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Outer membrane vesicles (OMVs) are vesicular nano-particles produced by Gram-negative bacteria that are recently being explored as vaccine vector. The fact that OMVs can be efficiently produced by a hypervesiculating Salmonella typhimurium strain, are packed with naturally-occurring adjuvants like lipopolysaccharides (LPS), and can be engineered to express any antigen of choice, makes them ideal candidates for vaccinology. However, it is unclear whether OMVs induce dendritic cell (DC)-mediated antigen-specific T cell responses and how immune activation is coordinated. Here, we show that OMVs induce maturation of human monocyte-derived DCs, murine bone marrow-derived DCs and CD11c+ splenic DCs. OMV-induced DC maturation was dependent on the presence of LPS and the myeloid differentiation primary response 88 (MyD88) adapter protein downstream of toll-like receptor signaling. Importantly, OMVs did not induce pyroptosis/cell death, but instead provided a significant survival benefit in DCs over non-stimulated DCs. OMVs displaying a sizeable ovalbumin fragment at the vesicle surface induce potent cross-presentation in BMDCs and splenic CD11c+ DCs to OTI CD8+ T cells, dependent on MyD88. Interestingly, the OMV-induced preference to cross-presentation was only partly dependent on the BATF3-dependent CD8a+ professional cross-presenting DC subset. Hence, an OMV-specific programming of DCs that induces maturation and provides a survival benefit for antigen presentation to T cells is identified. Additionally, for the first time, antigen-specific and potent cross-presentation of antigen-loaded OMVs to CD8+ T cells is demonstrated. These data provide mechanistical insight into the processes needed for the DC-mediated cross-presentation of OMV-derived antigens to CD8+ T cells with implications for therapeutic strategies. Bacteria are primarily known to cause disease. However, recent research has focused on using engineered bacteria and its byproducts as vaccine agents. In particular, outer membrane vesicles (OMVs) have shown promise in eliciting potent immunity against a variety of pathogens. While most vaccines rely on the generation of antibodies, the control of viral replication and tumor growth is driven by cytotoxic CD8+ T cells induced by dendritic cells (DCs). As such, there is a dire need for vaccines that use DCs to elicit CD8+ T cell responses. Studying OMVs as engineered biomaterial and its interaction with DCs allows tailored induction of immunity. This study includes important findings on OMV-dendritic cell interactions and for the first time supports OMVs as vehicles for the induction of antigen-specific CD8+ T cell responses. Additionally, important mechanistical insight into the molecular pathways needed for the cross-presentation of OMV-derived antigens to CD8+ T cells is provided. [ABSTRACT FROM AUTHOR]

Background: Emerging evidence suggests that peripheral immunity plays an important role in the progression of Alzheimer's disease (AD) (Gate et al., 2020). However, more understanding on how peripheral immune cells respond to AD pathology is needed before utilizing the immune system further for early diagnosis and therapeutic treatment. Here, we aimed to map the immune system in the early stages of amyloidosis. In addition, we aimed to characterize the aged immune system and to study the effect of age‐related circulating immune factors on the immune response. Method: We used 6‐month‐old APPswe/PS1dE9 (APP/PS1) transgenic and wild type (WT) mice to study the immune response to amyloid‐beta pathology and 20 month‐old WT mice for characterization of the aged immune system. In addition, both 6‐month‐old WT and APP/PS1 mice received multiple injections with aged blood plasma derived from 20‐month‐old WT mice. Next, immunohistochemical and high‐dimensional single‐cell analysis using time‐of‐flight mass cytometry (CyTOF), allowing detection of different immune populations and their activation status, was performed to map the circulating and brain‐resident immune cells in the different conditions (Figure 1). Result: Immunohistochemical analysis revealed that T cell infiltration in the 6‐month‐old APP/PS1 brain coincided with early amyloid‐beta plaque formation. Single cell analysis of circulating and brain‐resident immune cells of APP/PS1 mice showed that especially T cells clustered in different cell‐subsets and had increased expression of activation and cell‐adhesion molecules compared to young WT mice. In contrast, circulating and brain‐resident T cells of aged mice contained more regulatory cell subsets and increasingly expressed molecules involved in immune inhibition. Interestingly, initial analysis revealed that injections with aged WT blood plasma partially reduced the aforementioned differences in T cells between young WT and APP/PS1 mice. Conclusion: We found that circulating and brain‐resident T cells were different in their subsets and expression profile in early amyloid‐beta accumulation and in aging. In addition, the activation status of APP/PS1‐derived T cells was reduced after exposure to aged WT blood plasma resulting in a T‐cell signature more similar to young WT mice. Currently, we are further investigating the peripheral immune response to amyloid‐beta pathology by lipid‐ and RNA profiling of the circulating immune cells. [ABSTRACT FROM AUTHOR]