PubMed Health⌕ Search

Biomedical subjects

S Amigorena

Publications and source records attributed to S Amigorena.

At least 19 recordsLinked to original sources
PubMed2006

Induction of tolerance by exosomes and short-term immunosuppression in a fully MHC-mismatched rat cardiac allograft model.

Exosomes are MHC-bearing vesicles secreted by a wide array of cells. We have previously shown that donor-haplotype exosomes from bone marrow dendritic cells (DCs) injected before transplantation significantly prolong heart allograft survival in congenic and fully MHC-mismatched Lewis rats. Here we show that donor exosomes administered after transplantation are similarly able to prolong allograft survival, however, without inducing tolerance. We therefore tested the effect of exosomes combined with short-term LF 15-0195 (LF) treatment, which blocks the maturation of DCs, so that donor-MHC antigens from exosomes could be presented in a more tolerogenic environment. LF treatment does not preclude the development of a strong antidonor cellular response, and while LF, but not exosome, treatment inhibits the antidonor humoral response and decreases leukocyte graft infiltration, allografts from LF-treated recipients were either acutely or strongly chronically rejected. Interestingly, when combined with LF treatment, exosomes induced a donor-specific allograft tolerance characterized by a strong inhibition of the antidonor proliferative response. This donor-specific tolerance was transferable to naïve allograft recipients. Moreover, exosomes/LF treatment prevented or considerably delayed the appearance of chronic rejection. These results suggest that under LF treatment, presentation of donor-MHC antigens (from exosomes) can induce regulatory responses that are able to modulate allograft rejection and to induce donor-specific allograft tolerance.

Animals↗
PubMed2002

Tumor-derived exosomes: a new source of tumor rejection antigens.

Exosomes are small vesicles released by a broad array of hematopoietic cells. Previous studies showed that exosomes released by antigen loaded dendritic cells induce immune-mediated anti-tumor response in mice. Here, we will describe the biochemical properties of tumor-derived exosomes and, their pre-clinical activity as cancer vaccines.

Animals↗
PubMed2002

FcgammaRI (CD64) contributes substantially to severity of arthritis, hypersensitivity responses, and protection from bacterial infection.

The high-affinity receptor for IgG, FcgammaRI, shares its capacity to bind IgG2a immune complexes (IgG2a-IC) with the low-affinity receptor FcgammaRIII and complement factors, hampering the definition of its biological role. Moreover, in vivo, FcgammaRI is occupied by monomeric IgG2a, reducing its accessibility to newly formed IgG2a-IC. By using a variety of FcgammaR(-/-) mice, we demonstrate that in the absence of FcgammaRI, the IgG2a-IC-induced cellular processes of phagocytosis, cytokine release, cellular cytotoxicity, and antigen presentation are impaired. FcgammaRI(-/-) mice showed impaired hypersensitivity responses, strongly reduced cartilage destruction in an arthritis model, and impaired protection from a bacterial infection. We conclude that FcgammaRI contributes substantially to a variety of IgG2a-IC-dependent immune functions and immunopathological responses.

Animals↗
PubMed2001

Proteomic analysis of dendritic cell-derived exosomes: a secreted subcellular compartment distinct from apoptotic vesicles.

Dendritic cells constitutively secrete a population of small (50-90 nm diameter) Ag-presenting vesicles called exosomes. When sensitized with tumor antigenic peptides, dendritic cells produce exosomes, which stimulate anti-tumor immune responses and the rejection of established tumors in mice. Using a systematic proteomic approach, we establish the first extensive protein map of a particular exosome population; 21 new exosomal proteins were thus identified. Most proteins present in exosomes are related to endocytic compartments. New exosomal residents include cytosolic proteins most likely involved in exosome biogenesis and function, mainly cytoskeleton-related (cofilin, profilin I, and elongation factor 1alpha) and intracellular membrane transport and signaling factors (such as several annexins, rab 7 and 11, rap1B, and syntenin). Importantly, we also identified a novel category of exosomal proteins related to apoptosis: thioredoxin peroxidase II, Alix, 14-3-3, and galectin-3. These findings led us to analyze possible structural relationships between exosomes and microvesicles released by apoptotic cells. We show that although they both represent secreted populations of membrane vesicles relevant to immune responses, exosomes and apoptotic vesicles are biochemically and morphologically distinct. Therefore, in addition to cytokines, dendritic cells produce a specific population of membrane vesicles, exosomes, with unique molecular composition and strong immunostimulating properties.

Animals↗
PubMed2001

The cell biology of antigen presentation in dendritic cells.

Dendritic cells are the most efficient antigen-presenting cells. They take up antigens and pathogens, generate MHC-peptide complexes, migrate from the sites of antigen acquisition to secondary lymphoid organs and, finally, they physically interact with and stimulate T lymphocytes. Indeed, dendritic cells are the only antigen-presenting cells that induce the activation of resting T cells, both in vitro and in vivo. Thus, dendritic cells initiate adaptive immune responses and determine tolerance. To do so, dendritic cells have developed unique membrane transport pathways. The molecular mechanisms responsible for the control of antigen uptake and processing, for the generation of MHC-peptide complexes and for their transport to the cell surface have been partially unraveled in the past two years.

Animals↗
PubMed2001

Tumor-derived exosomes are a source of shared tumor rejection antigens for CTL cross-priming.

The initiation of T-cell-mediated antitumor immune responses requires the uptake and processing of tumor antigens by dendritic cells and their presentation on MHC-I molecules. Here we show in a human in vitro model system that exosomes, a population of small membrane vesicles secreted by living tumor cells, contain and transfer tumor antigens to dendritic cells. After mouse tumor exosome uptake, dendritic cells induce potent CD8+ T-cell-dependent antitumor effects on syngeneic and allogeneic established mouse tumors. Therefore, exosomes represent a novel source of tumor-rejection antigens for T-cell cross priming, relevant for immunointerventions.

Animals↗
PubMed2001

[Exosomes derived from dendritic cells].

Dendritic cells (DC) are potent antigen presenting cells and the only ones capable of inducing primary cytotoxic immune responses both in vivo and vitro. DCs secrete a 60-80 nm membrane vesicle population of endocytic origin, called exosomes. The protein composition of exosomes was analyzed using a systematic proteomic approach. Besides MHC and costimulatory molecules, exosomes bear several adhesion proteins, probably involved in their specific targeting. Exosomes also accumulate several cytosolic factors, most likely involved in exoxome's biogenesis in late endosomes. Like DCs, exosomes induce potent anti tumor immune responses in vivo. Indeed, a single injection of DC-derived exosomes sensitized with tumor peptides induced the eradication of established mouse tumors. Tumor-specific cytotoxic T lymphocytes were found in the spleen of exosome treated mice, and depletion of CD8+ T cells in vivo inhibited the anti tumor effect of exosomes. These results strongly support the implementation of human DC-derived exosomes for cancer immunotherapy.

Animals↗
PubMed2000

The B subunit of Shiga toxin fused to a tumor antigen elicits CTL and targets dendritic cells to allow MHC class I-restricted presentation of peptides derived from exogenous antigens.

Immunization with peptide or recombinant proteins generally fails to elicit CTL, which are thought to play a key role in the control of virus-infected cells and tumor growth. In this study we show that the nontoxic B subunit of Shiga toxin fused to a tumor peptide derived from the mouse mastocytoma P815 can induce specific CTL in mice without the use of adjuvant. The Shiga B subunit acts as a vector rather than as an adjuvant, because coinjection of the tumor peptide and the B subunit as separate entities does not lead to CTL induction. We also demonstrated that in vitro the B subunit mediates the delivery of various exogenous CD8 T cell epitopes into the conventional MHC class I-restricted pathway, as this process is inhibited by brefeldin A and lactacystin and requires a functional TAP system. In contrast to other nonviral methods for transport of exogenous Ags into the endogenous MHC class I pathway that involve macropinocytosis or phagocytosis, the Shiga B subunit targets this pathway in a receptor-dependent manner, namely via binding to the glycolipid Gb3. Because this receptor is highly expressed on various dendritic cells, it should allow preferential targeting of the Shiga B subunit to these professional APCs. Therefore, the Shiga B subunit appears to represent an attractive vector for vaccine development due to its ability to target dendritic cells and to induce specific CTL without the need for adjuvant.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Antigen traffic pathways in dendritic cells.

Dendritic cells (DC) are now believed to be the principal initiators of T cell-mediated immune responses. Their location in body tissues, migratory behaviour in response to inflammatory stimuli, endocytic properties, expression of MHC molecules and key T cell stimulatory molecules and many other attributes place these remarkable cells in a unique and influential position in the immune system. Progress in DC culture methods has recently allowed in-depth studies on the cell biological features that enable them to fulfill their crucial role in the immune response.

Animals↗
PubMed2000

Vimentin filaments in fibroblasts are a reservoir for SNAP23, a component of the membrane fusion machinery.

Soluble N-ethyl maleimide-sensitive fusion protein attachment protein receptors (SNAREs) are core machinery for membrane fusion during intracellular vesicular transport. Synaptosome-associated protein of 23 kDa (SNAP23) is a target SNARE previously identified at the plasma membrane, where it is involved in exocytotic membrane fusion. Here we show that SNAP23 associates with vimentin filaments in a Triton X-100 insoluble fraction in fibroblasts in primary culture and HeLa cells. Upon treatment of human fibroblasts with N-ethyl-maleimide, SNAP23 dissociates from vimentin filaments and forms a protein complex with syntaxin 4, a plasma membrane SNARE. The vimentin-associated pool of SNAP23 can therefore be a reservoir, which would supply the plasma membrane fusion machinery, in fibroblasts. Our observation points to a yet unexplored role of intermediate filaments.

Animals↗
PubMed2000

Paucity of functional T-cell memory to melanoma antigens in healthy donors and melanoma patients.

The functional characteristics of CD8+ T cells specific for melanoma antigens (MAs) have often been defined after in vitro culture using nonprofessional antigen-presenting cells. We have examined CD8+ T-cell immunity to MAs and a viral antigen (influenza) in uncultured T cells of healthy donors and melanoma patients using autologous, mature, monocyte-derived dendritic cells (DCs) pulsed with peptide antigens and viral vectors. Antigen-specific IFN-gamma-producing T cells reactive with HLA-A*0201-restricted peptides from four melanoma antigens (MelanA/MART-1, MAGE-3, tyrosinase, and gp100) were detected only at low frequencies (<30 per 2 x 10(5) peripheral blood mononuclear cells for each of the MAs) from HLA-A2.1-positive healthy donors (n = 12) and patients with stages III/IV melanoma (n = 8). Detection of MA-specific, but not influenza matrix peptide (Flu-MP)-specific, T cells required a high concentration (10 microg/ml) of the peptide in this assay. Furthermore, these T cells did not recognize endogenously processed antigen on tumor cell lines or cells infected with viral vectors capable of expressing MAs. The use of autologous, mature DCs led to a significant increase in the number of Flu-MP, but not MA-specific, T cells in 16-h ELISPOT assays for both melanoma patients and healthy donors. In 1-week cocultures with DCs pulsed with 10 microg/ml peptide, MelanA/MART-1-specific T cells did not readily proliferate or differentiate into lytic effectors, in contrast to strong influenza-specific lytic responses. Therefore, despite distinct memory responses to influenza antigens, melanoma patients and healthy controls have a paucity of MA-reactive memory T cells, failing to rapidly generate IFN-gamma-secreting lytic effectors in short-term assays, even when stimulated by DCs.

Antigens↗
PubMed2000

Cancer immunotherapy using dendritic cell-derived exosomes.

Dendritic cells (DCs) are the most potent antigen presenting cells and the only ones capable of inducing primary cytotoxic immune responses. We found that DCs secrete a population of membrane vesicles, called exosomes. Exosomes are 60-80 nm vesicles of endocytic origin. The protein composition of exosomes was subjected to a systematic proteomic analysis. Besides MHC and co-stimulatory molecules, exosomes bear several adhesion proteins, most likely involved in their specific subjected to targeting. We also found that exosomes accumulate several cytosolic factors, probably involved in their endosomal biogenesis. Like DCs, exosomes induced immune responses in vivo. Indeed, a single injection of DC-derived exosomes sensitized with tumor peptides induced potent anti tumor immune responses in mice and the eradication of established tumors. Tumor-specific cytotoxic T lymphocytes were found in the spleen of exosome-treated mice, and the anti tumor effect of exosomes was sensitive to in vivo depletion of CD8+ T cells. These results show that exosomes induce potent anti tumor effects in vivo, and strongly support the implementation of human DC-derived exosomes for cancer immunotherapy.

Animals↗
PubMed1999

Molecular characterization of dendritic cell-derived exosomes. Selective accumulation of the heat shock protein hsc73.

Exosomes are membrane vesicles secreted by hematopoietic cells upon fusion of late multivesicular endosomes with the plasma membrane. Dendritic cell (DC)-derived exosomes induce potent antitumor immune responses in mice, resulting in the regression of established tumors (Zitvogel, L., A. Regnault, A. Lozier, J. Wolfers, C. Flament, D. Tenza, P. Ricciardi-Castagnoli, G. Raposo, and S. Amigorena. 1998. Nat. Med. 4:594-600). To unravel the molecular basis of exosome-induced immune stimulation, we now analyze the regulation of their production during DC maturation and characterize extensively their protein composition by peptide mass mapping. Exosomes contain several cytosolic proteins (including annexin II, heat shock cognate protein hsc73, and heteromeric G protein Gi2alpha), as well as different integral or peripherally associated membrane proteins (major histocompatibility complex class II, Mac-1 integrin, CD9, milk fat globule-EGF-factor VIII [MFG-E8]). MFG-E8, the major exosomal component, binds integrins expressed by DCs and macrophages, suggesting that it may be involved in exosome targeting to these professional antigen-presenting cells. Another exosome component is hsc73, a cytosolic heat shock protein (hsp) also present in DC endocytic compartments. hsc73 was shown to induce antitumor immune responses in vivo, and therefore could be involved in the exosome's potent antitumor effects. Finally, exosome production is downregulated upon DC maturation, indicating that in vivo, exosomes are produced by immature DCs in peripheral tissues. Thus, DC-derived exosomes accumulate a defined subset of cellular proteins reflecting their endosomal biogenesis and accounting for their biological function.

Animals↗
PubMed1999

TGF-beta 1 prevents the noncognate maturation of human dendritic Langerhans cells.

TGF-beta 1 is critical for differentiation of epithelial-associated dendritic Langerhans cells (LC). In accordance with the characteristics of in vivo LC, we show that LC obtained from human monocytes in vitro in the presence of TGF-beta 1 1) express almost exclusively intracellular class II Ags, low CD80, and no CD83 and CD86 Ags and 2) down-regulate TNF-RI (p55) and do not produce IL-10 after stimulation, in contrast to dermal dendritic cells and monocyte-derived dendritic cells. Surprisingly, while LC exhibit E-cadherin down-regulation upon exposure to TNF-alpha and IL-1, TGF-beta 1 prevents the final LC maturation in response to TNF-alpha, IL-1, and LPS with respect to Class II CD80, CD86, and CD83 Ag expression, loss of FITC-dextran uptake, production of IL-12, and Ag presentation. In sharp contrast, CD40 ligand cognate signal induces full maturation of LC and is not inhibited by TGF-beta 1. The presence of emigrated immature LCs in human reactive skin-draining lymph nodes provides in vivo evidence that LC migration and final maturation may be differentially regulated. Therefore, due to the effects of TGF-beta 1, inflammatory stimuli may not be sufficient to induce full maturation of LC, thus avoiding potentially harmful immune responses. We conclude that TGF-beta 1 appears to be responsible for both the acquisition of LC phenotype, cytokine production pattern, and prevention of noncognate maturation.

Antigens, CD↗
PubMed1999

Fcgamma receptor-mediated induction of dendritic cell maturation and major histocompatibility complex class I-restricted antigen presentation after immune complex internalization.

Dendritic cells (DCs) express several receptors for the Fc portion of immunoglobulin (Ig)G (FcgammaR), which mediate internalization of antigen-IgG complexes (immune complexes, ICs) and promote efficient major histocompatibility complex (MHC) class II-restricted antigen presentation. We now show that FcgammaRs have two additional specific attributes in murine DCs: the induction of DC maturation and the promotion of efficient MHC class I-restricted presentation of peptides from exogenous, IgG-complexed antigens. Both FcgammaR functions require the FcgammaR-associated gamma chain. FcgammaR-mediated MHC class I-restricted antigen presentation is extremely sensitive and specific to immature DCs. It requires proteasomal degradation and is dependent on functional peptide transporter associated with antigen processing, TAP1-TAP2. By promoting DC maturation and presentation on both MHC class I and II molecules, ICs should efficiently sensitize DCs for priming of both CD4(+) helper and CD8(+) cytotoxic T lymphocytes in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Fc receptors for IgG and antigen presentation on MHC class I and class II molecules.

Antigens internalized through specific membrane receptors are presented to helper CD4(+) T cells at antigen concentrations 10(3) to 10(4) fold lower than antigens internalized by fluid phase. B lymphocyte antigen receptors, mannose receptors and receptors for the Fc region of immunoglobulins, promote both internalization and efficient presentation at low antigen concentrations. Thus, binding to specific membrane receptors concentrate antigens on antigen presenting cells and mediates efficient uptake. Is this 'quantitative' concentration of antigens on antigen presenting cells the end of the story? Or may 'quality', i.e. selective intracellular antigen targeting, somehow influence the efficiency or specificity of MHC class I and class II-restricted antigen presentation?

Antigen Presentation↗