A RORγt+ cell instructs gut microbiota-specific Treg cell differentiation.

The mutualistic relationship of gut-resident microbiota and the host immune system promotes homeostasis that ensures maintenance of the microbial community and of a largely non-aggressive immune cell compartment1,2. The consequences of disturbing this balance include proximal inflammatory conditions, such as Crohn's disease, and systemic illnesses. This equilibrium is achieved in part through the induction of both effector and suppressor arms of the adaptive immune system. Helicobacter species induce T regulatory (Treg) and T follicular helper (TFH) cells under homeostatic conditions, but induce inflammatory T helper 17 (TH17) cells when induced Treg (iTreg) cells are compromised3,4. How Helicobacter and other gut bacteria direct T cells to adopt distinct functions remains poorly understood. Here we investigated the cells and molecular components required for iTreg cell differentiation. We found that antigen presentation by cells expressing RORγt, rather than by classical dendritic cells, was required and sufficient for induction of Treg cells. These RORγt+ cells-probably type 3 innate lymphoid cells and/or Janus cells5-require the antigen-presentation machinery, the chemokine receptor CCR7 and the TGFß activator αv integrin. In the absence of any of these factors, there was expansion of pathogenic TH17 cells instead of iTreg cells, induced by CCR7-independent antigen-presenting cells. Thus, intestinal commensal microbes and their products target multiple antigen-presenting cells with pre-determined features suited to directing appropriate T cell differentiation programmes, rather than a common antigen-presenting cell that they endow with appropriate functions.

Wnt5A signaling supports antigen processing and CD8 T cell activation.

Antigen processing and antigen-specific CD8 T cell activation form part and parcel of cell-mediated immunity to infections. Yet, several lacunae remain in our understanding of how antigen processing and CD8 T cell response are coordinated. In this study, using mouse bone marrow-derived dendritic cells (BMDC) as antigen-presenting cells and Ovalbumin (OVA)/DQ-Ovalbumin (DQ-OVA) as model antigen we demonstrated that Wnt5A signaling in BMDC supports antigen processing/presentation and concomitant CD8 T cell activation through regulation of actin and proteasome dynamics. Recombinant Wnt5A conditioning of BMDC and associated actin assembly facilitated DQ-OVA processing, which was inhibited by the proteasome inhibitor MG132. Moreover, Wnt5A depletion led to a significant reduction in OVA processing and presentation. Impaired DQ-OVA processing in Wnt5A depleted BMDC correlated with altered dynamics of both actin and the proteasome regulator PA28α-PA28ß, and reduced association of DQ-OVA with actin and proteasome subunits. Inhibited OVA processing/presentation in the Wnt5A depleted BMDC also resulted in subdued activation of OVA-sensitized CD8 T cells in co-culture with the BMDC. In concurrence with these findings, we demonstrated reduced OVA processing and impaired CD8 T cell response to OVA immunization in Wnt5A heterozygous mice lacking a copy of the Wnt5A gene in comparison to the wild-type cohorts. Taken together, our results reveal a crucial requirement of Wnt5A signaling in antigen processing/presentation and CD8 T cell activation, thus unveiling a vital regulatory node of cell-mediated immunity, unidentified thus far.

Direct T-cell Presentation by cDC1: The Key Feature for Cancer Vaccine Success?

In this issue of Cancer Immunology Research, Ferris and colleagues demonstrate that type 1 conventional DC (cDC1) vaccines drive tumor rejection through direct antigen presentation, without the need of endogenous cDC1. This suggests that cDC1-based vaccines could represent an optimal strategy to induce antitumor immunity in patients. See related article by Ferris et al., p. 920 (7) .

Antigen cross-presentation in young tumor-bearing hosts promotes CD8+ T cell terminal differentiation.

The immune system undergoes a progressive functional remodeling with age. Understanding how age bias shapes antitumor immunity is essential in designing effective immunotherapies, especially for pediatric patients. Here, we explore antitumor CD8+ T cell responses generated in young (prepubescent) and adult (presenescent) mice. Using an MHCI-deficient tumor model, we observed that tumor-reactive CD8+ T cells expanded in young tumor-bearing (TB) mice acquired a terminally differentiated phenotype characterized by overexpression of inhibitory receptors and the transcription factor Tox1. Furthermore, tumor-infiltrating CD8+ T cells from young tumors yielded a poor cytokine response compared with CD8+ T cells infiltrating adult tumors. Young migratory dendritic cells (migDCs) from the draining lymph nodes (dLNs), and mononuclear phagocytic cells (MPCs) infiltrating young tumors, were more competent in capturing and cross-presenting tumor antigen, leading to enhanced priming of CD8+ T cells in dLNs and their subsequent terminal differentiation in the tumors. Single-cell transcriptional profiling of tumor-infiltrating MPCs demonstrated that young MPCs are polarized toward an inflammatory, effector phenotype. Consistent with our observations in young versus adult TB mice, analysis of immune infiltrates from pediatric solid tumors showed a correlation between tumor-infiltrating CD8+ T cells with an exhaustion phenotype and the frequency of PD-L1-expressing monocytes/macrophages. Collectively, these data indicate that a young tissue microenvironment contributes to the generation of an immune response skewed toward a less pliable terminal effector state, thus narrowing the window for immunotherapeutic interventions.

Regulation of MHC Class I Expression in Lung Epithelial Cells during Inflammation.

Lung infections are a perennial leading cause of death worldwide. The lung epithelium comprises three main cell types: alveolar type I (AT1), alveolar type II (AT2), and bronchiolar cells. Constitutively, these three cell types express extremely low amounts of surface MHC class I (MHC I) molecules, that is, <1% of levels found on medullary thymic epithelial cells (ECs). We report that inhalation of the TLR4 ligand LPS upregulates cell surface MHC I by ∼25-fold on the three subtypes of mouse lung ECs. This upregulation is dependent on Nlrc5, Stat1, and Stat2 and caused by a concerted production of the three IFN families. It is nevertheless hampered, particularly in AT1 cells, by the limited expression of genes instrumental in the peptide loading of MHC I molecules. Genes involved in production and response to cytokines and chemokines were selectively induced in AT1 cells. However, discrete gene subsets were selectively downregulated in AT2 or bronchiolar cells following LPS inhalation. Genes downregulated in AT2 cells were linked to cell differentiation and cell proliferation, and those repressed in bronchiolar cells were primarily involved in cilium function. Our study shows a delicate balance between the expression of transcripts maintaining lung epithelium integrity and transcripts involved in Ag presentation in primary lung ECs.

Photochemically-Mediated Inflammation and Cross-Presentation of Mycobacterium bovis BCG Proteins Stimulates Strong CD4 and CD8 T-Cell Responses in Mice.

Conventional vaccines are very efficient in the prevention of bacterial infections caused by extracellular pathogens due to effective stimulation of pathogen-specific antibodies. In contrast, considering that intracellular surveillance by antibodies is not possible, they are typically less effective in preventing or treating infections caused by intracellular pathogens such as Mycobacterium tuberculosis. The objective of the current study was to use so-called photochemical internalization (PCI) to deliver a live bacterial vaccine to the cytosol of antigen-presenting cells (APCs) for the purpose of stimulating major histocompatibility complex (MHC) I-restricted CD8 T-cell responses. For this purpose, Mycobacterium bovis BCG (BCG) was combined with the photosensitiser tetraphenyl chlorine disulfonate (TPCS2a) and injected intradermally into mice. TPCS2a was then activated by illumination of the injection site with light of defined energy. Antigen-specific CD4 and CD8 T-cell responses were monitored in blood, spleen, and lymph nodes at different time points thereafter using flow cytometry, ELISA and ELISPOT. Finally, APCs were infected and PCI-treated in vitro for analysis of their activation of T cells in vitro or in vivo after autologous vaccination of mice. Combination of BCG with PCI induced stronger BCG-specific CD4 and CD8 T-cell responses than treatment with BCG only or with BCG and TPCS2a without light. The overall T-cell responses were multifunctional as characterized by the production of IFN-γ, TNF-α, IL-2 and IL-17. Importantly, PCI induced cross-presentation of BCG proteins for stimulation of antigen-specific CD8 T-cells that were particularly producing IFN-γ and TNF-α. PCI further facilitated antigen presentation by causing up-regulation of MHC and co-stimulatory proteins on the surface of APCs as well as their production of TNF-α and IL-1ß in vivo. Furthermore, PCI-based vaccination also caused local inflammation at the site of vaccination, showing strong infiltration of immune cells, which could contribute to the stimulation of antigen-specific immune responses. This study is the first to demonstrate that a live microbial vaccine can be combined with a photochemical compound and light for cross presentation of antigens to CD8 T cells. Moreover, the results revealed that PCI treatment strongly improved the immunogenicity of M. bovis BCG.

N Protein of Viral Hemorrhagic Septicemia Virus Suppresses STAT1-Mediated MHC Class II Transcription to Impair Antigen Presentation in Sea Perch, Lateolabrax japonicus.

Upon virus invasion of the host, APCs process Ags to short peptides for presentation by MHC class II (MHC-II). The recognition of virus-derived peptides in the context of MHC-II by CD4+ T cells initiates the adaptive immune response for virus clearance. As a survival instinct, viruses have evolved mechanisms to evade Ag processing and presentation. In this study, we discovered that IFN-γ induced endogenous MHC-II expression by a sea perch brain cell line through the STAT1/IFN regulatory factor 1 (IRF1)/CIITA signaling pathway. Furthermore, viral hemorrhagic septicemia virus infection significantly inhibited the IFN-γ-induced expression of IRF1, CIITA, MHC-II-α, and MHC-II-ß genes. By contrast, although STAT1 transcript was upregulated, paradoxically, the STAT1 protein level was attenuated. Moreover, overexpression analysis revealed that viral hemorrhagic septicemia virus N protein blocked the IFN-γ-induced expression of IRF1, CIITA, MHC-II-α, and MHC-II-ß genes, but not the STAT1 gene. We also found out that N protein interacted with STAT1 and enhanced the overall ubiquitination level of proteins, including STAT1 in Lateolabrax japonicus brain cells. Enhanced ubiquitination of STAT1 through K48-linked ubiquitination led to its degradation through the ubiquitin-proteasome pathway, thereby inhibiting the biological function of STAT1. Our study suggests that aquatic viruses target Ag presentation in lower vertebrates for immune evasion as do mammalian viruses.

Gnawing Between Cells and Cells in the Immune System: Friend or Foe? A Review of Trogocytosis.

Trogocytosis occurs when one cell contacts and quickly nibbles another cell and is characterized by contact between living cells and rapid transfer of membrane fragments with functional integrity. Many immune cells are involved in this process, such as T cells, B cells, NK cells, APCs. The transferred membrane molecules including MHC molecules, costimulatory molecules, receptors, antigens, etc. An increasing number of studies have shown that trogocytosis plays an important role in the immune system and the occurrence of relevant diseases. Thus, whether trogocytosis is a friend or foe of the immune system is puzzling, and the precise mechanism underlying it has not yet been fully elucidated. Here, we provide an integrated view of the acquired findings on the connections between trogocytosis and the immune system.

Self-Tolerance of Vascular Tissues Is Broken Down by Vascular Dendritic Cells in Response to Systemic Inflammation to Initiate Regional Autoinflammation.

The correlation of infections with vascular autoinflammatory diseases such as vasculitis and atherosclerosis has been long recognized, and progressive inflammation with the formation of tertiary lymphoid organs in arterial adventitia intensively studied, the immunological basis of the nondiseased vasculatures that predispose to subsequent vascular autoimmunity during inflammation, however, is not well characterized. Here, we investigated the vascular immunity in situ of steady-state C57BL/6 mice and found that healthy vascular tissues contained a comprehensive set of immune cells with relatively higher proportion of innate components than lymphoid organs. Notably, a complete set of dendritic cell (DC) subsets was observed with monocyte-derived DCs (moDCs) constituting a major proportion; this is in contrast to moDCs being considered rare in the steady state. Interestingly, these vascular DCs constitutively expressed more suppressive factors with cDC1 for PD-L1 and moDCs for IL-10; this is concordant with the inhibitive phenotype of T cells in normal vascular tissues. The immunotolerant state of the vascular tissues, however, was readily eroded by systemic inflammation, demonstrated by the upregulation of proinflammatory cytokines and enhanced antigen presentation by vascular DCs to activate both cellular and humoral immunity in situ, which ultimately led to vascular destruction. Different vascular DC subsets elicited selective effects: moDCs were potent cytokine producers and B-cell activators, whereas cDCs, particularly, cDC1, were efficient at presenting antigens to stimulate T cells. Together, we unveil regional immunological features of vascular tissues to explain their dual facets under physiological versus pathological conditions for the better understanding and treatment of cardiovascular autoinflammation.

Spotlight on TAP and its vital role in antigen presentation and cross-presentation.

In the late 1980s and early 1990s, the hunt for a transporter molecule ostensibly responsible for the translocation of peptides across the endoplasmic reticulum (ER) membrane yielded the successful discovery of transporter associated with antigen processing (TAP) protein. TAP is a heterodimer complex comprised of TAP1 and TAP2, which utilizes ATP to transport cytosolic peptides into the ER across its membrane. In the ER, together with other components it forms the peptide loading complex (PLC), which directs loading of high affinity peptides onto nascent major histocompatibility complex class I (MHC-I) molecules that are then transported to the cell surface for presentation to CD8+ T cells. TAP also plays a crucial role in transporting peptides into phagosomes and endosomes during cross-presentation in dendritic cells (DCs). Because of the critical role that TAP plays in both classical MHC-I presentation and cross-presentation, its expression and function are often compromised by numerous types of cancers and viruses to evade recognition by cytotoxic CD8 T cells. Here we review the discovery and function of TAP with a major focus on its role in cross-presentation in DCs. We discuss a recently described emergency route of noncanonical cross-presentation that is mobilized in DCs upon TAP blockade to restore CD8 T cell cross-priming. We also discuss the various strategies employed by cancer cells and viruses to target TAP expression or function to evade immunosurveillance - along with some strategies by which the repertoire of peptides presented by cells which downregulate TAP can be targeted as a therapeutic strategy to mobilize a TAP-independent CD8 T cell response. Lastly, we discuss TAP polymorphisms and the role of TAP in inherited disorders.

Nanovaccines with cell-derived components for cancer immunotherapy.

Cancer nanovaccines as one of immunotherapeutic approaches are able to attack tumors by stimulating tumor-specific immunological responses. However, there still exist multiple challenges to be tackled for cancer nanovaccines to evoke potent antitumor immunity. Particularly, the administration of exogenous materials may cause the off-target immunotherapy responses. In recent years, biomimetic nanovaccines by using cell lysates, cell-derived nanovesicles, or extracted cell membranes as the functional components have received extensive attention. Such nanovaccines based on cell-derived components would show many unique advantages including inherent biocompatibility and the ability to trigger immune responses against a range of tumor-associated antigens. In this review article, we will introduce the recent research progresses of those cell-derived biomimetic nanovaccines for cancer immunotherapy, and discuss the perspectives and challenges associated with the future clinical translation of these emerging vaccine platforms.

A model of preferential pairing between epithelial and dendritic cells in thymic antigen transfer.

Medullary thymic epithelial cells (mTECs), which produce and present self-antigens, are essential for the establishment of central tolerance. Since mTEC numbers are limited, their function is complemented by thymic dendritic cells (DCs), which transfer mTEC-produced self-antigens via cooperative antigen transfer (CAT). While CAT is required for effective T cell selection, many aspects remain enigmatic. Given the recently described heterogeneity of mTECs and DCs, it is unclear whether the antigen acquisition from a particular TEC subset is mediated by preferential pairing with a specific subset of DCs. Using several relevant Cre-based mouse models that control for the expression of fluorescent proteins, we have found that, in regards to CAT, each subset of thymic DCs preferentially targets a distinct mTEC subset(s). Importantly, XCR1+-activated DC subset represented the most potent subset in CAT. Interestingly, thymic DCs can also acquire antigens from more than one mTEC, and of these, monocyte-derived dendritic cells (moDCs) were determined to be the most efficient. moDCs also represented the most potent DC subset in the acquisition of antigen from other DCs. These findings suggest a preferential pairing model for the distribution of mTEC-derived antigens among distinct populations of thymic DCs.

Receptor Mediated Effects of Advanced Glycation End Products (AGEs) on Innate and Adaptative Immunity: Relevance for Food Allergy.

As of late, evidence has been emerging that the Maillard reaction (MR, also referred to as glycation) affects the structure and function of food proteins. MR induces the conformational and chemical modification of food proteins, not only on the level of IgG/IgE recognition, but also by increasing the interaction and recognition of these modified proteins by antigen-presenting cells (APCs). This affects their biological properties, including digestibility, bioavailability, immunogenicity, and ultimately their allergenicity. APCs possess various receptors that recognize glycation structures, which include receptor for advanced glycation end products (RAGE), scavenger receptors (SRs), galectin-3 and CD36. Through these receptors, glycation structures may influence the recognition, uptake and antigen-processing of food allergens by dendritic cells (DCs) and monocytes. This may lead to enhanced cytokine production and maturation of DCs, and may also induce adaptive immune responses to the antigens/allergens as a result of antigen uptake, processing and presentation to T cells. Here, we aim to review the current literature on the immunogenicity of AGEs originating from food (exogenous or dietary AGEs) in relation to AGEs that are formed within the body (endogenous AGEs), their interactions with receptors present on immune cells, and their effects on the activation of the innate as well as the adaptive immune system. Finally, we review the clinical relevance of AGEs in food allergies.

Host-Adapted Gene Families Involved in Murine Cytomegalovirus Immune Evasion.

Cytomegaloviruses (CMVs) are host species-specific and have adapted to their respective mammalian hosts during co-evolution. Host-adaptation is reflected by "private genes" that have specialized in mediating virus-host interplay and have no sequence homologs in other CMV species, although biological convergence has led to analogous protein functions. They are mostly organized in gene families evolved by gene duplications and subsequent mutations. The host immune response to infection, both the innate and the adaptive immune response, is a driver of viral evolution, resulting in the acquisition of viral immune evasion proteins encoded by private gene families. As the analysis of the medically relevant human cytomegalovirus by clinical investigation in the infected human host cannot make use of designed virus and host mutagenesis, the mouse model based on murine cytomegalovirus (mCMV) has become a versatile animal model to study basic principles of in vivo virus-host interplay. Focusing on the immune evasion of the adaptive immune response by CD8+ T cells, we review here what is known about proteins of two private gene families of mCMV, the m02 and the m145 families, specifically the role of m04, m06, and m152 in viral antigen presentation during acute and latent infection.

Vectorized Treg-depleting αCTLA-4 elicits antigen cross-presentation and CD8+ T cell immunity to reject 'cold' tumors.

BACKGROUND: Immune checkpoint blockade (ICB) is a clinically proven concept to treat cancer. Still, a majority of patients with cancer including those with poorly immune infiltrated 'cold' tumors are resistant to currently available ICB therapies. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is one of few clinically validated targets for ICB, but toxicities linked to efficacy in approved αCTLA-4 regimens have restricted their use and precluded full therapeutic dosing. At a mechanistic level, accumulating preclinical and clinical data indicate dual mechanisms for αCTLA-4; ICB and regulatory T cell (Treg) depletion are both thought to contribute efficacy and toxicity in available, systemic, αCTLA-4 regimens. Accordingly, strategies to deliver highly effective, yet safe αCTLA-4 therapies have been lacking. Here we assess and identify spatially restricted exposure to a novel strongly Treg-depleting, checkpoint-blocking, vectorized αCTLA-4, as a highly efficacious and potentially safe strategy to target CTLA-4. METHODS: A novel human IgG1 CTLA-4 antibody (4-E03) was identified using function-first screening for monoclonal antibodies (mAbs) and targets associated with superior Treg-depleting activity. A tumor-selective oncolytic vaccinia vector was then engineered to encode this novel, strongly Treg-depleting, checkpoint-blocking, αCTLA-4 antibody or a matching surrogate antibody, and Granulocyte-macrophage colony-stimulating factor (GM-CSF) (VVGM-αCTLA-4). RESULTS: The identified 4-E03 antibody showed significantly stronger Treg depletion, but equipotent checkpoint blockade, compared with clinically validated αCTLA-4 ipilimumab against CTLA-4-expressing Treg cells in a humanized mouse model in vivo. Intratumoral administration of VVGM-αCTLA-4 achieved tumor-restricted CTLA-4 receptor saturation and Treg depletion, which elicited antigen cross-presentation and stronger systemic expansion of tumor-specific CD8+ T cells and antitumor immunity compared with systemic αCTLA-4 antibody therapy. Efficacy correlated with FcγR-mediated intratumoral Treg depletion. Remarkably, in a clinically relevant mouse model resistant to systemic ICB, intratumoral VVGM-αCTLA-4 synergized with αPD-1 to reject cold tumors. CONCLUSION: Our findings demonstrate in vivo proof of concept for spatial restriction of Treg depletion-optimized immune checkpoint blocking, vectorized αCTLA-4 as a highly effective and safe strategy to target CTLA-4. A clinical trial evaluating intratumoral VVGM-αhCTLA-4 (BT-001) alone and in combination with αPD-1 in metastatic or advanced solid tumors has commenced.

Lung tumor MHCII immunity depends on in situ antigen presentation by fibroblasts.

A key unknown of the functional space in tumor immunity is whether CD4 T cells depend on intratumoral MHCII cancer antigen recognition. MHCII-expressing, antigen-presenting cancer-associated fibroblasts (apCAFs) have been found in breast and pancreatic tumors and are considered to be immunosuppressive. This analysis shows that antigen-presenting fibroblasts are frequent in human lung non-small cell carcinomas, where they seem to actively promote rather than suppress MHCII immunity. Lung apCAFs directly activated the TCRs of effector CD4 T cells and at the same time produced C1q, which acted on T cell C1qbp to rescue them from apoptosis. Fibroblast-specific MHCII or C1q deletion impaired CD4 T cell immunity and accelerated tumor growth, while inducing C1qbp in adoptively transferred CD4 T cells expanded their numbers and reduced tumors. Collectively, we have characterized in the lungs a subset of antigen-presenting fibroblasts with tumor-suppressive properties and propose that cancer immunotherapies might be strongly dependent on in situ MHCII antigen presentation.

Regulation of Cutaneous Immunity In Vivo by Calcitonin Gene-Related Peptide Signaling through Endothelial Cells.

Calcitonin gene-related peptide (CGRP) can bias the outcome of Ag presentation to responsive T cells in vitro away from Th1-type immunity and toward the Th2 and Th17 poles through actions on endothelial cells (ECs). To test the in vivo significance of this observation, we engineered a mouse lacking functional CGRP receptors on ECs (EC receptor activity modifying protein 1 [RAMP1] knockout mice). On percutaneous immunization to 1-fluoro-2,4-dinitrobenzene, stimulated CD4+ T cells from draining lymph nodes showed significantly reduced IL-17A expression with significantly increased IFN-γ, IL-4, and IL-22 expression at the protein and mRNA levels compared with control mice. Retinoic acid receptor-related orphan receptor γ t mRNA was significantly reduced, while mRNAs for T-box expressed in T cells and GATA binding protein 3 were significantly increased. In addition, EC RAMP1 knockout mice had significantly reduced contact hypersensitivity responses, and systemic administration of a CGRP receptor antagonist similarly inhibited contact hypersensitivity in wild-type mice. These observations provide compelling evidence that CGRP is a key regulator of cutaneous immunity through effects on ECs and suggest a novel pathway for potential therapeutic manipulation.

Infiltration of LPAR5+ macrophages in osteosarcoma tumor microenvironment predicts better outcomes.

Introduction: Tumor microenvironment (TME) has been shown to be extensively involved in tumor development. However, the dynamic change of TME components and their effects are still unclear. Here, we attempted to identify TME-related genes that could help predict survival and may be potential therapeutic targets. Methods: Data was collected from UCSC Xena and GEO database. ESTIMATE and CIBERSORT algorithms were applied to estimate the components and the proportions of TIICs in TME. We analyzed the gene expression differences of immune components and stromal components, respectively, and finally got the overlapped DEGs. Through protein-protein interaction (PPI) network and univariate Cox regression analysis based on shared DEGs, we screened out and validated the TME-related genes. Focusing on this gene, we analyzed the expression and prognostic value of this gene, and investigated its relationship with immune cells by correlation analysis, single cell analysis, immunohistochemistry and immunofluorescence analysis. Results: Through a series analysis, we found that the proportion of immune and stromal components was an important prognostic factor, and screened out a key gene, LPAR5, which was highly correlated with prognosis and metastasis. And the expression of LPAR5 was positively correlated with immune cells, especially macrophages, indicating LPAR5+ macrophages played an important role in tumor microenvironment of osteosarcoma. Meanwhile, the genes in LPAR5 high expression group were enriched in immune-related activities and pathways, and differentially expressed genes between LPAR5+ macrophages and LPAR5- macrophages were enriched in the biological processes associated with phagocytosis and antigen presentation. What' more, we found that LPAR5 was mainly expressed in TME, and high LPAR5 expression predicting a better prognosis. Conclusion: We identified a TME-related gene, LPAR5, which is a promising indicator for TME remodeling in osteosarcoma. Particularly, LPAR5+ macrophages might have great potential to be a prognostic factor and therapeutic target for osteosarcoma.

Structure and Peptidomes of Swine MHC Class I with Long Peptides Reveal the Cross-Species Characteristics of the Novel N-Terminal Extension Presentation Mode.

Antigenic peptide presentation by the MHC is essential for activating T cells. The current view is that the peptide termini are tethered within the closed Ag-binding groove of MHC class I (MHC-I). Recently, the N-terminal extension mode of peptide presentation has been observed in human MHC-I (HLA-I). In this study, we found that the N terminus of the long peptide can extend beyond the groove of swine MHC-I (SLA-1*0401), confirming that this phenomenon can occur across species. Removal of the N-terminal extra (P-1) residue of the RW12 peptide significantly reduced the folding efficiency of the complex, but truncation of the second half of the peptide did not. Consistent with previous reports, the second (P1) residue of the peptide is twisted, and its side chain is inserted into the A pocket to form two hydrogen bonds with polymorphic E63 and conserved Y159. Mutations of E63 disrupt the binding of the peptide, indicating that E63 is necessary for this peptide-binding mode. Compared with W167, which exists in most MHC-Is, SLA-I-specific S167 ensures an open N-terminal groove of SLA-1*0401, enabling the P-1 residue to extend from the groove. In this MHC class II-like peptide-binding mode, the A pocket is restrictive to the P1 residue and is affected by the polymorphic residues. The peptidomes and refolding data indicated that the open N-terminal groove of SLA-1*0401 allows one to three residues to extend out of the Ag-binding groove. These cross-species comparisons can help us better understand the characteristics of this N-terminal extension presentation mode.

mRNA translation from an antigen presentation perspective: A tribute to the works of Nilabh Shastri.

The field of mRNA translation has witnessed an impressive expansion in the last decade. The once standard model of translation initiation has undergone, and is still undergoing, a major overhaul, partly due to more recent technical advancements detailing, for example, initiation at non-AUG codons. However, some of the pioneering works in this area have come from immunology and more precisely from the field of antigen presentation to the major histocompatibility class I (MHC-I) pathway. Despite early innovative studies from the lab of Nilabh Shastri demonstrating alternative mRNA translation initiation as a source for MHC-I peptide substrates, the mRNA translation field did not include these into their models. It was not until the introduction of the ribo-sequence technique that the extent of non-canonical translation initiation became widely acknowledged. The detection of peptides on MHC-I molecules by CD8 + T cells is extremely sensitive, making this a superior model system for studying alternative mRNA translation initiation from specific mRNAs. In view of this, we give a brief history on alternative initiation from an immunology perspective and its fundamental role in allowing the immune system to distinguish self from non-self and at the same time pay tribute to the works of Nilabh Shastri.