Mucosal-associated invariant T (MAIT) cells are unconventional T lymphocytes that express a semi-invariant T cell receptor (TCR) recognizing microbial vitamin B metabolites presented by the highly conserved major histocompatibility complex (MHC) class I like molecule, MR1. The vitamin B metabolites are produced by several commensal and pathogenic bacteria and yeast, but not viruses. Nevertheless, viral infections can trigger MAIT cell activation in a TCR-independent manner, through the release of pro-inflammatory cytokines by antigen-presenting cells (APCs). MAIT cells belong to the innate like T family of cells with a memory phenotype, which allows them to rapidly release Interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and in some circumstances Interleukin (IL)-17 and IL-10, exerting an immunomodulatory role on the ensuing immune response, akin to iNKT cells and γδ T cells. Recent studies implicate MAIT cells in a variety of inflammatory, autoimmune diseases, and in cancer. In addition, through the analysis of the transcriptome of MAIT cells activated in different experimental conditions, an important function in tissue repair and control of immune homeostasis has emerged, shared with other innate-like T cells. In this review, we discuss these recent findings, focussing on the understanding of the molecular mechanisms underpinning MAIT cell activation and effector function in health and disease, which ultimately will aid in clinically harnessing this unique, not donor-restricted cell subtype.

In autophagy, LC3-positive autophagophores fuse and encapsulate the autophagic cargo in a double-membrane structure. In contrast, lipidated LC3 (LC3-II) is directly formed at the phagosomal membrane in LC3-associated phagocytosis (LAP). In this study, we dissected the effects of autophagy inhibitors on LAP. SAR405, an inhibitor of VPS34, reduced levels of LC3-II and inhibited LAP. In contrast, the inhibitors of endosomal acidification bafilomycin A1 and chloroquine increased levels of LC3-II, due to reduced degradation in acidic lysosomes. However, while bafilomycin A1 inhibited LAP, chloroquine did not. Finally, EACC, which inhibits the fusion of autophagosomes with lysosomes, promoted LC3 degradation possibly by the proteasome. Targeting LAP with small molecule inhibitors is important given its emerging role in infectious and autoimmune diseases.

Many cellular processes are dependent on correct pH levels, and this is especially important for the secretory pathway. Defects in pH homeostasis in distinct organelles cause a wide range of diseases, including disorders of glycosylation and lysosomal storage diseases. Ratiometric imaging of the pH-sensitive mutant of green fluorescent protein, pHLuorin, has allowed for targeted pH measurements in various organelles, but the required sequential image acquisition is intrinsically slow and therefore the temporal resolution is unsuitable to follow the rapid transit of cargo between organelles. Therefore, we applied fluorescence lifetime imaging microscopy (FLIM) to measure intraorganellar pH with just a single excitation wavelength. We first validated this method by confirming the pH in multiple compartments along the secretory pathway and compared the pH values obtained by the FLIM-based measurements with those obtained by conventional ratiometric imaging. Then, we analyzed the dynamic pH changes within cells treated with Bafilomycin A1, to block the vesicular ATPase, and Brefeldin A, to block endoplasmic reticulum (ER)–Golgi trafficking. Finally, we followed the pH changes of newly synthesized molecules of the inflammatory cytokine tumor necrosis factor-α while they were in transit from the ER via the Golgi to the plasma membrane. The toolbox we present here can be applied to measure intracellular pH with high spatial and temporal resolution and can be used to assess organellar pH in disease models.

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Synthetic cancer vaccines may boost anticancer immune responses by co-delivering tumor antigens and adjuvants to dendritic cells (DCs). The accessibility of cancer vaccines to DCs and thereby the delivery efficiency of antigenic material greatly depends on the vaccine platform that is used. Three-dimensional scaffolds have been developed to deliver antigens and adjuvants locally in an immunostimulatory environment to DCs to enable sustained availability. However, current systems have little control over the release profiles of the cargo that is incorporated and are often characterized by an initial high-burst release. Here, an alternative system is designed that co-delivers antigens and adjuvants to DCs through cargo-loaded nanoparticles (NPs) incorporated within biomaterial-based scaffolds. This creates a programmable system with the potential for controlled delivery of their cargo to DCs. Cargo-loaded poly( d , l -lactic- co -glycolic acid) NPs are entrapped within the polymer walls of alginate cryogels with high efficiency while retaining the favorable physical properties of cryogels, including syringe injection. DCs cultured within these NP-loaded scaffolds acquire strong antigen-specific T cell-activating capabilities. These findings demonstrate that introduction of NPs into the walls of macroporous alginate cryogels creates a fully synthetic immunostimulatory niche that stimulates DCs and evokes strong antigen-specific T cell responses.

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