors of microbial products, TLR9 can detect CpG motifs and confer activation of APCs, such as dendritic cells. However, whether the immunogenic properties of plasmid DNA involve TLR9 signaling has not been clearly established. In the current study, we demonstrate that TLR9 determines the effectiveness of vaccination against lethal lymphocytic choriomeningitis virus infection using plasmid DNA in a prime, but not prime-boost, vaccination regimen. Furthermore, we provide evidence that the presence of TLR9 in dendritic cells is necessary for effective and functional priming of virus-specific CD8+ T cells upon plasmid exposure in vitro or single-dose vaccination in vivo. Therefore, at single or low vaccine doses that are often used in human-vaccination protocols, CpG/TLR9 interactions participate in the immunogenicity of plasmid DNA. These results suggest that the TLR9 signaling pathway is involved in the efficacy of plasmid vaccination; therefore, it should remain a focus in the development or amelioration of vaccines to treat infections in humans.

TGF-β suppresses the activation of CD8+ T cells when naïve but promotes their survival and function once antigen-experienced: a two-faced impact on autoimmunity

OBJECTIVE—Transforming growth factor-β (TGF-β) can exhibit strong immune suppression but has also been shown to promote T-cell growth. We investigated the differential effect of this cytokine on CD8+ T-cells in autoimmunity and antiviral immunity. RESEARCH DESIGN AND METHODS—We used mouse models for virally induced type 1 diabetes in conjunction with transgenic systems enabling manipulation of TGF-β expression or signaling in vivo. RESULTS—Surprisingly, when expressed selectively in the pancreas, TGF-β reduced apoptosis of differentiated autoreactive CD8+ T-cells, favoring their expansion and infiltration of the islets. These results pointed to drastically opposite roles of TGF-β on naïve compared with antigen-experienced/memory CD8+ T-cells. Indeed, in the absence of functional TGF-β signaling in T-cells, fast-onset type 1 diabetes caused by activation of naïve CD8+ T-cells occurred faster, whereas slow-onset disease depending on accumulation and activation of antigen-experienced/memory CD8+ T-cells was decreased. TGF-β receptor–deficient CD8+ T-cells showed enhanced activation and expansion after lymphocytic choriomeningitis virus infection in vivo but were more prone to apoptosis once antigen experienced and failed to survive as functional memory cells. In vitro, TGF-β suppressed naïve CD8+ T-cell activation and γ-interferon production, whereas memory CD8+ T-cells stimulated in the presence of TGF-β showed enhanced survival and increased production of interleukin-17 in conjunction with γ-interferon. CONCLUSIONS—The effect of TGF-β on CD8+ T-cells is dependent on their differentiation status and activation history. These results highlight a novel aspect of the pleiotropic nature of TGF-β and have implications for the design of immune therapies involving this cytokine.

Antigen-specific induction of regulatory T cells for type 1 diabetes therapy.

Since their discovery decades ago, regulatory T (Treg) cells have prompted many investigations into their potential role in the generation or prevention of autoimmune disorders such as type 1 diabetes (T1D). Initially identified based on their ability to maintain tolerance to self-antigens in peripheral organs, Treg cells have since been efficiently induced therapeutically and shown to prevent the progression of T1D as well as other autoimmune diseases. Beneficial modification of immunity through the induction of Treg cells has been successfully achieved by antigen-based therapy as well as non-antigen-specific (systemic) treatments. In the current article, we review different strategies that have proved effective in preventing autoimmune diabetes and analyze them with respect to translation into clinical applications. Current evidence indicates that antigen-specific induction of potent regulatory mechanisms is influenced by the systemic milieu, suggesting that systemic modulation might be an essential prerequisite for antigen-based therapy and the successful maintenance or reestablishment of tolerance.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: viruses, autoimmunity and immunoregulation.

Based on studies in animal models, viral infections, in particular by enteroviruses, can accelerate or halt type 1 diabetes (T1D) development. Among factors that determine the outcome are the degree of viral replication in the target organ (viral titres), the tropism of the virus for β cells, and the precise time‐point of infection in relation to the diabetogenic process. Mechanisms underlying these phenomena have been assessed in mouse studies and should now be verified for human T1D. For enhancement of diabetes development, up‐regulation of interferon pathways, expression of class‐I major histocompatibility complexes and Toll‐like receptor‐dependent immunity appear important. In contrast, prevention of T1D involves pathways that the immune system usually invokes to shut down anti‐viral responses to limit immunopathology, and which can ‘clean out’ autoreactive memory effector T cells as a bystander phenomenon: up‐regulation of inhibitory molecules and invigoration of regulatory T cell (Treg) function. Importantly, these immunoregulatory processes also appear to foster and sustain persistent viral infections. Induction of immunoregulatory mechanisms, and in particular the phenotype and function of Tregs, is of interest therapeutically and will be discussed.