ABSTRACT
Clinical trials have shown that administration of the nematode Trichuris suis can be beneficial in treating various immune disorders. To provide insight into the mechanisms by which this ...worm suppresses inflammatory responses, an active component was purified from T. suis soluble products (TsSPs) that suppress TNF and IL‐12 secretion from LPS‐activated human dendritic cells (DCs). Analysis by liquid chromatography tandem mass spectrometry identified this compound as prostaglandin (PG)E2. The purified compound showed similar properties compared with TsSPs and commercial PGE2 in modulating LPS‐induced expression of many cytokines and chemokines and in modulating Rab7B and P2RX7 expression in human DCs. Furthermore, the TsSP‐induced reduction of TNF secretion from DCs is reversed by receptor antagonists for EP2 and EP4, indicating PGE2 action. T. suis secretes extremely high amounts of PGE2 (45–90 ng/mg protein) within their excretory/secretory products but few related lipid mediators as established by metabololipidomic analysis. Culture of T. suis with several cyclooxygenase (COX) inhibitors that inhibit mammalian prostaglandin synthesis affected the worm's motility but did not inhibit PGE2 secretion, suggesting that the worms can synthesize PGE2 via a COX‐independent pathway. We conclude that T. suis secretes PGE2 to suppress proinflammatory responses in human DCs, thereby modulating the host's immune response.—Laan, L. C., Williams, A. R., Stavenhagen, K., Giera, M., Kooij, G., Vlasakov, I., Kalay, H., Kringel, H., Nejsum, P., Thamsborg, S. M., Wuhrer, M., Dijkstra, C. D., Cummings, R. D., van Die, I. The whipworm (Trichuris suis) secretes prostaglandin E2 to suppress proinflammatory properties in human dendritic cells. FASEB J. 31, 719–731 (2017). http://www.fasebj.org
Priming of CD8⁺ T cells by dendritic cells (DCs) is crucial for the generation of effective antitumor immune responses. Here, we describe a liposomal vaccine carrier that delivers tumor antigens to ...human CD169/Siglec-1⁺ antigen-presenting cells using gangliosides as targeting ligands. Ganglioside-liposomes specifically bound to CD169 and were internalized by in vitro-generated monocyte-derived DCs (moDCs) and macrophages and by ex vivo-isolated splenic macrophages in a CD169-dependent manner. In blood, high-dimensional reduction analysis revealed that ganglioside-liposomes specifically targeted CD14⁺ CD169⁺ monocytes and Axl⁺ CD169⁺ DCs. Liposomal codelivery of tumor antigen and Toll-like receptor ligand to CD169⁺ moDCs and Axl⁺ CD169⁺ DCs led to cytokine production and robust cross-presentation and activation of tumor antigen-specific CD8⁺ T cells. Finally, Axl⁺ CD169⁺ DCs were present in cancer patients and efficiently captured ganglioside-liposomes. Our findings demonstrate a nanovaccine platform targeting CD169⁺ DCs to drive antitumor T cell responses.
Sialic acids are negatively charged nine-carbon carboxylated monosaccharides that often cap glycans on glycosylated proteins and lipids. Because of their strategic location at the cell surface, ...sialic acids contribute to interactions that are critical for immune homeostasis via interactions with sialic acid-binding Ig-type lectins (siglecs). In particular, these interactions may be of importance in cases where sialic acids may be overexpressed, such as on certain pathogens and tumors. We now demonstrate that modification of antigens with sialic acids (Sia-antigens) regulates the generation of antigenspecific regulatory T (Treg) cells via dendritic cells (DCs). Additionally, DCs that take up Sia-antigen prevent formation of effector CD4⁺ and CD8⁺ T cells. Importantly, the regulatory properties endowed on DCs upon Sia-antigen uptake are antigen-specific: only T cells responsive to the sialylated antigen become tolerized. In vivo, injection of Sia-antigen–loaded DCs increased de novo Treg-cell numbers and dampened effector T-cell expansion and IFN-γ production. The dual tolerogenic features that Sia-antigen imposed on DCs are Siglec-E–mediated and maintained under inflammatory conditions. Moreover, loading DCs with Sia-antigens not only inhibited the function of in vitro–established Th1 and Th17 effector T cells but also significantly dampened ex vivo myelinreactive T cells, present in the circulation of mice with experimental autoimmune encephalomyelitis. These data indicate that sialic acid-modified antigens instruct DCs in an antigen-specific tolerogenic programming, enhancing Treg cells and reducing the generation and propagation of inflammatory T cells. Our data suggest that sialylation of antigens provides an attractive way to induce antigen-specific immune tolerance.
Splenic CD169+ macrophages are located in the marginal zone to efficiently capture blood-borne pathogens. Here, we investigate the requirements for the induction of CD8+ T cell responses by antigens ...(Ags) bound by CD169+ macrophages. Upon Ag targeting to CD169+ macrophages, we show that BATF3-dependent CD8α+ dendritic cells (DCs) are crucial for DNGR-1-mediated cross-priming of CD8+ T cell responses. In addition, we demonstrate that CD169, a sialic acid binding lectin involved in cell-cell contact, preferentially binds to CD8α+ DCs and that Ag transfer to CD8α+ DCs and subsequent T cell activation is dependent on the sialic acid-binding capacity of CD169. Finally, functional CD169 mediates optimal CD8+ T cell responses to modified vaccinia Ankara virus infection. Together, these data indicate that the collaboration of CD169+ macrophages and CD8α+ DCs for the initiation of effective CD8+ T cell responses is facilitated by binding of CD169 to sialic acid containing ligands on CD8α+ DCs.
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•CD169+ macrophages rely on BATF3-dependent DCs to cross-prime CD8+ T cells•DNGR-1 on cDC1s improves cross-priming to antigens targeted to CD169+ macrophages•CD169 binds to sialic acids on CD8α+ DCs•CD169 binding promotes T cell priming after non-replicative vaccinia virus infection
van Dinther et al. find that splenic CD169+ macrophages transfer antigens to BATF3-dependent cDC1s in a CD169-dependent manner and that these cDC1s cross-prime CD8+ T cell responses in a DNGR-1-dependent manner.
► Leb and LeX glycans achieve an efficient antigen-targeting to DCs through DC-SIGN. ► Glycan multivalency is a necessary condition for efficient targeting. ► DC-SIGN targeting results in robust CD4+ ...and CD8+ T cell responses.
Dendritic cells are the most efficient professional antigen-presenting cells in pathogen recognition and play a pivotal role in the control of the immune response. Pathogen recognition is ensured by the expression of a vast variety of pattern-recognition receptors. Amongst them are C-type lectins, a large family of receptors characterized by a domain that – in many cases – mediates calcium-dependent glycan binding. C-type lectins facilitate antigen uptake for efficient processing and presentation and, in some cases, also trigger signaling to modulate T cell responses. These properties make C-type lectin receptors ideal candidates for the targeting of antigens to dendritic cells for vaccination. DC-SIGN is a paradigmatic example of C-type lectin receptors on dendritic cells that facilitate vaccination strategies. DC-SIGN is highly expressed on immature conventional dendritic cells, particularly at the mucosa and the dermis, where DCs first encounter pathogens, but also can easily be accessed for vaccination. Upon ligand binding, DC-SIGN rapidly internalizes and directs its cargo into the endo-lysosomal pathway, which results in MHC-II presentation. But antigens targeted to DC-SIGN are also presented efficiently to CD8+ T cells, suggesting there is an additional endocytic route that leads to cross-presentation. Simultaneous triggering of DC-SIGN and TLRs results in the modulation of cytokine responses and facilitates cross-presentation to enhance CD4+ and CD8+ T cell responses. Because the glycan specificity of DC-SIGN has been characterized in detail, glycans can be used for the targeting of antigens to DCs in a DC-SIGN-dependent manner. Glycans represent a great advantage over monoclonal antibodies, they diminish the risk of side effects, are very small, and their production can rely entirely in organic chemistry approaches. Here, we discuss the capacity of glycan-based vaccines to enhance antigen-specific CD4+ and CD8+ T cell responses in human skin and mouse model systems.
Dendritic cells (DCs) are antigen-presenting cells efficient in capturing pathogens, and processing their antigenic determinants for presentation to antigen-specific T cells to induce robust immune ...responses. Their location at peripheral tissues and the expression of pattern-recognition receptors, among them DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), facilitates the capture of pathogens before spreading. However, some pathogens have developed strategies to escape the immune system. One of the most successful is HIV-1, which targets DC-SIGN for transport to the lymph node where the virus infects CD4(+) T cells. Contact of HIV-1 with DC-SIGN is thus the first event in the pathogenic cascade and, therefore, it is the primary target point for therapies aimed at HIV infection prevention. DC-SIGN recognizes specific glycans on HIV-1 and this interaction can be blocked by competitive inhibition through glycans. Although the affinity of glycans is relatively low, multivalency may increase avidity and the strength to compete with HIV-1 virions. We have designed multivalent dendrimeric compounds based on Lewis-type antigens that bind DC-SIGN with high selectivity and avidity and that effectively block gp120 binding to DC-SIGN and, consequently, HIV transmission to CD4(+) T cells. Binding to DC-SIGN and gp120 inhibition was higher on glycodendrimers with larger molecular diameter, indicating that the geometry of the compounds is an important factor determining their functionality. Our compounds elicited DC-SIGN internalization, a property of the receptor upon triggering, but did not affect the maturation status of DCs. Thus, Le(X) glycodendrimers could be incorporated into topic prophylactic approaches for the prevention of HIV-1 transmission.
Monocytes are antigen-presenting cells (APCs) that play diverse roles in promoting or regulating inflammatory responses, but their role in T cell stimulation is not well defined. In inflammatory ...conditions, monocytes frequently show increased expression of CD169/Siglec-1, a type-I interferon (IFN-I)-regulated protein. However, little is known about the phenotype and function of these CD169
+
monocytes. Here, we have investigated the phenotype of human CD169
+
monocytes in different diseases, their capacity to activate CD8
+
T cells, and the potential for a targeted-vaccination approach. Using spectral flow cytometry, we detected CD169 expression by CD14
+
CD16
-
classical and CD14
+
CD16
+
intermediate monocytes and unbiased analysis showed that they were distinct from dendritic cells, including the recently described CD14-expressing DC3. CD169
+
monocytes expressed higher levels of co-stimulatory and HLA molecules, suggesting an increased activation state. IFNα treatment highly upregulated CD169 expression on CD14
+
monocytes and boosted their capacity to cross-present antigen to CD8
+
T cells. Furthermore, we observed CD169
+
monocytes in virally-infected patients, including in the blood and bronchoalveolar lavage fluid of COVID-19 patients, as well as in the blood of patients with different types of cancers. Finally, we evaluated two CD169-targeting nanovaccine platforms, antibody-based and liposome-based, and we showed that CD169
+
monocytes efficiently presented tumor-associated peptides gp100 and WT1 to antigen-specific CD8
+
T cells. In conclusion, our data indicate that CD169
+
monocytes are activated monocytes with enhanced CD8
+
T cell stimulatory capacity and that they emerge as an interesting target in nanovaccine strategies, because of their presence in health and different diseases.
Glioblastoma is the most prevalent and aggressive primary brain tumour for which total tumour lysate-pulsed dendritic cell vaccination is currently under clinical evaluation. Glioblastoma ...extracellular vesicles (EVs) may represent an enriched cell-free source of tumour-associated (neo-) antigens to pulse dendritic cells (DCs) for the initiation of an anti-tumour immune response. Capture and uptake of EVs by DCs could occur in a receptor-mediated and presumably glycan-dependent way, yet the glycan composition of glioblastoma EVs is unknown. Here, we set out to characterize the glycocalyx composition of glioblastoma EVs by lectin-binding ELISA and comprehensive immunogold transmission electron microscopy (immuno-TEM). The surface glycan profile of human glioblastoma cell line-derived EVs (50-200 nm) was dominated by α-2,3- and α-2,6 linked sialic acid-capped complex N-glycans and bi-antennary N-glycans. Since sialic acids can trigger immune inhibitory sialic acid-binding Ig-like lectin (Siglec) receptors, we screened for Siglec ligands on the EVs. Glioblastoma EVs showed significant binding to Siglec-9, which is highly expressed on DCs. Surprisingly, however, glioblastoma EVs lack glycans that could bind Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN, CD209), a receptor that mediates uptake and induction of CD4
+
and CD8
+
T cell activation. Therefore, we explored whether modification of the EV glycan surface could reduce immune inhibitory Siglec binding, while enhancing EV internalization by DCs in a DC-SIGN dependent manner. Desialylation with a pan-sialic acid hydrolase led to reduction of sialic acid expression on EVs. Moreover, insertion of a high-affinity ligand (Lewis
Y
) for DC-SIGN resulted in a four-fold increase of uptake by monocyte-derived DCs. In conclusion, we show that the glycocalyx composition of EVs is a key factor of efficient DC targeting and that modification of the EV glycocalyx potentiates EVs as anti-cancer vaccine.
The C‐type lectin MGL activates the ERK‐p90RSK‐CREB axis, which together with TLR2 signaling leads to enhanced secretion of IL‐10 and TNFα.
DCs orchestrate immune responses to infectious pathogens ...and disturbances in tissue integrity. Equipped with C‐type lectins, DCs can respond to environmental changes in glycosylation. Many C‐type lectins are capable of modulating TLR activation, thereby facilitating tailor‐made immune reactions. Here, we investigated the signaling properties of the C‐type lectin MGL and show that MGL engagement by agonistic antibodies or carbohydrate ligands couples to TLR signal transduction for increased IL‐10 and TNF‐α secretion by human monocyte‐derived DCs. MGL triggering especially synergized with TLR2‐induced pathways, leading to elevated IL‐10 mRNA levels and enhanced TNF‐α mRNA stability. In addition, MGL signaling promoted phosphorylation of the MAPK ERK and the transcription factor CREB. Whereas specific inhibitors of p90RSK blocked the MGL‐induced cytokine secretion, AP‐1 was not involved. Strikingly, NF‐κB was only crucial for the IL‐10 response and dispensable for TNF‐α production. Together, our results demonstrate that MGL activation of the ERK‐p90RSK‐CREB axis converges with TLR2‐induced pathways, thereby fine‐tuning the DC maturation phenotype.
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