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R -2-hydroxyglutarate accumulates to millimolar levels in cancer cells with gain-of-function isocitrate dehydrogenase 1/2 mutations. These levels of R -2-hydroxyglutarate affect 2-oxoglutarate-dependent dioxygenases. Both metabolite enantiomers, R - and S -2-hydroxyglutarate, are detectible in healthy individuals, yet their physiological function remains elusive. Here we show that 2-hydroxyglutarate accumulates in mouse CD8 + T cells in response to T-cell receptor triggering, and accumulates to millimolar levels in physiological oxygen conditions through a hypoxia-inducible factor 1-alpha (HIF-1α)-dependent mechanism. S -2-hydroxyglutarate predominates over R -2-hydroxyglutarate in activated T cells, and we demonstrate alterations in markers of CD8 + T-cell differentiation in response to this metabolite. Modulation of histone and DNA demethylation, as well as HIF-1α stability, mediate these effects. S -2-hydroxyglutarate treatment greatly enhances the in vivo proliferation, persistence and anti-tumour capacity of adoptively transferred CD8 + T cells. Thus, S -2-hydroxyglutarate acts as an immunometabolite that links environmental context, through a metabolic–epigenetic axis, to immune fate and function. S -2-hydroxyglutarate produced by CD8+ T cells under hypoxic conditions affects locus-specific histone and DNA methylation patterns, which enhances T-cell proliferation, survival and recall responses. Broad immune stimulation by S -2-hydroxyglutarate Randall Johnson and colleagues demonstrate that CD8 + T cells produce the immunometabolite S -2-hydroxyglutarate ( S -2HG) in response to activation triggered by T-cell receptors under hypoxic conditions. The resulting S -2HG affects locus-specific histone and DNA methylation patterns, enhancing T-cell proliferation, survival and recall responses.

mRNA lipid nanoparticle (LNP) vaccines would be useful during an influenza virus pandemic since they can be produced rapidly and do not require the generation of egg-adapted vaccine seed stocks. Highly pathogenic avian influenza viruses from H5 clade 2.3.4.4b are circulating at unprecedently high levels in wild and domestic birds and have the potential to adapt to humans. Here, we generate an mRNA lipid nanoparticle (LNP) vaccine encoding the hemagglutinin (HA) glycoprotein from a clade 2.3.4.4b H5 isolate. The H5 mRNA-LNP vaccine elicits strong T cell and antibody responses in female mice, including neutralizing antibodies and broadly-reactive anti-HA stalk antibodies. The H5 mRNA-LNP vaccine elicits antibodies at similar levels compared to whole inactivated vaccines in female mice with and without prior H1N1 exposures. Finally, we find that the H5 mRNA-LNP vaccine is immunogenic in male ferrets and prevents morbidity and mortality of animals following 2.3.4.4b H5N1 challenge. Together, our data demonstrate that a monovalent mRNA-LNP vaccine expressing 2.3.4.4b H5 is immunogenic and protective in pre-clinical animal models. Highly pathogenic avian influenza viruses from H5 clade 2.3.4.4b are circulating widely in birds and have recently caused large outbreaks in mammals. Here, Furey et al. develop a clade 2.3.4.4b HA-expressing mRNA-LNP vaccine and show that it elicits strong protective immune responses in mice and ferrets.

Initial TCR engagement (priming) of naive CD8 + T cells results in T cell expansion, and these early events influence the generation of diverse effector and memory populations. During infection, activated T cells can re-encounter cognate antigen, but how these events influence local effector responses or formation of memory populations is unclear. To address this issue, OT-I T cells which express the Nur77-GFP reporter of TCR activation were paired with the parasite Toxoplasma gondii that expresses OVA to assess how secondary encounter with antigen influences CD8 + T cell responses. During acute infection, TCR stimulation in affected tissues correlated with parasite burden and was associated with markers of effector cells while Nur77-GFP - OT-I showed signs of effector memory potential. However, both Nur77-GFP - and Nur77-GFP + OT-I from acutely infected mice formed similar memory populations when transferred into naive mice. During the chronic stage of infection in the CNS, TCR activation was associated with large scale transcriptional changes and the acquisition of an effector T cell phenotype as well as the generation of a population of CD103 + CD69 + Trm like cells. While inhibition of parasite replication resulted in reduced effector responses it did not alter the Trm population. These data sets highlight that recent TCR activation contributes to the phenotypic heterogeneity of the CD8 + T cell response but suggest that this process has a limited impact on memory populations at acute and chronic stages of infection.

Many inflammatory stimuli can induce progenitor cells in the bone marrow to produce increased numbers of myeloid cells as part of the process of emergency myelopoiesis. These events are associated with trained immunity and have long-term impacts on hematopoietic stem and progenitor cell (HSPC) development but can also compromise their function. While many cytokines support emergency myelopoiesis, less is known about the mechanisms that temper these events. When mice that lack the cytokine IL-27 were infected with Toxoplasma gondii , there was enhanced generation of monocyte progenitors and increased numbers of inflammatory monocytes. In the bone marrow of infected mice, there was increased production of IL-27 that localized with HSPCs, and a survey of cytokine receptor expression highlighted that HSPCs were uniquely poised to respond to IL-27. Furthermore, the use of in vitro differentiation assays and mixed bone marrow chimeras revealed that HSPCs from IL-27-deficient mice are predisposed toward the monocyte lineage. Additional studies highlighted that after infection, loss of the IL-27R resulted in reduced HSPC fitness that manifested as reduced proliferative responses and a decreased ability to reconstitute the hematopoietic system. Thus, the ability of IL-27 to act on HSPC provides a regulatory brake on differentiation to limit monocyte induction and preserve HSPC stemness.

The molecule IL-27 is critical in limiting the immune response to the parasite Toxoplasma gondii . In the absence of IL-27, a lethal, overactive immune response develops during infection. However, when exactly in the course of infection this molecule is needed was unclear. By selectively inhibiting IL-27 during this parasitic infection, we discovered that IL-27 was only needed during, but not prior to, infection. Additionally, IL-27 is only needed in the active areas in which the parasite is replicating. Finally, our work found that a previously unstudied cell type, monocytes, was regulated by IL-27, which contributes further to our understanding of the regulatory networks established by this molecule.

Dermal resident memory CD4 + T cells (dTrm) provide protection against vector-borne infections. However, the factors that promote their development remain unclear. We tested if an mRNA vaccine, encoding a protective leishmanial antigen, induced dTrm cells. The mRNA vaccine induced robust systemic T-cell responses, but few Trm cells were found in the skin. Since IL-12 promotes Th1 responses, we tested whether IL-12 mRNA combined with the mRNA vaccine could enhance dTrm cell development. This combination significantly expanded Leishmania -specific Th1 cells expressing skin-homing molecules and memory T cell markers in the draining lymph node. Additionally, higher numbers of dTrm cells were maintained in the skin, and mice exhibited functional immunity indicated by a delayed hypersensitivity response and protection upon challenge with Leishmania . These findings highlight IL-12 as a key driver of CD4 + dTrm development, enabling their global seeding across the skin, and underscore the potential of IL-12-enhanced mRNA vaccines to generate durable immunity against cutaneous leishmaniasis and other skin-targeted infections.

The transcription factor Runx3 is identified as a central regulator of the development of tissue-resident memory CD8 + T cells, providing insights into the signals that promote T cell residency in non-lymphoid tissues and tumours. T cell residency run by Runx3 Memory T cells that reside in tissues around the body are positioned at points that are commonly exposed to pathogens, ready to launch their immune response. However, the molecular signals that control their activity here are not well understood. In this study Ananda Goldrath and co-workers identify the transcription factor Runx3 as a key regulator of the development and functionality of tissue-resident memory CD8 + T cells. They provide evidence that supports the establishment of a residence-fate commitment early during CD8 + T cell differentiation. Tissue-resident memory CD8 + T (T RM ) cells are found at common sites of pathogen exposure, where they elicit rapid and robust protective immune responses 1 , 2 . However, the molecular signals that control T RM cell differentiation and homeostasis are not fully understood. Here we show that mouse T RM precursor cells represent a unique CD8 + T cell subset that is distinct from the precursors of circulating memory cell populations at the levels of gene expression and chromatin accessibility. Using computational and pooled in vivo RNA interference screens, we identify the transcription factor Runx3 as a key regulator of T RM cell differentiation and homeostasis. Runx3 was required to establish T RM cell populations in diverse tissue environments, and supported the expression of crucial tissue-residency genes while suppressing genes associated with tissue egress and recirculation. Furthermore, we show that human and mouse tumour-infiltrating lymphocytes share a core tissue-residency gene-expression signature with T RM cells that is associated with Runx3 activity. In a mouse model of adoptive T cell therapy for melanoma, Runx3 -deficient CD8 + tumour-infiltrating lymphocytes failed to accumulate in tumours, resulting in greater rates of tumour growth and mortality. Conversely, overexpression of Runx3 enhanced tumour-specific CD8 + T cell abundance, delayed tumour growth, and prolonged survival. In addition to establishing Runx3 as a central regulator of T RM cell differentiation, these results provide insight into the signals that promote T cell residency in non-lymphoid sites, which could be used to enhance vaccine efficacy or adoptive cell therapy treatments that target cancer.

Adoptive T cell therapies (ACTs) hold great promise in cancer treatment, but low overall response rates in patients with solid tumors underscore remaining challenges in realizing the potential of this cellular immunotherapy approach. Promoting CD8+ T cell adaptation to tissue residency represents an underutilized but promising strategy to improve tumor-infiltrating lymphocyte (TIL) function. Here, we report that deletion of the HIF negative regulator von Hippel-Lindau (VHL) in CD8+ T cells induced HIF-1α/HIF-2α-dependent differentiation of tissue-resident memory-like (Trm-like) TILs in mouse models of malignancy. VHL-deficient TILs accumulated in tumors and exhibited a core Trm signature despite an exhaustion-associated phenotype, which led to retained polyfunctionality and response to αPD-1 immunotherapy, resulting in tumor eradication and protective tissue-resident memory. VHL deficiency similarly facilitated enhanced accumulation of chimeric antigen receptor (CAR) T cells with a Trm-like phenotype in tumors. Thus, HIF activity in CD8+ TILs promotes accumulation and antitumor activity, providing a new strategy to enhance the efficacy of ACTs.

The transcription factor HIF is induced in response to hypoxic stress, TCR activation and cytokines. Goldrath and colleagues show that HIF signaling enhances CTL effector responses and can render cells refractory to immune exhaustion. Cytolytic activity by CD8 + cytotoxic T lymphocytes (CTLs) is a powerful strategy for the elimination of intracellular pathogens and tumor cells. The destructive capacity of CTLs is progressively dampened during chronic infection, yet the environmental cues and molecular pathways that influence immunological 'exhaustion' remain unclear. Here we found that CTL immunity was regulated by the central transcriptional response to hypoxia, which is controlled in part by hypoxia-inducible factors (HIFs) and the von Hippel–Lindau tumor suppressor VHL. Loss of VHL, the main negative regulator of HIFs, led to lethal CTL-mediated immunopathology during chronic infection, and VHL-deficient CTLs displayed enhanced control of persistent viral infection and neoplastic growth. We found that HIFs and oxygen influenced the expression of pivotal transcription, effector and costimulatory-inhibitory molecules of CTLs, which was relevant to strategies that promote the clearance of viruses and tumors.

During an immune response, CD8+ T lymphocytes can undergo asymmetric division, giving rise to daughter cells that exhibit distinct tendencies to adopt terminal effector and memory cell fates. Here we show that \"pre-effector\" and \"pre-memory\" cells resulting from the first CD8+ T cell division in vivo exhibited low and high rates of endogenous proteasome activity, respectively. Pharmacologic reduction of proteasome activity in CD8+ T cells early during differentiation resulted in acquisition of terminal effector cell characteristics, whereas enhancement of proteasome activity conferred attributes of memory lymphocytes. Transcriptomic and proteomic analyses revealed that modulating proteasome activity in CD8+ T cells affected cellular metabolism. These metabolic changes were mediated, in part, through differential expression of Myc, a transcription factor that controls glycolysis and metabolic reprogramming. Taken together, these results demonstrate that proteasome activity is an important regulator of CD8+ T cell fate and raise the possibility that increasing proteasome activity may be a useful therapeutic strategy to enhance the generation of memory lymphocytes.