Activated effector T cells (Teff) and/or compromised regulatory T cells (Treg) underlie many chronic inflammatory diseases. We discovered a novel pathway to regulate survival and expansion of Teff without compromising Treg survival and a potential therapeutic to treat these diseases. We found dimethylguanidino valeric acid (DMGV) as a rheostat for Teff survival: while cell-intrinsic DMGV generated by Alanine-Glyoxylate Aminotransferase 2 (AGXT2) is essential for survival and expansion by inducing mitochondrial ROS and regulation of glycolysis, an excessive (or exogenous) DMGV level inhibits activated Teff survival, thereby the AGXT2-DMGV-ROS axis functioning as a switch to turn on and off Teff expansion. DMGV-induced ROS is essential for glycolysis in Teff, and paradoxically DMGV induces ROS only when glycolysis is active. Mechanistically, DMGV rapidly activates mitochondrial calcium uniporter (MCU), causing a surge in mitochondrial Ca2+ without provoking calcium influx to the cytosol. The mitochondrial Ca2+ surge in turn triggers the mitochondrial Na+/Ca2+ exchanger (NCLX) and the subsequent mitochondrial Na+ import induces ROS by uncoupling the Coenzyme Q cycle in Complex III of the electron transport chain. In preclinical studies, DMGV administration significantly diminished the number of inflammatory T cells, effectively suppressing chronic inflammation in mouse models of colitis and rheumatoid arthritis. DMGV also suppressed expansion of cancer cells in vitro and in a mouse T cell leukemic model by the same mechanism. Our data provide a new pathway regulating T cell survival and a novel mode to treat autoimmune diseases and cancers.

Innate anti-inflammatory mechanisms are essential for immune homeostasis and can present opportunities to intervene inflammatory diseases. In this report, we found that YAP isoform 9 (YAP9) is an essential negative regulator of the potent inflammatory stimuli such as TNFα, IL-1β, and LPS. YAP9 constitutively interacts with another anti-inflammatory regulator A20 (TNFAIP3) to suppress inflammatory responses, but A20 and YAP can function only in the presence of the other. YAP9 uses a short stretch of amino acids in the proline-rich domain (PRD) and transactivation domain (TAD) suppress the inflammatory signaling while A20 mainly uses the zinc finger domain 7 (ZF7). Cell-penetrating synthetic PRD, TAD, and ZF7 peptides act as YAP9 and A20 mimetics respectively to suppress the proinflammatory responses at the cellular level and in mice. Our data uncover a novel anti-inflammatory axis and anti-inflammatory agents that can be developed to treat acute or chronic conditions where TNFα, IL-1β, or LPS plays a key role in initiating and/or perpetuating inflammation.

During the last decade, immune checkpoint inhibition (ICI) has become a pillar of cancer therapy. Antibodies targeting CTLA-4 or PD-1/PD-L1 have been approved in several malignancies, with thousands of clinical trials currently underway. While the majority of cancer immunotherapies have traditionally focused on enhancing cytotoxic responses by CD8 + or NK cells, there are clear evidences that CD4 + T cell responses can modulate the immune response against tumors and influence the efficacy of ICI therapy. CD4 + T cells can differentiate into several subsets of helper T cells (Th) or regulatory T cells (Treg), with a wide range of effector and/or regulatory functions. Importantly, different Th subsets may have different and sometimes contrasting roles in the clinical response to ICI therapy, which in addition may vary depending on the organ and tumor niche. In this review, we discuss recent evidence that highlights how ICI therapy impacts Th1, Th9, and Th17 cells and vice versa . These data might be important designing better interventions that unleash the full potential of immune response against cancer.

In the last 20 years, remarkable advances in the field of immunotherapy have led to new therapeutic options for patients with a wide range of cancer types. Among the different immunotherapy approaches, immune checkpoint inhibition (ICI) therapy and chimeric antigen receptor (CAR) T cells have arguably shown the greatest potential. All immunotherapies share a common goal, which is to activate T lymphocytes and reinvigorate immune surveillance against cancer. While the role of CD8 T lymphocytes and other cytotoxic cells in tumor immunology has been extensively studied, the importance of CD4 T helper (Th) cells has been traditionally underestimated. In this special Research Topic, the relationship between different CD4 T cell subsets and the efficacy of current cancer immunotherapies has been highlighted by several reviews and an original article. A review article by Zuazo et al. puts systemic CD4 T cells in the spotlight of PD1/PD-L1 blocking therapies, with a special focus on non-small cell lung cancer (NSCLC). Rather than changes in the tumor microenvironment, the authors bring attention to the often overlooked but significant impact that these therapies exert over systemic immunity. Pharmacodynamic changes in circulating PD1 CD8 T cells after anti-PD-1 treatment have been correlated with clinical response (1) and recent evidence suggests that these changes, in turn, may depend on systemic CD4 cells (2). Hence, Zuazo et al. argue that targeting systemic CD4 immunity might be an important element of PD1-based therapies and propose that pre-treatment levels of specific CD4 T cell memory subsets in the periphery are correlated with response in NSCLC. DeRogatis et al. review the role of PSGL-1 (P-selectin glycoprotein ligand-1) as an immune checkpoint of CD4 T cells. PSGL-1 is highly expressed in CD4 T cells and binds to multiple proteins including P-selectin and VISTA. Psgl-1 mice mount a potent CD4 and CD8 T cell response against melanoma tumors compared to control mice. It is proposed that they energize CD8 T cells by targeting PSGL-1 in CD4 T cells or target PSGL-1 along with anti-PD-1/PD-L1 and/or anti-CTLA-4. Successful ICI therapy requires appropriate effector Th responses. The diverse and sometimes opposing roles of effector Th cells, in particular Th1, Th9, and Th17 cells, has also been reviewed in an article by Lee et al. The process of Th cell differentiation allows for considerable plasticity among different Th subpopulations, which may be exploited to increase the efficacy of ICI therapy. For this strategy to work, more data are necessary to clearly determine what type of Th subpopulation is beneficial in each particular cancer type, and then identify suitable approaches to convert other Th populations into that population. In a related article, Basu et al. discuss ways to exploit the opposing

Although cancers arise from genetic mutations enabling cells to proliferate uncontrollably, they cannot thrive without failure of the anticancer immunity due in a large part to the tumor environment's influence on effector and regulatory T cells. The field of immune checkpoint inhibitor (ICI) therapy for cancer was born out of the fact that tumor environments paralyze the immune cells that are supposed to clear them by activating the immune checkpoint molecules such as PD-1. While various subsets of effector T cells work collaboratively to eliminate cancers, Tregs enriched in the tumor environment can suppress not only the native anticancer immunity but also diminish the efficacy of ICI therapies. Because of their essential role in suppressing autoimmunity, various attempts to specifically deplete tumor-associated Tregs are currently underway to boost the efficacy of ICI therapies without causing systemic autoimmune responses. A better understanding the roles of Tregs in the anti-cancer immunity and ICI therapies should provide more specific targets to deplete intratumoral Tregs. Here, we review the current understanding on how Tregs inhibit the anti-cancer immunity and ICI therapies as well as the advances in the targeted depletion of intratumoral Tregs.

Allergic asthma is a chronic and heterogeneous pulmonary disease in which platelets can be activated in an IgE-mediated pathway and migrate to the airways via CCR3-dependent mechanism. Activated platelets secrete IL-33, Dkk-1, and 5-HT or overexpress CD40L on the cell surfaces to induce Type 2 immune response or interact with TSLP-stimulated myeloid DCs through the RANK-RANKL-dependent manner to tune the sensitization stage of allergic asthma. Additionally, platelets can mediate leukocyte infiltration into the lungs through P-selectin-mediated interaction with PSGL-1 and upregulate integrin expression in activated leukocytes. Platelets release myl9/12 protein to recruit CD4+CD69+ T cells to the inflammatory sites. Bronchoactive mediators, enzymes, and ROS released by platelets also contribute to the pathogenesis of allergic asthma. GM-CSF from platelets inhibits the eosinophil apoptosis, thus enhancing the chronic inflammatory response and tissue damage. Functional alterations in the mitochondria of platelets in allergic asthmatic lungs further confirm the role of platelets in the inflammation response. Given the extensive roles of platelets in allergic asthma, antiplatelet drugs have been tested in some allergic asthma patients. Therefore, elucidating the role of platelets in the pathogenesis of allergic asthma will provide us with new insights and lead to novel approaches in the treatment of this disease.

Experimental colitis is mediated by inflammatory or dysregulated immune responses to microbial factors of the gastrointestinal tract. In this study we observed that administration of Toll-like receptor 9 (TLR9) agonists suppressed the severity of experimental colitis in RAG1–/– but not in SCID mice. This differential responsiveness between phenotypically similar but genetically distinct animals was related to a partial blockade in TLR9 signaling and defective production of type I IFN (i.e., IFN-a/b) in SCID mice upon TLR9 stimulation. The addition of neutralization antibodies against type I IFN abolished the antiinflammatory effects induced by TLR9 agonists, whereas the administration of recombinant IFN-b mimicked the antiinflammatory effects induced by TLR9 agonists in this model. Furthermore, mice deficient in the IFN-a/b receptor exhibited more severe colitis than wild-type mice did upon induction of experimental colitis. These results indicate that TLR9-triggered type I IFN has antiinflammatory functions in colitis. They also underscore the important protective role of type I IFN in intestinal homeostasis and suggest that strategies to modulate innate immunity may be of therapeutic value for the treatment of intestinal inflammatory conditions. Article Immunology

Rapamycin has been used as a clinical immunosuppressant for many years; however, the molecular basis for its selective effects on lymphocytes remains unclear. We investigated the role of two canonical effectors of the mammalian target of rapamycin (mTOR): ribosomal S6 kinases (S6Ks) and eukaryotic initiation factor 4E (eIF4E)-binding proteins (4E-BPs). S6Ks are thought to regulate cell growth (increase in cell size), and 4E-BPs are thought to control proliferation (increase in cell number), with mTORC1 signaling serving to integrate these processes. However, we found that the 4E-BP-eIF4E signaling axis controlled both the growth and proliferation of lymphocytes, processes for which the S6Ks were dispensable. Furthermore, rapamycin disrupted eIF4E function selectively in lymphocytes, which was due to the increased abundance of 4E-BP2 relative to that of 4E-BP1 in these cells and the greater sensitivity of 4E-BP2 to rapamycin. Together, our findings suggest that the 4E-BP-eIF4E axis is uniquely rapamycin-sensitive in lymphocytes and that this axis promotes clonal expansion of these cells by coordinating growth and proliferation.

Significance Allergic asthma is characterized by Th2 type inflammation, leading to airway hyperresponsiveness and remodeling. However, the mechanisms by which DC promote Th2 differentiation remain unclear. Herein we demonstrate that low cAMP levels in DC induce Th2-biased responses in vitro and in vivo. Furthermore, mice with conditional deletion of Gnas in DC ( Gnas ΔCD11c mice) develop spontaneous bronchial asthma that shares multiple similarities with human asthma. In contrast, increasing cAMP levels inhibit these responses. Thus, regulators of cAMP levels in DC such as G-protein-coupled receptors are non-pattern recognition receptors that play a significant role in CD4 T cell differentiation.

The intestinal epithelium has a high rate of turnover, and dysregulation of pathways that regulate regeneration can lead to tumor development; however, the negative regulators of oncogenic events in the intestinal epithelium are not fully understood. Here we identified a feedback loop between the epidermal growth factor receptor (EGFR), a known mediator of proliferation, and the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), in intestinal epithelial cells (IECs). We found that TRPV1 was expressed by IECs and was intrinsically activated upon EGFR stimulation. Subsequently, TRPV1 activation inhibited EGFR-induced epithelial cell proliferation via activation of Ca2+/calpain and resulting activation of protein tyrosine phosphatase 1B (PTP1B). In a murine model of multiple intestinal neoplasia (Apc(Min/+) mice), TRPV1 deficiency increased adenoma formation, and treatment of these animals with an EGFR kinase inhibitor reversed protumorigenic phenotypes, supporting a functional association between TRPV1 and EGFR signaling in IECs. Administration of a TRPV1 agonist suppressed intestinal tumorigenesis in Apc(Min/+) mice, similar to - as well as in conjunction with - a cyclooxygenase-2 (COX-2) inhibitor, which suggests that targeting both TRPV1 and COX-2 has potential as a therapeutic approach for tumor prevention. Our findings implicate TRPV1 as a regulator of growth factor signaling in the intestinal epithelium through activation of PTP1B and subsequent suppression of intestinal tumorigenesis.

Phosphoinositide 3-kinases (PI3Ks) are promising targets for therapeutic development in cancer. The class I PI3K isoform p110α has received considerable attention in oncology because the gene encoding p110α (PIK3CA) is frequently mutated in human cancer. However, little is known about the function of p110α in lymphocyte populations that modulate tumorigenesis. We used recently developed investigational inhibitors to compare the function of p110α and other isoforms in natural killer (NK) cells, a key cell type for immunosurveillance and tumor immunotherapy. Inhibitors of all class I isoforms (pan-PI3K) significantly impaired NK cell-mediated cytotoxicity and antibody-dependent cellular cytotoxicity against tumor cells, whereas p110α-selective inhibitors had no effect. In NK cells stimulated through NKG2D, p110α inhibition modestly reduced PI3K signaling output as measured by AKT phosphorylation. Production of IFN-γ and NK cell-derived chemokines was blocked by a pan-PI3K inhibitor and partially reduced by a p110δinhibitor, with lesser effects of p110α inhibitors. Oral administration of mice with MLN1117, a p110α inhibitor in oncology clinical trials, had negligible effects on NK subset maturation or terminal subset commitment. Collectively, these results support the targeting of PIK3CA mutant tumors with selective p110α inhibitors to preserve NK cell function.

Signal Transducer and Activator of Transcription 3 (STAT3) is activated in a majority of cancers, and promotes tumorigenesis and even metastasis through transcriptional activation of its target genes. Recently, we discovered that STAT3 suppresses epithelial-to-mesenchymal transition (EMT) and thus metastasis in a mouse model of colorectal cancer (CRC), while it did not affect the overall tumor burden. Furthermore, we found that STAT3 in intestinal epithelial cells (IEC) suppresses EMT by regulating stability of an EMT inducer, SNAI-1 (Snail-1). Here, STAT3 functions as an adaptor rather than a transcription factor in the post-translational modification of SNAI-1. In this review, we discuss the unexpected and contradictory role of STAT3 in metastasis of CRC and its clinical implications.

BACKGROUND & AIMS:Foxp3(+) T-regulatory cells (Tregs) maintain intestinal homeostasis under conditions of continuous challenge with inflammatory microbes. However, plasticity of the Treg population under certain conditions has been reported; Foxp3(+) Tregs can be converted to Foxp3(-) CD4(+) T cells. METHODS:We used mice with a T cell-induced colitis model to study the regulatory role of type I interferons (IFNs) in adaptive immunity. We transferred CD4(+)CD45RB(hi) (RB(hi)) T cells, with or without CD4(+)CD45RB(lo) CD25(+) T cells, from wild-type or IFN-αβR(-/-) mice into Rag1(-/-) recipients. We analyzed induction of colitis by flow cytometry, confocal microscopy, and enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction analyses. IFN-αβR(-/-)Rag(-/-) mice were given injections of recombinant IFN-α following transfer of IFN-αβR(-/-) RB(hi) T cells and CD4(+)Foxp3(+) cells from Foxp3-eGFP mice. RESULTS:Signaling by type I IFNs was required for maintenance of Foxp3 expression and the suppressive activity of Tregs in mice. Transfer of CD4(+)CD45RB(lo)CD25(+) Tregs from IFN-αβR(-/-) mice did not prevent T-cell induction of colitis in mice. Foxp3 expression by Tregs transferred from IFN-αβR(-/-) mice was significantly lower than that of Tregs from wild-type mice. Administration of recombinant IFN-α reduced T cell-mediated colitis by increasing the number of Foxp3(+) Tregs and their suppressive functions. CONCLUSIONS:Type I IFNs regulate intestinal homeostasis by maintaining Foxp3 expression on Tregs in colons of mice under inflammatory conditions.

ATG16L1 is an essential component of the autophagasome. The T300A allele of ATG16L1 is associated with the increased susceptibility to Crohn disease. In this study, we identified a novel function of ATG16L1, which suppresses signaling of the pro-inflammatory cytokine IL-1β. Deletion of ATG16L1 in mouse embryonic fibroblasts significantly amplifies IL-1β signal transduction cascades. This amplification is due to elevated p62 levels in ATG16L1-deficient cells. We found that ATG16L1 regulates p62 levels via both autolysosomal and proteasomal pathways. For proteasomal degradation, we found that Cullin-3 (Cul-3) is a E3 ubiquitin ligase of p62 and that ATG16L1 is essential for neddylation of Cul-3, a step required for Cul-3 activation. Taken together our data indicate that loss-of-function of ATG16L1 results in a hyper-responsiveness to the IL-1β signaling because of the increased p62 level.

Type I interferons (IFNs) have become synonymous with antiviral immunity. But, as discussed in this Review, type I IFNs also have roles in bacterial infections, in intestinal homeostasis and in inflammatory and autoimmune diseases. Interferon-α (IFNα) and IFNβ, collectively known as type I IFNs, are the major effector cytokines of the host immune response against viral infections. However, the production of type I IFNs is also induced in response to bacterial ligands of innate immune receptors and/or bacterial infections, indicating a broader physiological role for these cytokines in host defence and homeostasis than was originally assumed. The main focus of this Review is the underappreciated immunomodulatory functions of type I IFNs in health and disease. We discuss their function in the regulation of innate and adaptive immune responses, the response to bacterial ligands, inflammasome activation, intestinal homeostasis and inflammatory and autoimmune diseases.

STAT3 was recently reported to suppress tumor invasion in Apc(min)(/+) mice. We investigated the mechanisms by which STAT3 inhibits intestinal epithelial tumors using Apc(min)(/+)/Stat3(IEC-KO) mice (intestinal epithelial cell (IEC)-specific deletion of STAT3 in the Apc(min)(/+) background) to determine the role of STAT3 in carcinogenesis in vivo as well as colorectal cancer cell lines in vitro. To inhibit invasion of IEC tumors, STAT3 functions as a molecular adaptor rather than a transcription factor. Accordingly, the tumors in Apc(min)(/+)/Stat3(IEC-KO) mice undergo adenoma-to-carcinoma transition and acquire an invasive phenotype. Similarly, STAT3 knockdown in a colorectal cell line enhances IEC invasion. We demonstrate that STAT3 down-regulates SNAI (Snail-1) expression levels and hence suppresses epithelial-mesenchymal transition of colorectal cancer cells. Mechanistically, STAT3 facilitates glycogen synthase kinase (GSK) 3β-mediated degradation of SNAI by regulating phosphorylation of GSK3β. Our data identified a new role for STAT3 in the adenoma-to-carcinoma sequence of intestinal tumors.