Macrophage Plasticity in Experimental Atherosclerosis

As in human disease, macrophages (MØ) are central players in the development and progression of experimental atherosclerosis. In this study we have evaluated the phenotype of MØ associated with progression of atherosclerosis in the apolipoprotein E (ApoE) knockout (KO) mouse model

Physiological Induction of Regulatory Qa-1-Restricted CD8+ T Cells Triggered by Endogenous CD4+ T Cell Responses

T cell-dependent autoimmune diseases are characterized by the expansion of T cell clones that recognize immunodominant epitopes on the target antigen. As a consequence, for a given autoimmune disorder, pathogenic T cell clones express T cell receptors with a limited number of variable regions that define antigenic specificity. Qa-1, a MHC class I-like molecule, presents peptides from the variable region of TCRs to Qa-1-restricted CD8+ T cells. The induction of Vß-specific CD8+ T cells has been harnessed in an immunotherapeutic strategy known as the “T cell vaccination” (TCV) that comprises the injection of activated and attenuated CD4+ T cell clones so as to induce protective CD8+ T cells. We hypothesized that Qa-1-restricted CD8+ regulatory T cells could also constitute a physiologic regulatory arm of lymphocyte responses upon expansion of endogenous CD4+ T cells, in the absence of deliberate exogenous T cell vaccination. We immunized mice with two types of antigenic challenges in order to sequentially expand antigen-specific endogenous CD4+ T cells with distinct antigenic specificities but characterized by a common Vß chain in their TCR. The first immunization was performed with a non-self antigen while the second challenge was performed with a myelin-derived peptide known to drive experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. We show that regulatory Vß-specific Qa-1-restricted CD8+ T cells induced during the first endogenous CD4+ T cell responses are able to control the expansion of subsequently mobilized pathogenic autoreactive CD4+ T cells. In conclusion, apart from the immunotherapeutic TCV, Qa-1-restricted specialized CD8+ regulatory T cells can also be induced during endogenous CD4+ T cell responses. At variance with other regulatory T cell subsets, the action of these Qa-1-restricted T cells seems to be restricted to the immediate re-activation of CD4+ T cells

Immune Responses Elicited in Tertiary Lymphoid Tissues Display Distinctive Features

During chronic inflammation, immune effectors progressively organize themselves into a functional tertiary lymphoid tissue (TLT) within the targeted organ. TLT has been observed in a wide range of chronic inflammatory conditions but its pathophysiological significance remains unknown. We used the rat aortic interposition model in which a TLT has been evidenced in the adventitia of chronically rejected allografts one month after transplantation. The immune responses elicited in adventitial TLT and those taking place in spleen and draining lymph nodes (LN) were compared in terms of antibody production, T cell activation and repertoire perturbations. The anti-MHC humoral response was more intense and more diverse in TLT. This difference was associated with an increased percentage of activated CD4+ T cells and a symmetric reduction of regulatory T cell subsets. Moreover, TCR repertoire perturbations in TLT were not only increased and different from the common pattern observed in spleen and LN but also “stochastic,” since each recipient displayed a specific pattern. We propose that the abnormal activation of CD4+ T cells promotes the development of an exaggerated pathogenic immune humoral response in TLT. Preliminary findings suggest that this phenomenon i) is due to a defective immune regulation in this non-professional inflammatory-induced lymphoid tissue, and ii) also occurs in human chronically rejected grafts

Study of CD8+ T cells restricted to Qa-1 (their induction and role in pathophysiology)

Les mécanismes régulateurs des cellules T utilisent une multitude de molécules. Les cellules T CD8+, en reconnaissant des peptides présentés par la molécule du CMH de classe Ib, le Qa-1, exercent un contrôle suppressif sur les cellules T cibles. Ces cellules T CD8+ restreintes au Qa-1 ont été initialement décrites dans le contexte de la vaccination cellulaire T, qui consiste à administrer des cellules T CD4+ autoréactives activées exprimant des complexes Qa-1/peptides. Les cellules T CD8+ induites contrôlent l expansion de cellules T CD4+ autoréactives endogènes et préviennent le développement de maladies autoimmunes. Ici, je montre que l induction de cellules T CD8+ régulatrices restreintes au Qa-1 est un processus physiopathologique faisant suite à l activation endogène des cellules T CD4+. La spécificité des cellules T CD8+ régulatrices induites est déterminée par la nature de la réponse T CD4+ endogène: l activation oligoclonale des cellules T favorise la présentation des peptides dérivés de la chaîne Vß de leur TCR et induit une réponse T CD8+ spécifique de la chaîne Vß; une activation T polyclonale conduit à la présentation de peptides dérivés de molécules d activation ou ergotopes et induit une réponse T CD8+ anti-ergotypique qui contrôle une plus vaste population de cellules T CD4+.Mes résultats montrent que les cellules T CD8+ Qa-1-restreintes induites lors d une réponse T CD4+ contre des antigènes étrangers, contrôlent l expansion ultérieure de cellules T similaires induites par les antigènes du Soi. Ce système de régulation reflète le caractère adaptatif du répertoire des cellules T dont le compartiment régulateur s adapte constamment à chaque réponse immunitaire.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Pathogenic immune response to therapeutic factor VIII: exacerbated response or failed induction of tolerance?

International audienceTherapeutic factor VIII is highly immunogenic. Despite intensive research in the last decades, the reasons why 5-30% of patients with hemophilia A (of all severities) develop inhibitory anti-factor VIII antibodies (inhibitors) following replacement therapy remain an enigma. Under physiological conditions, endogenous factor VIII is recognized by the immune system. Likewise, numerous observations indicate that, in hemophilia A patients without inhibitors, exogenous therapeutic factor VIII is immunologically assessed and tolerated. A large part of the research on the immunogenicity of therapeutic factor VIII is attempting to identify the ‘danger signals’ that act as adjuvants to the deleterious anti-factor VIII immune responses. However, several of the inflammatory assaults concomitant to factor VIII administration initially hypothesized as potential sources of danger signals (e.g., bleeding, infection, and vaccination) have been disproved to be such signals. Conversely, recent evidence suggests that cells from inhibitor-negative patients are able to activate anti-inflammatory and tolerogenic mechanisms required to suppress deleterious immune responses, while cells from inhibitor-positive patients are not. Based on the available observations, we propose a model in which all hemophilia A patients develop anti-factor VIII immune responses during replacement therapy irrespective of associated danger signals. We further postulate that the onset of clinically relevant factor VIII inhibitors results from an inability to develop counteractive tolerogenic responses to exogenous factor VIII rather than from an exacerbated activation of the immune system at the time of factor VIII administration. A better understanding of the pathogenesis of neutralizing anti-factor VIII antibodies will have repercussions on the clinical management of patients and highlight new strategies to achieve active immune tolerance to therapeutic factor VIII

L’athérogenèse

Les principaux acteurs de la réponse immunitaire adaptative sont impliqués lors du développement des lésions d’athérosclérose. Plusieurs antigènes cibles ont été identifiés. Il s’agit surtout de molécules du soi modifiées par le microenvironnement complexe de l’artère malade. Des lymphocytes T et des anticorps auto-réactifs ont été caractérisés. Si l’on ajoute que le transfert adoptif de lymphocytes est en mesure de moduler la maladie dans des modèles expérimentaux d’athérosclérose, les critères proposés par Witebsky et Rose pour définir une maladie comme étant auto-immune sont remplis. Cependant, ce processus pathologique présente des caractéristiques inédites pour une maladie auto-immune. Les défis thérapeutiques à venir devront s’attacher à renforcer les réponses protectrices tout en jugulant les réponses pathogènes

Origine et nature de la réponse immunitaire neutralisante contre le facteur VIII thérapeutique

L’utilisation de protéines thérapeutiques se heurte, chez certains patients, à l’apparition d’anticorps neutralisants. C’est le cas, par exemple, du facteur VIII pro-coagulant qui est utilisé pour traiter les patients atteints d’hémophilie A. Plusieurs paramètres, liés à la protéine elle-même, au type de pathologie ou aux patients, conditionnent l’immunogénicité d’une protéine thérapeutique. Les comprendre permettrait d’anticiper ou de prévenir la survenue d’anticorps neutralisants. Nous proposons dans cette revue de montrer que, dans le cas du facteur VIII, la survenue de ces anticorps neutralisants ne résulte pas d’une réponse immunitaire inopinée, mais plutôt de l’incapacité de l’organisme des patients à développer une réponse anti-inflammatoire ou régulatrice

TLR3-Induced Maturation of Murine Dendritic Cells Regulates CTL Responses by Modulating PD-L1 Trafficking

<div><p>Targeting TLR3 through formulations of polyI:C is widely studied as an adjuvant in cancer immunotherapy. The efficacy of such targeting has been shown to increase in combination with anti-PD-L1 treatment. Nevertheless, the mechanistic details of the effect of polyI:C on DC maturation and the impact on T-DC interactions upon PD-L1 blockade is largely unknown. Here we found that although DC treatment with polyI:C induced a potent inflammatory response including the production of type I interferon, polyI:C treatment of DCs impaired activation of peptide specific CD8⁺ T cells mainly due to PD-L1. Interestingly, we found that PD-L1 trafficking to the cell surface is regulated in two waves in polyI:C-treated DCs. One induced upon overnight treatment and a second more rapid one, specific to polyI:C treatment, was induced upon CD40 signaling leading to a further increase in surface PD-L1 in DCs. The polyI:C-induced cell surface PD-L1 reduced the times of contact between DCs and T cells, potentially accounting for limited T cell activation. Our results reveal a novel CD40-dependent regulation of PD-L1 trafficking induced upon TLR3 signaling that dictates its inhibitory activity. These results provide a mechanistic framework to understand the efficacy of anti-PD-L1 cancer immunotherapy combined with TLR agonists.</p></div

PD-L1 surface expression can regulate the DC-T time of contact.

<p>(<b>A</b>) Cell surface expression of PD-1 (left panel) and CD40L (right panel) was analysed by FACS on OT1 T cells activated with coated anti-CD3 and soluble anti-CD28 at 1, 2 and 3 days post-activation. (<b>B</b>) Time of contact between DCs and T cells. DCs from wildtype or PD-L1 KO mice were pre-treated with nothing (control), polyI:C (25 μg/mL) or LPS (10 ng/ml) and co-cultured with <i>Ubi</i>-GFP OT-I T cells pre-activated for 2 days with anti-CD3/CD28. The percentage of T cells forming contacts of <600 mins is plotted for each condition. More than 50 contacts were measured for each condition, pValues determined by Z-test (<b>C</b>) The cumulative distribution of the T-DC measured contact times. Only contact with duration <600 min are shown in the graph. ****: p<0.0001 and *: p <0.05. n.s., non-significant. Data is representative of 2 independent experiments.</p