Les cellules dendritiques humaines: inhibition fonctionnelle par les glucocorticoïdes et propriétés anti-tumorales intrinsèques

Doctorat en sciences médicalesinfo:eu-repo/semantics/nonPublishe

Antigen-specific central memory CD4+ T lymphocytes produce multiple cytokines and proliferate in vivo in humans.

The function of Ag-specific central (T(CM)) and effector (T(EM)) memory CD4+ T lymphocytes remains poorly characterized in vivo in humans. Using CD154 as a marker of Ag-specific CD4+T cells, we studied the differentiation of memory subsets following anti-hepatitis B immunization. Hepatitis B surface Ag (HBs)-specific memory CD4+T cells were heterogeneous and included T(CM) (CCR7+CD27+) and T(EM) (CCR7(-)CD27(+/-)). HBs-specific T(CM) and T(EM) shared the capacity to produce multiple cytokines, including IL-2 and IFN-gamma. Several years postimmunization, approximately 10% of HBs-specific memory CD4+ T cells were in cycle (Ki67+) and the proliferating cells were CCR7+. These results suggest that the model of functional specialization of T(CM) and T(EM) cannot be applied to protein vaccine Ags and support the concept that T(CM) are capable of self-renewal and contribute to maintain the pool of memory cells.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Distinct mechanisms are involved in tumoristatic and tumoricidal activities of monocyte-derived dendritic cells.

Monocyte-derived dendritic cells (DC) were found to inhibit proliferation of different tumor cell lines. LPS-induced maturation of DC strongly increased their capacity to inhibit tumor cell growth. We observed that tumoristatic activity of LPS-activated DC was independent of their cytotoxic potential. Indeed, LPS-activated DC were able to inhibit growth of caspase-8-deficient or Bcl-2-overexpressing Jurkat cells whereas they were not cytotoxic towards the same targets. On the other hand, we found that supernatant derived from LPS-activated DC exerted a significant anti-proliferative activity against Jurkat cells while it did not induce any cytotoxic effect. Tumor necrosis factor (TNF) was shown to critically contribute to tumor growth inhibition in this system.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

L’immunothérapie anti-tumorale à base de cellules dendritiques

L’utilisation de cellules dendritiques (DC) présentant des antigènes tumoraux s’est imposée en tant que stratégie d’avenir pour l’immunothérapie du cancer. Nous avons réalisé 3 essais cliniques de vaccination anti-tumorale utilisant des DC autologues chargées d’antigènes associés aux tumeurs (TAA). Ces essais ont montré que l’approche était sûre et associée à un accroissement considérable de la fréquence des lymphocytes producteurs d’IFN-γ en réponse au(x) TAA. Ces réponses se sont avérées transitoires malgré l’apport d’une aide sous la forme de la KLH. L’administration d’IL-2 par voie sous- cutanée était associée à l’induction d’une production d’IL-5 se maintenant au long cours. Des réponses cliniques ont été observée chez environ 1/3 des patients. Les améliorations du vaccin tireront parti de l’utilisation d’un nouveau type de DC (IL-3/IFN-β DC) et de cellules hybrides résultant de la fusion entre cellules tumorales et DC

Trypanosoma cruzi Infects Human Dendritic Cells and Prevents Their Maturation: Inhibition of Cytokines, HLA-DR, And Costimulatory Molecules

Trypanosoma cruzi, a parasitic protozoan, is the etiological agent of Chagas’ disease. Despite the many immune system disorders recognized in this infection and the crucial role played by dendritic cells (DC) in acquired immune responses, it was not known whether these cells could be infected by T. cruzi trypomastigotes and the consequences of such an infection on their immune functions. We now provide evidence that human monocyte-derived DC can be infected by T. cruzi and can support its intracellular multiplication. Interestingly, this infection has functional consequences on immature DC and on their maturation induced by lipopolysaccharide (LPS). First, after T. cruzi infection, the basal synthesis of interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-α) was impaired. Furthermore, the process of maturation of DC induced by LPS was drastically affected by T. cruzi infection. Indeed, secretion of cytokines such as IL-12, TNF-α, and IL-6, which are released normally at high levels by LPS-activated DC, as well as the up-regulation of HLA-DR and CD40 molecules, was significantly reduced after this infection. The same effects could be induced by T. cruzi-conditioned medium, indicating that at least these inhibitory effects were mediated by soluble factors released by T. cruzi. Taken together, these results provide new insights into a novel efficient mechanism, directly involving the alteration of DC function, which might be used by T. cruzi to escape the host immune responses in Chagas’ disease and thus might favor persistent infection

AS04, an aluminum salt- and TLR4 agonist-based adjuvant system, induces a transient localized innate immune response leading to enhanced adaptive immunity.

Adjuvant System 04 (AS04) combines the TLR4 agonist MPL (3-O-desacyl-4'-monophosphoryl lipid A) and aluminum salt. It is a new generation TLR-based adjuvant licensed for use in human vaccines. One of these vaccines, the human papillomavirus (HPV) vaccine Cervarix, is used in this study to elucidate the mechanism of action of AS04 in human cells and in mice. The adjuvant activity of AS04 was found to be strictly dependent on AS04 and the HPV Ags being injected at the same i.m. site within 24 h of each other. During this period, AS04 transiently induced local NF-kappaB activity and cytokine production. This led to an increased number of activated Ag-loaded dendritic cells and monocytes in the lymph node draining the injection site, which further increased the activation of Ag-specific T cells. AS04 was also found to directly stimulate those APCs in vitro but not directly stimulate CD4(+) T or B lymphocytes. These AS04-induced innate responses were primarily due to MPL. Aluminum salt appeared not to synergize with or inhibit MPL, but rather it prolonged the cytokine responses to MPL at the injection site. Altogether these results support a model in which the addition of MPL to aluminum salt enhances the vaccine response by rapidly triggering a local cytokine response leading to an optimal activation of APCs. The transient and confined nature of these responses provides further supporting evidence for the favorable safety profile of AS04 adjuvanted vaccines.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Expression of c-FLIP(L) and resistance to CD95-mediated apoptosis of monocyte-derived dendritic cells: inhibition by bisindolylmaleimide.

To gain insight into the mechanisms controlling apoptosis of dendritic cells (DC), human monocyte-derived DC were analyzed for their expression of CD95 (Fas/Apo-1) and their response to CD95 ligation. Although DC expressed the CD95 molecule on their membrane, they did not undergo apoptosis on CD95 ligation unless sensitized by cycloheximide. In parallel, DC synthesized c-FLIP(L), an inhibitor of the CD95-mediated death-signaling cascade. We also demonstrated that bisindolylmaleimide down-regulates c-FLIP(L) expression in DC and, in parallel, allows CD95-mediated apoptosis in these cells. In contrast, Bcl-2, Bcl-x(L), and Bax levels were not affected by bisindolylmaleimide. We conclude that DC resist CD95- mediated apoptosis in association with c-FLIP(L) expression and that the immunosuppressive potential of bisindolylmaleimide previously observed at the T-cell level also involves facilitation of CD95-mediated DC apoptosis.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe