Background and Aims Atherosclerosis is a chronic lipid-driven inflammatory disease and one of the leading underlying causes of cardiovascular morbidity and mortality in Western society. Macrophages are key players in atherosclerotic development. Although the cellular composition of carotid atherosclerotic lesions has been determined, macrophage population definitions lack granularity and lineage data. Moreover, to date no direct link has been established between cellular content of atherosclerotic lesions and secondary clinical outcome. This study is aimed at characterization of atherosclerotic lesion macrophages and identification of plaque cell types and marker genes that predict the risk of secondary major adverse cardiovascular events in a clinical setting.Methods Single-cell RNA sequencing on blood and plaques from 46 carotid endarterectomy patients enrolled in the AtheroExpress cohort. Deconvolution was done on bulk transcriptome data from 656 AtheroExpress patients, and findings were validated in 82 patients enrolled in the Carotid Plaque Imaging Project.Results Four major archetypes of plaque macrophages were identified: inflammatory macrophages, lipid-associated macrophages (LAMs), tissue-resident-like LAMs, and inflammatory LAMs. Cellular trajectory and fate analyses revealed that these are derived from both classical and non-classical monocytes. Functionally, this study demonstrated the capacity of monocytes to differentiate into inflammatory LAMs via inflammatory- or resident-like LAM and LAM stages. Next, the AtheroExpress bulk RNA-seq cohort was deconvoluted. Macrophages were shown to be the only cell population significantly associated with both symptoms at time of surgery and increased risk of major adverse cardiovascular events during a 3-year follow-up period. Within the macrophage population, mostly LAM and inflammatory LAM foam cell markers such as PLIN2 and TREM1 were associated with an increased risk of major adverse cardiovascular events after 3-year follow-up. These associations were validated in the Carotid Plaque Imaging Project cohort.Conclusions Together, these findings provide critical insights into the functional differences and origin of macrophage subpopulations in human atherosclerosis and show their clinical significance and risk prediction value in relation to future cardiovascular events.

Pattern recognition receptor (PRR) ligands represent a promising class of immunostimulants. Here, we demonstrate that the covalent conjugation of PRR ligands enables coordinated receptor engagement and amplifies immune responses beyond those achievable with unlinked mixtures. We synthesized a focused panel of chimeric PRR ligands comprising defined pairwise agonist combinations targeting selected extracellular and intracellular PRRs. Using phenotypic screening in human peripheral blood mononuclear cells, we identified conjugates that induced distinct cytokine signatures and enhanced cytotoxic immune activity. Among these, chimeric TLR4/TLR7 and TLR7/RIG-I ligands elicited broad innate immune activation in vitro and enhanced antigen-specific immune responses in murine vaccination models. Notably, intratumoral administration of the conjugated TLR4/TLR7 ligand resulted in significant antitumor activity in a syngeneic B16F10 melanoma model. Collectively, these findings establish covalent PRR ligand conjugation as a powerful chemical strategy for modulating innate immune signaling and support the development of conjugated PRR ligands as next-generation vaccine adjuvants and immunotherapeutics.

Abstract In vitro -transcribed messenger RNA (IVT mRNA) has emerged as a versatile protein expression platform with broad clinical potential. Current optimization strategies for IVT mRNA focus on untranslated regions (UTRs), mRNA stability, and codon usage, often guided by massively parallel screening and machine learning approaches. In contrast, the Kozak sequence, a key determinant of translation initiation, is often inconsistently incorporated into synthetic 5′ UTR design, and its contribution to translation efficiency remains poorly defined. Here, we systematically varied the Kozak sequence across diverse UTR contexts and performed combinatorial optimization using synthetic, established, and viral UTRs to identify design principles for enhanced translation. We show that a single-nucleotide deviation from the consensus Kozak sequence consistently enhances protein expression across UTR contexts and coding sequences. This effect is conserved across in vitro and in vivo models, highlighting the generalizability of the optimized Kozak sequence. These findings redefine the role of the Kozak sequence in synthetic mRNA design and demonstrate its substantial contribution to translation efficiency when optimized, enabling improved mRNA-based therapeutics.

Abstract Stereochemistry plays a crucial role in how molecules interact with complex physiological environments, affecting pharmacokinetics, pharmacodynamics, efficacy, and toxicity. Although these effects are well studied for small-molecular drugs, they are largely overlooked for supramolecular assemblies used in drug delivery. Even for lipid nanoparticles (LNPs)—the most advanced RNA delivery platform—stereochemical effects are rarely investigated and, when considered, are typically limited to the ionizable lipid rather than the overall stereochemical identity of the LNP. Here we separate the ionizable lipid cKK-E12 into its two stereoisomers ( trans : R,S / S,R ; cis : R,R / S,S ), which are normally used as a mixture. LNPs containing the cis isomer exhibit improved physicochemical properties, stability, and protein expression. By systematically varying the stereochemistry of the ionizable lipid, phospholipid, and cholesterol, we reveal stereochemistry-dependent differences in uptake and protein expression across six cell lines and in vivo in zebrafish embryos and mice. AI-assisted cryo-TEM analysis and SAXS link enhanced protein expression to structural differences, demonstrating control over internal lipid phases (lamellar and inverse hexagonal), influencing sample uniformity, and identifying stereochemical identity as a key determinant of functional RNA delivery.

Immune checkpoint inhibitors (ICIs), targeting checkpoint receptors such as programmed cell death protein 1 (PD-1), are associated with increased risk of cardiovascular events, but the underlying mechanisms remain poorly understood. Here we show that PD-1+ T cells from murine atherosclerotic aortas mainly display a progenitor exhausted phenotype (PD-1intSlamf6+Tim3−), produce IFNγ in vivo, exhibit signs of recent proliferation and maintain polyfunctionality. PD-1 blockade induced marked changes in plaque immune phenotype, with increased PD-1high T cell accumulation, IFNγ production, formation of lymphocyte foci and neutrophil recruitment. Depletion of PD-1high T cells prior to PD-1 blockade did not impede T cell recruitment, suggesting a role for progenitor exhausted PD-1int T cells in ICI-driven T cell plaque accumulation. Human circulating PD-1+ T cells produced IFNγ and were associated with subclinical coronary atherosclerosis. Our studies highlight IFNγ-producing PD-1+ T cells as a potential key immune cell population mediating increased cardiovascular risk in patients with cancer receiving ICI. Mulholland et al. identify progenitor exhausted T cells, expressing intermediate levels of PD-1 (PD-1int), as a prominent source of pro-inflammatory cytokines in the murine atherosclerotic aorta and potential cellular targets driving checkpoint inhibition-elicited pro-atherosclerotic immune responses. They further demonstrate elevated levels of circulating PD-1-expressing T cells in individuals with subclinical cardiovascular disease.

The clinical use of cancer vaccines is hampered by the low magnitude of induced T-cell responses and the need for repetitive antigen stimulation. Here, we demonstrate that liposomal formulations with incorporated STING agonists are optimally suited to deliver peptide antigens to dendritic cells in vivo and to activate dendritic cells in secondary lymphoid organs. One week after liposomal priming, systemic administration of peptides and a costimulatory agonistic CD40 antibody enables ultrarapid expansion of T cells, resulting in massive expansion of tumor-specific T cells in the peripheral blood two weeks after priming. In the MC-38 colon cancer model, this synthetic prime-boost regimen induces rapid regression and cure of large established subcutaneous cancers via the use of a single tumor-specific neoantigen. These experiments demonstrate the feasibility of liposome-based heterologous vaccination regimens to increase the therapeutic efficacy of peptide vaccines in the context of immunogenic adjuvants and costimulatory booster immunizations. Our results provide a rationale for the further development of modern liposomal peptide vaccines for cancer therapy.

Cardiovascular disease is the global number one cause of mortality and morbidity. The majority of cardiovascular diseases are caused by atherosclerosis, a lipid-driven, inflammatory disease of the middle- and large-sized arteries. The disease is characterized by the formation of atherosclerotic plaques throughout the arterial tree. Over the years, insights into the pathogenesis of atherosclerosis have shifted from a "lipid-driven" model to a "response-to-injury" perspective and more recently to a "lipid-driven inflammatory disease" viewpoint. We are now aware that a network of multiple immune cell types and subsets of the innate and adaptive immune system inhabit our arteries. Intricate interactions between these immune cell subsets, nonimmune cells, and local environmental substances such as lipids, cell debris, and calcium cause a fluidic balance of proinflammatory and regulatory responses. A dysregulation of this balance toward a proinflammatory milieu drives atherosclerotic disease progression. Although we have acknowledged that atherosclerosis is an inflammatory disease, state-of-the-art treatments are still based on lipid-lowering, antihypertensive, and lifestyle-changing strategies. In the past decade, clinical phase I, II, and III trials targeting the immune system revealed that patients tolerate immunotherapy, show decreased inflammation, and/or have a reduction in cardiovascular endpoints. However, the search for novel immunotherapeutic targets and treatment regimens as well as stratification of patients who would benefit from such treatments to combat atherosclerotic cardiovascular disease is only just beginning. In this review article, we will highlight the newest insights on the different cell subsets and components of the immune system in atherosclerosis and elaborate on current and future immunotherapeutics to treat atherosclerotic cardiovascular disease.

In vivo targeting of dendritic cells (DCs) with nanocarriers containing tolerogenic adjuvants is an attractive strategy to dampen inflammation. Here, we used ex vivo skin vaccination to examine the effect of intradermal injection of liposomes loaded with the tolerogenic adjuvants all-trans retinoic acid (RA) and vitamin D3 (VD3). We investigated the effect of intradermal liposome injection on skin DCs and the skin DC-induced T cell response. Our study shows that intradermal injection of RA or VD3-loaded anionic phospholipid 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) liposomes selectively induces CD14+ dermal DC (DDC) migration while reducing migration of CD1a dim DDCs. Migrated CD14+ DDCs displayed a partially immature phenotype. RA or VD3 liposome-treated CD1a dim DDCs exhibited reduced expression of maturation markers and induced expression of coinhibitory immunoglobulin-like transcript 3 (ILT3). VD3 liposome-treated CD14+ DDCs, as well as, CD1a dim DDCs, exhibited reduced expression of maturation markers, induction of coinhibitory molecules ILT3, and programmed death-ligand 1 (PD-L1). Migrated DCs from RA or VD3 liposome-injected skin differentiated naïve CD4+ T cells into FoxP3+ CD127 low and ICOS+ Tregs, expressing functional regulatory markers. Thus, our findings provide further substantiation for in vivo DC-modulating vaccines with tolerogenic liposomes as a putative clinical therapy for autoimmune diseases and allergies.

The active vitamin A metabolite, all-trans-retinoic acid (RA), primes precursor dendritic cells (DCs) into a mucosal phenotype with tolerogenic properties characterized by the expression of integrin CD103. CD103+ DCs can counteract pathogenic Th1 and Th17 in inflammatory bowel disease (IBD) or celiac disease (CD). Tolerogenic manipulation of DCs using nanoparticles carrying tolerogenic adjuvants and disease-specific antigens is a valuable treatment strategy to induce antigen-specific mucosal tolerance in vivo. Here, we investigated the effects of RA-loaded liposomes on human DC phenotype and function, including DC-driven T-cell development, both during the generation of monocyte-derived DCs (moDCs) as well as by priming immature moDCs. RA liposomes drove CD103+ DC differentiation as well as ALDH1A2 expression in DCs. Neutrophil-dependent Th17 cell development was reduced by RA-liposome-differentiated and RA-liposome-primed DCs. Moreover, RA liposome treatment shifted T-cell development toward a Th2 cell profile. Importantly, RA liposomes induced the development of IL-10-producing and FoxP3+ regulatory T cells (Tregs) of various Treg subsets, including ICOS+ Tregs, that were potent inhibitors of bystander memory T-cell proliferation. Taken together, RA-loaded liposomes could be a novel treatment avenue for IBD or CD patients.

Herein we report on the design, synthesis and biological evaluation of a series of nucleotide-binding oligomerization-domain-containing protein 2 (NOD2) desmuramylpeptide agonists. The structural prerequisites that shape both physicochemical and immunomodulatory profiles of desmuramylpeptide NOD2 agonists have been delineated. Within this context, we identified 3, a butyrylated desmuramylpeptide, as a potent in vitro NOD2 agonist (EC50 = 4.6 nM), exhibiting an almost 17-fold enhancement in potency compared to its unsubstituted counterpart 1 (EC50 = 77.0 nM). The novel set of desmuramylpeptides demonstrate unique in vitro immunomodulatory activities. They elicited cytokine production in peripheral blood mononuclear cells (PBMCs), both alone and in conjunction with lipopolysaccharide (LPS). The spermine-decorated 32 also stimulated the LPS-induced cytotoxic activity (2.95-fold) of PBMCs against K562 cancer cells. Notably, the cholesterol-conjugate 26 displayed anti-inflammatory actions, highlighted by its capacity to convert the inflammatory monocyte subset into an anti-inflammatory phenotype. Finally, the eicosapentaenoylated derivative 23 augmented antigen presentation by mouse bone marrow-derived dendritic cells (BMDCs), thus highlighting its potential as a vaccine adjuvant.

Purpose A dissolving microneedle array (dMNA) is a vaccine delivery device with several advantages over conventional needles. By incorporating particulate adjuvants in the form of poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) into the dMNA, the immune response against the antigen might be enhanced. This study aimed to prepare PLGA-NP-loaded dMNA and to compare T-cell responses induced by either intradermally injected aqueous-PLGA-NP formulation or PLGA-NP-loaded dMNA in mice. Methods PLGA NPs were prepared with microfluidics, and their physicochemical characteristics with regard to encapsulation efficiencies of ovalbumin (OVA) and CpG oligonucleotide (CpG), zeta potentials, polydispersity indexes, and sizes were analysed. PLGA NPs incorporated dMNA was produced with three different dMNA formulations by using the centrifugation method, and the integrity of PLGA NPs in dMNAs was evaluated. The immunogenicity was evaluated in mice by comparing the T-cell responses induced by dMNA and aqueous formulations containing ovalbumin and CpG (OVA/CpG) with and without PLGA NP. Results Prepared PLGA NPs had a size of around 100 nm. The dMNA formulations affected the particle integrity, and the dMNA with poly(vinyl alcohol) (PVA) showed almost no aggregation of PLGA NPs. The PLGA:PVA weight ratio of 1:9 resulted in 100% of penetration efficiency and the fastest dissolution in ex-vivo human skin (< 30 min). The aqueous formulation with soluble OVA/CpG and the aqueous-PLGA-NP formulation with OVA/CpG induced the highest CD4 + T-cell responses in blood and spleen cells. Conclusions PLGA NPs incorporated dMNA was successfully fabricated and the aqueous formulation containing PLGA NPs induce superior CD4 + and CD8 + T-cell responses.

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation Aging is an independent and dominant risk factor for atherosclerosis and is associated with a low-grade chronic inflammation termed inflammaging. This age-induced pro-inflammatory environment may have great impact on plaque-residing immune cells, including mast cells. Mast cells have been found to accumulate in the human atherosclerotic plaque upon disease progression and have been associated with plaque instability. However, it is currently unknown whether aging drives the pro-atherogenic effects of mast cells in atherosclerosis. To assess the effects of aging on mast cell phenotype, we examined mast cell populations in young and old male Ldlr-/- mice fed either a chow (CD) or Western-type (WD) diet. We observed a 6-fold increase in the number of mast cells in the aged atherosclerotic aorta compared to young (Y-CD: 4.5±0.7 vs. O-CD: 279.4±9 cells, p<0.01; Y-WD: 45.3±15.2 vs. O-CD: 279.4±9 cells, p<0.01). Furthermore, we detected a marked increase in activation status with age as shown by the significantly augmented number of CD63+ mast cells in the atherosclerotic aorta (Y-CD: 1.8±0.6 vs. O-CD: 259.7±85.4 cells, p<0.01; Y-WD: 41.3±13.6 vs. O-CD: 259.7±85.4 cells, p<0.01). In line, we identified that aged bone-marrow derived mast cells displayed elevated basal CD63 expression compared to young cells, indicative of intrinsic low-grade activation. Moreover, we demonstrated that aging increases the amount of MHCII+ mast cells in atherosclerosis, allowing them to act as antigen-presenting cells, which correspondingly led to increased CD4+ T cell proliferation in vitro (young: 35.2±1.2% vs. old: 45.8±1.2%, p<0.001). Finally, single-cell RNA sequencing of human atherosclerotic plaques confirmed mast cell-specific expression of MHC-II orthologs. To conclude, we established that aging induces phenotypic changes of mast cells in atherosclerosis, regarding both activation status and antigen presenting capacity, which can contribute to disease progression.

BACKGROUND: Tissue resident memory T (T RM ) cells are a T-cell subset that resides at the site of prior antigen recognition to protect the body against reoccurring encounters. Besides their protective function, T RM cells have also been implicated in inflammatory disorders. T RM cells are characterized by the expression of CD69 and transcription factors Hobit (homolog of Blimp-1 [B lymphocyte–induced maturation protein 1] in T cells) and Blimp-1. As the majority of T cells in the arterial intima expresses CD69, T RM cells may contribute to the pathogenesis of atherosclerosis as well. Here, we aimed to assess the presence and potential role of T RM cells in atherosclerosis. METHODS: To identify T RM cells in human atherosclerotic lesions, a single-cell RNA-sequencing data set was interrogated, and T-cell phenotypes were compared with that of integrated predefined T RM cells. The presence and phenotype of T RM in atherosclerotic lesions was corroborated using a mouse model that enabled tracking of Hobit-expressing T RM cells. To explore the function of T RM cells during atherogenesis, RAG1 −/− (recombination activating gene 1 deficient) LDLr −/− (low-density lipoprotein receptor knockout) mice received a bone marrow transplant from Hobit KO/CRE Blimp-1 flox/flox mice, which exhibit abrogated T RM cell formation, whereafter the mice were fed a Western-type diet for 10 weeks. RESULTS: Human atherosclerotic lesions contained T cells that exhibited a T RM cell–associated gene signature. Moreover, a fraction of these T cells clustered together with predefined T RM cells upon integration. The presence of Hobit-expressing T RM cells in the atherosclerotic lesion was confirmed in mice. These lesion-derived T RM cells were characterized by the expression of CD69 and CD49α. Moreover, we demonstrated that this small T-cell subset significantly affects lesion composition, by reducing the amount of intralesional macrophages and increasing collagen content. CONCLUSIONS: T RM cells, characterized by the expression of CD69 and CD49α, constitute a minor population in atherosclerotic lesions and are associated with increased lesion stability in a Hobit and Blimp-1 knockout mouse model.

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Research Council Veni grant. Netherlands Heart Foundation Atherosclerosis is characterized by inflammation and lipid accumulation, leading to complications such as stroke and myocardial infarction. Various macrophage subsets are present in human atherosclerotic plaques. However, it is unclear how subsets are interrelated and contribute to the disease process and its clinical outcomes. Here, we employed single-cell RNA-seq (scRNA-seq) on blood and plaque material from carotid endarterectomy patients enrolled in the AtheroExpress (AE) cohort to define regulatory pathways of macrophage recruitment, differentiation, and development. Additionally, we used these scRNA-seq data to deconvolute a large AE bulk RNA-seq cohort to allow correlating cellular subsets in plaques with clinical traits. Interestingly, we found that macrophages and their subsets are the only cell population significantly associated with major adverse cardiac events (MACE) during a 3-year follow-up period. Subsequently, we could divide plaque macrophages into 3 populations: inflammatory, tissue-resident / lipid-associated (TREM2 high), and foamy macrophages (TREM1 high). While the latter two are correlated with MACE, the inflammatory macrophages are inversely correlated with statin use. Cellular fate analyses revealed two major paths of macrophage development in the plaque. First, non-classical monocytes entering the plaque, turning into inflammatory cells before becoming foamy and eventually dying. Second, resident-like macrophages that turn into either inflammatory- or lipid-associated macrophages, before meeting their foamy demise. Together, these findings provide important insights on macrophages in atherosclerosis and suggest new leads to discover therapeutic targets for this disease.

Aims The interleukin-1 receptor accessory protein (IL1RAP) is a co-receptor required for signalling through the IL-1, IL-33, and IL-36 receptors. Using a novel anti-IL1RAP-blocking antibody, we investigated the role of IL1RAP in atherosclerosis.Methods and results Single-cell RNA sequencing data from human atherosclerotic plaques revealed the expression of IL1RAP and several IL1RAP-related cytokines and receptors, including IL1B and IL33. Histological analysis showed the presence of IL1RAP in both the plaque and adventitia, and flow cytometry of murine atherosclerotic aortas revealed IL1RAP expression on plaque leucocytes, including neutrophils and macrophages. High-cholesterol diet fed apolipoprotein E-deficient (Apoe-/-) mice were treated with a novel non-depleting IL1RAP-blocking antibody or isotype control for the last 6 weeks of diet. IL1RAP blockade in mice resulted in a 20% reduction in subvalvular plaque size and limited the accumulation of neutrophils and monocytes/macrophages in plaques and of T cells in adventitia, compared with control mice. Indicative of reduced plaque inflammation, the expression of several genes related to leucocyte recruitment, including Cxcl1 and Cxcl2, was reduced in brachiocephalic arteries of anti-IL1RAP-treated mice, and the expression of these chemokines in human plaques was mainly restricted to CD68+ myeloid cells. Furthermore, in vitro studies demonstrated that IL-1, IL-33, and IL-36 induced CXCL1 release from both macrophages and fibroblasts, which could be mitigated by IL1RAP blockade.Conclusion Limiting IL1RAP-dependent cytokine signalling pathways in atherosclerotic mice reduces plaque burden and plaque inflammation, potentially by limiting plaque chemokine production. Graphical Abstract