Circumventing pyroptosis via hyperactivation shapes superior immune responses of human type 2 dendritic cells compared to type 3 dendritic cells

Strategies of bacterial detection by inflammasomes

Mammalian innate immunity is regulated by pattern-recognition receptors (PRRs) and guard proteins, which use distinct strategies to detect infections. PRRs detect bacterial molecules directly, whereas guards detect host cell manipulations by microbial virulence factors. Despite sensing infection through different mechanisms, both classes of innate immune sensors can activate the inflammasome, an immune complex that can mediate cell death and inflammation. Inflammasome-mediated immune responses are crucial for host defense against many bacterial pathogens and prevent invasion by non-pathogenic organisms. In this review, we discuss the mechanisms by which inflammasomes are stimulated by PRRs and guards during bacterial infection, and the strategies used by virulent bacteria to evade inflammasome-mediated immunity.

Straight to the point: targeted mRNA-delivery to immune cells for improved vaccine design

With the deepening of our understanding of adaptive immunity at the cellular and molecular level, targeting antigens directly to immune cells has proven to be a successful strategy to develop innovative and potent vaccines. Indeed, it offers the potential to increase vaccine potency and/or modulate immune response quality while reducing off-target effects. With mRNA-vaccines establishing themselves as a versatile technology for future applications, in the last years several approaches have been explored to target nanoparticles-enabled mRNA-delivery systems to immune cells, with a focus on dendritic cells. Dendritic cells (DCs) are the most potent antigen presenting cells and key mediators of B- and T-cell immunity, and therefore considered as an ideal target for cell-specific antigen delivery. Indeed, improved potency of DC-targeted vaccines has been proved in vitro and in vivo. This review discusses the potential specific targets for immune system-directed mRNA delivery, as well as the different targeting ligand classes and delivery systems used for this purpose.

Targeting innate immune pathways for cancer immunotherapy

The innate immune system is critical for inducing durable and protective T cell responses to infection and has been increasingly recognized as a target for cancer immunotherapy. In this review, we present a framework wherein distinct innate immune signaling pathways activate five key dendritic cell activities that are important for T cell-mediated immunity. We discuss molecular pathways that can agonize these activities and highlight that no single pathway can agonize all activities needed for durable immunity. The immunological distinctions between innate immunotherapy administration to the tumor microenvironment versus administration via vaccination are examined, with particular focus on the strategies that enhance dendritic cell migration, interferon expression, and interleukin-1 family cytokine production. In this context, we argue for the importance of appreciating necessity vs. sufficiency when considering the impact of innate immune signaling in inflammation and protective immunity and offer a conceptual guideline for the development of efficacious cancer immunotherapies.

Unconventional protein secretion by gasdermin pores

Unconventional protein secretion (UPS) allows the release of specific leaderless proteins independently of the classical endoplasmic reticulum (ER)-Golgi secretory pathway. While it remains one of the least understood mechanisms in cell biology, UPS plays an essential role in immunity as it controls the release of the IL-1 family of cytokines, which coordinate host defense and inflammatory responses. The unconventional secretion of IL-1β and IL-18, the two most prominent members of the IL-1 family, is initiated by inflammasome complexes - cytosolic signaling platforms that are assembled in response to infectious or noxious stimuli. Inflammasomes activate inflammatory caspases that proteolytically mature IL-1β/- 18, but also induce pyroptosis, a lytic form of cell death. Pyroptosis is caused by gasdermin-D (GSDMD), a member of the gasdermin protein family, which is activated by caspase cleavage and forms large β-barrel plasma membrane pores. This pore-forming activity is shared with other family members that are activated during infection or upon treatment with chemotherapy drugs. While the induction of cell death was assumed to be the main function of gasdermin pores, accumulating evidence suggests that they have also non-lytic functions, such as in the release of cytokines and alarmins, or in regulating ion fluxes. This has raised the possibility that gasdermin pores are one of the main mediators of UPS. Here, I summarize and discuss new insights into gasdermin activation and pore formation, how gasdermin pores achieve selective cargo release, and how gasdermin pore formation and ninjurin-1-driven plasma membrane rupture are executed and regulated.