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Regulatory T (T(reg)) cells are an immunosuppressive population that are required to maintain peripheral tolerance and prevent tissue damage from immunopathology, via anti-inflammatory cytokines, inhibitor receptors and metabolic disruption. Here we show that T(reg) cells acquire an effector-like state, yet remain stable and functional, when exposed to interferon gamma (IFNγ) during infection with lymphocytic choriomeningitis and influenza A virus. T(reg) cell-restricted deletion of the IFNγ receptor (encoded by Ifngr1), but not the interleukin 12 (IL12) receptor (encoded by Il12rb2), prevented T(H)1-like polarization (decreased expression of T-bet, CXC motif chemokine receptor 3 and IFNγ) and promoted T(H)2-like polarization (increased expression of GATA-3, CCR4 and IL4). T(H)1-like T(reg) cells limited CD8(+) T cell effector function, proliferation and memory formation during acute and chronic infection. These findings provide fundamental insights into how T(reg) cells sense inflammatory cues from the environment (such as IFNγ) during viral infection to provide guidance to the effector immune response. This regulatory circuit prevents prolonged immunoinflammatory responses and shapes the quality and quantity of the memory T cell response.

β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is best known for its role in Alzheimer's disease amyloid plaque formation but also contributes to neurodegenerative processes triggered by CNS injury. In this article, we report that BACE1 is expressed in murine CD4+ T cells and regulates signaling through the TCR. BACE1-deficient T cells have reduced IL-17A expression under Th17 conditions and reduced CD73 expression in Th17 and inducible T regulatory cells. However, induction of the Th17 and T regulatory transcription factors RORγt and Foxp3 was unaffected. BACE1-deficient T cells showed impaired pathogenic function in experimental autoimmune encephalomyelitis. These data identify BACE1 as a novel regulator of T cell signaling pathways that impact autoimmune inflammatory T cell function.

Robertson et al. show that unlike T cells responding to conventional chemokines, T cells responding to the lipid chemoattractant S1P utilize a bleb-based mode of motility. This response involves myosin-induced increases in intracellular pressure and is directed by the cortical cytoskeletal proteins ezrin and moesin., Ezrin, radixin, and moesin (ERM) family proteins regulate cytoskeletal responses by tethering the plasma membrane to the underlying actin cortex. Mutations in ERM proteins lead to severe combined immunodeficiency, but the function of these proteins in T cells remains poorly defined. Using mice in which T cells lack all ERM proteins, we demonstrate a selective role for these proteins in facilitating S1P-dependent egress from lymphoid organs. ERM-deficient T cells display defective S1P-induced migration in vitro, despite normal responses to standard protein chemokines. Analysis of these defects revealed that S1P promotes a fundamentally different mode of migration than chemokines, characterized by intracellular pressurization and bleb-based motility. ERM proteins facilitate this process, controlling directional migration by limiting blebbing to the leading edge. We propose that the distinct modes of motility induced by S1P and chemokines are specialized to allow T cell migration across lymphatic barriers and through tissue stroma, respectively.

Regulatory T cells (Tregs) are an immunosuppressive cell population that inhibits immune cell function to maintain peripheral tolerance and homeostasis. We have previously shown that Treg-- response to interferon gamma (IFNγ) is required for response to cancer immunotherapy. We aimed to broaden these findings and determine the impact of Treg response to IFNγ and the IFNγ-inducing cytokine IL12, during viral infection. Mice with Treg-restricted deletion of the IFNγ receptor (IFNGR1, Ifngr1L/LFoxp3Cre-YFP) or the IL12 receptor β2 subunit (IL12Rβ2, Il12b2L/LFoxp3Cre-YFP), were infected with the acute (Armstrong), or chronic (Clone 13), strain of lymphocytic choriomeningitis virus (LCMV). Surprisingly, Treg response to IFNγ but not IL12 induced helper T cell 1 (TH1)-like polarization (expression of T-bet, CXCR3 and IFNγ) of Tregs in mice with chronic LCMV infection. Importantly, this effector-like TH1 Treg state was required for adequate suppression of effector T cells during LCMV infection. Additionally, during LCMV infection, Treg-restricted deletion of IFNGR1 not only prevented TH1-like polarization but also reverted these Tregs to a TH2-like state (expression of GATA-3, CCR4 and IL-4). scRNAseq of viral antigen-specific CD8+ T cells from Clone 13 infected mice showed that Ifngr1-deficient Tregs favored CD8+ T cell memory. These findings were confirmed in an Armstrong/Listeria monocytogenes-GP33 memory model. Further, Ifngr1 deletion from Tregs enhanced response to CD8+ T cell-mediated vaccination when challenged with Clone 13. These findings provide fundamental insight on how Tregs sense inflammatory cues from the environment (IFNγ) during viral infection to prevent overt tissue damage and shape the memory response. Supported by grants from NIH (F32 CA247004-01, T32 CA082084, P01 AI108545, R35 CA263850, R01 CA203689, R01 DK130897, P30 DK120531, P30 CA047904, R01 HL107380, R01 CA206517, R01 AI138504)

While T cells are important for the pathogenesis of systemic lupus erythematosus (SLE) and lupus nephritis, little is known about how T cells function after infiltrating the kidney. The current paradigm suggests that kidney-infiltrating T cells (KITs) are activated effector cells contributing to tissue damage and ultimately organ failure. Herein, we demonstrate that the majority of CD4+ and CD8+ KITs in 3 murine lupus models are not effector cells, as hypothesized, but rather express multiple inhibitory receptors and are highly dysfunctional, with reduced cytokine production and proliferative capacity. In other systems, this hypofunctional profile is linked directly to metabolic and specifically mitochondrial dysfunction, which we also observed in KITs. The T cell phenotype was driven by the expression of an "exhausted" transcriptional signature. Our data thus reveal that the tissue parenchyma has the capability of suppressing T cell responses and limiting damage to self. These findings suggest avenues for the treatment of autoimmunity based on selectively exploiting the exhausted phenotype of tissue-infiltrating T cells.

Herpes simplex virus 1 (HSV-1) causes a lifelong infection of neurons that innervate barrier sites like the skin and mucosal surfaces like the eye. After primary infection of the cornea, the virus enters latency within the trigeminal ganglion (TG), from which it can reactivate throughout the life of the host. Viral latency is maintained, in part, by virus-specific CD8+ T cells that nonlethally interact with infected neurons. When CD8+ T cell responses are inhibited, HSV-1 can reactivate, and these recurrent reactivation events can lead to blinding scarring of the cornea. In the C57BL/6 mouse, CD8+ T cells specific for the immunodominant epitope from glycoprotein B maintain functionality throughout latency, while CD8+ T cells specific for subdominant epitopes undergo functional impairment that is associated with the expression of the inhibitory checkpoint molecule programmed death 1 (PD-1). Here, we investigate the checkpoint molecule T cell immunoglobulin and mucin domain-containing 3 (Tim-3), which has traditionally been associated with CD8+ T cell exhaustion. Unexpectedly, we found that Tim-3 was preferentially expressed on highly functional ganglionic CD8+ T cells during acute and latent HSV-1 infection. This, paired with data that show that Tim-3 expression on CD8+ T cells in the latently infected TG is influenced by viral gene expression, suggests that Tim-3 is an indicator of recent T cell stimulation, rather than functional compromise, in this model. We conclude that Tim-3 expression is not sufficient to define functional compromise during latency; however, it may be useful in identifying activated cells within the TG during HSV-1 infection.IMPORTANCE Without an effective means of eliminating HSV-1 from latently infected neurons, efforts to control the virus have centered on preventing viral reactivation from latency. Virus-specific CD8+ T cells within the infected TG have been shown to play a crucial role in inhibiting viral reactivation, and with a portion of these cells exhibiting functional impairment, checkpoint molecule immunotherapies have presented a potential solution to enhancing the antiviral response of these cells. In pursuing this potential treatment strategy, we found that Tim-3 (often associated with CD8+ T cell functional exhaustion) is not upregulated on impaired cells but instead is upregulated on highly functional cells that have recently received antigenic stimulation. These findings support a role for Tim-3 as a marker of activation rather than exhaustion in this model, and we provide additional evidence for the hypothesis that there is persistent viral gene expression in the HSV-1 latently infected TG.

Herpes simplex virus 1 (HSV-1) causes a lifelong infection of neurons that innervate barrier sites like the skin and mucosal surfaces like the eye. After primary infection of the cornea, the virus enters latency within the trigeminal ganglion (TG), from which it can reactivate throughout the life of the host. Viral latency is maintained, in part, by virus-specific CD8(+) T cells that nonlethally interact with infected neurons. When CD8(+) T cell responses are inhibited, HSV-1 can reactivate, and these recurrent reactivation events can lead to blinding scarring of the cornea. In the C57BL/6 mouse, CD8(+) T cells specific for the immunodominant epitope from glycoprotein B maintain functionality throughout latency, while CD8(+) T cells specific for subdominant epitopes undergo functional impairment that is associated with the expression of the inhibitory checkpoint molecule programmed death 1 (PD-1). Here, we investigate the checkpoint molecule T cell immunoglobulin and mucin domain-containing 3 (Tim-3), which has traditionally been associated with CD8(+) T cell exhaustion. Unexpectedly, we found that Tim-3 was preferentially expressed on highly functional ganglionic CD8(+) T cells during acute and latent HSV-1 infection. This, paired with data that show that Tim-3 expression on CD8(+) T cells in the latently infected TG is influenced by viral gene expression, suggests that Tim-3 is an indicator of recent T cell stimulation, rather than functional compromise, in this model. We conclude that Tim-3 expression is not sufficient to define functional compromise during latency; however, it may be useful in identifying activated cells within the TG during HSV-1 infection. IMPORTANCE Without an effective means of eliminating HSV-1 from latently infected neurons, efforts to control the virus have centered on preventing viral reactivation from latency. Virus-specific CD8(+) T cells within the infected TG have been shown to play a crucial role in inhibiting viral reactivation, and with a portion of these cells exhibiting functional impairment, checkpoint molecule immunotherapies have presented a potential solution to enhancing the antiviral response of these cells. In pursuing this potential treatment strategy, we found that Tim-3 (often associated with CD8(+) T cell functional exhaustion) is not upregulated on impaired cells but instead is upregulated on highly functional cells that have recently received antigenic stimulation. These findings support a role for Tim-3 as a marker of activation rather than exhaustion in this model, and we provide additional evidence for the hypothesis that there is persistent viral gene expression in the HSV-1 latently infected TG.

T cell activation by dendritic cells (DCs) involves forces exerted by the T cell actin cytoskeleton, which are opposed by the cortical cytoskeleton of the interacting APC. During an immune response, DCs undergo a maturation process that optimizes their ability to efficiently prime naïve T cells. Using atomic force microscopy, we find that during maturation, DC cortical stiffness increases via process that involves actin polymerization. Using stimulatory hydrogels and DCs expressing mutant cytoskeletal proteins, we find that increasing stiffness lowers the agonist dose needed for T cell activation. CD4+ T cells exhibit much more profound stiffness-dependency than CD8+ T cells. Finally, stiffness responses are most robust when T cells are stimulated with pMHC rather than anti-CD3ε, consistent with a mechanosensing mechanism involving receptor deformation. Taken together, our data reveal that maturation-associated cytoskeletal changes alter the biophysical properties of DCs, providing mechanical cues that costimulate T cell activation.

There is growing appreciation that cellular metabolic and bioenergetic pathways do not play merely passive roles in activated leukocytes. Rather, metabolism has important roles in controlling cellular activation, differentiation, survival, and effector function. Much of this work has been performed in T cells; however, there is still very little information regarding mast cell metabolic reprogramming and its effect on cellular function. Mast cells perform important barrier functions and help control type 2 immune responses. In this study we show that murine bone marrow–derived mast cells rapidly alter their metabolism in response to stimulation through the FcεRI. We also demonstrate that specific metabolic pathways appear to be differentially required for the control of mast cell function. Manipulation of metabolic pathways may represent a novel point for the manipulation of mast cell activation.

Tim-3 is highly expressed on a subset of T cells during T cell exhaustion in settings of chronic viral infection and tumors. Using lymphocytic choriomeningitis virus (LCMV) Clone 13, a model for chronic infection, we found that Tim-3 was neither necessary nor sufficient for the development of T cell exhaustion. Nonetheless, expression of Tim-3 was sufficient to drive resistance to PD-L1 blockade therapy during chronic infection. Strikingly, expression of Tim-3 promoted the development of short-lived effector T cells, at the expense of memory precursor development, after acute LCMV infection. These effects were accompanied by increased Akt/mTOR signaling in T cells expressing endogenous or ectopic Tim-3. Conversely, Akt/mTOR signaling was reduced in effector T cells from Tim-3-deficient mice. Thus, Tim-3 is essential for optimal effector T cell responses, and may also contribute to exhaustion by restricting the development of long-lived memory T cells. Taken together, our results suggest that Tim-3 is actually more similar to costimulatory receptors that are up-regulated after T cell activation than to a dominant inhibitory protein like PD-1. These findings have significant implications for the development of anti-Tim-3 antibodies as therapeutic agents.

Tim-3 is highly expressed on a subset of T cells during T cell exhaustion, in settings of chronic viral infection and tumors (1, 2). Using LCMV Clone-13, a model for chronic infection, we have found that Tim-3 is neither necessary nor sufficient for the development of T cell exhaustion. Nonetheless, expression of Tim-3 was sufficient to drive resistance to PD-L1 blockade therapy during chronic infection. Strikingly, expression of Tim-3 promoted development of short-term effector T cells, at the expense of memory precursor development, after acute LCMV infection. These effects were accompanied by increased Akt/mTOR signaling in T cells expressing endogenous or ectopic Tim-3. Conversely, Akt/mTOR signaling was reduced in effector T cells from Tim-3 deficient mice. Thus, Tim-3 is essential for optimal effector T cell responses, but may also contribute to exhaustion, by restricting development of long-lived memory T cells, including PD-1int “stem-like” exhausted T cells that expand during PD-1 pathway blockade. Taken together, our results suggest that Tim-3 is actually more similar to co-stimulatory receptors that are upregulated after T cell activation, rather than a dominant inhibitory protein like PD-1. These findings have significant implications for the development of anti-Tim-3 antibodies as therapeutic agents.SignificanceDuring a chronic viral infection, prolonged exposure to viral antigens leads to dysfunction or “exhaustion” of T cells specific to the virus, a condition also observed in T cells that infiltrate tumors. The exhausted state is associated with expression of specific cell-surface proteins, some of which may inhibit T cell activation. Expression of Tim-3 is associated with acquisition of T cell exhaustion, although it is also expressed transiently during acute infection. Here we provide evidence that a major function of Tim-3 is to enhance T cell activation, during either acute or chronic viral infection. However, Tim-3 is not required for development of exhaustion. Thus, we propose that Tim-3 would be better described as a stimulatory, rather than inhibitory, protein.

Micropipetting is an essential skill for the budding immunologist and is widely used across biological and physical science disciplines, yet few undergraduates are adequately introduced to this skill. The mentors of undergraduates seeking research experience point to micropipette inexperience as a common barrier to success. As part of our SEA-PHAGES authentic research laboratory, we designed a hands-on intervention to give thorough training in micropipetting to first-year undergraduates. The intervention included assignment of a pre-class video on micropipetting, an activity to orient students to the micropipette parts and functions, and a TA-led demonstration of proper micropipette use and volume adjustment. Success of the intervention was analyzed using data collected from a practical test following the lab activity. In addition, we compared the students’ end-of-semester experimental success to that of students from previous semesters lacking the micropipetting activity, using archived electronic laboratory notebooks. We found that students progressed through experiments faster and with more success after experiencing the micropipette intervention. Our analysis showed that some aspects of proper micropipette use need to be emphasized, such as proper depth of tip entry and the correct tactile discrimination of the first/second stop on the micropipette. In addition, we found that students have misconceptions and gaps in knowledge about the metric system that are an additional barrier to proper micropipette use. This project presents a successful platform for teaching micropipette technique, and demonstrates that this leads to increased likelihood of success for the students in this real-world laboratory setting.

IL-10 production during intracellular bacterial infections is generally thought to be detrimental because of its role in suppressing protective T-helper cell 1 (Th1) responses. Francisella tularensis is a facultative intracellular bacterium that activates both Th1 and Th17 protective immune responses. Herein, we report that IL-10-deficient mice (Il10(-/-)), despite having increased Th1 and Th17 responses, exhibit increased mortality after pulmonary infection with F. tularensis live vaccine strain. We demonstrate that the increased mortality observed in Il10(-/-)-infected mice is due to exacerbated IL-17 production that causes increased neutrophil recruitment and associated lung pathology. Thus, although IL-17 is required for protective immunity against pulmonary infection with F. tularensis live vaccine strain, its production is tightly regulated by IL-10 to generate efficient induction of protective immunity without mediating pathology. These data suggest a critical role for IL-10 in maintaining the delicate balance between host immunity and pathology during pulmonary infection with F. tularensis live vaccine strain.

Programmed Death 1 (PD-1) and T cell Ig and mucin domain-3 protein (Tim-3) are immune checkpoint receptors highly expressed on tumor infiltrating T lymphocytes (TIL). PD-1 inhibits T cell activation and type-1 T cell responses, while Tim-3 is proposed to mark more extensively exhausted cells, although the mechanisms underlying Tim-3 function are not clear. Trials of anti-PD-1 therapy have identified a large subset of non-responder patients, likely due to expression of alternative checkpoint molecules like Tim-3. We investigated the phenotypic and functional characteristics of T cells with differential expression of PD-1 (high/low) and Tim-3 (positive/negative), using TIL directly isolated from head and neck squamous cell carcinomas (HNSCC). Unexpectedly, we found that expression of Tim-3 alone does not necessarily mark TIL as dysfunctional/exhausted. In Tim-3-TIL, PD-1 levels correlate with T cell dysfunction, with a PD-1low/intermed phenotype identifying recently activated and still functional cells, whereas PD-1hiTim-3− T cells are actually exhausted. Nonetheless, PD-1intermed cells are still potently suppressed by PD-L1. PD-1 expression was associated with reduced phosphorylation of ribosomal protein S6 (pS6), whereas Tim-3 expression was associated with increased pS6. Using a novel mouse model for inducible Tim-3 expression, we confirmed that expression of Tim-3 does not necessarily render T cells refractory to further activation. These results suggest the existence of PD-1 and Tim-3 crosstalk in regulating antitumor T cell responses, with important implications for anti-PD-1 immunotherapy.

Phong et al. show that depending on the expression of p-Lyn, mast cell activation by antigen can result in dichotomous effects on mast cell function and signaling that can be accentuated by Tim-3 ligation., T cell (or transmembrane) immunoglobulin and mucin domain protein 3 (Tim-3) has attracted significant attention as a novel immune checkpoint receptor (ICR) on chronically stimulated, often dysfunctional, T cells. Antibodies to Tim-3 can enhance antiviral and antitumor immune responses. Tim-3 is also constitutively expressed by mast cells, NK cells and specific subsets of macrophages and dendritic cells. There is ample evidence for a positive role for Tim-3 in these latter cell types, which is at odds with the model of Tim-3 as an inhibitory molecule on T cells. At this point, little is known about the molecular mechanisms by which Tim-3 regulates the function of T cells or other cell types. We have focused on defining the effects of Tim-3 ligation on mast cell activation, as these cells constitutively express Tim-3 and are activated through an ITAM-containing receptor for IgE (FcεRI), using signaling pathways analogous to those in T cells. Using a variety of gain- and loss-of-function approaches, we find that Tim-3 acts at a receptor-proximal point to enhance Lyn kinase-dependent signaling pathways that modulate both immediate-phase degranulation and late-phase cytokine production downstream of FcεRI ligation.

Programmed Death 1 (PD-1) and T cell Ig and mucin domain-3 protein (Tim-3) are immune checkpoint receptors highly expressed on tumor infiltrating T lymphocytes (TIL). PD-1 inhibits T cell activation and type-1 T cell responses, while Tim-3 is proposed to mark more extensively exhausted cells, although the mechanisms underlying Tim-3 function are not clear. Trials of anti-PD-1 therapy have identified a large subset of non-responder patients, likely due to expression of alternative checkpoint molecules like Tim-3. We investigated the phenotypic and functional characteristics of T cells with differential expression of PD-1 (high/low) and Tim-3 (positive/negative), using TIL directly isolated from head and neck squamous cell carcinomas (HNSCC). Unexpectedly, we found that expression of Tim-3 alone does not necessarily mark TIL as dysfunctional/exhausted. In Tim-3-TIL, PD-1 levels correlate with T cell dysfunction, with a PD-1low/intermed phenotype identifying recently activated and still functional ce...

Chronic viral infection and the tumor microenvironment are two settings in which persistent immune stimulation can occur. Under such conditions, T cell activation becomes downregulated, likely in order to reduce immune pathology, resulting in a phenotype known as T cell ‘exhaustion’. Functionally exhausted T cells are characterized by reduced cytokine production, proliferative capability, and cytotoxic activity, with a corresponding expression of checkpoint receptors, including PD-1, CTLA-4, LAG-3 and Tim-3. While PD-1, CTLA-4, and LAG-3 have known mechanisms for reducing T cell effector function, the intrinsic effects of Tim-3 on T cell activation are largely unknown. In fact, recent evidence reveals divergent effects of Tim-3 in various infectious models. Data from our lab indicate that Tim-3 can enhance acute TCR signaling, while much of the existing literature associates Tim-3 expression with diminished effector function. Current approaches to study Tim-3 require persistent antigen stimulation or ectopic expression. We have developed a novel mouse model where the expression of Tim-3 is induced in vivo by Cre-mediated recombination. We hypothesize that inducible Tim-3 expression may cause T cells to become dysfunctional earlier by enhancing the initial response to stimulation. Using this model, we have found that the presence of Tim-3 enhances T cell activation after acute in vitro stimulation. We are currently testing how induction of Tim-3 will affect responses to a murine model of chronic viral infection, LCMV-clone13. Results from this study will address knowledge gaps about the effects of Tim-3 on T cells and will have practical applications in both chronic viral infection and cancer immunotherapy.

Chronic viral infection and the tumor microenvironment provide settings where T cells are persistently stimulated by their cognate antigen. These T cells are often ‘exhausted’ and exhibit decreased effector function and proliferative potential. Tim-3 is an inhibitory receptor upregulated on the surface of exhausted T cells, and Tim-3 blockade has shown potential for reversal of this phenotype. Understanding mechanisms that regulate Tim-3 expression and signaling can provide insight into therapeutics to rescue exhausted T cell function. Upon T cell activation, the unfolded protein response (UPR) is initiated to resolve a build-up of newly translated protein in the endoplasmic reticulum (ER). Bat3, an ER chaperone upregulated during the UPR, was suggested to be a repressor of Tim-3 cytoplasmic signaling. XBP1, a transcription factor activated during the UPR, is predicted to bind the Tim-3 gene. We aim to confirm the interaction of XBP1 with the Tim-3 gene, as well as understand its functional significance. Linking the UPR and Tim-3 could provide novel information on pathways that drive exhaustion and offer insight into therapies for diseases where chronic antigen stimulation occurs.