Andrew E. Hogan

Mucosal-associated invariant T (MAIT) cells are a population of innate-like, unconventional T cells characterized by the expression of a semi-invariant, non-MHC–restricted T cell receptor (TCR), which play an important role in mediating innate immune responses to bacterial and viral pathogens. Emerging research continues to describe the many environmental signals that influence the types of responses elicited downstream of MAIT cell activation. In this Review, we highlight five key factors that determine the metabolic and functional responses of MAIT cells, including TCR engagement, costimulation, chemokine signaling, cytokine stimulation, and nutrient availability. We further define the importance of optimal nutrient availability as “signal 5” in promoting MAIT cell fitness and in governing their capacity to respond appropriately to challenge. In understanding the ways in which MAIT cells are influenced by their microenvironment, we can continue to identify the potential factors that drive dysregulated responses in hostile circumstances, enabling restoration of their protective nature in the context of infection or in the tumor microenvironment.

Obesity represents a major global healthcare crisis, with childhood obesity rising at an alarming rate. Children with obesity are highly likely to carry it into adulthood, bringing numerous associated health risks. Even more troubling is the emerging understanding of “obesity memory”, which contributes to the frequent issue of weight regain. Here, we show that obesity imprints CD4 T cells through DNA methylation, leading to a long-time lag, spanning years, before adaptive immune homeostasis is restored after weight loss. Differential DNA methylation analysis highlights autophagy and immune senescence as potential key mechanisms underpinning this memory of obesity in CD4 T cells. In addition, particularly palmitate could be a key saturated fatty acid that can contribute to epigenetic alterations in CD4 T cells, potentially perpetuating this altered state. We identify molecular candidates (i.e., Stk26 and Cdkn1c) underpinning key cell functions (autophagy and immune senescence) that could be targeted to promote a return to immune homeostasis alongside weight loss. These findings raise the possibility that targeting such pathways could support the restoration of immune homeostasis alongside weight loss therapies.

α/β-hydrolase domain-containing protein 11 (ABHD11) is a mitochondrial hydrolase that maintains the catalytic function of α-ketoglutarate dehydrogenase (α-KGDH), and its expression in CD4 + T-cells has been linked to remission status in rheumatoid arthritis (RA). However, the importance of ABHD11 in regulating T-cell metabolism and function is yet to be explored. Here, we show that pharmacological inhibition of ABHD11 dampens cytokine production by human and mouse T-cells. Mechanistically, the anti-inflammatory effects of ABHD11 inhibition are attributed to increased 24,25-epoxycholesterol (24,25-EC) biosynthesis and subsequent liver X receptor (LXR) activation, which arise from a compromised TCA cycle. The impaired cytokine profile established by ABHD11 inhibition is extended to two patient cohorts of autoimmunity. Importantly, using murine models of accelerated type 1 diabetes (T1D), we show that targeting ABHD11 suppresses cytokine production in antigen-specific T-cells and delays the onset of diabetes in vivo in female mice. Collectively, our work provides pre-clinical evidence that ABHD11 is an encouraging drug target in T-cell-mediated inflammation.

Adenoviral (Ad) vectors and mRNA vaccines exhibit distinct patterns of immune responses and reactogenicity, but underpinning mechanisms remain unclear. We longitudinally compared homologous ChAdOx1 nCoV-19 and BNT162b2 vaccination, focusing on cytokine-responsive innate-like lymphocytes—mucosal-associated invariant T (MAIT) cells and Vδ2 ⁺ γδ T cells—which sense and tune innate-adaptive cross-talk. Ad priming elicited robust type I interferon (IFN)–mediated innate-like T cell activation, augmenting T cell responses (innate-to-adaptive signaling), which was dampened at boost by antivector immunity. Conversely, mRNA boosting enhanced innate-like responses, driven by prime-induced spike-specific memory T cell–derived IFN-γ (adaptive-to-innate signaling). Extending the dosing interval dampened inflammation at boost because of waning T cell memory. In a separate vaccine trial, preboost spike-specific T cells predicted severe mRNA reactogenicity regardless of the priming platform or interval. Overall, bidirectional innate-like and adaptive cross-talk, and IFN-γ–licensed innate-like T cells, orchestrate interval-dependent early vaccine responses, suggesting modifiable targets for safer, more effective regimens.

Background: The immunomodulatory function of human mesenchymal stromal cells (MSCs) strongly depends on external factors; such as cytokines and other signalling molecules encountered in the disease microenvironment. An insufficiently inflammatory environment can fail to activate MSCs, and certain signals can impair their function. Obesity is on the rise worldwide, making it an additional factor to be considered prior to MSC therapy, as the microenvironment presents its own challenges. Elevated levels of serum free fatty acids, specifically palmitate, have the potential to affect MSC therapy. Palmitate-exposure has been shown to impair MSC immunomodulation of T cells in vitro. However, this is yet to be studied in the context of macrophages. Methods: MSCs from three independent donors were exposed to 0.4mM of palmitate for 6–24 h. Gene expression, protein production and functional capacity were then assessed in response to palmitate. A ceramide synthesis inhibitor (Fumonisin B1) and a CC-chemokine ligand 2 (CCL2)-neutralising antibody were further used to assess the impact of these components on palmitate-associated immunomodulation. Results: We demonstrated that palmitate-exposed MSCs have enhanced suppression of human monocyte-derived macrophage (MDM) production of tumour necrosis factor α (TNFα), in a CCL2-dependent manner. We further elucidated parts of the pathway, such as ceramide synthesis, through which palmitate promotes this enhanced immunomodulation of macrophages. Conclusion: Palmitate-exposed MSCs show enhanced immunomodulation of human MDMs, through the ceramide/CCL2 axis in vitro.

Chronic inflammation in autoimmunity is driven by T cell hyperactivation. This unregulated response to self is fuelled by heightened metabolic programmes, which offers a promising new direction to uncover novel treatment strategies. α/β-hydrolase domain-containing protein 11 (ABHD11) is a mitochondrial hydrolase that maintains the catalytic function of α-ketoglutarate dehydrogenase (α-KGDH), and its expression in CD4+ T cells has been linked to remission status in rheumatoid arthritis (RA). However, the importance of ABHD11 in regulating T cell metabolism and function – and thus, the downstream implication for autoimmunity – is yet to be explored. Here, we show that pharmacological inhibition of ABHD11 dampens cytokine production by human and mouse T cells. Mechanistically, the anti-inflammatory effects of ABHD11 inhibition are attributed to increased 24,25-epoxycholesterol (24,25-EC) biosynthesis and subsequent liver X receptor (LXR) activation, which arise from a compromised TCA cycle. The impaired cytokine profile established by ABHD11 inhibition is extended to two patient cohorts of autoimmunity. Importantly, using a murine model of accelerated type 1 diabetes (T1D), we show that targeting ABHD11 suppresses cytokine production in antigen-specific T cells and delays the onset of diabetes in vivo . Collectively, our work provides pre-clinical evidence that ABHD11 is an encouraging drug target in T cell-mediated autoimmunity. Graphical

Introduction: Obesity is a worldwide epidemic, with over 1 billion people worldwide living with obesity. It is associated with an increased risk of over 200 chronic co-morbidities, including an increased susceptibility to infection. Numerous studies have highlighted the dysfunction caused by obesity on a wide range of immune cell subsets, including dendritic cells (DCs). DCs are innate immune sentinels that bridge the innate and adaptive immune systems. DCs provide critical signals that instruct and shape the immune response. Our group has previously reported that DCs from people with obesity display defective cytokine production; however, the mechanisms underpinning these defects are unclear. Methods: We investigated the functional responses of DCs using a murine-specific single-stranded RNA virus, Sendai virus, in mice on a standard diet and in a model of diet-induced obesity. Results: Here, we demonstrate that GM-CSF cultured bone marrow–derived DCs (GM-DCs) from mice on a high-fat diet (HFD) have reduced cytokine production following viral challenge. This was associated with a dysfunctional metabolism through reduced translation in the HFD GM-DCs. Conclusions: We propose that obesity-mediated effects on DCs have downstream consequences on their ability to effectively mediate subsequent immune responses, especially during viral infection.

Objective: Glucagon‐like peptide‐1 (GLP‐1) analogues are currently the most widely used pharmacotherapies for weight loss. Their primary mechanism of action is attributed to reduction in energy intake. Data from murine studies also support an additional impact of those agents on energy homeostasis through upregulation of visceral adipose tissue (VAT) metabolic activity, but this remains uncertain in humans.Methods: Here, we present data from a proof‐of‐concept study on 30 individuals with obstructive sleep apnea and obesity who were randomized to a GLP‐1 therapy‐based weight loss regimen, continuous positive airway pressure, or a combination of both for 24 weeks. At baseline and study completion, 18F‐fluorodeoxyglucose (18F‐FDG) positron emission tomography‐computed tomography (PET‐CT) was performed to evaluate VAT metabolic activity, expressed as VAT target to background ratio.Results: Treatment with GLP‐1, but not with continuous positive airway pressure, was associated with a significant increase in VAT target to background ratio. There was a strong correlation between the increase in VAT metabolic activity and the degree of weight loss.Conclusions: These data support the hypothesis that upregulation of VAT metabolic activity by GLP‐1 contributes to its weight loss action in humans, and this subject warrants further detailed investigation.