Type I interferons (IFNs) can reprogram the cholesterol biosynthetic pathway to facilitate innate immune responses. In this issue of Immunity, Xiao et al. (2020) reveal that type I IFN signaling and 7-dehydrocholesterol (7-DHC) accumulation form a positive feedback loop to amplify innate immune responses to control viral infections by activating AKT3.

Sensing tissue damage is an ancient function of immune cells that is central to the regulation of inflammation, tissue repair, and immunity. In this issue of Immunity, Lai et al. (2020) uncover a role for the C-type lectin receptor Clec2d as a sensor of cell death, which directly detects histones released during necrosis and thus contributes to inflammation and immunopathology.

Understanding how cytotoxic T cells are regulated is key for enhancing or suppressing their activity in tumor or transplantation settings. A study by Morris et al. (2020) in this issue of Immunity shows that crosslinking of inhibitory Fc receptor FcγRIIb by the suppressive cytokine Fgl2 limits cytotoxic CD8+ T cell responses by inducing T cell apoptosis.

Multiple sclerosis is a chronic inflammatory disease characterized by demyelination in the central nervous system. In this issue of Immunity, Werneberg et al. report a striking loss of synapses driven by excessive microglial pruning early in demyelinating disease, which can be rescued by inhibiting the complement component C3.

In the search for therapeutic combinations for the treatment of cancer, the pairing of targeted inhibitors of oncogenic driver pathways with immunotherapy has largely been overlooked. In Nature, Canon et al. (2019) describe how the novel KRAS-G12C inhibitor AMG 510 can potentiate immune rejection in combination with immune checkpoint blockade.

Cancer immunotherapy is a validated and critically important approach for treating patients with cancer. Given the vast research and clinical investigation efforts dedicated to advancing both endogenous and synthetic immunotherapy approaches, there is a need to focus on crucial questions and define roadblocks to the basic understanding and clinical progress. Here, we define ten key challenges facing cancer immunotherapy, which range from lack of confidence in translating pre-clinical findings to identifying optimal combinations of immune-based therapies for any given patient. Addressing these challenges will require the combined efforts of basic researchers and clinicians, and the focusing of resources to accelerate understanding of the complex interactions between cancer and the immune system and the development of improved treatment options for patients with cancer.

Therapeutics that target the T cell inhibitory checkpoint proteins CTLA-4 and PD(L)1 are efficacious across a broad range of cancers, resulting in reductions in tumor burden and increased long-term survival in subsets of patients. The significant and wide-ranging effects of these immunotherapies have prompted the clinical investigation of additional therapies that modulate anti-tumor immunity through effects on T cells, myeloid cells, and other cell types within the tumor microenvironment. The clinical activity of these newer investigational therapies has been mixed, with some therapeutics showing promise but others not exhibiting appreciable efficacy. In this review, we summarize the results of select recent clinical studies of cancer immunotherapies beyond anti-CTLA-4 and anti-PD(L)1 and discuss how these results are providing new insights into the regulation of human anti-tumor immunity.

Cancer is a complex disease whose outcome depends largely on the cross-talk between the tumor and its microenvironment. Here, we review the evolution of the field of tumor immunology and the advances, in lockstep, of our understanding of cancer as a disease. We discuss the involvement of different immune cells at distinct stages of tumor progression and how immune contexture determinants shaping tumor development are being exploited therapeutically. Current clinical stratification schemes focus on the tumor histopathology and the molecular characteristics of the tumor cell. We argue for the importance of revising these stratification systems to include immune parameters so as to address the immediate need for improved prognostic and/or predictive information to guide clinical decisions.

Recent years have witnessed a revolution in our understanding of microglia biology, including their major role in the etiology and pathogenesis of neurodegenerative diseases. Technological advances have enabled the identification of microglial signatures in health and disease, including the development of new models to investigate and manipulate human microglia in vivo in the context of disease. In parallel, genetic association studies have identified several gene risk factors associated with Alzheimer’s disease that are specifically or highly expressed by microglia in the central nervous system (CNS). Here, we discuss evidence for the effect of stress, diet, sleep patterns, physical activity, and microbiota composition on microglia biology and consider how lifestyle might influence an individual’s predisposition to neurodegenerative diseases. We discuss how different lifestyles and environmental factors might regulate microglia, potentially leading to increased susceptibility to neurodegenerative disease, and we highlight the need to investigate the contribution of modern environmental factors on microglia modulation in neurodegeneration.

Promising vaccines and results from recent clinical trials of therapeutic antibodies against Ebola virus offer hope for an end to this devastating disease. We asked three investigators in the field to share their views on the remaining challenges and important future research directions as we work toward controlling Ebola virus infection.

Exhausted CD8+ T cells adopt a functionally attenuated state but still confer a certain degree of pathogen control. Chen et al., 2019, Hudson et al., 2019, and Zander et al. (2019) assign the lasting maintenance of this restrained pathogen control to an equilibrium of effector-like, transitory, terminal, and memory-like exhausted T cells.

Targeting the CTLA-4 and PD-1 “checkpoints” is an effective treatment for a number of cancers. In this issue of Immunity, Hui et al. reveal that interaction between a CTLA-4 ligand, CD80, and its counterpart in the PD-1 pathway, PD-L1, affects both PD-1 and CTLA-4 function, raising new questions about the biological effects of using checkpoint inhibitors alone and in combination.

Integrating transcriptomic, proteomic, and metabolomic data, Lercher et al. show in a mouse model of LCMV infection that type I interferon alters the expression and function of key enzymes of the urea cycle in hepatocytes. This results in altered systemic metabolism, attenuating antiviral T cell responses and ameliorating liver injury.

In this issue of Immunity, Wang et al. identify a developmental transition of neural-immune interactions from postnatal to adult lung. Their findings implicate sympathetic nerve production of dopamine as a contributor to the susceptibility of children to allergen-induced asthmatic responses.

In a recent issue of Nature, Zhang et al. (2019) describe an additional histone post-translational modification, named histone lactylation. Following increased lactate production as a consequence of M1 polarization, histone lactylation regulates the induction of an M2-like phenotype in late stages of M1 macrophage activation to promote wound healing.

The direct ligands recognized by γδ T cell receptors (γδ TCRs) remain uncertain and controversial. In a study appearing in this issue, Willcox et al. use surface plasmon resonance and isothermal titration calorimetry to demonstrate that B7-like molecule BTNL3 makes physical contact with V4γ-bearing TCRs on γδ T cells.

Our knowledge of T cell metabolism relies primarily on studies performed in vitro that may not fully recapitulate physiological conditions in vivo. In this issue of Immunity, Ma et al. find that the in vivo environment dictates the metabolic phenotype of effector CD8+ T cells—particularly their glucose utilization.

It is poorly understood how group 3 innate lymphoid cells (ILC3s) recognize metabolites produced by the gut microbiota. In this issue of Immunity, Chun et al. show that short-chain fatty acids sensed through the G protein-coupled receptor Ffar2 promote ILC3 function in the colon.

In this issue of Immunity, Zeng et al. use single-cell RNA sequencing analyses of rare samples to shed light on the emergence of thymic stromal cell types, the first developing T lymphocytes, and their possible pre-thymic precursors in the early human fetus.

The cytokine TNF is thought to play a major role in the immunopathogenesis of ulcerative colitis, and anti-TNF antibodies are considered as cornerstones of clinical therapy. Two clinical trials published in The New England Journal of Medicine now challenge this paradigm and suggest new avenues for research.

The consumption of Western-type calorically rich diets combined with chronic overnutrition and a sedentary lifestyle in Western societies evokes a state of chronic metabolic inflammation, termed metaflammation. Metaflammation contributes to the development of many prevalent non-communicable diseases (NCDs), and these lifestyle-associated pathologies represent a rising public health problem with global epidemic dimensions. A better understanding of how modern lifestyle and Western diet (WD) activate immune cells is essential for the development of efficient preventive and therapeutic strategies for common NCDs. Here, we review the current mechanistic understanding of how the Western lifestyle can induce metaflammation, and we discuss how this knowledge can be translated to protect the public from the health burden associated with their selected lifestyle.

CD4+CD3- cells are the predominant hematopoietic cells found in mouse fetal intestine. We prove their role as Peyer's patch (PP)-inducing cells by transfer into neonatal PP-deficient mice. To test the requirement of chemokines and adhesion molecules in induction of PP, we studied mice deficient in CXCR5 and/or alpha4beta1 integrin-mediated adhesion. CXCR5-/- mice have CD4+CD3- cells, which are inefficient in inducing PP formation. We show here that CXCR5/CXCL13 signaling activates alpha4beta1 integrin on CD4+CD3- cells. Blocking of beta1 integrin or VCAM-1, the ligand of alpha4beta1 integrin, inhibits PP formation. This study demonstrates the link between chemokine receptors and adhesion molecules that regulates stromal/hematopoietic cell interaction leading to PP formation.

Autoreactive B cells that appear to be inactivated can be found in healthy individuals. In this study, we examined the potential of these anergic cells to become activated. We show that anergy of anti-double-stranded DNA (dsDNA) B cells in BALB/c mice is readily reversed, requiring only the provision of T cell help. We further show that spontaneous loss of anergy among anti-dsDNA B cells in autoimmune lpr/lpr mice occurs in two phases: an abortive initial response to T help followed by full loss of tolerance. Strikingly, the abortive response can be reproduced in nonautoimmune mice when CD4+CD25+ T regulatory cells are administered in conjunction with CD4+ T helper cells, suggesting that loss of B cell tolerance may require both the production of T cell help and the overcoming of T suppression.

CXCR5, the receptor for B lymphocyte chemoattractant (BLC), is required for normal development of Peyer's patches, inguinal lymph nodes, and splenic follicles. To test the in vivo activity of BLC in isolation of other lymphoid organizers, transgenic mice were generated expressing BLC in the pancreatic islets. In addition to attracting B cells, BLC expression led to development of lymph node-like structures that contained B and T cell zones, high endothelial venules, stromal cells, and the chemokine SLC. Development of these features was strongly dependent on B lymphocytes and on lymphotoxin alpha1beta2 and could be reversed by blocking lymphotoxin alpha1beta2. These findings establish that BLC is sufficient to activate a pathway of events leading to formation of organized lymphoid tissue.

For a brief period during fetal lymph node organogenesis in mice, lymph node postcapillary high endothelial venules surprisingly express the Peyer's patch addressin MAdCAM-1. This expression allows initial seeding of this incipient structure by two unusual lymphocyte populations selectively expressing the Peyer's patch homing receptor integrin alpha4beta7: CD4+CD3- oligolineage progenitors and TCR gammadelta+ T cells. We show here that CD4+CD3- cells are lineage-restricted progenitors that express surface lymphotoxin-beta (LTbeta) and the chemokine receptor BLR1 and that can become natural killer cells, dendritic antigen-presenting cells, and follicular cells of unknown outcome, but these cells do not become T or B lymphocytes. Since the necessity of lymphotoxin in lymphoid organ development has been shown, we propose that the novel subset of CD4+CD3-LTbeta+ fetal cells is instrumental in the development of lymphoid tissue architecture.

Cytolysis of target cells by natural killer (NK) cells and by some cytotoxic T cells occurs unless prevented by inhibitory receptors that recognize MHC class I on target cells. Human NK cells express a p58 inhibitory receptor specific for HLA-C. We report association of the tyrosine phosphatase HCP with the p58 receptor in NK cells. HCP association was dependent on tyrosine phosphorylation of p58. Phosphotyrosyl peptides corresponding to the p58 tail bound and activated HCP in vitro. Furthermore, introduction of an inactive mutant HCP into an NK cell line prevented the p58-mediated inhibition of target cell lysis. These data imply that the inhibitory function of p58 is dependent on its tyrosine phosphorylation and on recruitment and activation of HCP.