Antigen-presenting Cells In Lymph Nodes Research Articles

Ena/VASP Protein-Mediated Actin Polymerization Contributes to Naïve CD8+ T Cell Activation and Expansion by Promoting T Cell-APC Interactions In Vivo.

Naïve T cell activation in secondary lymphoid organs such as lymph nodes (LNs) occurs upon recognition of cognate antigen presented by antigen presenting cells (APCs). T cell activation requires cytoskeleton rearrangement and sustained interactions with APCs. Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) proteins are a family of cytoskeletal effector proteins responsible for actin polymerization and are frequently found at the leading edge of motile cells. Ena/VASP proteins have been implicated in motility and adhesion in various cell types, but their role in primary T cell interstitial motility and activation has not been explored. Our goal was to determine the contribution of Ena/VASP proteins to T cell–APC interactions, T cell activation, and T cell expansion in vivo. Our results showed that naïve T cells from Ena/VASP-deficient mice have a significant reduction in antigen-specific T cell accumulation following Listeria monocytogenes infection. The kinetics of T cell expansion impairment were further confirmed in Ena/VASP-deficient T cells stimulated via dendritic cell immunization. To investigate the cause of this T cell expansion defect, we analyzed T cell–APC interactions in vivo by two-photon microscopy and observed fewer Ena/VASP-deficient naïve T cells interacting with APCs in LNs during priming. We also determined that Ena/VASP-deficient T cells formed conjugates with significantly less actin polymerization at the T cell–APC synapse, and that these conjugates were less stable than their WT counterparts. Finally, we found that Ena/VASP-deficient T cells have less LFA-1 polarized to the T cell–APC synapse. Thus, we conclude that Ena/VASP proteins contribute to T cell actin remodeling during T cell–APC interactions, which promotes the initiation of stable T cell conjugates during APC scanning. Therefore, Ena/VASP proteins are required for efficient activation and expansion of T cells in vivo.

Ena/VASP protein-mediated actin polymerization contributes to naive CD8+ T cell activation and expansion by promoting T cell-APC interactions in vivo

Abstract Naive T cell activation in secondary lymphoid organs such as lymph nodes (LNs) occurs upon recognition of cognate antigens presented by antigen presenting cells (APCs). T cell activation requires cytoskeleton rearrangement and sustained interactions with APCs. Ena/VASP proteins are a family of cytoskeletal effector proteins responsible for actin polymerization and are frequently found at the leading edge of motile cells. Ena/VASP proteins have been implicated in motility and adhesion in various cell types, but their role in primary T cell activation has not been explored. Our goal was to determine the contribution of Ena/VASP proteins to T cell activation and expansion in vivo. Our results showed that naïve T cells from Ena/VASP-deficient mice have a significant reduction in antigen-specific T cell accumulation following Listeria monocytogenes infection. The kinetics of antigen-specific T cell impairment were further confirmed in Ena/VASP-deficient T cells stimulated via dendritic cell immunization. To investigate the cause of this T cell expansion defect, we analyzed T cell-APC interactions in vivo by 2-photon microscopy and observed fewer Ena/VASP-deficient naïve T cells interacting with APCs in LNs during priming. We also found that Ena/VASP-deficient T cells formed conjugates with significantly less actin polymerization at the T cell-APC synapse, and that these conjugates were less stable than their WT counterparts. Thus, we conclude that Ena/VASP proteins contribute to T cell actin remodeling downstream of T-APC interactions required for the initiation of stable T cell conjugates during APC scanning and for efficient activation and expansion of T cells in vivo. Supported by NIH (R01AI125553; T32AI007405)

Abstract 1916: Lymph node targeting double stranded CpG act effective adjuvant in cancer peptide vaccine

Abstract Background: Adjuvants can enhance immune responses of vaccinated antigen by inducing host innate immune responses. While cancer peptide vaccines were largely studied in recent years, effective cancer peptide vaccines have not been found yet so far because of their poor immunogenicity. Developing an effective vaccine adjuvant suitable for peptide antigen is a promising approach. CpG oligodeoxynucleotides(CpG) are a toll-like receptor 9 agonists and effectively elicit innate immune responses. In order to improve adjuvanticity of CpG, we designed a novel lymph-node targeting CpG, which is composed from a single stranded CpG and a modified complementary strand with amphiphilic chain. Methods: S-540956 is a double stranded oligodeoxynucleotide composed from a single stranded phosphorothioate oligonucleotide and the complementary strand with amphiphilic chain at the 5' end. Accumulating capability to lymph nodes of fluorescent labeled S-540956 was analyzed by flow cytometer, IVIS imaging system, and 2-photon microscopy. Incorporation of S-540956 by antigen-presenting cells in lymph nodes was assessed by Image Stream® imaging cytometer. To test cellular immune responses, three types of MHC class-I epitope peptides were employed as antigenic peptides. Therapeutic effect of S-540956 adjuvanted HPV E7 peptide vaccine was evaluated in TC-1 tumor model. Results:S-540956 exhibited higher accumulating capacity to lymph nodes in mice compared to a typical CpG adjuvant, ODN2006. Systemic proinflammatory cytokine responses were decreased by combining the complementary strand with amphiphilic chain. S-540956 was efficiently incorporated into plasmacytoid DCs and induced the expression of costimulatory molecules. Cellular immune responses induced by S-540956 adjuvanted peptide vaccine were significantly higher than ODN2006 adjuvanted peptide vaccine. And this enhanced adjuvant effect was observed also in protein vaccine. In TC-1 tumor model, therapeutically administered S-540956 adjuvanted HPV-E7 peptide vaccine lead to significant tumor shrinkage compared to ODN2006 adjuvanted peptide vaccine. Conclusion: S-540956 acted as a potent adjuvant for peptide vaccine by inducing cellular immune responses effectively. Accumulating capacity to lymph nodes of S-540956 is a promising adjuvant for not only for peptide but for protein or other biologic antigens. Citation Format: Takayuki Nakagawa, Motoyasu Onishi, Soichi Tofukuji, Shinya Omoto, Kazufumi Katayama, Akira Kugimiya, Morio Nagira, Ken J. Ishii. Lymph node targeting double stranded CpG act effective adjuvant in cancer peptide vaccine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1916.

Applications of Melanin and Melanin-Like Nanoparticles in Cancer Therapy: A Review of Recent Advances.

Thanks to the growing knowledge about cancers and their interactions with the immune system, a huge number of therapeutic cancer vaccines have been developed in the past two decades. Despite encouraging results in pre-clinical models, cancer vaccines have not yet achieved significant clinical efficacy. Several factors may contribute to such poor results, including the difficulty of triggering a strong immune response and the immunosuppressive tumor microenvironment. Many strategies are currently being explored. Different types of adjuvants have been incorporated into vaccine formulations to improve their efficacy, as cancer antigens are usually poorly immunogenic. Nanoparticle systems are promising tools as they act as carriers for antigens and can be surface-modified so that they specifically target antigen-presenting cells in lymph nodes. Bioinspired nanomaterials are ideal candidates thanks to their biocompatibility. Recently, melanin-based nanoparticles were reported to efficiently localize into draining lymphoid tissues and trigger immune responses against loaded antigens. In addition, by virtue of their photochemical properties, melanin-based nanoparticles can also play an immunomodulatory role to promote anti-cancer responses in the context of photothermal therapy. In this review, we discuss the above-mentioned properties of melanin, and summarize the promising results of the melanin-based cancer vaccines recently reported in preclinical models.

Goblet cell loss abrogates ocular surface immune tolerance.

Intestinal epithelial cells condition tolerogenic properties in DCs. Aqueous-deficient dry eye is associated with goblet cell (GC) loss and increased IFN-γ expression in the conjunctiva. We hypothesized that loss of GCs reduces tolerance-inducing properties of antigen presenting cells (APCs) in the conjunctiva and draining nodes. Mice lacking the SAM pointed domain containing ETS transcription factor (Spdef) that is required for GC differentiation had an increased frequency of macrophages in the conjunctiva and CD11b+CD11c+ DCs in the conjunctiva and draining nodes, and these cells had greater IL-12 expression than WT mice. Conditioned media from cultured WT conjunctival GCs suppressed LPS-induced IL-12 production by conjunctival APCs. OVA antigen-specific OTII CD4+ T cells primed by Spdef-KO draining lymph node APCs showed greater proliferation, lower frequency of Foxp3+, increased frequency of IFN-γ+ and IL-17+ cells, and greater IFN-γ production than those primed by WT APCs. The immune tolerance to OVA antigen topically applied to the conjunctiva measured by cutaneous delayed type hypersensitivity (DTH) reaction, OVA-specific T cell proliferation, Foxp3 induction, and IFN-γ production observed in WT mice was lost in the Spdef-KO mice. We concluded that conjunctival GCs condition tolerogenic properties in APCs that suppress IL-12 production and Th1 polarization.

Turning the Old Adjuvant from Gel to Nanoparticles to Amplify CD8+ T Cell Responses.

Due to its safety and efficacy, aluminum hydroxide is used as an immune adjuvant in human vaccines for over 80 years. Being a Th2 stimulator, the classical gel‐like adjuvant, however, fails to generate CD8+ T cell responses, which are important for cancer vaccines. Here, aluminum hydroxide is turned from gel into nano‐sized vaccine carriers AlO(OH)‐polymer nanoparticles (APNs) to promote their lymphatic migration. After actively uptaken via scavenger receptor‐A by antigen‐presenting cells (APCs) resident in lymph nodes (LNs), APNs destabilize lysosomes resulting in efficient cytosolic delivery and cross‐presentation of antigens. It is demonstrated that administration of APNs loaded with ovalbumin (OVA) and CpG led to the codelivery of both cargos into APCs in LNs, leading to their activation and subsequent adaptive immunity. A prime‐boost strategy with low doses of OVA (1.5 µg) and CpG (0.45 µg) induces potent CD8+ T cell responses and dramatically prolongs the survival of B16‐OVA tumor‐bearing mice. More impressively, when using B16F10 lysates instead of OVA as antigen, substantial antitumor effects on B16F10 tumor model are observed by using APN‐CpG. These results suggest the great potential of APNs as vaccine carriers that activate CD8+ T cell responses and the bright prospect of aluminum adjuvant in a nanoparticle formulation.

Delivering adjuvants and antigens in separate nanoparticles eliminates the need of physical linkage for effective vaccination

DNA rich in unmethylated CG motifs (CpGs) engage Toll-Like Receptor 9 (TLR-9) in endosomes and are well described stimulators of the innate and adaptive immune system. CpGs therefore can efficiently improve vaccines' immunogenicity. Packaging CpGs into nanoparticles, in particular into virus-like particles (VLPs), improves the pharmacological characteristics of CpGs as the protein shell protects them from DNAse activity and delivers the oligomers to the endosomal compartments of professional antigen presenting cells (APCs). The current consensus in packaging and delivering CpGs in VLP-based vaccines is that both adjuvants and antigens should be kept in close proximity (i.e. physically linked) to ensure delivery of antigens and adjuvants to the same APCs. In the current study, we harness the draining properties of the lymphatic system and show that also non-linked VLPs are efficiently co-delivered to the same APCs in lymph nodes. Specifically, we have shown that CpGs can be packaged in one VLP and mixed with another VLP displaying the antigen prior to administration in vivo. Both VLPs efficiently reached the same draining lymph node where they were taken up and processed by the same APCs, namely dendritic cells and macrophages. This resulted in induction of specific CTLs producing cytokines and killing target cells in vivo at levels seen when using VLPs containing both CpGs and chemically conjugated antigen. Thus, delivery of antigens and adjuvants in separate nanoparticles eliminates the need of physical conjugation and thus can be beneficial when designing precision medicine VLP-based vaccines or help to re-formulate existing VLP vaccines not naturally carrying immunostimulatory sequences.

Targeted delivery of lipid antigen to macrophages via the CD169/sialoadhesin endocytic pathway induces robust invariant natural killer T cell activation

Invariant natural killer T (iNKT) cells induce a protective immune response triggered by foreign glycolipid antigens bound to CD1d on antigen-presenting cells (APCs). A limitation of using glycolipid antigens to stimulate immune responses in human patients has been the inability to target them to the most effective APCs. Recent studies have implicated phagocytic CD169(+) macrophages as major APCs in lymph nodes for priming iNKT cells in mice immunized with glycolipid antigen in particulate form. CD169 is known as sialoadhesin (Sn), a macrophage-specific adhesion and endocytic receptor of the siglec family that recognizes sialic acid containing glycans as ligands. We have recently developed liposomes decorated with glycan ligands for CD169/Sn suitable for targeted delivery to macrophages via CD169/Sn-mediated endocytosis. Here we show that targeted delivery of a lipid antigen to CD169(+) macrophages in vivo results in robust iNKT cell activation in liver and spleen using nanogram amounts of antigen. Activation of iNKT cells is abrogated in Cd169(-/-) mice and is macrophage-dependent, demonstrating that targeting CD169(+) macrophages is sufficient for systemic activation of iNKT cells. When pulsed with targeted liposomes, human monocyte-derived dendritic cells expressing CD169/Sn activated human iNKT cells, demonstrating the conservation of the CD169/Sn endocytic pathway capable of presenting lipid antigens to iNKT cells.

Chemokines control naive CD8+ T cell selection of optimal lymph node antigen presenting cells

Naive antiviral CD8(+) T cells are activated in the draining LN (DLN) by dendritic cells (DCs) presenting viral antigens. However, many viruses infect LN macrophages, which participate in initiation of innate immunity and B cell activation. To better understand how and why T cells select infected DCs rather than macrophages, we performed intravital microscopy and ex vivo analyses after infecting mice with vaccinia virus (VV), a large DNA virus that infects both LN macrophages and DCs. Although CD8(+) T cells interact with both infected macrophages and DCs in the LN peripheral interfollicular region (PIR), DCs generate more frequent and stable interactions with T cells. VV infection induces rapid release of CCR5-binding chemokines in the LN, and administration of chemokine-neutralizing antibodies diminishes T cell activation by increasing T cell localization to macrophages in the macrophage-rich region (MRR) at the expense of PIR DCs. Similarly, DC ablation increases both T cell localization to the MRR and the duration of T cell-macrophage contacts, resulting in suboptimal T cell activation. Thus, virus-induced chemokines in DLNs enable antiviral CD8(+) T cells to distinguish DCs from macrophages to optimize T cell priming.

T cell responses in lymph nodes

Activation of T cells by antigen-presenting cells (APCs) in lymph nodes (LNs) is a key initiating event in many immune responses. Our understanding of this process has been both improved and complicated in recent years by evidence from techniques such as intravital microscopy that has revealed new levels of dynamism in the interaction of T cells and APCs. In particular, the complex motility of T cells within LNs, and their serial interactions with many APCs, imply that earlier static models of T cell activation need to be updated. Here we review the first attempts to model T cell interactions with APCs in LNs that incorporate simulations of T cell motility, based on experimental observations. We show that lattice-based modeling approaches are the dominant trend in these models, and then chart a possible course for development of these models toward spatially-resolved models of immune responses within LNs.

B cell‐Dendritic Cell interaction during influenza infection

Strong antibody responses against influenza virus are mounted rapidly in the respiratory tract following an infection. These B cell responses contribute to immune protection, but how they are regulated is still incompletely understood. Antigen‐presenting cells (APC) can directly support B cell activation and class switch recombination in the absence of T cells. We aimed to determine whether influenza infection‐induced respiratory tract APC support virus‐specific B cell responses. We conducted co‐culture experiments of enriched influenza virus‐specific B cells with FACS‐purified dendritic cells (DC) and macrophages from three‐day infected lung and draining lymph nodes. B cells from MCMV‐infected mice served as controls. B cell proliferation was assessed by CFSE‐staining, total and virus‐specific antibody‐secretion was measured by ELISA and the Ig isotype profile was determined by bead array. Overall, respiratory tract APC did not support clonal B cell expansion but had significant effects on virus‐specific IgG‐secretion. Surprisingly, lung APC, particularly DC, were superior in their ability to provide help compared to lymph node APC. The effects were virus‐specific and required no additional antigen. Our data provide evidence that respiratory tract APC can drive specific B cell differentiation and they suggest an important role for tissue‐resident APC in B cell response induction. NIH A1055881.

Ultraviolet B but Not A Radiation Activates Suppressor B Cells in Draining Lymph Nodes

Immunosuppressive doses of solar-simulated UV radiation activate lymph node B cells that can suppress primary immunity by inhibiting the function of dendritic cells. The aim of this study was to determine the waveband responsible for activation of these suppressor B cells. We exposed C57BL/6 mice to various doses of either UVA or UVB radiation and analyzed the number and activation state of lymph node antigen-presenting cells (APC). Immunosuppressive doses of UVB but not UVA activated B cells as assessed by major histocompatibility complex II (MHC II) expression and doubled their numbers in draining lymph nodes. Higher doses of UVA that were not immunosuppressive actually suppressed B cell activation. Our results show that UVA and UVB suppress systemic immunity via different mechanisms. Lymph node B cells are activated in response to immunosuppressive doses of UVB but not UVA. Thus, the activation state of lymph node APC appears to be important for UV immunomodulation.

FTY720-Induced Sequestration of Donor T Cells in Lymph Nodes Leads to Activation-Induced Apoptosis of Alloreactive T Cells and Reduced Graft-Versus-Host Disease.

Interaction of donor T cells and host antigen-presenting cells (APCs) in secondary lymphoid organs is critical for inducing graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). Activation-induced cell death (AICD) is a chief mechanism of clonal deletion that is responsible for the rapid contraction of alloreactive donor T cells following an initial massive expansion. We hypothesized that sequestration of donor T cells in lymph nodes (LNs) would lead to prolonged interaction of donor T cells and host APCs in LNs and cause AICD of alloreactive donor T cells after allogeneic BMT. To test this hypothesis, recipient mice were given FTY720, which inhibits migration of T cells from LNs, after BMT. Lethally irradiated B6 (H-2b) mice were injected with 10 x 106 purified T cells and 5 x 106 bone marrow cells harvested from congeneic B6.Ly-5a (H-2b, CD45.1+) donors. FTY720 was administered by daily oral gavage at a dose of 0.3mg/kg from day 0. Six days after congeneic BMT, numbers of donor T cells in mesenteric LNs were greater in FTY720-treated mice as expected. By contrast, when B6D2F1 (H-2b/d) recipients were transplanted with 4 x 106 purified T cells and 5 x 106 bone marrow cells from allogeneic B6. Ly-5a donors, numbers of donor T cells in mesenteric LNs were greater in FTY720-treated mice than controls 4 days after allogeneic BMT but were subsequently less in FTY720-treated mice than controls (Figure). Five days after allogeneic BMT, frequencies of apoptotic donor T cells assessed by AnnexinV positivity were significantly greater in FTY720-treated mice (33±3 vs 24±5%, P<.05) than those in controls. Serum level of IFN-γ (7.4±1.1 ng/ml vs 12.4±1.6 ng/ml, P<.05), an index of systemic T cell responses, was significantly reduced in FTY720-treated mice on day7. These results suggest that administration of FTY720 enhances contraction of donor T cells by inducing apoptosis of donor T cells after allogeneic BMT. This FTY720-induced reduction of serum levels of IFN-γ was similarly observed when Fas-deficient B6-lpr/lpr mice were used as donors, indicating Fas-independent AICD in this phenomenon. Administration of FTY720 until day10 after allogeneic BMT improved survivals of recipients (67% vs 0% at day 21, P<.05). When reduced number of T cells (1 x 106) were infused, administration of FTY720 until day10 improved clinical GVHD scores (6.0±0.5 vs 4.1±0.3 at day14, P<.05) and survivals (100% vs 50% at day 30, P<.05) of recipients. Next, 1 x 106 donor T cells isolated from FTY720-treated and control-treated recipients 6 days after allogeneic BMT were adoptively transferred to lethally irradiated B6D2F1 mice together with 2 x 106 bone marrow cells from syngeneic B6D2F1 donors. T cells from FTY720-treated mice caused significantly decreased GVH reaction compared to T cells from control-treated mice (p<.01), suggesting the reduced alloreactivity of T cells from FTY720-treated mice. These findings suggest that FTY720 could modulate GVHD by the induction of AICD of donor T cells in LNs as well as by the inhibition of migration of donor T cells to target tissue. [Display omitted]

Morphofunctional characteristics of antigen-presenting cells in lymph node in mice with experimental West Nile fever.

Pronounced transformation of cells in mesenteric lymph nodes, mainly in the thymus-independent zone and sinuses, was detected in albino mice experimentally infected with West Nile fever (strain 986). Maximum antigen-presenting activity was exhibited by activated macrophages, minimum activity--by dendritic cells of lymphoid follicles.

Cross-linking the B7 family molecule B7-DC directly activates immune functions of dendritic cells.

B7-DC molecules are known to function as ligands on antigen-presenting cells (APCs), enhancing T cell activation. In this study, cross-linking B7-DC with the monoclonal antibody sHIgM12 directly potentiates dendritic cell (DC) function by enhancing DC presentation of major histocompatibility complex–peptide complexes, promoting DC survival; and increasing secretion of interleukin (IL)-12p70, a key T helper cell type 1 promoting cytokine. Furthermore, ex vivo treatment of DCs or systemic treatment of mice with sHIgM12 increases the number of transplanted DCs that reach draining lymph nodes and increases the ability of lymph node APCs to activate naive T cells. Systemic administration of the antibody has an equivalent effect on DCs transferred at a distant site. These findings implicate B7-DC expressed on DCs in bidirectional communication. In addition to the established costimulatory and inhibitory functions associated with B7-DC, this molecule can also function as a conduit for extracellular signals to DCs modifying DC functions.