The Translocon Protein Sec61 Mediates Antigen Transport from Endosomes in the Cytosol for Cross-Presentation to CD8+ T Cells

Allostimulation leads to emergence of a human B cell population with increased expression of HLA class I antigen presentation-associated molecules and the immunoglobulin receptor FcRL5

In the extensive literature characterizing lymphocyte contributions to transplant-related pathologies including allograft rejection and graft-versus-host disease, T cell-focused investigation has outpaced investigation of B cells. Most B cell-related reports describe regulatory and antibody-producing functions, with less focus on the potential role of antigen-presenting capacity. Using in vitro human mixed lymphocyte reactions (MLRs) to model allostimulation, we analyzed responder B cells using transcriptional analysis, flow cytometry, and microscopy. We observed emergence of an activated responder B cell subpopulation phenotypically similar to that described in individuals with graft-versus-host disease or allograft rejection. This population had markedly increased expression of FcRL5 (Fc receptor like 5) and molecules associated with human leukocyte antigen class I antigen presentation. Consistent with this phenotype, these cells demonstrated increased internalization of irradiated cell debris and dextran macromolecules. The proportion of this subpopulation within MLR responders also correlated with emergence of activated, cytotoxic CD8+ T cells. B cells of similar profile were quite infrequent in unstimulated blood from healthy individuals but readily identifiable in disaggregated human splenocytes and increased in both cases upon allostimulation. Further characterization of the emergence and function of this subpopulation could potentially contribute to identification of novel biomarkers and targeted therapeutics relevant to curbing transplant-related pathology.

FcRn regulates antigen presentation in dendritic cells downstream of DEC205-targeted vaccines

Dendritic cell (DC)-targeted vaccination is a new mode of antigen delivery that relies on the use of monoclonal antibodies (mAb) to target antigen to specific DC subsets. The neonatal Fc receptor (FcRn) is a non-classical Fc receptor that binds to immunoglobulin G (IgG) in acidified endosomes and controls its intracellular transport and recycling. FcRn is known to participate in the antigen presentation of immune complexes, however its contribution to DC-targeted vaccination has not previously been examined. Here we have investigated the role of FcRn in antigen presentation using antigen conjugated to IgG mAb which target specific DC receptors, including DEC205 and Clec9A expressed by the conventional DC 1 (cDC1) subset. We show that FcRn is expressed at high levels by cDC1, both at steady-state and following activation and plays a significant role in MHC I cross-presentation and MHC II presentation of antigens that are targeted to cDC1 via mAb specific for DEC205. This effect of FcRn is intrinsic to cDC1 and FcRn impacts the efficacy of anti-DEC205-mediated vaccination against B cell lymphoma. In contrast, FcRn does not impact presentation of antigens targeted to Clec9A and does not regulate presentation of cell-associated antigen. These data highlight a new and unique role of FcRn in controlling the immunogenicity of anti-DEC205-based vaccination, with consequences for exploiting this pathway to improve DC-targeted vaccine outcomes.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

The transcription factor Zeb1 controls homeostasis and function of type 1 conventional dendritic cells

Type 1 conventional dendritic cells (cDC1) are the most efficient cross-presenting cells that induce protective cytotoxic T cell response. However, the regulation of their homeostasis and function is incompletely understood. Here we observe a selective reduction of splenic cDC1 accompanied by excessive cell death in mice with Zeb1 deficiency in dendritic cells, rendering the mice more resistant to Listeria infection. Additionally, cDC1 from other sources of Zeb1-deficient mice display impaired cross-presentation of exogenous antigens, compromising antitumor CD8+ T cell responses. Mechanistically, Zeb1 represses the expression of microRNA-96/182 that target Cybb mRNA of NADPH oxidase Nox2, and consequently facilitates reactive-oxygen-species-dependent rupture of phagosomal membrane to allow antigen export to the cytosol. Cybb re-expression in Zeb1-deficient cDC1 fully restores the defective cross-presentation while microRNA-96/182 overexpression in Zeb1-sufficient cDC1 inhibits cross-presentation. Therefore, our results identify a Zeb1-microRNA-96/182-Cybb pathway that controls cross-presentation in cDC1 and uncover an essential role of Zeb1 in cDC1 homeostasis.

Controlling Antigen Fate in Therapeutic Cancer Vaccines by Targeting Dendritic Cell Receptors

Antigen-presenting cells (APCs) orchestrate immune responses and are therefore of interest for the targeted delivery of therapeutic vaccines. Dendritic cells (DCs) are professional APCs that excel in presentation of exogenous antigens toward CD4+ T helper cells, as well as cytotoxic CD8+ T cells. DCs are highly heterogeneous and can be divided into subpopulations that differ in abundance, function, and phenotype, such as differential expression of endocytic receptor molecules. It is firmly established that targeting antigens to DC receptors enhances the efficacy of therapeutic vaccines. While most studies emphasize the importance of targeting a specific DC subset, we argue that the differential intracellular routing downstream of the targeted receptors within the DC subset should also be considered. Here, we review the mouse and human receptors studied as target for therapeutic vaccines, focusing on antibody and ligand conjugates and how their targeting affects antigen presentation. We aim to delineate how targeting distinct receptors affects antigen presentation and vaccine efficacy, which will guide target selection for future therapeutic vaccine development.

Major histocompatibility complex class I assembly within endolysosomal pathways

Major histocompatibility complex class I (MHC class I) molecules facilitate subcellular immune surveillance by presenting peptides on the cell surface. MHC class I assembly with peptides generally happens in the endoplasmic reticulum (ER). Peptides are processed in the cytosol, transported into the ER, and assembled with MHC class I heavy and light chains. However, as many pathogens reside within multiple subcellular organelles, peptide sampling across non-cytosolic compartments is also important. MHC class I molecules internalize from the cell surface into endosomes and constitutively traffic between endosomes and the cell surface. Within endosomes, MHC class I molecules assemble with both exogenous and endogenous antigens processed within these compartments. Human MHC classI polymorphisms, well known to affect ER assembly modes, also influence endosomal assembly outcomes, an area of current interest to the field.

Surface immunogenic protein from Streptococcus agalactiae and Fissurella latimarginata hemocyanin are TLR4 ligands and activate MyD88- and TRIF dependent signaling pathways

The development of vaccine adjuvants is of interest for the management of chronic diseases, cancer, and future pandemics. Therefore, the role of Toll-like receptors (TLRs) in the effects of vaccine adjuvants has been investigated. TLR4 ligand-based adjuvants are the most frequently used adjuvants for human vaccines. Among TLR family members, TLR4 has unique dual signaling capabilities due to the recruitment of two adapter proteins, myeloid differentiation marker 88 (MyD88) and interferon-β adapter inducer containing the toll-interleukin-1 receptor (TIR) domain (TRIF). MyD88-mediated signaling triggers a proinflammatory innate immune response, while TRIF-mediated signaling leads to an adaptive immune response. Most studies have used lipopolysaccharide-based ligands as TLR4 ligand-based adjuvants; however, although protein-based ligands have been proven advantageous as adjuvants, their mechanisms of action, including their ability to undergo structural modifications to achieve optimal immunogenicity, have been explored less thoroughly. In this work, we characterized the effects of two protein-based adjuvants (PBAs) on TLR4 signaling via the recruitment of MyD88 and TRIF. As models of TLR4-PBAs, we used hemocyanin from Fissurella latimarginata (FLH) and a recombinant surface immunogenic protein (rSIP) from Streptococcus agalactiae. We determined that rSIP and FLH are partial TLR4 agonists, and depending on the protein agonist used, TLR4 has a unique bias toward the TRIF or MyD88 pathway. Furthermore, when characterizing gene products with MyD88 and TRIF pathway-dependent expression, differences in TLR4-associated signaling were observed. rSIP and FLH require MyD88 and TRIF to activate nuclear factor kappa beta (NF-κB) and interferon regulatory factor (IRF). However, rSIP and FLH have a specific pattern of interleukin 6 (IL-6) and interferon gamma-induced protein 10 (IP-10) secretion associated with MyD88 and TRIF recruitment. Functionally, rSIP and FLH promote antigen cross-presentation in a manner dependent on TLR4, MyD88 and TRIF signaling. However, FLH activates a specific TRIF-dependent signaling pathway associated with cytokine expression and a pathway dependent on MyD88 and TRIF recruitment for antigen cross-presentation. Finally, this work supports the use of these TLR4-PBAs as clinically useful vaccine adjuvants that selectively activate TRIF- and MyD88-dependent signaling to drive safe innate immune responses and vigorous Th1 adaptive immune responses.

The functional response of human monocyte-derived macrophages to serum amyloid A and Mycobacterium tuberculosis infection

Introduction

In the course of tuberculosis (TB), the level of major acute phase protein, namely serum amyloid A (hSAA-1), increases up to a hundredfold in the pleural fluids of infected individuals. Tubercle bacilli infecting the human host can be opsonized by hSAA-1, which affects bacterial entry into human macrophages and their intracellular multiplication.

Methods

We applied global RNA sequencing to evaluate the functional response of human monocyte-derived macrophages (MDMs), isolated from healthy blood donors, under elevated hSAA-1 conditions and during infection with nonopsonized and hSAA-1-opsonized Mycobacterium tuberculosis (Mtb). In the same infection model, we also examined the functional response of mycobacteria to the intracellular environment of macrophages in the presence and absence of hSAA-1. The RNASeq analysis was validated using qPCR. The functional response of MDMs to hSAA-1 and/or tubercle bacilli was also evaluated for selected cytokines at the protein level by applying the Milliplex system.

Findings

Transcriptomes of MDMs cultured in the presence of hSAA-1 or infected with Mtb showed a high degree of similarity for both upregulated and downregulated genes involved mainly in processes related to cell division and immune response, respectively. Among the most induced genes, across both hSAA-1 and Mtb infection conditions, CXCL8, CCL15, CCL5, IL-1β, and receptors for IL-7 and IL-2 were identified. We also observed the same pattern of upregulated pro-inflammatory cytokines (TNFα, IL-6, IL-12, IL-18, IL-23, and IL-1) and downregulated anti-inflammatory cytokines (IL-10, TGFβ, and antimicrobial peptide cathelicidin) in the hSAA-1 treated-MDMs or the phagocytes infected with tubercle bacilli. At this early stage of infection, Mtb genes affected by the inside microenvironment of MDMs are strictly involved in iron scavenging, adaptation to hypoxia, low pH, and increasing levels of CO2. The genes for the synthesis and transport of virulence lipids, but not cholesterol/fatty acid degradation, were also upregulated.

Conclusion

Elevated serum hSAA-1 levels in tuberculosis enhance the response of host phagocytes to infection, including macrophages that have not yet been in contact with mycobacteria. SAA induces antigen processing and presentation processes by professional phagocytes reversing the inhibition caused by Mtb infection.

Dendritic cell-based vaccine prepared with recombinant Lactococcus lactis enhances antigen cross-presentation and antitumor efficacy through ROS production

Introduction

Lactococcus lactis (L.L) is safe and can be used as vehicle. In this study, the immunoregulatory effect of L.L on dendritic cell (DC) activation and mechanism were investigated. The immune responses and antigen cross-presentation mechanism of DC-based vaccine prepared with OVA recombinant L.L were explored.

Methods

Confocal microscopy and flow cytometry were used to analyze the mechanism of L.L promoting DC maturation, phagosome membrane rupture and antigen presentation. The antitumor effect of DC vaccine prepared with L.L-OVA was assessed in the B16-OVA tumor mouse model.

Results

L.L significantly promoted DC maturation, which was partially dependent on TLR2 and downstream MAPK and NF-κB signaling pathways. L.L was internalized into DCs by endocytosis and did not co-localized with lysosome. OVA recombinant L.L enhanced antigen cross-presentation of DCs through the phagosome-to-cytosol pathway in a reactive oxygen species (ROS)- and proteasome-dependent manner. In mouse experiments, L.L increased the migration of DCs to draining lymph node and DC vaccine prepared with OVA recombinant L.L induced strong antigen-specific Th1 and cytotoxic T lymphocyte responses, which significantly inhibited B16-OVA tumor growth.

Conclusion

This study demonstrated that recombinant L.L as an antigen delivery system prepared DC vaccine can enhance the antigen cross-presentation and antitumor efficacy.

Saponin-based adjuvants enhance antigen cross-presentation in human CD11c+ CD1c+ CD5- CD163+ conventional type 2 dendritic cells

BACKGROUND

Adjuvants are key for effective vaccination against cancer and chronic infectious diseases. Saponin-based adjuvants (SBAs) are unique among adjuvants in their ability to induce robust cell-mediated immune responses in addition to antibody responses. Recent preclinical studies revealed that SBAs induced cross-presentation and lipid bodies in otherwise poorly cross-presenting CD11b+ murine dendritic cells (DCs).

METHOD

Here, we investigated the response of human DC subsets to SBAs with RNA sequencing and pathway analyses, lipid body induction visualized by laser scanning microscopy, antigen translocation to the cytosol, and antigen cross-presentation to CD8+ T cells.

RESULTS

RNA sequencing of SBA-treated conventional type 1 DC (cDC1) and type 2 DC (cDC2) subsets uncovered that SBAs upregulated lipid-related pathways in CD11c+ CD1c+ cDC2s, especially in the CD5- CD163+ CD14+ cDC2 subset. Moreover, SBAs induced lipid bodies and enhanced endosomal antigen translocation into the cytosol in this particular cDC2 subset. Finally, SBAs enhanced cross-presentation only in cDC2s, which requires the CD163+ CD14+ cDC2 subset.

CONCLUSIONS

These data thus identify the CD163+ CD14+ cDC2 subset as the main SBA-responsive DC subset in humans and imply new strategies to optimize the application of saponin-based adjuvants in a potent cancer vaccine.

Recent progress in type 1 classical dendritic cell cross-presentation - cytosolic, vacuolar, or both?

Type 1 classical dendritic cells (cDC1s) have emerged as the major antigen-presenting cell performing cross-presentation (XP) in vivo, but the antigen-processing pathway in this cell remains obscure. Two competing models for in vivo XP of cell-associated antigens by cDC1 include a vacuolar pathway and cytosolic pathway. A vacuolar pathway relies on directing antigens captured in vesicles toward a class I major histocompatibility complex loading compartment independently of cytosolic entry. Alternate proposals invoke phagosomal rupture, either constitutive or triggered by spleen tyrosine kinase (SYK) signaling in response to C-type lectin domain family 9 member A (CLEC9A) engagement, that releases antigens into the cytosol for proteasomal degradation. The Beige and Chediak-Higashi (BEACH) protein WD repeat- and FYVE domain-containing protein 4 (WDFY4) is strictly required for XP of cell-associated antigens in vivo. However, the cellular mechanism for WDFY4 activity remains unknown and its requirement in XP in vivo is currently indifferent regarding the vacuolar versus cytosolic pathways. Here, we review the current status of these models and discuss the need for future investigation.

Channeling antigens to CD8+ T cells

Perforin-2 facilitates antigen translocation to the cytosol in cross-presenting dendritic cells.

Perforin-2 is a pore-forming effector of endocytic escape in cross-presenting dendritic cells

During initiation of antiviral and antitumor T cell-mediated immune responses, dendritic cells (DCs) cross-present exogenous antigens on major histocompatibility complex (MHC) class I molecules. Cross-presentation relies on the unusual "leakiness" of endocytic compartments in DCs, whereby internalized proteins escape into the cytosol for proteasome-mediated generation of MHC I-binding peptides. Given that type 1 conventional DCs excel at cross-presentation, we searched for cell type-specific effectors of endocytic escape. We devised an assay suitable for genetic screening and identified a pore-forming protein, perforin-2 (Mpeg1), as a dedicated effector exclusive to cross-presenting cells. Perforin-2 was recruited to antigen-containing compartments, where it underwent maturation, releasing its pore-forming domain. Mpeg1-/- mice failed to efficiently prime CD8+ T cells to cell-associated antigens, revealing an important role for perforin-2 in cytosolic entry of antigens during cross-presentation.

Pathways of MHC I cross-presentation of exogenous antigens

Phagocytes, particularly dendritic cells (DCs), generate peptide-major histocompatibility complex (MHC) I complexes from antigens they have collected from cells in tissues and report this information to CD8 T cells in a process called cross-presentation. This process allows CD8 T cells to detect, respond and eliminate abnormal cells, such as cancers or cells infected with viruses or intracellular microbes. In some settings, cross-presentation can help tolerize CD8 T cells to self-antigens. One of the principal ways that DCs acquire tissue antigens is by ingesting this material through phagocytosis. The resulting phagosomes are key hubs in the cross-presentation (XPT) process and in fact experimentally conferring the ability to phagocytize antigens can be sufficient to allow non-professional antigen presenting cells (APCs) to cross-present. Once in phagosomes, exogenous antigens can be cross-presented (XPTed) through three distinct pathways. There is a vacuolar pathway in which peptides are generated and then bind to MHC I molecules within the confines of the vacuole. Ingested exogenous antigens can also be exported from phagosomes to the cytosol upon vesicular rupture and/or possibly transport. Once in the cytosol, the antigen is degraded by the proteasome and the resulting oligopeptides can be transported to MHC I molecule in the endoplasmic reticulum (ER) (a phagosome-to-cytosol (P2C) pathway) or in phagosomes (a phagosome-to-cytosol-to-phagosome (P2C2P) pathway). Here we review how phagosomes acquire the necessary molecular components that support these three mechanisms and the contribution of these pathways. We describe what is known as well as the gaps in our understanding of these processes.

The evolving biology of cross-presentation

Cross-priming was first recognized in the context of in vivo cytotoxic T lymphocyte (CTL) responses generated against minor histocompatibility antigens induced by immunization with lymphoid cells. Even though the basis for T cell antigen recognition was still largely unclear at that time, these early studies recognized the implication that such minor histocompatibility antigens were derived from the immunizing cells and were obtained exogenously by the host's antigen presenting cells (APCs) that directly prime the CTL response. As antigen recognition by the T cell receptor became understood to involve peptides derived from antigens processed by the APCs and presented by major histocompatibility molecules, the "cross-priming" phenomenon was subsequently recast as "cross-presentation" and the scope considered for examining this process gradually broadened to include many different forms of antigens, including soluble proteins, and different types of APCs that may not be involved in in vivo CTL priming. Many studies of cross-presentation have relied on in vitro cell models that were recently found to differ from in vivo APCs in particular mechanistic details. A recent trend has focused on the APCs and pathways of cross-presentation used in vivo, especially the type 1 dendritic cells. Current efforts are also being directed towards validating the in vivo role of various putative pathways and gene candidates in cross-presentation garnered from various in vitro studies and to determine the relative contributions they make to CTL responses across various forms of antigens and immunologic settings. Thus, cross-presentation appears to be carried by different pathways in various types of cells for different forms under different physiologic settings, which remain to be evaluated in an in vivo physiologic setting.

Ultrasound molecular imaging of p32 protein translocation for evaluation of tumor metastasis

Protein translocation is an essential process for living cells to respond to different physiological, pathological or environmental stimuli. However, its abnormal occurrence usually results in undesirable outcomes such as tumors. To date, there is still a lack of appropriate methods to detect this event in live animals in a real-time manner. Here, we identified the gradually increased cell-surface translocation of p32 protein from mitochondria during tumor progression. LyP-1-modified gas vesicles (LyP-1-GVs) were developed through conjugating LyP-1 (p32-targeting peptide) to the biosynthetic GVs to monitor the cell-surface level of p32 translocation. The resulting LyP-1-GVs have about 200 nm particle size and good tumor cell targeting performance. Upon systemic administration, LyP-1-GVs can traverse through blood vessels and bind to the tumor cells, producing strong contrast imaging signals in comparison with the non-targeted GVs. The contrast imaging signals correlate well with the cell-surface translocation level of p32 protein and tumor metastatic ability. To our knowledge, this is the first report about the in vivo detection of protein translocation to cell membrane from mitochondria by ultrasound molecular imaging. Our study provides a new strategy to explore the molecular events of protein membrane translocations for evaluation of tumor metastasis at the live animal level.

The neuroimmune axis of Alzheimer's disease

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder with multifaceted neuropathological features, including β-amyloid plaques, neurofibrillary tangles, and neuroinflammation. Over the past decade, emerging evidence has implicated both beneficial and pathological roles for innate immune genes and immune cells, including peripheral immune cells such as T cells, which can infiltrate the brain and either ameliorate or exacerbate AD neuropathogenesis. These findings support a neuroimmune axis of AD, in which the interplay of adaptive and innate immune systems inside and outside the brain critically impacts the etiology and pathogenesis of AD. In this review, we discuss the complexities of AD neuropathology at the levels of genetics and cellular physiology, highlighting immune signaling pathways and genes associated with AD risk and interactions among both innate and adaptive immune cells in the AD brain. We emphasize the role of peripheral immune cells in AD and the mechanisms by which immune cells, such as T cells and monocytes, influence AD neuropathology, including microglial clearance of amyloid-β peptide, the key component of β-amyloid plaque cores, pro-inflammatory and cytotoxic activity of microglia, astrogliosis, and their interactions with the brain vasculature. Finally, we review the challenges and outlook for establishing immune-based therapies for treating and preventing AD.

Multifunctional role of the ubiquitin proteasome pathway in phagocytosis

Phagocytosis is a specialized form of endocytosis where large cells and particles (>0.5μm) are engulfed by the phagocytic cells, and ultimately digested in the phagolysosomes. This process not only eliminates unwanted particles and pathogens from the extracellular sources, but also eliminates apoptotic cells within the body, and is critical for maintenance of tissue homeostasis. It is believed that both endocytosis and phagocytosis share common pathways after particle internalization, but specialized features and differences between these two routes of internalization are also likely. The recruitment and removal of each protein/particle during the maturation of endocytic/phagocytic vesicles has to be tightly regulated to ensure their timely action. Ubiquitin proteasome pathway (UPP), degrades unwanted proteins by post-translational modification of proteins with chains of conserved protein Ubiquitin (Ub), with subsequent recognition of Ub chains by the 26S proteasomes and substrate degradation by this protease. This pathway utilizes different Ub linkages to modify proteins to regulate protein-protein interaction, localization, and activity. Due to its vast number of targets, it is involved in many cellular pathways, including phagocytosis. This chapters describes the basic steps and signaling in phagocytosis and different roles that UPP plays at multiple steps in regulating phagocytosis directly, or through its interaction with other phagosomal proteins. How aberrations in UPP function affect phagocytosis and their association with human diseases, and how pathogens exploit this pathway for their own benefit is also discussed.

Kinetics of antigen cross-presentation assessed experimentally and by a model of the complete endomembrane system

Dendritic cells (DCs) have a specialized endomembrane system capable of presenting exogenous antigens in the context of MHC class I (MHC-I) molecules. This process, named cross-presentation, is crucial to activate CD8+ T lymphocytes and initiate cytotoxic immune responses. In this report, we present an Agent-Based Model in combination with Ordinary Differential Equations with enough complexity to reproduce cross-presentation. The model embraces the secretory and endocytic pathways, in connection with the plasma membrane, the endoplasmic reticulum, and the cytosol. Key molecules required for cross-presentation were included as cargoes. In the simulations, the kinetics of MHC-I uptake and recycling, and cross-presentation accurately reproduced experimental values. The model proved to be a suitable tool to elaborate hypotheses and design experiments. In particular, the model predictions and the experimental results obtained indicate that the rate-limiting step in cross-presentation of soluble ovalbumin is MHC-I loading after proteasomal processing of the antigenic protein.

A rationally designed cancer vaccine based on NIR-II fluorescence image-guided light-triggered remote control of antigen cross-presentation and autophagy

Cancer vaccines represent a promising immunotherapeutic treatment modality. The promotion of cross-presentation of extracellular tumor-associated antigens on the major histocompatibility complex (MHC) class I molecules and dendritic cell maturation at the appropriate time and place is crucial for cancer vaccines to prime cytolytic T cell response with reduced side effects. Current vaccination strategies, however, are not able to achieve the spatiotemporal control of antigen cross-presentation. Here, we report a liposomal vaccine loading the second near-infrared window (NIR-II, 1000-1700 nm) fluorophore BPBBT with an efficient photothermal conversion effect that offers an NIR-light-triggered endolysosomal escape under the imaging guidance. The NIR-II image-guided vaccination strategy specifically controls the cytosolic delivery of antigens for cross-presentation in the draining lymph nodes (DLNs). Moreover, the photothermally induced endolysosomal rupture initiates autophagy. We also find that the adjuvant simvastatin acts as an autophagy activator through inhibiting the PI3K/AKT/mTOR pathway. The light-induced autophagy in the DLNs together with simvastatin treatment cooperatively increase MHC class II expression by activating autophagy machinery for dendritic cell maturation. This study presents a paradigm of NIR-II image-guided light-triggered vaccination. The approach for remote control of antigen cross-presentation and autophagy represents a new strategy for vaccine development.

Antigen targeting to dendritic cells: Still a place in future immunotherapy?

The hallmark of DCs is their potent and outstanding capacity to activate naive resting T cells. As such, DCs are the sentinels of the immune system and instrumental for the induction of immune responses. This is one of the reasons, why DCs became the focus of immunotherapeutical strategies to fight infections, cancer, and autoimmunity. Besides the exploration of adoptive DC-therapy for which DCs are generated from monocytes or purified in large numbers from the blood, alternative approaches were developed such as antigen targeting of DCs. The idea behind this strategy is that DCs resident in patients' lymphoid organs or peripheral tissues can be directly loaded with antigens in situ. The proof of principle came from mouse models; subsequent translational studies confirmed the potential of this therapy. The first clinical trials demonstrated feasibility and the induction of T-cell immunity in patients. This review will cover: (i) the historical aspects of antigen targeting, (ii) briefly summarize the biology of DCs and the immunological functions upon which this concept rests, (iii) give an overview on attempts to target DC receptors with antibodies or (glycosylated) ligands, and finally, (iv) discuss the translation of antigen targeting into clinical therapy.

Endocytic membrane repair by ESCRT-III controls antigen export to the cytosol during antigen cross-presentation

Despite its crucial role in initiation of cytotoxic immune responses, the molecular pathways underlying antigen cross-presentation remain incompletely understood. The mechanism of antigen exit from endocytic compartments into the cytosol is a long-standing matter of controversy, confronting two main models: transfer through specific channels/transporters or rupture of endocytic membranes and leakage of luminal content. By monitoring the occurrence of intracellular damage in conventional dendritic cells (cDCs), we show that cross-presenting cDC1s display more frequent endomembrane injuries and increased recruitment of endosomal sorting complex required for transport (ESCRT)-III, the main repair system for intracellular membranes, relative to cDC2s. Silencing of CHMP2a or CHMP4b, two effector subunits of ESCRT-III, enhances cytosolic antigen export and cross-presentation. This phenotype is partially reversed by chemical inhibition of RIPK3, suggesting that endocytic damage is related to basal activation of the necroptosis pathway. Membrane repair therefore proves crucial in containing antigen export to the cytosol and cross-presentation in cDCs.

Vaccine adjuvants to engage the cross-presentation pathway

Adjuvants are indispensable components of vaccines for stimulating optimal immune responses to non-replicating, inactivated and subunit antigens. Eliciting balanced humoral and T cell-mediated immunity is paramount to defend against diseases caused by complex intracellular pathogens, such as tuberculosis, malaria, and AIDS. However, currently used vaccines elicit strong antibody responses, but poorly stimulate CD8 cytotoxic T lymphocyte (CTL) responses. To elicit potent CTL memory, vaccines need to engage the cross-presentation pathway, and this requirement has been a crucial bottleneck in the development of subunit vaccines that engender effective T cell immunity. In this review, we focus on recent insights into DC cross-presentation and the extent to which clinically relevant vaccine adjuvants, such as aluminum-based nanoparticles, water-in oil emulsion (MF59) adjuvants, saponin-based adjuvants, and Toll-like receptor (TLR) ligands modulate DC cross-presentation efficiency. Further, we discuss the feasibility of using carbomer-based adjuvants as next generation of adjuvant platforms to elicit balanced antibody- and T-cell based immunity. Understanding of the molecular mechanism of DC cross-presentation and the mode of action of adjuvants will pave the way for rational design of vaccines for infectious diseases and cancer that require balanced antibody- and T cell-based immunity.

The Delivery of Extracellular “Danger” Signals to Cytosolic Sensors in Phagocytes

Phagocytes, such as macrophages and dendritic cells, possess the ability to ingest large quantities of exogenous material into membrane-bound endocytic organelles such as macropinosomes and phagosomes. Typically, the ingested material, which consists of diverse macromolecules such as proteins and nucleic acids, is delivered to lysosomes where it is digested into smaller molecules like amino acids and nucleosides. These smaller molecules can then be exported out of the lysosomes by transmembrane transporters for incorporation into the cell’s metabolic pathways or for export from the cell. There are, however, exceptional instances when undigested macromolecules escape degradation and are instead delivered across the membrane of endocytic organelles into the cytosol of the phagocyte. For example, double stranded DNA, a damage associated molecular pattern shed by necrotic tumor cells, is endocytosed by phagocytes in the tumor microenvironment and delivered to the cytosol for detection by the cytosolic “danger” sensor cGAS. Other macromolecular “danger” signals including lipopolysaccharide, intact proteins, and peptidoglycans can also be actively transferred from within endocytic organelles to the cytosol. Despite the obvious biological importance of these processes, we know relatively little of how macromolecular “danger” signals are transferred across endocytic organelle membranes for detection by cytosolic sensors. Here we review the emerging evidence for the active cytosolic transfer of diverse macromolecular “danger” signals across endocytic organelle membranes. We will highlight developing trends and discuss the potential molecular mechanisms driving this emerging phenomenon.

DCs at the center of help: Origins and evolution of the three-cell-type hypothesis

Last year was the 10th anniversary of Ralph Steinman's Nobel Prize awarded for his discovery of dendritic cells (DCs), while next year brings the 50th anniversary of that discovery. Current models of anti-viral and anti-tumor immunity rest solidly on Steinman's discovery of DCs, but also rely on two seemingly unrelated phenomena, also reported in the mid-1970s: the discoveries of "help" for cytolytic T cell responses by Cantor and Boyse in 1974 and "cross-priming" by Bevan in 1976. Decades of subsequent work, controversy, and conceptual changes have gradually merged these three discoveries into current models of cell-mediated immunity against viruses and tumors.

Antigen Presentation in the Lung

The lungs are constantly exposed to environmental and infectious agents such as dust, viruses, fungi, and bacteria that invade the lungs upon breathing. The lungs are equipped with an immune defense mechanism that involves a wide variety of immunological cells to eliminate these agents. Various types of dendritic cells (DCs) and macrophages (MACs) function as professional antigen-presenting cells (APCs) that engulf pathogens through endocytosis or phagocytosis and degrade proteins derived from them into peptide fragments. During this process, DCs and MACs present the peptides on their major histocompatibility complex class I (MHC-I) or MHC-II protein complex to naïve CD8⁺ or CD4⁺ T cells, respectively. In addition to these cells, recent evidence supports that antigen-specific effector and memory T cells are activated by other lung cells such as endothelial cells, epithelial cells, and monocytes through antigen presentation. In this review, we summarize the molecular mechanisms of antigen presentation by APCs in the lungs and their contribution to immune response.

CD206+ tumor-associated macrophages cross-present tumor antigen and drive anti-tumor immunity

In many solid cancers, tumor-associated macrophages (TAM) represent the predominant myeloid cell population. Antigen (Ag) cross-presentation leading to tumor Ag–directed cytotoxic CD8⁺ T cell responses is crucial for antitumor immunity. However, the role of recruited monocyte-derived macrophages, including TAM, as potential cross-presenting cells is not well understood. Here, we show that primary human as well as mouse CD206⁺ macrophages are effective in functional cross-presentation of soluble self-Ag and non–self-Ag, including tumor-associated Ag (TAA), as well as viral Ag. To confirm the presence of cross-presenting TAM in vivo, we performed phenotypic and functional analysis of TAM from B16-F10 and CT26 syngeneic tumor models and have identified CD11b+F4/80hiCD206+ TAM to effectively cross-present TAA. We show that CD11b+CD206+ TAM represent the dominant tumor-infiltrating myeloid cell population, expressing a unique cell surface repertoire, promoting Ag cross-presentation and Ag-specific CD8+ T cell activation comparable with cross-presenting CLEC9A+ DCs (cDC1). The presence of cross-presenting CD206+ TAM is associated with reduced tumor burden in mouse syngeneic tumor models and with improved overall survival in cutaneous melanoma patients. Therefore, the demonstration of effective Ag cross-presentation capabilities of CD206+ TAM, including their clinical relevance, expands our understanding of TAM phenotypic diversity and functional versatility.

Antigen Cross-Presentation by Murine Proximal Tubular Epithelial Cells Induces Cytotoxic and Inflammatory CD8+ T Cells

Immune-mediated glomerular diseases are characterized by infiltration of T cells, which accumulate in the periglomerular space and tubulointerstitium in close contact to proximal and distal tubuli. Recent studies described proximal tubular epithelial cells (PTECs) as renal non-professional antigen-presenting cells that stimulate CD4⁺ T-cell activation. Whether PTECs have the potential to induce activation of CD8⁺ T cells is less clear. In this study, we aimed to investigate the capacity of PTECs for antigen cross-presentation thereby modulating CD8⁺ T-cell responses. We showed that PTECs expressed proteins associated with cross-presentation, internalized soluble antigen via mannose receptor-mediated endocytosis, and generated antigenic peptides by proteasomal degradation. PTECs induced an antigen-dependent CD8⁺ T-cell activation in the presence of soluble antigen in vitro. PTEC-activated CD8⁺ T cells expressed granzyme B, and exerted a cytotoxic function by killing target cells. In murine lupus nephritis, CD8⁺ T cells localized in close contact to proximal tubuli. We determined enhanced apoptosis in tubular cells and particularly PTECs up-regulated expression of cleaved caspase-3. Interestingly, induction of apoptosis in the inflamed kidney was reduced in the absence of CD8⁺ T cells. Thus, PTECs have the capacity for antigen cross-presentation thereby inducing cytotoxic CD8⁺ T cells in vitro, which may contribute to the pathology of immune-mediated glomerulonephritis.

Saponin-based adjuvant-induced dendritic cell cross-presentation is dependent on PERK activation

Saponin-based adjuvants (SBAs) are promising new adjuvants that stand out as they not only enforce CD4 + T cell-mediated immunity and antibody responses, but also induce an unprecedented level of antigen cross-presentation by dendritic cells (DC) and subsequent CD8 + T cell activation. We discovered that SBA’s ability to boost cross-presentation depends on the induction of lipid bodies (LBs). Moreover, the MHCII^loCD11b^hi DC subset was identified to be most responsive to SBA-induced cross-presentation. The aim is to further unravel the mechanisms behind the induction of DC cross-presentation by SBAs. Here we show that SBAs specifically induce the PKR-like Endoplasmic Reticulum kinase (PERK) pathway and that SBA-induced DC cross-presentation is dependent on activation of the PERK pathway. PERK activation and LB formation are both crucial for SBA-induced cross-presentation and PERK inhibition has little or no effect on SBA-induced LB formation. SBA’s responsiveness, LB formation and PERK activation are specific for the MHCII^loCD11b^hi DCs. These findings contribute to understanding the pathways involved in SBA-induced cross-presentation and immune activation which will ultimately lead to the development of vaccines with improved efficiency and safety.

Promoting antigen escape from dendritic cell endosomes potentiates anti-tumoral immunity

The cross-presenting capacity of dendritic cells (DCs) can be limited by non-specific degradation during endosome maturation. To bypass this limitation, we present in this study a new Accum-based formulation designed to promote endosome-to-cytosol escape. Treatment of primary DCs with Accum linked to the xenoantigen ovalbumin (OVA) triggers endosomal damages and enhances protein processing. Despite multiple challenges using ascending doses of tumor cells, DC prophylactic vaccination results in complete protection due to increased levels of effector CD4 and CD8 T cells as well as high production of pro-inflammatory mediators. When combined with anti-PD-1, therapeutic vaccination using both syngeneic and allogeneic Accum-OVA-pulsed DCs triggers potent anti-tumoral responses. The net outcome culminates in increased CD11c, CD8, and NK infiltration along with a high CD8/Treg ratio. These highly favorable therapeutic effects highlight the promising potential of Accum as a distinct and potent technology platform suitable for the design of next generation cell cancer vaccines.

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Accum-linked antigen enhances antigen processing and presentation

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Pulsed dendritic cells elicit potent effector T cell responses

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Therapeutic vaccination using allogeneic DCs controls pre-established tumors

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The vaccine boosts tumor-infiltrating lymphocytes and increases the CD8/Treg ratio

Lysosomes and lysosome‐related organelles in immune responses

The catabolic, degradative capacity of the endo‐lysosome system is put to good use in mammalian immune responses as is their recently established status as signaling platforms. From the ‘creative destruction’ of antigenic and ‘self’ material for antigen presentation to T cells to the re‐purposing of lysosomes as toxic exocytosable lysosome‐related organelles (granules) in leukocytes such as CD8 T cells and eosinophils, endo‐lysosomes are key players in host defense. Signaled responses to some pathogen products initiate in endo‐lysosomes and these organelles are emerging as important in distinct ways in the unique immunobiology of dendritic cells. Potential self‐inflicted toxicity from lysosomal and granule proteases is countered by expression of serpin and cystatin family members.

Liposomes as Adjuvants and Vaccine Delivery Systems

The review considers liposomes as systems of substantial interest as adjuvant carriers in vaccinology due to their versatility and maximal biocompatibility. Research and development on the use of liposomes and lipid nanoparticles to create subunit vaccines for the prevention and treatment of infectious diseases has been going on for several decades. In recent years, the area has seen serious progress due to the improvement of the technology of industrial production of various high-grade lipids suitable for parenteral administration and the emergence of new technologies and equipment for the production of liposomal preparations. When developing vaccines, it is necessary to take into account how the body’s immune system (innate and adaptive immunity) functions. The review briefly describes some of the fundamental mechanisms underlying the mobilization of immunity when encountering an antigen, as well as the influence of liposome carriers on the processes of internalization of antigens by immunocompetent cells and ways of immune response induction. The results of the studies on the interactions of liposomes with antigen-presenting cells in function of the liposome size, charge, and phase state of the bilayer, which depends on the lipid composition, are often contradictory and should be verified in each specific case. The introduction of immunostimulant components into the composition of liposomal vaccine complexes—ligands of the pathogen-associated molecular pattern receptors—permits modulation of the strength and type of the immune response. The review briefly discusses liposome-based vaccines approved for use in the clinic for the treatment and prevention of infectious diseases, including mRNA-loaded lipid nanoparticles. Examples of liposomal vaccines that undergo various stages of clinical trials are presented.

Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection

BACKGROUND & AIMS

Annexin A11 was identified as autoantigen in IgG4-related cholangitis (IRC), a B-cell driven disease. Annexin A11 modulates calcium-dependent exocytosis, a crucial mechanism for insertion of proteins into their target membranes. Human cholangiocytes form an apical 'biliary bicarbonate umbrella' regarded as defense against harmful hydrophobic bile acid influx. The bicarbonate secretory machinery comprises the chloride/bicarbonate exchanger AE2 and the chloride channel ANO1. We aimed to investigate the expression and function of annexin A11 in human cholangiocytes and a potential role of IgG1/IgG4-mediated autoreactivity against annexin A11 in the pathogenesis of IRC.

METHODS

Expression of annexin A11 in human liver was studied by immunohistochemistry and immunofluorescence. In human control and ANXA11 knockdown H69 cholangiocytes, intracellular pH, AE2 and ANO1 surface expression, and bile acid influx were examined using ratio microspectrofluorometry, cell surface biotinylation, and 22,23-3H-glycochenodeoxycholic acid permeation, respectively. The localization of annexin A11-mEmerald and ANO1-mCherry was investigated by live-cell microscopy in H69 cholangiocytes after incubation with IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies or disease control serum.

RESULTS

Annexin A11 was strongly expressed in human cholangiocytes, but not hepatocytes. Knockdown of ANXA11 led to reduced plasma membrane expression of ANO1, but not AE2, alkalization of intracellular pH and uncontrolled bile acid influx. High intracellular calcium conditions led to annexin A11 membrane shift and colocalization with ANO1. Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression.

CONCLUSION

Cholangiocellular annexin A11 mediates apical membrane abundance of the chloride channel ANO1, thereby supporting biliary bicarbonate secretion. Insertion is inhibited by IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies. Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary bicarbonate umbrella'.

LAY SUMMARY

We previously identified annexin A11 as a specific autoantigen in immunoglobulin G4-related cholangitis (IRC), a B-cell driven disease affecting the bile ducts. Human cholangiocytes are protected against harmful hydrophobic bile acid influx by a defense mechanism referred to as the 'biliary bicarbonate umbrella'. We found that annexin A11 is required for the formation of a robust bicarbonate umbrella. Binding of patient-derived annexin A11 autoantibodies inhibits annexin A11 function, possibly contributing to bile duct damage by weakening the biliary bicarbonate umbrella in patients with IRC.

Dendritic cells in cancer immunology

The clinical success of immune checkpoint therapy (ICT) has produced explosive growth in tumor immunology research because ICT was discovered through basic studies of immune regulation. Much of the current translational efforts are aimed at enhancing ICT by identifying therapeutic targets that synergize with CTLA4 or PD1/PD-L1 blockade and are solidly developed on the basis of currently accepted principles. Expanding these principles through continuous basic research may help broaden translational efforts. With this mindset, we focused this review on three threads of basic research directly relating to mechanisms underlying ICT. Specifically, this review covers three aspects of dendritic cell (DC) biology connected with antitumor immune responses but are not specifically oriented toward therapeutic use. First, we review recent advances in the development of the cDC1 subset of DCs, identifying important features distinguishing these cells from other types of DCs. Second, we review the antigen-processing pathway called cross-presentation, which was discovered in the mid-1970s and remains an enigma. This pathway serves an essential in vivo function unique to cDC1s and may be both a physiologic bottleneck and therapeutic target. Finally, we review the longstanding field of helper cells and the related area of DC licensing, in which CD4 T cells influence the strength or quality of CD8 T cell responses. Each topic is connected with ICT in some manner but is also a fundamental aspect of cell-mediated immunity directed toward intracellular pathogens.

Engineering immunoproteasome-expressing mesenchymal stromal cells: A potent cellular vaccine for lymphoma and melanoma in mice

Dendritic cells (DCs) excel at cross-presenting antigens, but their effectiveness as cancer vaccine is limited. Here, we describe a vaccination approach using mesenchymal stromal cells (MSCs) engineered to express the immunoproteasome complex (MSC-IPr). Such modification instills efficient antigen cross-presentation abilities associated with enhanced major histocompatibility complex class I and CD80 expression, de novo production of interleukin-12, and higher chemokine secretion. This cross-presentation capacity of MSC-IPr is highly dependent on their metabolic activity. Compared with DCs, MSC-IPr hold the ability to cross-present a vastly different epitope repertoire, which translates into potent re-activation of T cell immunity against EL4 and A20 lymphomas and B16 melanoma tumors. Moreover, therapeutic vaccination of mice with pre-established tumors efficiently controls cancer growth, an effect further enhanced when combined with antibodies targeting PD-1, CTLA4, LAG3, or 4-1BB under both autologous and allogeneic settings. Therefore, MSC-IPr constitute a promising subset of non-hematopoietic antigen-presenting cells suitable for designing universal cell-based cancer vaccines.

Targeting Cross-Presentation as a Route to Improve the Efficiency of Peptide-Based Cancer Vaccines

Cross-presenting dendritic cells (DC) offer an attractive target for vaccination due to their unique ability to process exogenous antigens for presentation on MHC class I molecules. Recent reports have established that these DC express unique surface receptors and play a critical role in the initiation of anti-tumor immunity, opening the way for the development of vaccination strategies specifically targeting these cells. This study investigated whether targeting cross-presenting DC by two complementary mechanisms could improve vaccine effectiveness, in both a viral setting and in a murine melanoma model. Our novel vaccine construct contained the XCL1 ligand, to target uptake to XCR1+ cross-presenting DC, and a cell penetrating peptide (CPP) with endosomal escape properties, to enhance antigen delivery into the cross-presentation pathway. Using a prime-boost regimen, we demonstrated robust expansion of antigen-specific T cells following vaccination with our CPP-linked peptide vaccine and protective immunity against HSV-1 skin infection, where vaccine epitopes were natively expressed by the virus. Additionally, our novel vaccination strategy slowed tumor outgrowth in a B16 murine melanoma model, compared to adjuvant only controls, suggesting antigen-specific anti-tumor immunity was generated following vaccination. These findings suggest that novel strategies to target the antigen cross-presentation pathway in DC may be beneficial for the generation of anti-tumor immunity.

Host Genetic Associations with Salivary Microbiome in Oral Cancer

Despite the growing recognition of a host genetic effect on shaping gut microbiota composition, the genetic determinants of oral microbiota remain largely unexplored, especially in the context of oral diseases. Here, we performed a microbiome genome-wide association study in 2 independent cohorts of patients with oral squamous cell carcinoma (OSCC, n = 144 and 67) and an additional group of noncancer individuals (n = 104). Besides oral bacterial dysbiosis and signatures observed in OSCC, associations of 3 loci with the abundance of genus-level taxa and 4 loci with β diversity measures were detected (q < 0.05) at the discovery stage. The most significant hit (rs10906082 with the genus Lachnoanaerobaculum, P = 3.55 × 10^-9 at discovery stage) was replicated in a second OSCC cohort. Moreover, the other 2 taxonomical associations, rs10973953 with the genus Kingella (P = 1.38 × 10^-9) and rs4721629 with the genus Parvimonas (P = 3.53 × 10^-8), were suggestive in the meta-analysis combining 2 OSCC cohorts. Further pathway analysis revealed that these loci were enriched for genes in regulation of oncogenic and angiogenic responses, implicating a genetic anchor to the oral microbiome in estimation of casual relationships with OSCC. Our findings delineate the role of host genotypes in influencing the structure of oral microbial communities.

Strategy and clinical application of up-regulating cross presentation by DCs in anti-tumor therapy

The cross presentation of exogenous antigen (Ag) by dendritic cells (DCs) facilitates a diversified mode of T-cell activation, orchestrates specific humoral and cellular immunity, and contributes to an efficient anti-tumor immune response. DCs-mediated cross presentation is subject to both intrinsic and extrinsic factors, including the homing and phenotype of DCs, the spatiotemporal trafficking and degradation kinetics of Ag, and multiple microenvironmental clues, with many details largely unexplored. Here, we systemically review the current mechanistic understanding and regulation strategies of cross presentation by heterogeneous DC populations. We also provide insights into the future exploitation of DCs cross presentation for a better clinical efficacy in anti-tumor therapy.

Regulation of dendritic cell function by Fc-γ-receptors and the neonatal Fc receptor

Dendritic cells (DCs) express receptors to sense pathogens and/or tissue damage and to communicate with other immune cells. Among those receptors, Fc receptors (FcRs) are triggered by the Fc region of antibodies produced during adaptive immunity. In this review, the role of FcγR and neonatal Fc receptor (FcRn) in DC immunity will be discussed. Their expression in DC subsets and impact on antigen uptake and presentation, DC maturation and polarisation of T cell responses will be described. Lastly, we will discuss the importance of FcR-mediated DC function in the context of immunity during viral infection, inflammatory disease, cancer and immunotherapy.

Recent Advances in Engineered Materials for Immunotherapy-Involved Combination Cancer Therapy

Immunotherapy that can activate immunity or enhance the immunogenicity of tumors has emerged as one of the most effective methods for cancer therapy. Nevertheless, single-mode immunotherapy is still confronted with several critical challenges, such as the low immune response, the low tumor infiltration, and the complex immunosuppression tumor microenvironment. Recently, the combination of immunotherapy with other therapeutic modalities has emerged as a powerful strategy to augment the therapeutic outcome in fighting against cancer. In this review, recent research advances of the combination of immunotherapy with chemotherapy, phototherapy, radiotherapy, sonodynamic therapy, metabolic therapy, and microwave thermotherapy are summarized. Critical challenges and future research direction of immunotherapy-based cancer therapeutic strategy are also discussed.

Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex

The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.

Complement C5a promotes antigen cross-presentation by Peyer's patch monocyte-derived dendritic cells and drives a protective CD8+ T cell response

The complement fragment C5a is closely associated with adaptive immune induction in the mucosa. However, the mechanisms that control CD8⁺ T cell responses by C5a have not been extensively explored. This study reveals that C5/C5a in the Peyer's patch (PP) subepithelial dome increases upon oral Listeria infection. We hypothesize that C5aR⁺ PP cells play an important role in the induction of antigen-specific T cell immunity. Using single-cell RNA sequencing, we identify C5aR- and lysozyme-expressing dendritic cells (C5aR⁺ LysoDCs) in PP and examine their role in CD8⁺ T cell immune induction. Stimulation of C5aR⁺ LysoDCs by C5a increases reactive oxygen species levels, leading to efficient antigen cross-presentation, which elicits an antigen-specific CD8⁺ T cell response. In C5-deficient mice, oral co-administration of C5a and Listeria enhances Listeria-specific cytotoxic T cell levels. Collectively, these findings suggest a role of the complement system in intestinal T cell immunity.

A Vaccination with Boosted Cross Presentation by ER-Targeted Antigen Delivery for Anti-Tumor Immunotherapy

Vaccination is a widely-accepted resort against the invasion or proliferation of bacteria, parasites, viruses, and even cancer, which accounts heavily on an active involvement of CD8⁺ T cells. As one of the pivotal strategies taken by dendritic cells (DCs) to promote the responsiveness of CD8⁺ T cells to exogenous antigens, cross presentation culminates in an elevated overall host defense against cancer or infection. However, the precise mechanisms regulating such a process remains elusive, and current attempts to fuel cross presentation usually fail to exert efficiency. Here, model antigen OVA-loaded, endoplasmic reticulum (ER)-targeting cationic liposome (OVA@lipoT) is developed and characterized with a booster effect on the activation and maturation of DCs. Moreover, OVA@lipoT pulsed DCs exhibit overwhelming superiority in triggering cytotoxic T lymphocyte response both in vivo and in vitro. Data reveal that lipoT alters the intracellular trafficking and presenting pathway of antigen, which promotes cross presentation and bears close relationship to the ER-associated degradation (ERAD). These results may drop a hint about the interconnectivity between cross presentation and ER-targeted antigen delivery, provide extra information to the understanding of ERAD-mediated cross priming, and even shed new light on the design and optimization of vaccines against currently intractable cancers or virus-infection.

K48-Linked Ubiquitination Contributes to Nicotine-Augmented Bone Marrow-Derived Dendritic-Cell-Mediated Adaptive Immunity

K48-linked ubiquitination determining antigen degradation and the endosomal recruitments of p97 and Sec61 plays vital roles in dendritic cell (DC) cross-presentation. Our previous studies revealed that nicotine treatment increases bone marrow-derived dendritic cell (BM-DC) cross-presentation and promotes BM-DC-based cytotoxic T lymphocyte (CTL) priming. But the effect of nicotine on K48-linked ubiquitination and the mechanism of nicotine-increased BM-DC cross-presentation are still uncertain. In this study, we first demonstrated that ex vivo nicotine administration obviously increased K48-linked ubiquitination in BM-DC. Then, we found that K48-linked ubiquitination was essential for nicotine-augmented cross-presentation, BM-DC-based CTL priming, and thereby the superior cytolytic capacity of DC-activated CTL. Importantly, K48-linked ubiquitination was verified to be necessary for nicotine-augmented endosomal recruitments of p97 and Sec61. Importantly, mannose receptor (MR), which is an important antigenic receptor for cross-presentation, was exactly catalyzed with K48-linked ubiquitination by the treatment with nicotine. Thus, these data suggested that K48-linked ubiquitination contributes to the superior adaptive immunity of nicotine-administrated BM-DC. Regulating K48-linked ubiquitination might have therapeutic potential for DC-mediated immune therapy.

T Cell Proliferative Responses and IgG Antibodies to β2GPI in Patients with Diabetes and Atherosclerosis

BACKGROUND

Diabetes increases the risk of myocardial infarction (MI) by 2 to 3 folds. Tlymphocytes play a role in atherosclerosis, which is the main pathology behind MI. Cellular immune responses to beta-2 glycoprotein I (β2GPI) are shown in carotid atherosclerosis.

OBJECTIVE

To investigate the self-reactive, β2GPI-specific T-lymphocytes in patients with and without diabetes and atherosclerosis.

METHODS

Collectively, 164 subjects with and without diabetes that underwent coronary angiography were divided into four groups based on their diabetes status and coronary stenosis. Group I=Diabetic with ≥50% stenosis: A+D+ (n=66); Group II=Non-diabetic with ≥50% stenosis, A+D- (n=39); Group III=Diabetic with <50% stenosis: A-D+ (n=28); and Group IV=Non-diabetic with <50% stenosis: AD- (n=31). All groups were evaluated for anti-β2GPI IgG antibody by ELISA method. Then, PBMCs were isolated from 18 subjects and were stimulated with β2GPI-derived peptides to assess their proliferation in accordance with their HLA-DRB1 alleles.

RESULTS

Mean β2GPI IgG levels were higher in groups with ≥50% stenosis (A+) compared to those with <50% stenosis (A-), (P=0.02). The co-presence of diabetes in A+ individuals increased mean β2GPI-specific IgG. Auto-reactive β2GPI-specific T cells were detected in the repertoire of T-lymphocytes in all groups. β2GPI-peptides showed promiscuous restriction by various HLADRB1.

CONCLUSION

β2GPI is the target of cellular and humoral immune responses in patients with atherosclerosis. Since the T cell responses but not antibodies were detectable in A-D+ and A-D- groups, it is reasonable to assume that cellular responses preceded the humoral responses. Post-translation modifications of β2GPI under oxidative and glycemic stresses may have increased the IgG levels in patients with diabetes. Finally, identification of antigens that trigger immuno-pathogenesis in atherosclerosis and diabetes may help the development of immunomodulation methods to prevent or treat these debilitating diseases.

Genetics in the Host-Mycobacterium ulcerans interaction

Buruli ulcer is an emerging infectious disease associated with high morbidity and unpredictable outbreaks. It is caused by Mycobacterium ulcerans, a slow-growing pathogen evolutionarily shaped by the acquisition of a plasmid involved in the production of a potent macrolide-like cytotoxin and by genome rearrangements and downsizing. These events culminated in an uncommon infection pattern, whereby M. ulcerans is both able to induce the initiation of the inflammatory cascade and the cell death of its proponents, as well as to survive within the phagosome and in the extracellular milieu. In such extreme conditions, the host is sentenced to rely on a highly orchestrated genetic landscape to be able to control the infection. We here revisit the dynamics of M. ulcerans infection, drawing parallels from other mycobacterioses and integrating the most recent knowledge on its evolution and pathogenicity in its interaction with the host immune response.

RNF41 regulates the damage recognition receptor Clec9A and antigen cross-presentation in mouse dendritic cells

The dendritic cell receptor Clec9A facilitates processing of dead cell-derived antigens for cross-presentation and the induction of effective CD8⁺ T cell immune responses. Here, we show that this process is regulated by E3 ubiquitin ligase RNF41 and define a new ubiquitin-mediated mechanism for regulation of Clec9A, reflecting the unique properties of Clec9A as a receptor specialized for delivery of antigens for cross-presentation. We reveal RNF41 is a negative regulator of Clec9A and the cross-presentation of dead cell-derived antigens by mouse dendritic cells. Intriguingly, RNF41 regulates the downstream fate of Clec9A by directly binding and ubiquitinating the extracellular domains of Clec9A. At steady-state, RNF41 ubiquitination of Clec9A facilitates interactions with ER-associated proteins and degradation machinery to control Clec9A levels. However, Clec9A interactions are altered following dead cell uptake to favor antigen presentation. These findings provide important insights into antigen cross-presentation and have implications for development of approaches to modulate immune responses.

Aquaporin-3 regulates endosome-to-cytosol transfer via lipid peroxidation for cross presentation

Antigen cross presentation, whereby exogenous antigens are presented by MHC class I molecules to CD8+ T cells, is essential for generating adaptive immunity to pathogens and tumor cells. Following endocytosis, it is widely understood that protein antigens must be transferred from endosomes to the cytosol where they are subject to ubiquitination and proteasome degradation prior to being translocated into the endoplasmic reticulum (ER), or possibly endosomes, via the TAP1/TAP2 complex. Revealing how antigens egress from endocytic organelles (endosome-to-cytosol transfer, ECT), however, has proved vexing. Here, we used two independent screens to identify the hydrogen peroxide-transporting channel aquaporin-3 (AQP3) as a regulator of ECT. AQP3 overexpression increased ECT, whereas AQP3 knockout or knockdown decreased ECT. Mechanistically, AQP3 appears to be important for hydrogen peroxide entry into the endosomal lumen where it affects lipid peroxidation and subsequent antigen release. AQP3-mediated regulation of ECT was functionally significant, as AQP3 modulation had a direct impact on the efficiency of antigen cross presentation in vitro. Finally, AQP3^-/- mice exhibited a reduced ability to mount an anti-viral response and cross present exogenous extended peptide. Together, these results indicate that the AQP3-mediated transport of hydrogen peroxide can regulate endosomal lipid peroxidation and suggest that compromised membrane integrity and coordinated release of endosomal cargo is a likely mechanism for ECT.

Akt+ IKKα/β+ Rab5+ Signalosome Mediate the Endosomal Recruitment of Sec61 and Contribute to Cross-Presentation in Bone Marrow Precursor Cells

Cross-presentation in dendritic cells (DC) requires the endosomal relocations of internalized antigens and the endoplasmic reticulum protein Sec61. Despite the fact that endotoxin-containing pathogen and endotoxin-free antigen have different effects on protein kinase B (Akt) and I-kappa B Kinase α/β (IKKα/β) activation, the exact roles of Akt phosphorylation, IKKα or IKKβ activation in endotoxin-containing pathogen-derived cross-presentation are poorly understood. In this study, endotoxin-free ovalbumin supplemented with endotoxin was used as a model pathogen. We investigated the effects of endotoxin-containing pathogen and endotoxin-free antigen on Akt phosphorylation, IKKα/β activation, and explored the mechanisms that the endotoxin-containing pathogen orchestrating the endosomal recruitment of Sec61 of the cross-presentation in bone marrow precursor cells (BMPC). We demonstrated that endotoxin-containing pathogen and endotoxin-free antigen efficiently induced the phosphorylation of Akt-IKKα/β and Akt-IKKα, respectively. Endotoxin-containing pathogen derived Akt+ IKKα/β+ Rab5+ signalosome, together with augmented the recruitment of Sec61 toward endosome, lead to the increased cross-presentation in BMPC. Importantly, the endosomal recruitment of Sec61 was partly mediated by the formation of Akt+ IKKα/β+ signalosome. Thus, these data suggest that Akt+ IKKα/β+ Rab5+ signalosome contribute to endotoxin-containing pathogen-induced the endosomal recruitment of Sec61 and the superior efficacy of cross-presentation in BMPC.