Publicação
Reprogramming the immune system with anti-CD4 monoclonal antibodies
| Resumo: | Immune tolerance is a state where the immune system does not respond aggressively towards a set of antigens while remaining fully competent to mount protective responses. The immune system is usually tolerant to our own antigens (self), to food antigens (oral tolerance), and to several other foreign substances to which we are regularly exposed (such as pollens and other potential allergens). Nevertheless, under certain conditions (genetic or environmental) there is a breakdown of tolerance to certain antigens, thus originating the onset of autoimmune and allergic pathologies. Regulatory T cells (Tregs) are central players in the maintenance of peripheral tolerance, having an essential role in preventing autoimmunity, as well as hypersensitivity reactions. However, the molecular mechanisms which mediate suppression are still obscure, and their investigation is a current priority, as it may reveal important targets for immune intervention. Studies in mouse models show that monoclonal antibodies (mAbs) targeting key lymphocyte molecules are able to produce long‐term tolerance following a shortterm therapy. This concept became known as immune reprogramming or therapeutic tolerance induction. Non‐depleting anti‐CD4 mAb have been shown to induce long term tolerance in transplantation through induction of Treg cells. Here I describe my research on the impact of non‐depleting anti‐CD4 mAb in different immune‐mediated pathologies aiming to reprogram the immune system towards tolerance induction. Furthermore, I studied the cellular and molecular mechanisms that mediate tolerance induction. The first step in this study was to assess tolerance induction in murine models of autoimmune diseases, where self‐tolerance is broken. We took advantage of well established animal models of rheumatoid arthritis (RA) and multiple sclerosis (MS), which are known to be mediated by Th1 and Th17 cells, thus indicating CD4 would be an optimal therapeutic target. Treatment with anti‐CD4 was successful in both models, being able to prevent the onset of the disease, and impairing disease progression. We found the mechanism characterizing anti‐CD4 effect relies on resetting the balance between effector and Treg cells towards a tolerance‐favoring ratio. In autoimmune arthritis we found this effect to be especially evident locally at the site of inflammation (within the synovia), where Th17 effector cells are markedly reduced and the Treg frequency is increased in anti‐CD4 treated mice. The study of experimental autoimmune encephalomyelitis (EAE) allowed us to track antigen‐specific T cells, and further study the impact of anti‐CD4 treatment on naïve and pre‐activated T cells. We found anti‐CD4 prevented the proliferation and differentiation of naïve T cells into effector cells producing pro‐inflammatory cytokines (such as IL‐17 and IFN‐γ), with a progressive accumulation of Treg cells at a later time that are important in maintaining long‐term protection from the disease. Furthermore, anti‐CD4 therapy targets pre‐activated T cells in a different way by committing effector T cells towards apoptosis, thus leading to a ratio between effector and regulatory cells that once again favors tolerance. Importantly, the reprogramming is specific for the antigens present at the time of anti‐CD4‐treatment, with tolerant mice remaining fully competent to mount protective immune responses, namely to eradicate viral infections. Having established the efficacy of anti‐CD4‐induced tolerance induction in Th1/Th17 mediated diseases, I wanted to evaluate the impact of anti‐CD4‐treatment in a stringent model of Th2‐induced pathology, studying whether the mAb treatment could prevent peanut‐induced anaphylaxis in C3H/HeJ mice. Treatment with anti‐CD4 at the time of exposure to peanut antigens led to long‐term protection from further sensitization with peanut‐antigens and the development of anaphylaxis. Such long‐term tolerance was antigen specific as mice remained competent to respond to different antigens, namely by producing Th2‐mediated responses leading to IgE production. We found that long‐term tolerance appeared to be dependent on Treg cells: not only anti‐CD4 treated mice exhibited an increased frequency of Foxp3+ Tregs, but also CD25 depletion at the time of anti‐CD4 treatment abrogated tolerance induction. Taken together the results presented in this thesis suggest CD4 is a promising therapeutic target for the treatment of immune‐mediated pathologies, as different as autoimmune and allergic diseases. |
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| Autores principais: | Duarte, Joana Duarte Nunes, 1981- |
| Assunto: | Sistema imunológico Antígenos CD4 Linfócitos T Factores imunológicos Doenças auto-imunes Tolerância imunológica Processos do sistema imunológico Teses de doutoramento - 2011 |
| Ano: | 2011 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Immune tolerance is a state where the immune system does not respond aggressively towards a set of antigens while remaining fully competent to mount protective responses. The immune system is usually tolerant to our own antigens (self), to food antigens (oral tolerance), and to several other foreign substances to which we are regularly exposed (such as pollens and other potential allergens). Nevertheless, under certain conditions (genetic or environmental) there is a breakdown of tolerance to certain antigens, thus originating the onset of autoimmune and allergic pathologies. Regulatory T cells (Tregs) are central players in the maintenance of peripheral tolerance, having an essential role in preventing autoimmunity, as well as hypersensitivity reactions. However, the molecular mechanisms which mediate suppression are still obscure, and their investigation is a current priority, as it may reveal important targets for immune intervention. Studies in mouse models show that monoclonal antibodies (mAbs) targeting key lymphocyte molecules are able to produce long‐term tolerance following a shortterm therapy. This concept became known as immune reprogramming or therapeutic tolerance induction. Non‐depleting anti‐CD4 mAb have been shown to induce long term tolerance in transplantation through induction of Treg cells. Here I describe my research on the impact of non‐depleting anti‐CD4 mAb in different immune‐mediated pathologies aiming to reprogram the immune system towards tolerance induction. Furthermore, I studied the cellular and molecular mechanisms that mediate tolerance induction. The first step in this study was to assess tolerance induction in murine models of autoimmune diseases, where self‐tolerance is broken. We took advantage of well established animal models of rheumatoid arthritis (RA) and multiple sclerosis (MS), which are known to be mediated by Th1 and Th17 cells, thus indicating CD4 would be an optimal therapeutic target. Treatment with anti‐CD4 was successful in both models, being able to prevent the onset of the disease, and impairing disease progression. We found the mechanism characterizing anti‐CD4 effect relies on resetting the balance between effector and Treg cells towards a tolerance‐favoring ratio. In autoimmune arthritis we found this effect to be especially evident locally at the site of inflammation (within the synovia), where Th17 effector cells are markedly reduced and the Treg frequency is increased in anti‐CD4 treated mice. The study of experimental autoimmune encephalomyelitis (EAE) allowed us to track antigen‐specific T cells, and further study the impact of anti‐CD4 treatment on naïve and pre‐activated T cells. We found anti‐CD4 prevented the proliferation and differentiation of naïve T cells into effector cells producing pro‐inflammatory cytokines (such as IL‐17 and IFN‐γ), with a progressive accumulation of Treg cells at a later time that are important in maintaining long‐term protection from the disease. Furthermore, anti‐CD4 therapy targets pre‐activated T cells in a different way by committing effector T cells towards apoptosis, thus leading to a ratio between effector and regulatory cells that once again favors tolerance. Importantly, the reprogramming is specific for the antigens present at the time of anti‐CD4‐treatment, with tolerant mice remaining fully competent to mount protective immune responses, namely to eradicate viral infections. Having established the efficacy of anti‐CD4‐induced tolerance induction in Th1/Th17 mediated diseases, I wanted to evaluate the impact of anti‐CD4‐treatment in a stringent model of Th2‐induced pathology, studying whether the mAb treatment could prevent peanut‐induced anaphylaxis in C3H/HeJ mice. Treatment with anti‐CD4 at the time of exposure to peanut antigens led to long‐term protection from further sensitization with peanut‐antigens and the development of anaphylaxis. Such long‐term tolerance was antigen specific as mice remained competent to respond to different antigens, namely by producing Th2‐mediated responses leading to IgE production. We found that long‐term tolerance appeared to be dependent on Treg cells: not only anti‐CD4 treated mice exhibited an increased frequency of Foxp3+ Tregs, but also CD25 depletion at the time of anti‐CD4 treatment abrogated tolerance induction. Taken together the results presented in this thesis suggest CD4 is a promising therapeutic target for the treatment of immune‐mediated pathologies, as different as autoimmune and allergic diseases. |
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