Dendritic Cells Crosspresent Antigens from Live B16 Cells More Efficiently than from Apoptotic Cells and Protect from Melanoma in a Therapeutic Model

Dendritic cells (DC) are able to elicit anti-tumoral CD8+ T cell responses by cross-presenting exogenous antigens in association with major histocompatibility complex (MHC) class I molecules. Therefore they are crucial actors in cell-based cancer immunotherapy. Although apoptotic cells are usually considered to be the best source of antigens, live cells are also able to provide antigens for cross-presentation by DC. We have recently shown that prophylactic immunotherapy by DC after capture of antigens from live B16 melanoma cells induced strong CD8+ T-cell responses and protection against a lethal tumor challenge in vivo in C57Bl/6 mice. Here, we showed that DC cross-presenting antigens from live B16 cells can also inhibit melanoma lung dissemination in a therapeutic protocol in mice. DC were first incubated with live tumor cells for antigen uptake and processing, then purified and irradiated for safety prior to injection. This treatment induced stronger tumor-specific CD8+ T-cell responses than treatment by DC cross-presenting antigens from apoptotic cells. Apoptotic B16 cells induced more IL-10 secretion by DC than live B16 cells. They underwent strong native antigen degradation and led to the expression of fewer MHC class I/epitope complexes on the surface of DC than live cells. Therefore, the possibility to use live cells as sources of tumor antigens must be taken into account to improve the efficiency of cancer immunotherapy

Arrest of WNT/β-catenin signaling enables the transition from pluripotent to differentiated germ cells in mouse ovaries

International audienceGerm cells form the basis for sexual reproduction by producing gametes. In ovaries, primordial germ cells exit the cell cycle and the pluripotency-associated state, differentiate into oogonia, and initiate meiosis. Despite the importance of germ cell differentiation for sexual reproduction, signaling pathways regulating their fate remain largely unknown. Here, we show in mouse embryonic ovaries that germ cell–intrinsic β-catenin activity maintains pluripotency and that its repression is essential to allow differentiation and meiosis entry in a timely manner. Accordingly, in β-catenin loss-of-function and gain-of-function mouse models, the germ cells precociously enter meiosis or remain in the pluripotent state, respectively. We further show that interaction of β-catenin and the pluripotent-associated factor POU5F1 in the nucleus is associated with germ cell pluripotency. The exit of this complex from the nucleus correlates with germ cell differentiation, a process promoted by the up-regulation of Znrf3 , a negative regulator of WNT/β-catenin signaling. Together, these data identify the molecular basis of the transition from primordial germ cells to oogonia and demonstrate that β-catenin is a central gatekeeper in ovarian differentiation and gametogenesis

Epitope Specificity and Relative Clonal Abundance Do Not Affect CD8 Differentiation Patterns during Lymphocytic Choriomeningitis Virus Infection▿

To evaluate the impact of immunodominance on CD8 T-cell properties, we compared the functional properties of dominant and subdominant populations in the response to lymphocytic choriomeningitis virus (LCMV). To improve functional discrimination, in addition to the usual tests of phenotype and function, we used a sensitive technique that allows the screening of all CD8 effector genes simultaneously in single cells. Surprisingly, these methods failed to reveal a major impact of clonal dominance in CD8 properties throughout the response. Aiming to increase clonal dominance, we examined high-frequency transferred P14 T-cell receptor transgenic (TCR Tg) cells. Under these conditions LCMV is cleared faster, and accordingly we found an accelerated response. However, when Tg and endogenous cells were studied in the same mice, where they should be subjected to the same antigen load, they showed overlapping properties, and the presence of P14 cells did not modify endogenous responses to other LCMV epitopes or a perturbed immunodominance hierarchy in the memory phase. Using allotype-labeled Tg cells, we found that during acute infection up to 80% downregulated their TCR and were undetectable by tetramer binding, and that tetramer-negative and tetramer-positive cells had very different features. Since Tg cells are not available to evaluate immune responses in humans and, in many cases, are not available from the mouse, the tetramer-based evaluation of early immune responses in most situations of high viremia may be incomplete and biased

Vaccine-induced tumor regression requires a dynamic cooperation between T cells and myeloid cells at the tumor site

International audienceMost cancer immunotherapies under present investigation are based on the belief that cytotoxic T cells are the most important anti-tumoral immune cells, whereas intra-tumoral macrophages would rather play a pro-tumoral role. We have challenged this antagonistic point of view and searched for collaborative contributions by tumor-infiltrating T cells and macrophages, reminiscent of those observed in anti-infectious responses. We demonstrate that, in a model of therapeutic vaccination, cooperation between myeloid cells and T cells is indeed required for tumor rejection. Vaccination elicited an early rise of CD11b + myeloid cells that preceded and conditioned the intra-tumoral accumulation of CD8 + T cells. Conversely, CD8 + T cells and IFNγ production activated myeloid cells were required for tumor regression. A 4-fold reduction of CD8 + T cell infiltrate in CXCR3KO mice did not prevent tumor regression, whereas a reduction of tumor-infiltrating myeloid cells significantly interfered with vaccine efficiency. We show that macrophages from regressing tumors can kill tumor cells in two ways: phagocytosis and TNFα release. Altogether, our data suggest new strategies to improve the efficiency of cancer immunotherapies, by promoting intra-tumoral cooperation between macrophages and T cells

DC cytokine profile after culture with live or apoptotic B16 cells.

<p>DC were cultured alone (DC) or with live (zVAD treated) or apoptotic (γ-irradiated) B16 cells for 24 h and stimulated or not with LPS and IFNγ. As controls, B16 zVAD and B16γ cells were also cultured alone. DC were then assessed for their ability to produce IL-12p70 (A) or IL-10 (B) by ELISA. In the upper panels, data from one out of three independent experiments are shown. In the bottom panels, for LPS and IFNγ stimulation, relative IL-12p70 and IL-10 productions are expressed as a percentage of the cytokine production obtained for DC alone. Mean percentage values±SEM are shown. The significance of differences between series of results was assessed using a paired t test (n = 3, 3 independent experiments).</p

More native antigen in live than in apoptotic donor cells: improved antigen crosspresentation by DC.

<p>A, B, 30.10⁶ live (zVAD treated) or apoptotic (γ-irradiated) B16 cells (A) or L-OVA cells (B) were lysed for protein extraction. Lysates from B16 cells were analysed using anti-gp100, anti-TRP2 and anti-actin antibodies (A). Lysates from L-OVA cells were analysed using anti-OVA and anti-actin antibodies antibodies (B). Anti-actin antibodies were used as controls. C, DC were cultured with different numbers of live (filled triangle) or apoptotic (open triangle) L-OVA cells or live L cells (filled square). DC were then purified by magnetic sorting using anti-CD11c microbeads and cultured with B3Z-T cells hybridoma cells for 18 h. Activation after recognition of the SIINFEKL-K^b complex was detected by optical density measurement at 560 nm after addition of the CPRG substrate. The significance of differences between series of results was assessed using a two-tailed unpaired t test. **p<0.01, *p<0,05, n.s. not significant. Mean ± SEM, representative of two independent experiments.</p

DC maturation after culture with live or apoptotic B16 cells.

<p>DC were cultured with live (zVAD treated) or apoptotic (γ-irradiated) B16 cells for 24 h in the presence of culture medium or LPS and IFNγ. The expression of maturation molecules was then tested by flow cytometry. One representative experiment out of three independent experiments is shown.</p

Type 1 interferons and Foxo1 down-regulation play a key role in age-related T-cell exhaustion in mice

Abstract Foxo family transcription factors are critically involved in multiple processes, such as metabolism, quiescence, cell survival and cell differentiation. Although continuous, high activity of Foxo transcription factors extends the life span of some species, the involvement of Foxo proteins in mammalian aging remains to be determined. Here, we show that Foxo1 is down-regulated with age in mouse T cells. This down-regulation of Foxo1 in T cells may contribute to the disruption of naive T-cell homeostasis with age, leading to an increase in the number of memory T cells. Foxo1 down-regulation is also associated with the up-regulation of co-inhibitory receptors by memory T cells and exhaustion in aged mice. Using adoptive transfer experiments, we show that the age-dependent down-regulation of Foxo1 in T cells is mediated by T-cell-extrinsic cues, including type 1 interferons. Taken together, our data suggest that type 1 interferon-induced Foxo1 down-regulation is likely to contribute significantly to T-cell dysfunction in aged mice

Autopsie du musée

Observer en grand angle le musée du xxe siècle comme objet historique compose une démarche inédite. Elle suppose d’apprécier les enjeux politiques, sociaux, culturels et économiques qu’il suscite, à l’échelle de l’État comme des collectivités territoriales, dans des perspectives hexagonales comme transnationales. Car le musée évolue aujourd’hui dans une société ouverte à la novation esthétique et patrimoniale en même temps qu’il adopte l’acculturation des codes hiérarchiques et les évolutions entrepreneuriales ou technologiques. Partagé en deux parties (« Figures » et « Territoires »), cet ouvrage aborde des situations aux registres et répertoires différenciés. Les textes réunis ici questionnent, en longue durée, le musée et ses représentations, entre élitisme social, promotion de la culture pour tous, merchandising, aussi, des biens culturels pour chacun. Sont ouvertes ou creusées - souvent en diachronie par le témoignage d’anciens et nouveaux acteurs - plusieurs pistes amenant à discuter la place du musée dans les imaginaires collectifs, le capital symbolique d’un geste ou d’un espace architectural, le trilogue entre l’œuvre, l’artiste et celles et ceux, qui désormais pluriels et parfois concurrents, participent à sa « vie » au musée.En hommage à Daniel Fabre (†) Directeur d’études à l’EHES

XCR1 + dendritic cells promote memory CD8 + T cell recall upon secondary infections with Listeria monocytogenes or certain viruses

International audienceNaive CD8(+) T cell priming during tumor development or many primary infections requires cross-presentation by XCR1(+) dendritic cells (DCs). Memory CD8(+) T lymphocytes (mCTLs) harbor a lower activation threshold as compared with naive cells. However, whether their recall responses depend on XCR1(+) DCs is unknown. By using a new mouse model allowing fluorescent tracking and conditional depletion of XCR1(+) DCs, we demonstrate a differential requirement of these cells for mCTL recall during secondary infections by different pathogens. XCR1(+) DCs were instrumental to promote this function upon secondary challenges with Listeria monocytogenes, vesicular stomatitis virus, or Vaccinia virus, but dispensable in the case of mouse cytomegalovirus. We deciphered how XCR1(+) DCs promote mCTL recall upon secondary infections with Listeria. By visualizing for the first time the in vivo choreography of XCR1(+) DCs, NK cells and mCTLs during secondary immune responses, and by neutralizing in vivo candidate molecules, we demonstrate that, very early after infection, mCTLs are activated, and attracted in a CXCR3-dependent manner, by NK cell-boosted, IL-12-, and CXCL9-producing XCR1(+) DCs. Hence, depending on the infectious agent, strong recall of mCTLs during secondary challenges can require cytokine-and chemokine-dependent cross-talk with XCR1(+) DCs and NK cells