Atheroprotective Vaccination with MHC-II Restricted Peptides from ApoB-100

Identification of Major Histocompatibility Complex Class II Epitopes From Lyme Autoantigen Apolipoprotein B-100 and Borrelia burgdorferi Mcp4 in Murine Lyme Arthritis

BACKGROUND

During infection with the Lyme arthritis (LA) pathogen Borrelia burgdorferi, T-cell responses to both host and pathogen are dysregulated, resulting in chronic infection and frequent development of autoimmunity.

METHODS

To assess CD4+ T-cell epitopes presented during development of LA, we used an unbiased, immunopeptidomics approach to characterize the major histocompatibility complex (MHC) class II immunopeptidome in B burgdorferi-infected C57BL/6 (B6) mice, which develop mild, self-limiting LA, and infected B6 Il10-/- mice, which develop severe, persistent LA at 0, 4, and 16 weeks postinfection (22-23 mice per group).

RESULTS

Peptides derived from proteins involved in adaptive T- and B-cell responses and cholesterol metabolism, including human Lyme autoantigen apolipoprotein B-100 (apoB-100), were enriched in infected Il10-/- mice; whereas peptides derived from proteins involved in neutrophil extracellular net formation were enriched in infected B6 mice. Presentation of apoB-100 peptides showed evidence of epitope expansion during infection. Of several identified B burgdorferi peptides, only 1, a methyl-accepting chemotaxis protein peptide Mcp4442-462, was immunogenic.

CONCLUSIONS

ApoB-100, a human Lyme autoantigen, undergoes marked epitope expansion during LA development. The paucity of immunogenic B burgdorferi epitopes supports previous findings suggesting CD4+ T-cell responses are suppressed in murine LA.

The role of γδT lymphocytes in atherosclerosis

Atherosclerosis poses a significant threat to human health, impacting overall well-being and imposing substantial financial burdens. Current treatment strategies mainly focus on managing low-density lipids (LDL) and optimizing liver functions. However, it's crucial to recognize that Atherosclerosis involves more than just lipid accumulation; it entails a complex interplay of immune responses. Research highlights the pivotal role of lipid-laden macrophages in the formation of atherosclerotic plaques. These macrophages attract lymphocytes like CD4 and CD8 to the inflamed site, potentially intensifying the inflammatory response. γδ T lymphocytes, with their diverse functions in innate and adaptive immune responses, pathogen defense, antigen presentation, and inflammation regulation, have been implicated in the early stages of Atherosclerosis. However, our understanding of the roles of γδ T cells in Atherosclerosis remains limited. This mini-review aims to shed light on the characteristics and functions of γδ T cells in Atherosclerosis. By gaining insights into the roles of γδ T cells, we may uncover a promising strategy to mitigate plaque buildup and dampen the inflammatory response, thereby opening new avenues for effectively managing this condition.

Dysregulated cellular metabolism in atherosclerosis: mediators and therapeutic opportunities

Accumulating evidence over the past decades has revealed an intricate relationship between dysregulation of cellular metabolism and the progression of atherosclerotic cardiovascular disease. However, an integrated understanding of dysregulated cellular metabolism in atherosclerotic cardiovascular disease and its potential value as a therapeutic target is missing. In this Review, we (1) summarize recent advances concerning the role of metabolic dysregulation during atherosclerosis progression in lesional cells, including endothelial cells, vascular smooth muscle cells, macrophages and T cells; (2) explore the complexity of metabolic cross-talk between these lesional cells; (3) highlight emerging technologies that promise to illuminate unknown aspects of metabolism in atherosclerosis; and (4) suggest strategies for targeting these underexplored metabolic alterations to mitigate atherosclerosis progression and stabilize rupture-prone atheromas with a potential new generation of cardiovascular therapeutics.

Identification of human exTreg cells as CD16+CD56+ cytotoxic CD4+ T cells

In atherosclerosis, some regulatory T (Treg) cells become exTreg cells. We crossed inducible Treg and exTreg cell lineage-tracker mice (FoxP3eGFP-Cre-ERT2ROSA26CAG-fl-stop-fl-tdTomato) to atherosclerosis-prone Apoe-/- mice, sorted Treg cells and exTreg cells and determined their transcriptomes by bulk RNA sequencing (RNA-seq). Genes that were differentially expressed between mouse Treg cells and exTreg cells and filtered for their presence in a human single-cell RNA-sequencing (scRNA-seq) panel identified exTreg cell signature genes as CST7, NKG7, GZMA, PRF1, TBX21 and CCL4. Projecting these genes onto the human scRNA-seq with CITE-seq data identified human exTreg cells as CD3+CD4+CD16+CD56+, which was validated by flow cytometry. Bulk RNA-seq of sorted human exTreg cells identified them as inflammatory and cytotoxic CD4+T cells that were significantly distinct from both natural killer and Treg cells. DNA sequencing for T cell receptor-β showed clonal expansion of Treg cell CDR3 sequences in exTreg cells. Cytotoxicity was functionally demonstrated in cell killing and CD107a degranulation assays, which identifies human exTreg cells as cytotoxic CD4+T cells.

Role of inflammation and immune response in atherosclerosis: Mechanisms, modulations, and therapeutic targets

Cardiovascular diseases (CVDs) have emerged as the leading cause of mortality globally, with atherosclerosis being a prominent focus of investigation among medical researchers worldwide. Atherosclerosis is characterized as a disease of the large and medium-sized arteries that is multifocal, accumulative, and immunoinflammatory in nature, resulting from the deposition of lipids. Accumulating evidence suggests that inflammatory responses and immunoregulation play a vital role in the occurrence and development of atherosclerosis. While existing treatments for atherosclerosis can assist in symptom management and slowing disease progression, a complete cure remains elusive. Consequently, there is significant interest in research and development of potential new drugs for this condition. Therefore, this review aims to consolidate the current understanding of the pathogenesis of atherosclerosis with an emphasis on inflammation, immune response and infection. Besides, it examines the effects and mechanisms of immunological modulations in atherosclerosis, and the potential therapeutic targets and drugs for intervening in the inflammatory responses and immunoregulation associated with atherosclerosis. Additionally, novel drug options for treating atherosclerosis are explored within the context of this review.

Immunomodulation Therapies for Atherosclerosis: The Past, the Present, and the Future

Atherosclerotic cardiovascular disease is the most common cause of morbidity and death worldwide. Recent studies have demonstrated that this chronic inflammatory disease of the arterial wall can be controlled through the modulation of immune system activity. Many patients with cardiovascular disease remain at elevated risk of recurrent events despite receiving current, state-of-the-art preventive medical treatment. Much of this residual risk is attributed to inflammation. Therefore, finding new treatment strategies for this category of patients became of common interest. This review will discuss the experimental and clinical data supporting the possibility of developing immune-based therapies for lowering cardiovascular risk, explicitly focusing on vaccination strategies.

Two decades of vaccine development against atherosclerosis

Atherosclerosis is an immune-mediated chronic inflammatory disease that leads to the development of fatty plaques in the arterial walls, ultimately increasing the risk of thrombosis, stroke, and myocardial infarction. The immune response in this complex disease is both atheroprotective and pro-atherogenic, involving both innate and adaptive immunity. Current treatments include the adjustment of lifestyle factors, cholesterol-lowering drugs such as statins, and immunotherapy, whereas vaccine development has received comparatively little attention. In this review, we discuss the potential of antigen-specific vaccination as a preventative approach based on more than 20 years of research and innovation. Vaccination targets include proteins that are more abundant in atherosclerotic patients, such as oxidized low-density lipoprotein (LDL), apolipoprotein B-100, proprotein convertase subtilisin/kexin type-9 serine protease (PCSK9), cholesteryl ester transfer protein (CETP), and heat shock proteins HSP60 and HSP65. Immunization with such proteins or their peptide epitopes has been shown to induce T-cell activation, produce antigen-specific antibodies, reduce the size of atherosclerotic lesions, and/or reduce serum cholesterol levels. Vaccination against atherosclerosis therefore offers a new strategy to address the burden on healthcare systems caused by cardiovascular disease, the leading cause of death worldwide.

Deleting interleukin-10 from myeloid cells exacerbates atherosclerosis in Apoe-/- mice

Atherosclerosis is initiated by subendothelial retention of lipoproteins and cholesterol, which triggers a non-resolving inflammatory process that over time leads to plaque progression in the artery wall. Myeloid cells and in particular macrophages are the primary drivers of the inflammatory response and plaque formation. Several immune cells including macrophages, T cells and B cells secrete the anti-inflammatory cytokine IL-10, known to be essential for the atherosclerosis protection. The cellular source of IL-10 in natural atherosclerosis progression is unknown. This study aimed to determine the main IL10-producing cell type in atherosclerosis. To do so, we crossed VertX mice, in which IRES-green fluorescent protein (eGFP) was placed downstream of exon 5 of the Il10 gene, with atherosclerosis-prone Apoe-/- mice. We found that myeloid cells express high levels of IL-10 in VertX Apoe-/- mice in both chow and western-diet fed mice. By single cell RNA sequencing and flow cytometry analysis, we identified resident and inflammatory macrophages in atherosclerotic plaques as the main IL-10 producers. To address whether IL-10 secreted by myeloid cells is essential for the protection, we utilized LyzMCre+Il10fl/fl mice crossed into the Apoe-/- background and confirmed that macrophages were unable to secrete IL-10. Chow and western diet-fed LyzMCre+Il10fl/fl Apoe-/- mice developed significantly larger atherosclerotic plaques as measured by en face morphometry than LyzMCre-Il10 fl/flApoe-/-. Flow cytometry and cytokine measurements suggest that the depletion of IL-10 in myeloid cells increases Th17 cells with elevated CCL2, and TNFα in blood plasma. We conclude that macrophage-derived IL-10 is critical for limiting atherosclerosis in mice.

The yin/yang balance of the MHC-self-immunopeptidome

The MHC-self immunopeptidome of professional antigen presenting cells is a cognate ligand for the TCRs expressed on both conventional and thymic-derived natural regulatory T cells. In regulatory T cells, the TCR signaling associated with MHC-peptide recognition induces antigen specific as well as bystander immunosuppression. On the other hand, TCR activation of conventional T cells is associated with protective immunity. As such the peripheral T cell repertoire is populated by a number of T cells with different phenotypes and different TCRs, which can recognize the same MHC-self-peptide complex, resulting in opposite immunological outcomes. This article summarizes what is known about regulatory and conventional T cell recognition of the MHC-self-immunopeptidome at steady state and in inflammatory conditions associated with increased T and B cell self-reactivity, discussing how changes in the MHC-ligandome including epitope copy number and post-translational modifications can tilt the balance toward the expansion of pro-inflammatory or regulatory T cells.

How the immune system shapes atherosclerosis: roles of innate and adaptive immunity

Atherosclerosis is the root cause of many cardiovascular diseases. Extensive research in preclinical models and emerging evidence in humans have established the crucial roles of the innate and adaptive immune systems in driving atherosclerosis-associated chronic inflammation in arterial blood vessels. New techniques have highlighted the enormous heterogeneity of leukocyte subsets in the arterial wall that have pro-inflammatory or regulatory roles in atherogenesis. Understanding the homing and activation pathways of these immune cells, their disease-associated dynamics and their regulation by microbial and metabolic factors will be crucial for the development of clinical interventions for atherosclerosis, including potentially vaccination-based therapeutic strategies. Here, we review key molecular mechanisms of immune cell activation implicated in modulating atherogenesis and provide an update on the contributions of innate and adaptive immune cell subsets in atherosclerosis.

Redox regulation of age-associated defects in generation and maintenance of T cell self-tolerance and immunity to foreign antigens

Thymic atrophy reduces naive T cell production and contributes to increased susceptibility to viral infection with age. Expression of tissue-restricted antigen (TRA) genes also declines with age and has been thought to increase autoimmune disease susceptibility. We find that diminished expression of a model TRA gene in aged thymic stromal cells correlates with impaired clonal deletion of cognate T cells recognizing an autoantigen involved in atherosclerosis. Clonal deletion in the polyclonal thymocyte population is also perturbed. Distinct age-associated defects in the generation of antigen-specific T cells include a conspicuous decline in generation of T cells recognizing an immunodominant influenza epitope. Increased catalase activity delays thymic atrophy, and here, we show that it mitigates declining production of influenza-specific T cells and their frequency in lung after infection, but does not reverse declines in TRA expression or efficient negative selection. These results reveal important considerations for strategies to restore thymic function.

Oxidized Lipids: Common Immunogenic Drivers of Non-Alcoholic Fatty Liver Disease and Atherosclerosis

The prevalence of non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis to inflammatory steatohepatitis (NASH) and cirrhosis, continues to rise, making it one of the major chronic liver diseases and indications for liver transplantation worldwide. The pathological processes underlying NAFLD not only affect the liver but are also likely to have systemic effects. In fact, growing evidence indicates that patients with NAFLD are at increased risk for developing atherosclerosis. Indeed, cardiovascular complications are the leading cause of mortality in NAFLD patients. Here, we aim to address common pathophysiological molecular pathways involved in chronic fatty liver disease and atherosclerosis. In particular, we focus on the role of oxidized lipids and the formation of oxidation-specific epitopes, which are important targets of host immunity. Acting as metabolic danger signals, they drive pro-inflammatory processes and thus contribute to disease progression. Finally, we summarize encouraging studies indicating that oxidized lipids are promising immunological targets to improve intervention strategies for NAFLD and potentially limit the risk of developing atherosclerosis.

Autoimmune Regulator (AIRE) Deficiency Does Not Affect Atherosclerosis and CD4 T Cell Immune Tolerance to Apolipoprotein B

Atherosclerosis is a chronic, lipid-driven disease of medium sized arteries which causes myocardial infarction and stroke. Recently, an adaptive immune response against the plaque-associated autoantigen Apolipoprotein B100 (ApoB), the structural protein component of low-density lipoprotein, has been implicated in atherogenesis. In healthy individuals, CD4⁺ T cells responding to ApoB mainly comprised regulatory T cells, which confer immune tolerance and atheroprotection. Mice and patients with atherosclerosis harbor increased numbers of proatherogenic ApoB-reactive T-helper cell subsets. Given the lack of therapies targeting proatherogenic immunity, clarification of the underlying mechanisms is of high clinical relevance. T cells develop in the thymus, where strong autoreactive T cells are eliminated in the process of negative selection. Herein, we investigated whether the transcription factor autoimmune regulator (AIRE), which controls expression of numerous tissue-restricted self-antigens in the thymus, is involved in mediating tolerance to ApoB and whether Aire deficiency might contribute to atherogenesis. Mice deficient for Aire were crossbred to apolipoprotein E-deficient mice to obtain atherosclerosis-prone Aire^−/−Apoe^−/− mice, which were fed a regular chow diet (CD) or western-type diet (WD). CD4⁺ T cells responding to the ApoB peptide p6 were analyzed by flow cytometry. We demonstrate that Aire deficiency influences neither generation nor activation of ApoB-reactive T cells and has only minor and overall inconsistent impacts on their phenotype. Furthermore, we show that atherosclerotic plaque size is not affected in Aire^−/−Apoe^−/− compared to Aire^+/+Apoe^−/−, irrespective of diet and gender. In conclusion, our data suggests that AIRE is not involved in regulating thymic expression of ApoB or atherosclerosis. Alternative mechanisms how ApoB-reactive CD4 T cells are selected in the thymus will have to be investigated.

Immunotherapeutic Strategies in Cancer and Atherosclerosis-Two Sides of the Same Coin

The development and clinical approval of immunotherapies has revolutionized cancer therapy. Although the role of adaptive immunity in atherogenesis is now well-established and several immunomodulatory strategies have proven beneficial in preclinical studies, anti-atherosclerotic immunotherapies available for clinical application are not available. Considering that adaptive immune responses are critically involved in both carcinogenesis and atherogenesis, immunotherapeutic approaches for the treatment of cancer and atherosclerosis may exert undesirable but also desirable side effects on the other condition, respectively. For example, the high antineoplastic efficacy of immune checkpoint inhibitors, which enhance effector immune responses against tumor cells by blocking co-inhibitory molecules, was recently shown to be constrained by substantial proatherogenic properties. In this review, we outline the specific role of immune responses in the development of cancer and atherosclerosis. Furthermore, we delineate how current cancer immunotherapies affect atherogenesis and discuss whether anti-atherosclerotic immunotherapies may similarly have an impact on carcinogenesis.

Immune Mechanisms of Plaque Instability

Inflammation crucially drives atherosclerosis from disease initiation to the emergence of clinical complications. Targeting pivotal inflammatory pathways without compromising the host defense could compliment therapy with lipid-lowering agents, anti-hypertensive treatment, and lifestyle interventions to address the substantial residual cardiovascular risk that remains beyond classical risk factor control. Detailed understanding of the intricate immune mechanisms that propel plaque instability and disruption is indispensable for the development of novel therapeutic concepts. In this review, we provide an overview on the role of key immune cells in plaque inception and progression, and discuss recently identified maladaptive immune phenomena that contribute to plaque destabilization, including epigenetically programmed trained immunity in myeloid cells, pathogenic conversion of autoreactive regulatory T-cells and expansion of altered leukocytes due to clonal hematopoiesis. From a more global perspective, the article discusses how systemic crises such as acute mental stress or infection abruptly raise plaque vulnerability and summarizes recent advances in understanding the increased cardiovascular risk associated with COVID-19 disease. Stepping outside the box, we highlight the role of gut dysbiosis in atherosclerosis progression and plaque vulnerability. The emerging differential role of the immune system in plaque rupture and plaque erosion as well as the limitations of animal models in studying plaque disruption are reviewed.

Effects of fatty acids on T cell function: role in atherosclerosis

T cells are among the most common cell types present in atherosclerotic plaques and are increasingly being recognized as a central mediator in atherosclerosis development and progression. At the same time, triglycerides and fatty acids have re-emerged as crucial risk factors for atherosclerosis. Triglycerides and fatty acids are important components of the milieu to which the T cell is exposed from the circulation to the plaque, and increasing evidence shows that fatty acids influence T cell function. In this Review, we discuss the effects of fatty acids on four components of the T cell response - metabolism, activation, proliferation and polarization - and the influence of these changes on the pathogenesis of atherosclerosis. We also discuss how quiescent T cells can undergo a type of metabolic reprogramming induced by exposure to fatty acids in the circulation that influences the subsequent functions of T cells after activation, such as in atherosclerotic plaques.

Promoting athero-protective immunity by vaccination with low density lipoprotein-derived antigens

Immune responses activated by LDL particles that have been trapped and oxidized in the arterial wall play an important role in atherosclerosis. Some of these immune responses are protective by facilitating the removal of pro-inflammatory and toxic lipid species formed as result of LDL oxidation. However, should these protective immune responses be insufficient, other more potent pro-inflammatory immune responses instead contributing to disease progression will gradually become dominant. The importance of the balance between protective and pathogenic immunity is particularly apparent when it comes to the adaptive immune system where pro-inflammatory T helper 1 (Th1) type T cells aggravate atherosclerosis, while regulatory T cells (Tregs) have an opposing role. As oxidized LDL is a key autoantigen in atherosclerosis, it has become an interesting possibility that immune-modulatory therapy that favors the activity of apolipoprotein B peptide-specific Tregs could be developed into a novel treatment strategy for prevention/stabilization of atherosclerosis and ischemic cardiovascular events. Indeed, several such oxidized LDL tolerance vaccines have shown promising results in animal models of atherosclerosis. This review will discuss the experimental background for development of atherosclerosis vaccines based on LDL-derived antigens as well as the challenges involved in translating these findings into clinical application.

Anti-inflammatory and Immunomodulatory Therapies in Atherosclerosis

Hypercholesterolemia is a major risk factor in atherosclerosis development and lipid-lowering drugs (i.e., statins) remain the treatment of choice. Despite effective reduction of LDL cholesterol in patients, a residual cardiovascular risk persists in some individuals, highlighting the need for further therapeutic intervention. Recently, the CANTOS trial paved the way toward the development of specific therapies targeting inflammation, a key feature in atherosclerosis progression. The pre-existence of multiple drugs modulating both innate and adaptive immune responses has significantly accelerated the number of translational studies applying these drugs to atherosclerosis. Additional preclinical research has led to the discovery of new therapeutic targets, offering promising perspectives for the treatment and prevention of atherosclerosis. Currently, both drugs with selective targeting and broad unspecific anti-inflammatory effects have been tested. In this chapter, we aim to give an overview of current advances in immunomodulatory treatment approaches for atherosclerotic cardiovascular diseases.

Immune responses against oxidized LDL as possible targets for prevention of atherosclerosis in systemic lupus erythematosus

Patients suffering from systemic lupus erythematosus (SLE) are at increased risk of developing cardiovascular disease (CVD) and traditional therapies including statins provide insufficient protection. Impaired removal of apoptotic material is a common pathogenic mechanism in both SLE and atherosclerosis and is considered to be a key factor in the development of autoimmunity. Since oxidized LDL and apoptotic material bind to the same receptors, we aimed to investigate if targeting the oxidized LDL autoimmunity can affect atherosclerosis in SLE. To investigate the possible role of oxidized LDL autoimmunity in the accelerated atherosclerosis associated with SLE we used a hypercholesterolemic SLE mouse model (B6.lpr.ApoE^-/- mice). Promoting LDL tolerance through mucosal immunization with an apolipoprotein B-100 peptide p45 (amino acids 661-680) and cholera toxin B-subunit fusion protein increased regulatory T cells and B cells in mesenteric lymph nodes and reduced plaque development in the aorta by 33%. Treatment with the oxidized LDL-specific antibody Orticumab reduced aortic atherosclerosis by 43%, subvalvular plaque area by 50% and the macrophage content by 31%. The present study provides support for oxLDL as a possible target for prevention of cardiovascular complications in SLE.

ApoB-Specific CD4+ T Cells in Mouse and Human Atherosclerosis

Atherosclerosis is a chronic inflammatory condition of the arterial wall that leads to the formation of vessel-occluding plaques within the subintimal space of middle-sized and larger arteries. While traditionally understood as a myeloid-driven lipid-storage disease, growing evidence suggests that the accumulation of low-density lipoprotein cholesterol (LDL-C) ignites an autoimmune response with CD4+ T-helper (TH) cells that recognize self-peptides from Apolipoprotein B (ApoB), the core protein of LDL-C. These autoreactive CD4+ T cells home to the atherosclerotic plaque, clonally expand, instruct other cells in the plaque, and induce clinical plaque instability. Recent developments in detecting antigen-specific cells at the single cell level have demonstrated that ApoB-reactive CD4+ T cells exist in humans and mice. Their phenotypes and functions deviate from classical immunological concepts of distinct and terminally differentiated TH immunity. Instead, ApoB-specific CD4+ T cells have a highly plastic phenotype, can acquire several, partially opposing and mixed transcriptional programs simultaneously, and transit from one TH subset into another over time. In this review, we highlight adaptive immune mechanisms in atherosclerosis with a focus on CD4+ T cells, introduce novel technologies to detect ApoB-specific CD4+ T cells at the single cell level, and discuss the potential impact of ApoB-driven autoimmunity in atherosclerosis.

Functional Role of B Cells in Atherosclerosis

Atherosclerosis is a lipid-driven inflammatory disease of blood vessels, and both innate and adaptive immune responses are involved in its development. The impact of B cells on atherosclerosis has been demonstrated in numerous studies and B cells have been found in close proximity to atherosclerotic plaques in humans and mice. B cells exert both atheroprotective and pro-atherogenic functions, which have been associated with their B cell subset attribution. While B1 cells and marginal zone B cells are considered to protect against atherosclerosis, follicular B cells and innate response activator B cells have been shown to promote atherosclerosis. In this review, we shed light on the role of B cells from a different, functional perspective and focus on the three major B cell functions: antibody production, antigen presentation/T cell interaction, and the release of cytokines. All of these functions have the potential to affect atherosclerosis by multiple ways and are dependent on the cellular milieu and the activation status of the B cell. Moreover, we discuss B cell receptor signaling and the mechanism of B cell activation under atherosclerosis-prone conditions. By summarizing current knowledge of B cells in and beyond atherosclerosis, we are pointing out open questions and enabling new perspectives.

Vaccination in Atherosclerosis

Atherosclerosis is the major underlying pathology of cardiovascular diseases that together are the leading cause of death worldwide. The formation of atherosclerotic plaques is driven by chronic vascular inflammation. Although several risk factors have been identified and significant progress in disease prevention and treatment has been made, no therapeutic agents targeting inflammation are clinically available. Recent clinical trials established the potential of anti-inflammatory therapies as a treatment of atherosclerosis. However, adverse impacts on host defense have raised safety concerns about these therapies. Scientific evidence during the past 40 years implicated an adaptive immune response against plaque-associated autoantigens in atherogenesis. Preclinical data have underscored the protective potential of immunization against such targets precisely and without the impairment of host defense. In this review, we discuss the current vaccination strategies against atherosclerosis, supposed mechanisms of action, therapeutic potential, and the challenges that must be overcome in translating this idea into clinical practice.

Role of the adaptive immune system in atherosclerosis

Atherosclerosis, the pathology underlying heart attacks, strokes and peripheral artery disease, is a chronic inflammatory disease of the artery wall initiated by elevated low-density lipoprotein (LDL) cholesterol levels. LDL accumulates in the artery wall, where it can become oxidized to oxLDL. T cell responses to ApoB, a core protein found in LDL and other lipoproteins, are detectable in healthy mice and people. Most of the ApoB-specific CD4T cells are FoxP3+ regulatory T cells (Treg). In the course of atherosclerosis development, the number of ApoB-reactive T cells expands. At the same time, their phenotype changes, showing cell surface markers, transcription factors and transcriptomes resembling other T-helper lineages like Th17, Th1 and follicular helper (TFH) cells. TFH cells enter germinal centers and provide T cell help to B cells, enabling antibody isotype switch from IgM to IgG and supporting affinity maturation. In people and mice with atherosclerosis, IgG and IgM antibodies to oxLDL are detectable. Higher IgM antibody titers to oxLDL are associated with less, IgG antibodies with more atherosclerosis. Thus, both T and B cells play critical roles in atherosclerosis. Modifying the adaptive immune response to ApoB holds promise for preventing atherosclerosis and reducing disease burden.

Pathogenic Autoimmunity in Atherosclerosis Evolves From Initially Protective Apolipoprotein B100-Reactive CD4+ T-Regulatory Cells

BACKGROUND

Throughout the inflammatory response that accompanies atherosclerosis, autoreactive CD4⁺ T-helper cells accumulate in the atherosclerotic plaque. Apolipoprotein B₁₀₀ (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (T_H1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4⁺ T cells with an atheroprotective, regulatory T cell (T_reg) phenotype in healthy individuals. Yet, the function of apoB-reactive T_regs and their relationship with pathogenic T_H1 cells remain unknown.

METHODS

To interrogate the function of autoreactive CD4⁺ T cells in atherosclerosis, we used a novel tetramer of major histocompatibility complex II to track T cells reactive to the mouse self-peptide apo B_978-993 (apoB⁺) at the single-cell level.

RESULTS

We found that apoB⁺ T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a T_reg-like transcriptome, although only 21% of all apoB⁺ T cells expressed the T_reg transcription factor FoxP3 (Forkhead Box P3) protein as detected by flow cytometry. In single-cell RNA sequencing, apoB⁺ T cells formed several clusters with mixed T_H signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of T_H1, T helper cell type 2 (T_H2), and T helper cell type 17 (T_H17), and of follicular-helper T cells. ApoB⁺ T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic T_H1/T_H17-like cells with proinflammatory properties and only a residual T_reg transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed T_H1/T_H17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB⁺ T_regs in lineage tracing of hyperlipidemic Apoe^-/- mice. In adoptive transfer experiments, converting apoB⁺ T_regs failed to protect from atherosclerosis.

CONCLUSIONS

Our results demonstrate an unexpected mixed phenotype of apoB-reactive autoimmune T cells in atherosclerosis and suggest an initially protective autoimmune response against apoB with a progressive derangement in clinical disease. These findings identify apoB autoreactive T_regs as a novel cellular target in atherosclerosis.

T cell subsets and functions in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall and the primary underlying cause of cardiovascular disease. Data from in vivo imaging, cell-lineage tracing and knockout studies in mice, as well as clinical interventional studies and advanced mRNA sequencing techniques, have drawn attention to the role of T cells as critical drivers and modifiers of the pathogenesis of atherosclerosis. CD4+ T cells are commonly found in atherosclerotic plaques. A large body of evidence indicates that T helper 1 (TH1) cells have pro-atherogenic roles and regulatory T (Treg) cells have anti-atherogenic roles. However, Treg cells can become pro-atherogenic. The roles in atherosclerosis of other TH cell subsets such as TH2, TH9, TH17, TH22, follicular helper T cells and CD28null T cells, as well as other T cell subsets including CD8+ T cells and γδ T cells, are less well understood. Moreover, some T cells seem to have both pro-atherogenic and anti-atherogenic functions. In this Review, we summarize the knowledge on T cell subsets, their functions in atherosclerosis and the process of T cell homing to atherosclerotic plaques. Much of our understanding of the roles of T cells in atherosclerosis is based on findings from experimental models. Translating these findings into human disease is challenging but much needed. T cells and their specific cytokines are attractive targets for developing new preventive and therapeutic approaches including potential T cell-related therapies for atherosclerosis.

Tolerogenic vaccines for the treatment of cardiovascular diseases

Atherosclerosis is the main pathology behind most cardiovascular diseases. It is a chronic inflammatory disease characterized by the formation of lipid-rich plaques in arteries. Atherosclerotic plaques are initiated by the deposition of cholesterol-rich LDL particles in the arterial walls leading to the activation of innate and adaptive immune responses. Current treatments focus on the reduction of LDL blood levels using statins, however the critical components of inflammation and autoimmunity have been mostly ignored as therapeutic targets. The restoration of immune tolerance towards atherosclerosis-relevant antigens can arrest lesion development as shown in pre-clinical models. In this review, we evaluate the clinical development of similar strategies for the treatment of inflammatory and autoimmune diseases like rheumatoid arthritis, type 1 diabetes or multiple sclerosis and analyse the potential of tolerogenic vaccines for atherosclerosis and the challenges that need to be overcome to bring this therapy to patients.

Opportunities for an atherosclerosis vaccine: From mice to humans

Atherosclerosis, the major underlying cause of cardiovascular diseases (CVD), is the number one killer globally. The disease pathogenesis involves a complex interplay between metabolic and immune components. Although lipid-lowering drugs such as statins curb the risks associated with CVD, significant residual inflammatory risk remains. Substantial evidence from experimental models and clinical studies has established the role of inflammation and immune effector mechanisms in the pathogenesis of atherosclerosis. Several stages of the disease are affected by host-mediated antigen-specific adaptive immune responses that play either protective or proatherogenic roles. Therefore, strategies to boost an anti-atherogenic humoral and T regulatory cell response are emerging as preventative or therapeutic strategies to lowering inflammatory residual risks. Vaccination holds promise as an efficient, durable and relatively inexpensive approach to induce protective adaptive immunity in atherosclerotic patients. In this review, we discuss the status and opportunities for a human atherosclerosis vaccine. We describe (1) some of the immunomodulatory therapeutic interventions tested in atherosclerosis (2) the immune targets identified in pre-clinical and clinical investigations (3) immunization strategies evaluated in animal models (4) past and ongoing clinical trials to examine the safety and efficacy of human atherosclerosis vaccines and (5) strategies to improve and optimize vaccination in humans (antigen selection, formulation, dose and delivery).

Long-Term Efficacy and Safety of Immunomodulatory Therapy for Atherosclerosis

BACKGROUND AND AIMS

The long-term effect of immune tolerance has not been explored so far in atherosclerosis. In the present study, we assessed the effect of mucosal tolerance to a multi antigenic construct expressing three peptides from ApoB, HSP60, and outer membrane protein from Chlamydia pneumonia (AHC) for 30 weeks at every 6-week interval to understand the kinetics of immune modulation in disease progression. The safety profile of the molecule was also evaluated in mice.

METHODS

Apob^tm2SgyLdlr^tm1Her/J mice (5-6 weeks) were orally dosed with multi antigenic construct (AHC) molecule on alternate days, followed by high-fat diet feeding to initiate atherosclerosis.

RESULTS

Treated animals showed an efficient reduction in plaque growth and lipid accumulation at 6 weeks (49%, p < 0.01) and 12 weeks (42.3%, p < 0.01) which decreased to 29% (p = 0.0001) at 18 weeks and at later time points. Macrophage accumulation was significantly lower at all time points (53% at 12 weeks to 27% at 30 weeks). Regulatory T cells increased in the spleen following treatment until 12 weeks (week 0 (2.57 ± 0.18 vs. 6.36 ± 0.03, p = 0.02), week 6 (4.52 ± 0.2 vs. 8.87 ± 0.32, p = 0.02), and week 12 (8.74 ± 0.37 vs. 15.4 ± 0.27, p = 0.02)) but showed a decline later. A similar trend was observed with tolerogenic dendritic cells. We observed an increase in antibody levels to low-density lipoprotein and oxidized LDL at later stages. AHC molecule was found to be safe in acute and repeated dose toxicity studies.

CONCLUSIONS

Our results suggest that immune tolerance to AHC protein by oral administration is able to provide efficient atheroprotection up to 18 weeks and moderately at later stages. Apart from immune regulatory cells, protective antibodies may also have a role in controlling atherosclerosis.

Immunity and Inflammation in Atherosclerosis

There is now overwhelming experimental and clinical evidence that atherosclerosis is a chronic inflammatory disease. Lessons from genome-wide association studies, advanced in vivo imaging techniques, transgenic lineage tracing mice, and clinical interventional studies have shown that both innate and adaptive immune mechanisms can accelerate or curb atherosclerosis. Here, we summarize and discuss the pathogenesis of atherosclerosis with a focus on adaptive immunity. We discuss some limitations of animal models and the need for models that are tailored to better translate to human atherosclerosis and ultimately progress in prevention and treatment.

How Oxidized Low-Density Lipoprotein Activates Inflammatory Responses

Cardiovascular disease (CVD) is the number one cause of death in the United States and worldwide. The most common cause of cardiovascular disease is atherosclerosis, or formation of fatty plaques in the arteries. Low-density lipoprotein (LDL), termed "bad cholesterol", is a large molecule comprised of many proteins as well as lipids including cholesterol, phospholipids, and triglycerides. Circulating levels of LDL are directly associated with atherosclerosis disease severity. Once thought to simply be caused by passive retention of LDL in the vasculature, atherosclerosis studies over the past 40-50 years have uncovered a much more complex mechanism. It has now become well established that within the vasculature, LDL can undergo many different types of oxidative modifications such as esterification and lipid peroxidation. The resulting oxidized LDL (oxLDL) has been found to have antigenic potential and contribute heavily to atherosclerosis associated inflammation, activating both innate and adaptive immunity. This review discusses the many proposed mechanisms by which oxidized LDL modulates inflammatory responses and how this might modulate atherosclerosis.

A Novel Animal Model of Emphysema Induced by Anti-Elastin Autoimmunity

Loss of immune tolerance to self-antigens can promote chronic inflammation and disrupt the normal function of multiple organs, including the lungs. Degradation of elastin, a highly insoluble protein and a significant component of the lung structural matrix, generates proinflammatory molecules. Elastin fragments (EFs) have been detected in the serum of smokers with emphysema, and elastin-specific T cells have also been detected in the peripheral blood of smokers with emphysema. However, an animal model that could recapitulate T cell-specific autoimmune responses by initiating and sustaining inflammation in the lungs is lacking. In this study, we report an animal model of autoimmune emphysema mediated by the loss of tolerance to elastin. Mice immunized with a combination of human EFs plus rat EFs but not mouse EFs showed increased infiltration of innate and adaptive immune cells to the lungs and developed emphysema. We cloned and expanded mouse elastin-specific CD4+ T cells from the lung and spleen of immunized mice. Finally, we identified TCR sequences from the autoreactive T cell clones, suggesting possible pathogenic TCRs that can cause loss of immune tolerance against elastin. This new autoimmune model of emphysema provides a useful tool to examine the immunological factors that promote loss of immune tolerance to self.

Anti-inflammatory Therapies for Cardiovascular Disease: Signaling Pathways and Mechanisms

Cardiovascular diseases (CVD) are the clinical manifestation of atherosclerosis, a chronic inflammatory disease promoted by several risk factors such as dyslipidemia, type 2 diabetes mellitus, hypertension, and smoking. Acute CVD events are the result of an unresolved inflammatory chronic state that promotes the rupture of unstable plaque lesions. Of note, the existing intensive therapies modify risk factors but do not prevent life-threatening recurrent ischemic events in high-risk patients, who have a residual inflammatory risk displayed by increased C-reactive protein (CRP) levels. Better understanding of the role of innate and adaptive immunity in plaque development and rupture has led to intensive investigation of anti-inflammatory strategies for CVD. Some of them are being tested in specific clinical trials and use lower doses of existing medications originally developed for other inflammatory diseases such as rheumatoid arthritis and psoriasis, which have high CVD risk. Other investigations are retrospective and meta-analyses of existing clinical trials that evaluate the incidence of CVD in these inflammatory diseases. Others are based on preclinical testing such as vaccines. In this article, we summarize the main anti-inflammatory strategies and associated molecular mechanisms that are being evaluated in preclinical or clinical CVD studies.

[Immunity and inflammation in atherosclerosis]

There is now overwhelming experimental and clinical evidence that arteriosclerosis is a chronic inflammatory disease. Lessons learned from genome-wide association studies, advanced in vivo imaging techniques, transgenic lineage tracing mice models and clinical interventional studies have shown that both innate and adaptive immune mechanisms can accelerate or curb arteriosclerosis. This article summarizes and discusses the pathogenesis of arteriosclerosis with a focus on the role of the adaptive immune system. Some limitations of animal models are discussed and the need for models that are tailored to better translate to human atherosclerosis and ultimately progress in prevention and treatment are emphasized.

Vaccination against atherosclerosis

Atherosclerosis is a chronic inflammatory disease that causes most heart attacks and strokes, making it the biggest killer in the world. Although cholesterol-lowering drugs have dramatically reduced these major adverse cardiovascular events, there remains a high residual risk called inflammatory risk. Atherosclerosis has an autoimmune component that can be manipulated by immunologic approaches including vaccination. Vaccination is attractive, because it is antigen-specific, does not impair host defense, and provides long-term protection. Several candidate antigens for atherosclerosis vaccine development have been identified and have been shown to reduce atherosclerosis in animal models. In this review, we focus on two different types of atherosclerosis vaccines: antibody-inducing and regulatory T cell-inducing.

Keratin 8 is a potential self-antigen in the coronary artery disease immunopeptidome: A translational approach

Background

Inflammation is an important risk factor in atherosclerosis, the underlying cause of coronary artery disease (CAD). Unresolved inflammation may result in maladaptive immune responses and lead to immune reactivity to self-antigens. We hypothesized that inflammation in CAD patients would manifest in immune reactivity to self-antigens detectable in soluble HLA-I/peptide complexes in the plasma.

Methods

Soluble HLA-I/peptide complexes were immuno-precipitated from plasma of male acute coronary syndrome (ACS) patients or age-matched controls and eluted peptides were subjected to mass spectrometry to generate the immunopeptidome. Self-peptides were ranked according to frequency and signal intensity, then mouse homologs of selected peptides were used to test immunologic recall in spleens of male apoE-/- mice fed either normal chow or high fat diet. The peptide detected with highest frequency in patient plasma samples and provoked T cell responses in mouse studies was selected for use as a self-antigen to stimulate CAD patient peripheral blood mononuclear cells (PBMCs).

Results

The immunopeptidome profile identified self-peptides unique to the CAD patients. The mouse homologs tested showed immune responses in apoE-/- mice. Keratin 8 was selected for further study in patient PBMCs which elicited T Effector cell responses in CAD patients compared to controls, associated with reduced PD-1 mRNA expression.

Conclusion

An immunopeptidomic strategy to search for self-antigens potentially involved in CAD identified Keratin 8. Self-reactive immune response to Keratin 8 may be an important factor in the inflammatory response in CAD.

Macrophage Foam Cell-Targeting Immunization Attenuates Atherosclerosis

Background: Macrophage foam cells (FCs) play a crucial role in the initiation and progression of atherosclerosis. Reducing the formation or inducing the removal of FCs could ameliorate atherosclerosis. The present study examined whether the whole-cell vaccination using FCs could be used as novel prevention and treatment strategies to battle atherosclerosis.

Methods: ApoE^−/− mice with initial or established atherosclerosis were subcutaneously immunized three times with FCs in Freund's adjuvant.

Results: Immunization with FCs resulted in an overt reduction of atherosclerotic lesion in the whole aorta and the aortic root with enhanced lesion stability. Subsequent study in mechanism showed that FCs vaccination dramatically increased CD4⁺ T cell and CD8⁺ T cell populations. Immunization with FCs significantly raised the plasma FCs-specific IgG antibodies. Of note, the FCs immune plasma could selectively recognize and bind to FC. FCs immune plasma significantly blocked the process of FCs formation, finally reduced the accumulation of FCs in plaque. Additionally, it was observed that FCs immunization down-regulated the expression level of atherosclerosis related pro-inflammatory cytokines, including IFN-γ, MCP-1, and IL-6 and enhanced the lesion stability with a significant increase in TGF-β1 level and collagen content.

Conclusions: These findings demonstrate that the whole-cell vaccination using FCs significantly decreased lesion development and positively modulated lesion progression and stability by targeting FCs. The whole-cell FCs vaccine might represent a potential novel strategy for development of new antibodies and vaccines to the prevention or treatment of atherosclerosis.

Anionic 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) liposomes induce antigen-specific regulatory T cells and prevent atherosclerosis in mice

Atherosclerosis is the predominant underlying pathology of many types of cardiovascular disease and is one of the leading causes of death worldwide. It is characterized by the retention of oxidized low-density lipoprotein (ox-LDL) in lipid-rich macrophages (foam cells) in the intima of arteries. Autoantigens derived from oxLDL can be used to vaccinate against atherosclerosis. However, a major challenge is the induction of antigen-specific Tregs in a safe and effective way. Here we report that liposomes containing the anionic phospholipid 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) induce Tregs that are specific for the liposomes' cargo. Mechanistically, we show a crucial role for the protein corona that forms on the liposomes in the circulation, as uptake of DSPG-liposomes by antigen-presenting cells is mediated via complement component 1q (C1q) and scavenger receptors (SRs). Vaccination of atherosclerotic mice on a western-type diet with DSPG-liposomes encapsulating an LDL-derived peptide antigen significantly reduced plaque formation by 50% and stabilized the plaques, and reduced serum cholesterol concentrations. These results indicate that DSPG-liposomes have potential as a delivery system in vaccination against atherosclerosis.

Lipid-driven immunometabolic responses in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is a chronic inflammatory disease in which subendothelial infiltration of lipoproteins leads to inflamed lesions in arteries. Despite improvements in secondary prevention, most cardiovascular events cannot be avoided with current therapies. This review focuses on novel mechanistic insights on lipid-driven immune activation, which could pave the way for new anti-inflammatory treatments for atherosclerosis.

RECENT FINDINGS

Immunometabolic interactions can shape the immune response. Within atherosclerotic plaques, macrophages and T cells are the dominant immune cell populations. Using multiple mechanisms, lipoprotein-derived components activate both the innate and adaptive immune systems. Cholesterol crystals and apolipoprotein B-peptides have been shown to activate macrophages and T cells, respectively. Lipoproteins are also important modulators of regulatory T cells that can hamper vascular inflammation. In the liver, T cells can influence hepatic inflammation and lipoprotein metabolism. Hence, there is an intricate crosstalk between the immune system and lipoprotein metabolism.

SUMMARY

Novel treatments are needed to prevent clinical manifestations of atherosclerosis. Improved understanding of lipid-driven immunometabolic responses is likely to reveal new therapeutic targets.

Regulatory CD4+ T Cells Recognize Major Histocompatibility Complex Class II Molecule-Restricted Peptide Epitopes of Apolipoprotein B

BACKGROUND

CD4+ T cells play an important role in atherosclerosis, but their antigen specificity is poorly understood. Immunization with apolipoprotein B (ApoB, core protein of low density lipoprotein) is known to be atheroprotective in animal models. Here, we report on a human APOB peptide, p18, that is sequence-identical in mouse ApoB and binds to both mouse and human major histocompatibility complex class II molecules.

METHODS

We constructed p18 tetramers to detect human and mouse APOB-specific T cells and assayed their phenotype by flow cytometry including CD4 lineage transcription factors, intracellular cytokines, and T cell receptor activation. Apolipoprotein E-deficient ( Apoe-/-) mice were vaccinated with p18 peptide or adjuvants alone, and atherosclerotic burden in the aorta was determined.

RESULTS

In human peripheral blood mononuclear cells from donors without cardiovascular disease, p18 specific CD4+ T cells detected by a new human leukocyte antigen-antigen D related-p18 tetramers were mostly Foxp3+ regulatory T cells (Tregs). Donors with subclinical cardiovascular disease as detected by carotid artery ultrasound had Tregs coexpressing retinoic acid-related orphan receptor gamma t or T-bet, which were both almost absent in donors without cardiovascular disease. In Apoe-/- mice, immunization with p18 induced Tregs and reduced atherosclerotic lesions. After peptide restimulation, responding CD4+ T cells identified by Nur77-GFP (green fluorescent protein) were highly enriched in Tregs. A new mouse I-Ab-p18 tetramer identified the expansion of p18-specific CD4+ T cells on vaccination, which were enriched for interleukin-10-producing Tregs.

CONCLUSIONS

These findings show that APOB p18-specific CD4+ T cells are mainly Tregs in healthy donors, but coexpress other CD4 lineage transcription factors in donors with subclinical cardiovascular disease. This study identifies ApoB peptide 18 as the first Treg epitope in human and mouse atherosclerosis.

A clinically applicable adjuvant for an atherosclerosis vaccine in mice

Vaccination with MHC-II-restricted peptides from Apolipoprotein B (ApoB) with complete and incomplete Freund's adjuvant (CFA/IFA) is known to protect mice from atherosclerosis. This vaccination induces antigen-specific IgG1 and IgG2c antibody responses and a robust CD4 T cell response in lymph nodes. However, CFA/IFA cannot be used in humans. To find a clinically applicable adjuvant, we tested the effect of vaccinating Apoe-deficient mice with ApoB peptide P6 (TGAYSNASSTESASY). In a broad screening experiment, Addavax, a squalene-based oil-in-water adjuvant similar to MF59, was the only adjuvant that showed similar efficacy as CFA/IFA. This was confirmed in a confirmation experiment for both the aortic arch and whole aorta analyzed by en face analysis after atherosclerotic lesion staining. Mechanistically, restimulated peritoneal cells from mice immunized with P6 in Addavax released significant amounts of IL-10. Unlike P6 in CFA/IFA, vaccination with P6 in Addavax did not induce any detectable IgG1 or IgG2c antibodies to P6. These data suggest that squalene-based adjuvants such as MF59 are good candidate adjuvants for developing a clinically effective atherosclerosis vaccine.

Inflammation: A Novel Therapeutic Target/Direction in Atherosclerosis

Over the past two decades, the viewpoint of atherosclerosis has been replaced gradually by a lipid-driven, chronic, low-grade inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatment targeting the inflammatory nature of atherosclerosis is still very limited and deserves further attention to fight atherosclerosis successfully. Here, we review the current development of inflammation and atherosclerosis to discuss novel insights and potential targets in atherosclerosis, and to address drug discovery based on anti-inflammatory strategy in atherosclerotic disease.

The cathelicidin protein CRAMP is a potential atherosclerosis self-antigen in ApoE(-/-) mice

Auto-immunity is believed to contribute to inflammation in atherosclerosis. The antimicrobial peptide LL-37, a fragment of the cathelicidin protein precursor hCAP18, was previously identified as an autoantigen in psoriasis. Given the reported link between psoriasis and coronary artery disease, the biological relevance of the autoantigen to atherosclerosis was tested in vitro using a truncated (t) form of the mouse homolog of hCAP18, CRAMP, on splenocytes from athero-prone ApoE(-/-) mice. Stimulation with tCRAMP resulted in increased CD8+ T cells with Central Memory and Effector Memory phenotypes in ApoE(-/-) mice, differentially activated by feeding with normal chow or high fat diet. Immunization of ApoE(-/-) with different doses of the shortened peptide (Cramp) resulted in differential outcomes with a lower dose reducing atherosclerosis whereas a higher dose exacerbating the disease with increased neutrophil infiltration of the atherosclerotic plaques. Low dose Cramp immunization also resulted in increased splenic CD8+ T cell degranulation and reduced CD11b+CD11c+ conventional dendritic cells (cDCs), whereas high dose increased CD11b+CD11c+ cDCs. Our results identified CRAMP, the mouse homolog of hCAP-18, as a potential self-antigen involved in the immune response to atherosclerosis in the ApoE(-/-) mouse model.

ATVB Distinguished Scientist Award: How Costimulatory and Coinhibitory Pathways Shape Atherosclerosis

OBJECTIVE

Immune cells play a critical role in atherosclerosis. Costimulatory and coinhibitory molecules of the tumor necrosis factor receptor and CD28 immunoglobulin superfamilies not only shape T-cell and B-cell responses but also have a major effect on antigen-presenting cells and nonimmune cells.

APPROACH AND RESULTS

Pharmacological inhibition or activation of costimulatory and coinhibitory molecules and genetic deletion demonstrated their involvement in atherosclerosis. This review highlights recent advances in understanding how costimulatory and coinhibitory pathways shape the immune response in atherosclerosis.

CONCLUSIONS

Insights gained from costimulatory and coinhibitory molecule function in atherosclerosis may inform future therapeutic approaches.

The immunology of atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, both in the general population and among patients with chronic kidney disease (CKD). In most cases, the underlying cause of the cardiovascular event is atherosclerosis - a chronic inflammatory disease. CKD accelerates atherosclerosis via augmentation of inflammation, perturbation of lipid metabolism, and other mechanisms. In the artery wall, subendothelial retention of plasma lipoproteins triggers monocyte-derived macrophages and T helper type 1 (T_H1) cells to form atherosclerotic plaques. Inflammation is initiated by innate immune reactions to modified lipoproteins and is perpetuated by T_H1 cells that react to autoantigens from the apolipoprotein B100 protein of LDL. Other T cells are also active in atherosclerotic lesions; regulatory T cells inhibit pathological inflammation, whereas T_H17 cells can promote plaque fibrosis. The slow build-up of atherosclerotic plaques is asymptomatic, but plaque rupture or endothelial erosion can induce thrombus formation, leading to myocardial infarction or ischaemic stroke. Targeting risk factors for atherosclerosis has reduced mortality, but a need exists for novel therapies to stabilize plaques and to treat arterial inflammation. Patients with CKD would likely benefit from such preventive measures.