Microbiome-modulated immunotherapy in oncology: Current applications and future prospects.

Like other Gram-negative pathogens, Vibrio cholerae, the causative agent of the diarrheal disease cholera, secretes outer membrane vesicles (OMVs). OMVs are complex entities composed of a subset of envelope lipid and protein components and play a role in the delivery of effector molecules to host cells. We previously showed that V. cholerae O395 cells secrete OMVs that are internalized by host cells, but their role in pathogenesis has not been well elucidated. In the present study, we evaluated the interaction of OMVs with intestinal epithelial cells. These vesicles induced expression of proinflammatory cytokines such as IL-8 and GM-CSF and chemokines such as CCL2, CCL20, and thymic stromal lymphopoietin in epithelial cells through activation of MAPK and NF-κB pathways in NOD1-dependent manner. Epithelial cells stimulated with OMVs activated dendritic cells (DCs) in a direct co-culture system. Activated DCs expressed high levels of co-stimulatory molecules; released inflammatory cytokines IL-1β, IL-6, TNF-α, and IL-23 and chemokines CCL22 and CCL17; and subsequently primed CD4(+) T cells leading to IL-4, IL-13, and IL-17 expression. These results suggest that V. cholerae O395 OMVs modulate the epithelial proinflammatory response and activate DCs, which promote T cell polarization toward an inflammatory Th2/Th17 response.

Bacterial Outer Membrane Vesicles from Dextran Sulfate Sodium-Induced Colitis Differentially Regulate Intestinal UDP-Glucuronosyltransferase 1A1 Partially Through Toll-Like Receptor 4/Mitogen-Activated Protein Kinase/Phosphatidylinositol 3-Kinase Pathway.

Microbiota and cancer immunotherapy: Mechanisms, clinical implications, and precision therapeutics.

<p indent="0mm">Sepsis is a life-threatening disease that characterized by systemic inflammatory response and multiple organ dysfunction and mostly caused by Gram-negative bacterial infections. Outer membrane vesicles (OMVs) are multifunctional spherical structures <sc>(10−300 nm)</sc> released from outer membrane of Gram-negative bacteria. Usually, OMVs carry a variety of virulence factors and pathogen-associated molecular patterns (PAMPs), such as toxins, digestive enzymes, lipopolysaccharide (LPS), peptidoglycan, bacterial DNA, etc. Roles of OMVs in bacterial survival include nutrient acquisition, bacterial biofilm formation, antibiotic resistance delivery, and killing of competing microbes. In the pathogenesis of sepsis, OMVs have versatile effects on host cells (such as epithelial cells, immune cells, endothelial cells and platelets, etc.), causing the immune response out of control and the positive feedback loop of inflammation and coagulation formed, which ultimately leading to the systemic inflammatory response and multiple organ dysfunction. Pathogenic effects of OMVs are versatile, including adhesion of host cells, delivery of virulence factors and PAMPs, promotion of inflammatory and immune responses, and facilitation of bacteria survival in the host. Moreover, the main mechanism of bacterial OMVs invading host cells and causing sepsis is related to the recognition of their carried PAMPs with pattern recognition receptors (PRRs) of host cells, including Toll-like receptors (TLRs) on the surface of cell membrane, NOD-like Receptors (NLRs) and cysteinyl aspartate specific proteinases (Caspases) in the cytoplasm. Here, we will briefly introduce the structure composition, biosynthesis and functions of OMVs, particularly focuses on the pathogenic roles of OMVs in the occurrence of sepsis. In addition, the coping strategies of bacterial OMVs in sepsis have been recently investigated since OMVs can carry and transmit a variety of virulence factors. Firstly, OMVs vaccines can prevent the bacterial infection and reduce the OMVs production from the source. Secondly, therapeutic molecules, such as antimicrobial peptides and polymyxin B, can target LPS directly, the common toxic component of bacterial out membranes, and other drugs using TLR4 and Caspase-4/5/11 as targets, also have therapeutic potential to block the inflammatory pathways activated by LPS. Recently, the new drug screening system was established based on bacterial OMVs directly. The treatment effects of the existing drugs for sepsis, including blocking the release of inflammatory factors induced by OMVs, and alleviating the clinical symptoms of sepsis, were reevaluated. Cationic antimicrobial polymers could adsorb the anionic groups of bacterial membrane through the electrostatic interaction, followed by inserting the phospholipid bilayer to destroy the integrity of bacterial membrane and ultimately kill bacteria. Based on the outer membrane structure characteristics of bacterial OMVs (the outmost LPS with more negative charges, toxic protein components, and the inner phospholipid layer with hydrophobicity), the development of cationic antibacterial materials with the integrated function of adsorption and removal of OMVs is feasible to prevent sepsis and other bacterial infection related diseases. Recently, our team designed and synthesized a series of cationic antibacterial polymers, and observed the adsorption capacity of different polymer surfaces to the OMVs of <italic>Pseudomonas aeruginosa</italic> by electron microscopy. The results confirmed that both the cationic polymer membrane and the cation-modified polyurethane foam could adsorb the OMVs. However, the antimicrobial polymers have the possibility to stimulate the release of bacterial OMVs. Therefore, the simultaneous effects of cationic polymers with antimicrobial activities need to be investigated on the release and removal of OMVs in future studies. This review briefly introduces the structural composition, biosynthesis and functions of OMVs, particularly focuses on the pathogenic roles of OMVs in the occurrence of sepsis, and the corresponding coping strategies for the clinical prevention and treatment of sepsis.

Immune checkpoint inhibitors (ICIs) have revolutionized the field of oncology since the last decade. However, heterogeneous treatment responses among patients and immune-related adverse effects (irAEs) are critical challenges and limitations in current clinical practice. Emerging studies have now indicated that microbiota may influence the clinical responses and toxicity of cancer therapy across multiple cancer types. Early evidence has demonstrated promising results by manipulating the gut microbial composition via faecal microbiota transplantation (FMT) to improve immunotherapeutic efficacy. This chapter will start from the basics by exploring the mechanisms of pharmacomicrobiomics interactions in the context of ICIs, which can be summarised by the “TIME” mechanistic framework—T cell modulation, innate immunity, metabolites & molecular mimicry, and epithelial injury. The chapter will further discuss the translational potential of these laboratory findings in clinical settings for truly benefiting cancer patients. Gut microbial features can potentially be predictive biomarkers for therapeutic responses, guiding treatment selection for patients. Importantly, unlike host genetics, the gut microbial composition can be easily modified by prebiotics, probiotics, antibiotics, dietary modulations, and FMT, which serves as a potential strategy to augment cancer therapeutic responses and toxicity. Pharmacomicrobiomics may play an essential role in future cancer therapeutic interventions opening a new avenue for precision medicine in oncology.KeywordsGut microbiotaImmunotherapyPharmacomicrobiomicsMicrobiota modulation

Bacterial outer membrane vesicles (OMVs) have emerged as promising vehicles for anticancer drug delivery due to their inherent tumor tropism, immune-stimulatory properties, and potential for functionalization with therapeutic proteins. Despite their advantages, the high lipopolysaccharide (LPS) endotoxin content in the OMVs raises significant safety and regulatory challenges. In this work, we produce LPS-attenuated and LPS-free OMVs and systematically assess the effects of LPS modification on OMVs' physicochemical characteristics, membrane protein content, immune-stimulatory capacity, tolerability, and anticancer efficacy. Our findings reveal that LPS removal increased the maximal tolerated dose of the OMVs by over 25-fold. When adjusted for comparable safety profiles, LPS-free OMVs exhibit superior anticancer effects compared with wild-type OMVs. Mechanistic investigations indicate that the LPS removal obviates immune cell death caused by LPS and reduces the negatory effects of wild type of OMVs on tumor immune cell infiltrates. We further show the functionality of the LPS-free OMV through the incorporation of an IL-2 variant protein (Neo-2/15). This functionalization augments OMV's ability of the OMV to inhibit tumor growth and promote lymphocyte infiltration into the tumor microenvironment. This study presents a safe and functionalizable OMV with improved translational prospect.

Neisseria gonorrhoeae is a strict human pathogen that causes the sexually transmitted disease gonorrhoea, which affects approximately 106 million people worldwide. It has evolved a diverse range of strategies to establish long-term colonisation of the human mucosal surfaces. Importantly, N. gonorrhoeae resists clearance by innate immune cells, such as macrophages, which can result in sustained inflammation, tissue damage, and bacterial dissemination. The underlying molecular mechanism of innate immune evasion remains largely unknown, given that there is little evidence that N. gonorrhoeae secrete effector proteins to modulate host cell responses. The major focus of the work described in this thesis was to determine how N. gonorrhoeae controls macrophage immune responses. In particular, I focused on the role of outer membrane vesicles (OMVs) that are shed by an increasing number of bacteria, enabling potential communication with host cells. In chapter 3 of this thesis, I was able to establish a method that allowed me to isolate highly purified OMVs from N. gonorrhoeae. Using quantitative proteomic approaches, I determined that the protein content of purified N. gonorrhoeae OMVs is enriched for outer-membrane proteins, whereby the porin PorB is the most abundant protein, constituting 35 % of the total OMV proteome. Purified OMVs also contained proteins known to be important for N. gonorrhoeae virulence, such as opacity proteins, but also proteins that may affect vesicle formation (NlpD, AmiC, and RmpM) as well as several uncharacterised proteins. In contrast, traditional purification of OMVs resulted in crude preparations that contained numerous cytosolic proteins. PorB has previously been shown to damage the mitochondria of host cells during infection, but the trafficking route from the outer-membrane of N. gonorrhoeae has never been characterised. In Chapter 3, I have now described the cellular route of PorB, which includes the uptake of OMVs by bone marrow-derived macrophages (BMDMs) and trafficking of PorB to mitochondria. In confocal and single molecule localisation microscopy, PorB co-localised to the mitochondrial outer-membrane marker, Tom20. Furthermore, N. gonorrhoeae secreted OMVs induce apoptotic cell death in macrophages, as evidenced by the release of mitochondrial cytochrome c and caspase activation, which followed localisation of PorB to mitochondria. In addition to PorB, host factors also regulate macrophage apoptosis. In this context, I have now shown for the first time that OMVs can induce rapid extrinsic apoptosis dependent on caspase-8 (Chapter 3). In addition, the pro-survival protein BCL-XL prevented OMV-induced intrinsic apoptosis (Chapter 3). Finally, I have uncovered a novel of the pro-apoptotic MCL-1S as an essential host factor that regulates macrophage apoptosis in response to N. gonorrhoeae OMVs (Chapter 3). Little is known about how Gram-negative bacteria regulate OMV biogenesis. The proteome of N. gonorrhoeae OMVs contains several proteins that may directly, or indirectly, affect OMV biogenesis. In Chapter 4, I have focused on the proteins TsaP, NlpD, FtsN, AmiC. HldA and GmhB, which are thought to function in peptidoglycan (PG) binding, cell division, and lipid chain biosynthesis, and may thus regulate OMV abundance. To directly test this, defined genetic mutants of N. gonorrhoeae were generated and OMV biogenesis was determined. By electron microscopy, I identified that loss of AmiC and NlpD induced hyper-blebbing cellular morphology, resulting in increased levels of OMVs compared to wild-type. Given that there is great interest in developing a vaccine against N. gonorrhoeae based on naturally produced OMVs, these genetically-engineered hyper-blebbing mutants may enable more effective vaccine approaches. Thus, the molecular characterisation of OMVs coupled with the identification of their roles in N. gonorrhoeae infection may open up new strategies to improve immune clearance of Neisseria, as well as dampen inflammatory responses, both of which are of interest in the treatment of gonococcal-induced sexually transmitted infections.

Objective Gastrointestinal (GI) tract, like other mucosal surface, is colonized with a microbial population known as gut microbiota. Outer membrane vesicles (OMVs) which are produced by gram negative bacteria could be sensed by Toll like receptors (TLRs). The interaction between gut microbiota and TLRs affects homeostasis and immune responses. In this study, we evaluated TLR2, TLR4 genes expression and cytokines concentration in Caco-2 cell line treated with Bacteroides fragilis (B. fragilis) and its OMVs. Materials and Methods In this experimental study, OMVs were extracted using sequential centrifugation and their physicochemical properties were evaluated as part of quality control assessment. Caco-2 cells were treated with B. fragilis and its OMVs (180 and 350 µg/ml). Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was performed to assess TLR2 and TLR4 mRNA expression levels. Pro-inflammatory (IFNᵧ) and anti-inflammatory (IL- 4 and IL-10) cytokines were evaluated by ELISA. Results B. fragilis significantly decreased TLR2 and slightly increased TLR4 mRNA levels in Caco-2 cell line. The TLR2 mRNA level was slightly increased at 180 and 350 µg/ml of OMVs. Conversely, the TLR4 mRNA level was decreased at 180 µg/ml of OMVs, while it was significantly increased at 350 µg/ml of OMVs. Furthermore, B. fragilis and its OMVs significantly increased and decreased IFNᵧ concentration, respectively. Anti-inflammatory cytokines were increased by B. fragilis and its OMVs. ConclusionB. fragilis and its OMVs have pivotal role in the cross talk between gut microbiota and the host especially in the modulation of the immune system. Based on the last studies on immunomodulatory effect of B. fragilis derived OMVs on immune cells and our results, we postulate that B. fragilis derived OMVs could be possible candidates for the reduction of immune responses.

Bacterial outer membrane vesicles (OMVs) are naturally produced by all Gram-negative bacteria and, thanks to their plasticity and unique adjuvanticity, are emerging as an attractive vaccine platform. To test the applicability of OMVs in cancer immunotherapy, we decorated them with either one or two protective epitopes present in the B16F10EGFRvIII cell line and tested the protective activity of OMV immunization in C57BL/6 mice challenged with B16F10EGFRvIII. The 14 amino acid B cell epitope of human epidermal growth factor receptor variant III (EGFRvIII) and the mutation-derived CD4+ T cell neo-epitope of kif18b gene (B16-M30) were used to decorate OMVs either alone or in combination. C57BL/6 were immunized with the OMVs and then challenged with B16F10EGFRvIII cells. Immunogenicity and protective activity was followed by measuring anti-EGFRvIII antibodies, M30-specific T cells, tumor-infiltrating cell population, and tumor growth. Immunization with engineered EGFRvIII-OMVs induced a strong inhibition of tumor growth after B16F10EGFRvIII challenge. Furthermore, mice immunized with engineered OMVs carrying both EGFRvIII and M30 epitopes were completely protected from tumor challenge. Immunization was accompanied by induction of high anti-EGFRvIII antibody titers, M30-specific T cells, and infiltration of CD4+ and CD8+ T cells at the tumor site. OMVs can be decorated with tumor antigens and can elicit antigen-specific, protective antitumor responses in immunocompetent mice. The synergistic protective activity of multiple epitopes simultaneously administered with OMVs makes the OMV platform particularly attractive for cancer immunotherapy.

The role of gut microbiota and its products in human health and disease is profoundly investigated. The communication between gut microbiota and the host involves a complicated network of signaling pathways via biologically active molecules generated by intestinal microbiota. Some of these molecules could be assembled within nanoparticles known as outer membrane vesicles (OMVs). Recent studies propose that OMVs play a critical role in shaping immune responses, including homeostasis and acute inflammatory responses. Moreover, these OMVs have an immense capacity to be applied in medical research, such as OMV-based vaccines and drug delivery. This review presents a comprehensive overview of emerging knowledge about biogenesis, the role, and application of these bacterial-derived OMVs, including OMV-based vaccines, OMV adjuvants characteristics, OMV vehicles (in conjugated vaccines), cancer immunotherapy, and drug carriers and delivery systems. Moreover, we also highlight the significance of the potential role of these OMVs in diagnosis and therapy.

ABSTRACTOuter membrane vesicles (OMVs) are spontaneously released by Gram-negative bacteria, including Actinobacillus pleuropneumoniae, which causes contagious pleuropneumonia in pigs and leads to considerable economic losses in the swine industry worldwide. A. pleuropneumoniae OMVs have previously been demonstrated to contain Apx toxins and proteases, as well as antigenic proteins. Nevertheless, comprehensive characterizations of their contents and interactions with host immune cells have not been made. Understanding the protein compositions and immunomodulating ability of A. pleuropneumoniae OMVs could help illuminate their biological functions and facilitate the development of OMV-based applications. In the current investigation, we comprehensively characterized the proteome of native A. pleuropneumoniae OMVs. Moreover, we qualitatively and quantitatively compared the OMV proteomes of a wild-type strain and three mutant strains, in which relevant genes were disrupted to increase OMV production and/or produce OMVs devoid of superantigen PalA. Furthermore, the interaction between A. pleuropneumoniae OMVs and porcine alveolar macrophages was also characterized. Our results indicate that native OMVs spontaneously released by A. pleuropneumoniae MIDG2331 appeared to dampen the innate immune responses by porcine alveolar macrophages stimulated by either inactivated or live parent cells. The findings suggest that OMVs may play a role in manipulating the porcine defense during the initial phases of the A. pleuropneumoniae infection.IMPORTANCE Owing to their built-in adjuvanticity and antigenicity, bacterial outer membrane vesicles (OMVs) are gaining increasing attention as potential vaccines for both human and animal use. OMVs released by Actinobacillus pleuropneumoniae, an important respiratory pathogen in pigs, have also been investigated for vaccine development. Our previous studies have shown that A. pleuropneumoniae secretes OMVs containing multiple immunogenic proteins. However, immunization of pigs with these vesicles was not able to relieve the pig lung lesions induced by the challenge with A. pleuropneumoniae, implying the elusive roles that A. pleuropneumoniae OMVs play in host-pathogen interaction. Here, we showed that A. pleuropneumoniae secretes OMVs whose yield and protein content can be altered by the deletion of the nlpI and palA genes. Furthermore, we demonstrate that A. pleuropneumoniae OMVs dampen the immune responses in porcine alveolar macrophages stimulated by A. pleuropneumoniae cells, suggesting a novel mechanism that A. pleuropneumoniae might use to evade host defense.

In recent years, cancer immunotherapy has undergone a transformative shift toward personalized and targeted therapeutic strategies. Bacteria-derived outer membrane vesicles (OMVs) have emerged as a promising and adaptable platform for cancer immunotherapy due to their unique properties, including natural immunogenicity and the ability to be engineered for specific therapeutic purposes. In this review, a comprehensive overview is provided of state-of-the-art techniques and methodologies employed in the engineering of versatile OMVs for cancer immunotherapy. Beginning by exploring the biogenesis and composition of OMVs, unveiling their intrinsic immunogenic properties for therapeutic appeal. Subsequently, innovative approaches employed to engineer OMVs are delved into, ranging from the genetic engineering of parent bacteria to the incorporation of functional molecules. The importance of rational design strategies is highlighted to enhance the immunogenicity and specificity of OMVs, allowing tailoring for diverse cancer types. Furthermore, insights into clinical studies and potential challenges utilizing OMVs as cancer vaccines or adjuvants are also provided, offering a comprehensive assessment of the current landscape and future prospects. Overall, this review provides valuable insights for researchers involved in the rapidly evolving field of cancer immunotherapy, offering a roadmap for harnessing the full potential of OMVs as a versatile and adaptable platform for cancer treatment.

Outer membrane vesicles (OMVs), originating from the outermost membrane of cells, are the extracellular vesicles released by bacteria, containing bacterial outer membrane components such as phospholipids, lipopolysaccharides (LPS), outer membrane proteins, and bacteria-specific antigens. OMVs have progressively been acknowledged as a novel secretory system, playing a pivotal role in mediating bacterial infections and modulating host immune responses. They are anticipated to emerge as a promising therapeutic target for the intervention of bacterial infectious diseases in the future. Based on this, the present article provides a comprehensive review of the role of OMVs in bacterial infections and immune modulation. This article summarizes that OMVs can mediate bacterial infections by transporting virulence genes and antibiotic resistance genes, as well as by carrying pathogen-associated molecular patterns (PAMPs). Additionally, they modulate host immune functions through direct interactions with immune cells such as neutrophils, macrophages, and dendritic cells. Furthermore, OMVs can facilitate bacterial immune evasion by modulating biofilm formation, resisting host antimicrobial peptides, and inhibiting the functionality of the complement system. Given that OMVs are non-replicative and contain a wealth of bacterial antigens, coupled with their ability to effectively activate the immune system, they are regarded as highly promising vaccine candidates. This article concludes by summarizing the concepts and strategies for developing vaccines based on OMVs. It is anticipated that this article will provide a more comprehensive understanding of the role of OMVs in research related to bacterial infectious diseases.

Background: Several trials combining microbiome-based interventions with immune checkpoints inhibitors (ICI) are currently underway. Previous studies showed the potential of fecal microbiota transplant (FMT) to circumvent secondary anti-PD-1 resistance or improve first-line anti-PD-1 response in patients with advanced melanoma. Whether FMT can be used safely in combination with anti-PD-1/anti-CTLA-4 (dual ICI) and its impact on the microbiome composition remain unknown. Here, we report results from combining FMT with dual ICI in previously untreated patients (pts) with advanced melanoma (NCT04951583). Methods: 20 pts with previously untreated advanced melanoma were included. FMT from healthy donors was administered in oral capsules after bowel preparation 1 week prior to start of dual ICI. A total of 6 different donors were used. The primary endpoint was safety. Secondary endpoints included objective response rate (ORR) and microbiome shift using shotgun metagenomic sequencing. Longitudinal serum Il1rl1 gene product (sST2) epithelial integrity marker was measured. Stool from pts before and after FMT were transplanted into avatar mice (MCA-205 or B16 OVA) and then treated with dual ICI. Results: In the 20 pts enrolled, 13 (65%) were male and median age was 56. Median follow-up was 6 months (range (IQR) 3.23; 12.33). FMT alone resulted in grade 1 toxicities. Grade 1-2 immune related adverse event (irAE) occurred in 80% of pts and 65% developed grade &amp;gt;3 irAE. Diarrhea or colitis was the most frequent grade 3 irAE occurring in 4 (20%). 2 pts developed myocarditis (grade 3 and grade 4, respectively). 6 (30%) pts completed all 4 cycles of dual ICI. 6 (43%) pts that developed irAE grade 3 received FMT from the same donor. ORR was 70% (2 complete responses (CR) and 12 partial responses (PR)). Two pts died; one from unknown cause in PR and one from disease progression. Microbiome profiling beta-diversity analyses revealed separate clustering of responders (R) and non-responders (NR) post-FMT (p=0.024). We observed an enrichment of Prevotella copri, Ruminoccocaceae and Eubacterium in R pts post-FMT. Pts who developed colitis were found to have a higher level of sST2 in plasma 1 week after FMT in comparison to those who did not develop colitis (p&amp;lt;0.05). In both avatar murine tumor models, microbiome composition with R pts’ feces (without ICI) 1 month post-FMT had reduced tumor growth compared to those treated with respective NR pt feces. Additionally, dual ICI led to significantly improved tumor control in mice treated with R pts’ feces post-FMT(p&amp;lt;0.005). Conclusions: The addition of FMT to dual ICI resulted in significant irAEs that occurred earlier, although the proportion was similar to previously described literature, with encouraging ORR. Metagenomic analysis depicted differences in the microbiome profiles of R compared to NR pts post FMT. These results support the study of FMT and immunotherapy in the randomized setting. Citation Format: Sreya Duttagupta, Meriem Messaoudene, Rahima Jamal, Catalin Mihalcioiu, Karl Belanger, John Lenehan, Wiam Belkaid, Seema Nair Parvathy, Jade Maillou, Yongjia Hu, Mayra Ponce, Taiki Hakozaki, Eder Mendez Salazar, Michael Silverman, Saman Maleki Vareki, Arielle Elkrief, Bertrand Routy. Phase II trial of fecal microbiota transplantation in combination with ipilimumab and nivolumab in patients with advanced cutaneous melanoma (FMT-LUMINate trial) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT258.

Bacterial outer membrane vesicles (OMVs), naturally released by Gram-negative bacteria, are a type of lipid bilayer nanoparticles containing many components found within the parent bacterium. Despite OMVs were first considered mere by-products of bacterial growth, recent studies have shown them as a highly adaptable platform for tumor vaccine. Here, we first demonstrate the biogenesis of OMVs, then review the strong immunogenicity of OMVs as an immune adjuvant in tumor vaccine and its excellent vaccine delivery capability, and finally discuss OMVs' engineering potentials through summarizing recent scientific advancements in genetic engineering, chemical modification, and nanotechnology. We also point out the clinical trials and future challenges of OMV-based vaccine. Overall, this review offers valuable insights into cancer immunotherapy, providing a roadmap for leveraging OMVs as a versatile platform for next-generation cancer vaccines.