Top 40 papers of 2016

No.. no.. this is NOT a list of the best Immunology papers of 2016; Instead this is a very self-centered list of 40 papers that we really liked – i.e. they are directly or indirectly related to the areas of research in our lab. The list is not ranked or ordered or comprehensive … but just sorted alphabetically by first author names. It was hard to settle on 40; but of course, as we stumble upon more papers that we missed from last year, we will amend this list. Nevertheless these are 40 cool papers from a great (and busy) year in Immunology research, that we hope everyone reads ….

Basu, R., et al. (2016). "Cytotoxic T Cells Use Mechanical Force to Potentiate Target Cell Killing." Cell 165(1): 100-110.

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       The immunological synapse formed between a cytotoxic T lymphocyte (CTL) and an infected or transformed target cell is a physically active structure capable of exerting mechanical force. Here, we investigated whether synaptic forces promote the destruction of target cells. CTLs kill by secreting toxic proteases and the pore forming protein perforin into the synapse. Biophysical experiments revealed a striking correlation between the magnitude of force exertion across the synapse and the speed of perforin pore formation on the target cell, implying that force potentiates cytotoxicity by enhancing perforin activity. Consistent with this interpretation, we found that increasing target cell tension augmented pore formation by perforin and killing by CTLs. Our data also indicate that CTLs coordinate perforin release and force exertion in space and time. These results reveal an unappreciated physical dimension to lymphocyte function and demonstrate that cells use mechanical forces to control the activity of outgoing chemical signals.

Bautista, B. L., et al. (2016). "Short-Lived Antigen Recognition but Not Viral Infection at a Defined Checkpoint Programs Effector CD4 T Cells To Become Protective Memory." J Immunol 197(10): 3936-3949.

       Although memory CD4 T cells are critical for effective immunity to pathogens, the mechanisms underlying their generation are still poorly defined. We find that following murine influenza infection, most effector CD4 T cells undergo apoptosis unless they encounter cognate Ag at a defined stage near the peak of effector generation. Ag recognition at this memory checkpoint blocks default apoptosis and programs their transition to long-lived memory. Strikingly, we find that viral infection is not required, because memory formation can be restored by the addition of short-lived, Ag-pulsed APC at this checkpoint. The resulting memory CD4 T cells express an enhanced memory phenotype, have increased cytokine production, and provide protection against lethal influenza infection. Finally, we find that memory CD4 T cell formation following cold-adapted influenza vaccination is boosted when Ag is administered during this checkpoint. These findings imply that persistence of viral Ag presentation into the effector phase is the key factor that determines the efficiency of memory generation. We also suggest that administering Ag at this checkpoint may improve vaccine efficacy.

Beura, L. K., et al. (2016). "Normalizing the environment recapitulates adult human immune traits in laboratory mice." Nature 532(7600): 512-516.

      Our current understanding of immunology was largely defined in laboratory mice, partly because they are inbred and genetically homogeneous, can be genetically manipulated, allow kinetic tissue analyses to be carried out from the onset of disease, and permit the use of tractable disease models. Comparably reductionist experiments are neither technically nor ethically possible in humans. However, there is growing concern that laboratory mice do not reflect relevant aspects of the human immune system, which may account for failures to translate disease treatments from bench to bedside. Laboratory mice live in abnormally hygienic specific pathogen free (SPF) barrier facilities. Here we show that standard laboratory mouse husbandry has profound effects on the immune system and that environmental changes produce mice with immune systems closer to those of adult humans. Laboratory mice–like newborn, but not adult, humans–lack effector-differentiated and mucosally distributed memory T cells. These cell populations were present in free-living barn populations of feral mice and pet store mice with diverse microbial experience, and were induced in laboratory mice after co-housing with pet store mice, suggesting that the environment is involved in the induction of these cells. Altering the living conditions of mice profoundly affected the cellular composition of the innate and adaptive immune systems, resulted in global changes in blood cell gene expression to patterns that more closely reflected the immune signatures of adult humans rather than neonates, altered resistance to infection, and influenced T-cell differentiation in response to a de novo viral infection. These data highlight the effects of environment on the basal immune state and response to infection and suggest that restoring physiological microbial exposure in laboratory mice could provide a relevant tool for modelling immunological events in free-living organisms, including humans.

Calabro, S., et al. (2016). "Bridging channel dendritic cells induce immunity to transfused red blood cells." J Exp Med.

      Red blood cell (RBC) transfusion is a life-saving therapeutic tool. However, a major complication in transfusion recipients is the generation of antibodies against non-ABO alloantigens on donor RBCs, potentially resulting in hemolysis and renal failure. Long-lived antibody responses typically require CD4+ T cell help and, in murine transfusion models, alloimmunization requires a spleen. Yet, it is not known how RBC-derived antigens are presented to naive T cells in the spleen. We sought to answer whether splenic dendritic cells (DCs) were essential for T cell priming to RBC alloantigens. Transient deletion of conventional DCs at the time of transfusion or splenic DC preactivation before RBC transfusion abrogated T and B cell responses to allogeneic RBCs, even though transfused RBCs persisted in the circulation for weeks. Although all splenic DCs phagocytosed RBCs and activated RBC-specific CD4+ T cells in vitro, only bridging channel 33D1+ DCs were required for alloimmunization in vivo. In contrast, deletion of XCR1+CD8+ DCs did not alter the immune response to RBCs. Our work suggests that blocking the function of one DC subset during a narrow window of time during RBC transfusion could potentially prevent the detrimental immune response that occurs in patients who require lifelong RBC transfusion support.

Campisi, L., et al. (2016). "Apoptosis in response to microbial infection induces autoreactive TH17 cells." Nat Immunol.

      Microbial infections often precede the onset of autoimmunity. How infections trigger autoimmunity remains poorly understood. We investigated the possibility that infection might create conditions that allow the stimulatory presentation of self peptides themselves and that this might suffice to elicit autoreactive T cell responses that lead to autoimmunity. Self-reactive CD4+ T cells are major drivers of autoimmune disease, but their activation is normally prevented through regulatory mechanisms that limit the immunostimulatory presentation of self antigens. Here we found that the apoptosis of infected host cells enabled the presentation of self antigens by major histocompatibility complex class II molecules in an inflammatory context. This was sufficient for the generation of an autoreactive TH17 subset of helper T cells, prominently associated with autoimmune disease. Once induced, the self-reactive TH17 cells promoted auto-inflammation and autoantibody generation. Our findings have implications for how infections precipitate autoimmunity.

Chu, H. H., et al. (2016). "Continuous Effector CD8(+) T Cell Production in a Controlled Persistent Infection Is Sustained by a Proliferative Intermediate Population." Immunity 45(1): 159-171.

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        Highly functional CD8(+) effector T (Teff) cells can persist in large numbers during controlled persistent infections, as exemplified by rare HIV-infected individuals who control the virus. Here we examined the cellular mechanisms that maintain ongoing T effector responses using a mouse model for persistent Toxoplasma gondii infection. In mice expressing the protective MHC-I molecule, H-2L(d), a dominant T effector response against a single parasite antigen was maintained without a contraction phase, correlating with ongoing presentation of the dominant antigen. Large numbers of short-lived Teff cells were continuously produced via a proliferative, antigen-dependent intermediate (Tint) population with a memory-effector hybrid phenotype. During an acute, resolved infection, decreasing antigen load correlated with a sharp drop in the Tint cell population and subsequent loss of the ongoing effector response. Vaccination approaches aimed at the development of Tint populations might prove effective against pathogens that lead to chronic infection.

Gerlach, C., et al. (2016). "The Chemokine Receptor CX3CR1 Defines Three Antigen-Experienced CD8 T Cell Subsets with Distinct Roles in Immune Surveillance and Homeostasis." Immunity 45(6): 1270-1284.

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      Infections induce pathogen-specific T cell differentiation into diverse effectors (Teff) that give rise to memory (Tmem) subsets. The cell-fate decisions and lineage relationships that underlie these transitions are poorly understood. Here, we found that the chemokine receptor CX3CR1 identifies three distinct CD8+ Teff and Tmem subsets. Classical central (Tcm) and effector memory (Tem) cells and their corresponding Teff precursors were CX3CR1- and CX3CR1high, respectively. Viral infection also induced a numerically stable CX3CR1int subset that represented approximately 15% of blood-borne Tmem cells. CX3CR1int Tmem cells underwent more frequent homeostatic divisions than other Tmem subsets and not only self-renewed, but also contributed to the expanding CX3CR1- Tcm pool. Both Tcm and CX3CR1int cells homed to lymph nodes, but CX3CR1int cells, and not Tem cells, predominantly surveyed peripheral tissues. As CX3CR1int Tmem cells present unique phenotypic, homeostatic, and migratory properties, we designate this subset peripheral memory (tpm) cells and propose that tpm cells are chiefly responsible for the global surveillance of non-lymphoid tissues.

Goplen, N. P., et al. (2016). "IL-12 Signals through the TCR To Support CD8 Innate Immune Responses." J Immunol 197(6): 2434-2443.

        CD8 T cells must integrate antigenic and inflammatory signals to differentiate into efficient effector and memory T cells able to protect us from infections. The mechanisms by which TCR signaling and proinflammatory cytokine receptor signaling cooperate in these processes are poorly defined. In this study, we show that IL-12 and other proinflammatory cytokines transduce signals through the TCR signalosome in a manner that requires Fyn activity and self-peptide-MHC (self-pMHC) interactions. This mechanism is crucial for CD8 innate T cell functions. Loss of Fyn activity or blockade of self-pMHC interactions severely impaired CD8 T cell IFN-gamma and NKG2D expression, proliferation, and cytotoxicity upon cytokine-mediated bystander activation. Most importantly, in the absence of self-pMHC interactions, CD8 memory T cells fail to undergo bystander activation upon an unrelated infection. Thus, CD8 T cell bystander activation, although independent of cognate Ag, still requires self-pMHC and TCR signaling.

Halle, S., et al. (2016). "In Vivo Killing Capacity of Cytotoxic T Cells Is Limited and Involves Dynamic Interactions and T Cell Cooperativity." Immunity 44(2): 233-245.

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      According to in vitro assays, T cells are thought to kill rapidly and efficiently, but the efficacy and dynamics of cytotoxic T lymphocyte (CTL)-mediated killing of virus-infected cells in vivo remains elusive. We used two-photon microscopy to quantify CTL-mediated killing in mice infected with herpesviruses or poxviruses. On average, one CTL killed 2-16 virus-infected cells per day as determined by real-time imaging and by mathematical modeling. In contrast, upon virus-induced MHC class I downmodulation, CTLs failed to destroy their targets. During killing, CTLs remained migratory and formed motile kinapses rather than static synapses with targets. Viruses encoding the calcium sensor GCaMP6s revealed strong heterogeneity in individual CTL functional capacity. Furthermore, the probability of death of infected cells increased for those contacted by more than two CTLs, indicative of CTL cooperation. Thus, direct visualization of CTLs during killing of virus-infected cells reveals crucial parameters of CD8(+) T cell immunity.

Hilpert, C., et al. (2016). "Dendritic Cells Are Dispensable for T Cell Priming and Control of Acute Lymphocytic Choriomeningitis Virus Infection." J Immunol 197(7): 2780-2786.

      Dendritic cells (DCs) are considered to be the major APCs with potent activity for priming of naive CD4 and CD8 T cells. However, T cell priming can also be achieved by other APCs including macrophages, B cells, or even nonhematopoietic cell types. Systemic low-dose infection of mice with lymphocytic choriomeningitis virus (LCMV) results in massive expansion of virus-specific CD4 and CD8 T cells. To determine the role of DCs as APCs and source of type I IFNs in this infection model, we used DeltaDC mice in which DCs are constitutively ablated because of expression of the diphtheria toxin alpha subunit within developing DCs. DeltaDC mice showed lower serum concentrations of IFN-beta and IL-12p40, but normal IFN-alpha levels during the first days postinfection. No differences were found for proliferation of transferred TCR-transgenic cells during the early phase of infection, suggesting that T cell priming occurred with the same efficiency in wild-type and DeltaDC mice. Expansion and cytokine expression of endogenous LCMV-specific T cells was comparable between wild-type and DeltaDC mice during primary infection and upon rechallenge of memory mice. In both strains of infected mice the viral load was reduced below the limit of detection with the same kinetic. Further, germinal center formation and LCMV-specific Ab responses were not impaired in DeltaDC mice. This indicates that DCs are dispensable as APCs for protective immunity against LCMV infection.

Im, S. J., et al. (2016). "Defining CD8+ T cells that provide the proliferative burst after PD-1 therapy." Nature.

                    Chronic viral infections are characterized by a state of CD8+ T cell dysfunction that is associated with expression of the programmed cell death 1 (PD-1) inhibitory receptor1-4. A better understanding of the mechanisms that regulate CD8+ T cell responses during chronic infection is required to improve immunotherapies that restore function in exhausted CD8+ T cells. Here we identify the population of virus-specific CD8+ T cells that proliferate after blockade of the PD-1 inhibitory pathway in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). These LCMV-specific CD8+ T cells expressed the PD-1 inhibitory receptor but at the same time also expressed several co-stimulatory molecules such as ICOS, OX-40 and CD28. This CD8+ T cell subset was characterized by a unique gene signature that was related to CD4+ T follicular helper (Tfh) cells, CD8+ T cell memory precursors and hematopoietic stem cell progenitors, but that was distinct from CD4+ Th1 cells and CD8+ terminal effectors. This CD8+ T cell population was only found in lymphoid tissues and resided predominantly in the T cell zones along with naive CD8+ T cells. These PD-1+CD8+ T cells were stem cell-like during chronic LCMV infection, undergoing self-renewal and also differentiating into the terminally exhausted CD8+ T cells that were present in both lymphoid and non-lymphoid tissues. The proliferative burst after PD-1 blockade came almost exclusively from this CD8+ T cell subset. Importantly, the transcription factor TCF1 played a cell-intrinsic and essential role in the generation of this CD8+ T cell subset. These findings provide a better understanding of T cell exhaustion and have implications towards optimizing PD-1-directed immunotherapy in chronic infections and cancer.

Kalekar, L. A., et al. (2016). "CD4(+) T cell anergy prevents autoimmunity and generates regulatory T cell precursors." Nat Immunol 17(3): 304-314.

                    The role of anergy, an acquired state of T cell functional unresponsiveness, in natural peripheral tolerance remains unclear. In this study, we found that anergy was selectively induced in fetal antigen-specific maternal CD4(+) T cells during pregnancy. A naturally occurring subpopulation of anergic polyclonal CD4(+) T cells, enriched for self antigen-specific T cell antigen receptors, was also present in healthy hosts. Neuropilin-1 expression in anergic conventional CD4(+) T cells was associated with hypomethylation of genes related to thymic regulatory T cells (Treg cells), and this correlated with their ability to differentiate into Foxp3(+) Treg cells that suppressed immunopathology. Thus, our data suggest that not only is anergy induction important in preventing autoimmunity but also it generates the precursors for peripheral Treg cell differentiation.

Khan, T. N., et al. (2016). "Local antigen in nonlymphoid tissue promotes resident memory CD8+ T cell formation during viral infection." J Exp Med.

      Tissue-resident memory (Trm) CD8+ T cells are functionally distinct from their circulating counterparts and are potent mediators of host protection against reinfection. Whether local recognition of antigen in nonlymphoid tissues during infection can impact the formation of Trm populations remains unresolved. Using skin infections with vaccinia virus (VacV)-expressing model antigens, we found that local antigen recognition had a profound impact on Trm formation. Activated CD8+ T cells trafficked to VacV-infected skin in an inflammation-dependent, but antigen-independent, manner. However, after viral clearance, there was a subsequent approximately 50-fold increase in Trm formation when antigen was present in the tissue microenvironment. Secondary antigen stimulation in nonlymphoid tissue caused CD8+ T cells to rapidly express CD69 and be retained at the site of infection. Finally, Trm CD8+ T cells that formed during VacV infection in an antigen-dependent manner became potent stimulators of localized antigen-specific inflammatory responses in the skin. Thus, our studies indicate that the presence of antigen in the nonlymphoid tissue microenvironment plays a critical role in the formation of functional Trm CD8+ T cell populations, a finding with relevance for both vaccine design and prevention of inflammatory disorders.

Kieback, E., et al. (2016). "Thymus-Derived Regulatory T Cells Are Positively Selected on Natural Self-Antigen through Cognate Interactions of High Functional Avidity." Immunity 44(5): 1114-1126.

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                    Regulatory T (Treg) cells expressing Foxp3 transcripton factor are essential for immune homeostasis. They arise in the thymus as a separate lineage from conventional CD4(+)Foxp3(-) T (Tconv) cells. Here, we show that the thymic development of Treg cells depends on the expression of their endogenous cognate self-antigen. The formation of these cells was impaired in mice lacking this self-antigen, while Tconv cell development was not negatively affected. Thymus-derived Treg cells were selected by self-antigens in a specific manner, while autoreactive Tconv cells were produced through degenerate recognition of distinct antigens. These distinct modes of development were associated with the expression of T cell receptor of higher functional avidity for self-antigen by Treg cells than Tconv cells, a difference subsequently essential for the control of autoimmunity. Our study documents how self-antigens define the repertoire of thymus-derived Treg cells to subsequently endow this cell type with the capacity to undermine autoimmune attack.

Kim, K. S., et al. (2016). "Dietary antigens limit mucosal immunity by inducing regulatory T cells in the small intestine." Science.

                  Dietary antigens are normally rendered non-immunogenic through a poorly understood "oral tolerance" mechanism that involves immunosuppressive regulatory T (Treg) cells, especially Treg cells induced from conventional T cells in the periphery (pTregs). While orally introducing nominal protein antigens induces such pTreg cells, whether a typical diet induces a population of pTreg cells under normal conditions is unknown. By using germ-free mice raised and bred on an elemental diet devoid of dietary antigens, we demonstrate that the vast majority of the small intestinal pTreg cells under normal conditions is induced by dietary antigens from solid foods. Moreover, these pTreg cells have a limited lifespan, are distinguishable from microbiota-induced pTreg cells, and repress underlying strong immunity to ingested protein antigens.

Luo, C. T., et al. (2016). "Graded Foxo1 activity in Treg cells differentiates tumour immunity from spontaneous autoimmunity." Nature 529(7587): 532-536.

                  Regulatory T (Treg) cells expressing the transcription factor Foxp3 have a pivotal role in maintaining immunological self-tolerance; yet, excessive Treg cell activities suppress anti-tumour immune responses. Compared to the resting Treg (rTreg) cell phenotype in secondary lymphoid organs, Treg cells in non-lymphoid tissues exhibit an activated Treg (aTreg) cell phenotype. However, the function of aTreg cells and whether their generation can be manipulated are largely unexplored. Here we show that the transcription factor Foxo1, previously demonstrated to promote Treg cell suppression of lymphoproliferative diseases, has an unexpected function in inhibiting aTreg-cell-mediated immune tolerance in mice. We find that aTreg cells turned over at a slower rate than rTreg cells, but were not locally maintained in tissues. aTreg cell differentiation was associated with repression of Foxo1-dependent gene transcription, concomitant with reduced Foxo1 expression, cytoplasmic localization and enhanced phosphorylation at the Akt sites. Treg-cell-specific expression of an Akt-insensitive Foxo1 mutant prevented downregulation of lymphoid organ homing molecules, and impeded Treg cell homing to non-lymphoid organs, causing CD8(+) T-cell-mediated autoimmune diseases. Compared to Treg cells from healthy tissues, tumour-infiltrating Treg cells downregulated Foxo1 target genes more substantially. Expression of the Foxo1 mutant at a lower dose was sufficient to deplete tumour-associated Treg cells, activate effector CD8(+) T cells, and inhibit tumour growth without inflicting autoimmunity. Thus, Foxo1 inactivation is essential for the migration of aTreg cells that have a crucial function in suppressing CD8(+) T-cell responses; and the Foxo signalling pathway in Treg cells can be titrated to break tumour immune tolerance preferentially.

Malandro, N., et al. (2016). "Clonal Abundance of Tumor-Specific CD4(+) T Cells Potentiates Efficacy and Alters Susceptibility to Exhaustion." Immunity 44(1): 179-193.

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                    Current approaches to cancer immunotherapy aim to engage the natural T cell response against tumors. One limitation is the elimination of self-antigen-specific T cells from the immune repertoire. Using a system in which precursor frequency can be manipulated in a murine melanoma model, we demonstrated that the clonal abundance of CD4(+) T cells specific for self-tumor antigen positively correlated with antitumor efficacy. At elevated precursor frequencies, intraclonal competition impaired initial activation and overall expansion of the tumor-specific CD4(+) T cell population. However, through clonally derived help, this population acquired a polyfunctional effector phenotype and antitumor immunity was enhanced. Conversely, development of effector function was attenuated at low precursor frequencies due to irreversible T cell exhaustion. Our findings assert that the differential effects of T cell clonal abundance on phenotypic outcome should be considered during the design of adoptive T cell therapies, including use of engineered T cells.

Malchow, S., et al. (2016). "Aire Enforces Immune Tolerance by Directing Autoreactive T Cells into the Regulatory T Cell Lineage." Immunity 44(5): 1102-1113.

                  The promiscuous expression of tissue-restricted antigens in the thymus, driven in part by autoimmune regulator (Aire), is critical for the protection of peripheral tissues from autoimmune attack. Aire-dependent processes are thought to promote both clonal deletion and the development of Foxp3(+) regulatory T (Treg) cells, suggesting that autoimmunity associated with Aire deficiency results from two failed tolerance mechanisms. Here, examination of autoimmune lesions in Aire(-/-) mice revealed an unexpected third possibility. We found that the predominant conventional T cell clonotypes infiltrating target lesions express antigen receptors that were preferentially expressed by Foxp3(+) Treg cells in Aire(+/+) mice. Thus, Aire enforces immune tolerance by ensuring that distinct autoreactive T cell specificities differentiate into the Treg cell lineage; dysregulation of this process results in the diversion of Treg cell-biased clonotypes into pathogenic conventional T cells.

Malhotra, D., et al. (2016). "Tolerance is established in polyclonal CD4(+) T cells by distinct mechanisms, according to self-peptide expression patterns." Nat Immunol 17(2): 187-195.

                  Studies of repertoires of mouse monoclonal CD4(+) T cells have revealed several mechanisms of self-tolerance; however, which mechanisms operate in normal repertoires is unclear. Here we studied polyclonal CD4(+) T cells specific for green fluorescent protein expressed in various organs, which allowed us to determine the effects of specific expression patterns on the same epitope-specific T cells. Peptides presented uniformly by thymic antigen-presenting cells were tolerated by clonal deletion, whereas peptides excluded from the thymus were ignored. Peptides with limited thymic expression induced partial clonal deletion and impaired effector T cell potential but enhanced regulatory T cell potential. These mechanisms were also active for T cell populations specific for endogenously expressed self antigens. Thus, the immunotolerance of polyclonal CD4(+) T cells was maintained by distinct mechanisms, according to self-peptide expression patterns.

Mehta, A. K., et al. (2016). "Rhinovirus infection interferes with induction of tolerance to aeroantigens through OX40 ligand, thymic stromal lymphopoietin, and IL-33." J Allergy Clin Immunol 137(1): 278-288.e276.

                  BACKGROUND: Rhinovirus infection at an early age has been associated with development of asthma, but how rhinovirus influences the immune response is not clear. OBJECTIVE: Tolerance to inhaled antigen is mediated through induction of regulatory T (Treg) cells, and we examined whether rhinovirus infection of the respiratory tract can block airway tolerance by modulating Treg cells. METHODS: The immune response to intranasal ovalbumin in mice was assessed with concomitant infection with RV1B, and the factors induced in vivo were compared with those made by human lung epithelial cells infected in vitro with RV16. RESULTS: RV1B infection of mice abrogated tolerance induced by inhalation of soluble ovalbumin, suppressing the normal generation of forkhead box protein 3-positive Treg cells while promoting TH2 cells. Furthermore, RV1B infection led to susceptibility to asthmatic lung disease when mice subsequently re-encountered aeroantigen. RV1B promoted early in vivo expression of the TNF family protein OX40 ligand on lung dendritic cells that was dependent on the innate cytokine thymic stromal lymphopoietin (TSLP) and also induced another innate cytokine, IL-33. Inhibiting each of these pathways allowed the natural development of Treg cells while minimizing TH2 differentiation and restored tolerance in the face of RV1B infection. In accordance, RV16 infection of human lung epithelial cells upregulated TSLP and IL-33 expression. CONCLUSIONS: These results suggest that infection of the respiratory epithelium with rhinovirus can antagonize tolerance to inhaled antigen through combined induction of TSLP, IL-33, and OX40 ligand and that this can lead to susceptibility to asthmatic lung inflammation.

Merkenschlager, J., et al. (2016). "Stepwise B-cell-dependent expansion of T helper clonotypes diversifies the T-cell response." Nat Commun 7: 10281

                  Antigen receptor diversity underpins adaptive immunity by providing the ground for clonal selection of lymphocytes with the appropriate antigen reactivity. Current models attribute T cell clonal selection during the immune response to T-cell receptor (TCR) affinity for either foreign or self peptides. Here, we report that clonal selection of CD4(+) T cells is also extrinsically regulated by B cells. In response to viral infection, the antigen-specific TCR repertoire is progressively diversified by staggered clonotypic expansion, according to functional avidity, which correlates with self-reactivity. Clonal expansion of lower-avidity T-cell clonotypes depends on availability of MHC II-expressing B cells, in turn influenced by B-cell activation. B cells clonotypically diversify the CD4(+) T-cell response also to vaccination or tumour challenge, revealing a common effect.

Monaco, S., et al. (2016). "Nuclear calcium is required for human T cell activation." J Cell Biol 215(2): 231-243.

                  Calcium signals in stimulated T cells are generally considered single entities that merely trigger immune responses, whereas costimulatory events specify the type of reaction. Here we show that the "T cell calcium signal" is a composite signal harboring two distinct components that antagonistically control genomic programs underlying the immune response. Using human T cells from healthy individuals, we establish nuclear calcium as a key signal in human T cell adaptogenomics that drives T cell activation and is required for signaling to cyclic adenosine monophosphate response element-binding protein and the induction of CD25, CD69, interleukin-2, and gamma-interferon. In the absence of nuclear calcium signaling, cytosolic calcium activating nuclear factor of activated T cells translocation directed the genomic response toward enhanced expression of genes that negatively modulate T cell activation and are associated with a hyporesponsive state. Thus, nuclear calcium controls the T cell fate decision between a proliferative immune response and tolerance. Modulators of nuclear calcium-driven transcription may be used to develop a new type of pro-tolerance immunosuppressive therapy.

Nakahashi-Oda, C., et al. (2016). "Apoptotic epithelial cells control the abundance of T cells at barrier surfaces." Nat Immunol.

                  Epithelial tissues continually undergo apoptosis. Commensal organisms that inhabit the epithelium influence tissue homeostasis, in which regulatory T cells (Treg cells) have a central role. However, the physiological importance of epithelial cell apoptosis and how the number of Treg cells is regulated are both incompletely understood. Here we found that apoptotic epithelial cells negatively regulated the commensal-stimulated proliferation of Treg cells. Gut commensals stimulated CX3CR1+CD103-CD11b+ dendritic cells (DCs) to produce interferon-beta (IFN-beta), which augmented the proliferation of Treg cells in the intestine. Conversely, phosphatidylserine exposed on apoptotic epithelial cells suppressed IFN-beta production by the DCs via inhibitory signaling mediated by the cell-surface glycoprotein CD300a and thus suppressed Treg cell proliferation. Our findings reveal a regulatory role for apoptotic epithelial cells in maintaining the number of Treg cell and tissue homeostasis.

Nish, S. A., et al. (2017). "CD4+ T cell effector commitment coupled to self-renewal by asymmetric cell divisions." J Exp Med 214(1): 39-47.

                  Upon infection, an activated CD4+ T cell produces terminally differentiated effector cells and renews itself for continued defense. In this study, we show that differentiation and self-renewal arise as opposing outcomes of sibling CD4+ T cells. After influenza challenge, antigen-specific cells underwent several divisions in draining lymph nodes (LN; DLNs) while maintaining expression of TCF1. After four or five divisions, some cells silenced, whereas some cells maintained TCF1 expression. TCF1-silenced cells were T helper 1-like effectors and concentrated in the lungs. Cells from earliest divisions were memory-like and concentrated in nondraining LN. TCF1-expressing cells from later divisions in the DLN could self-renew, clonally yielding a TCF1-silenced daughter cell as well as a sibling cell maintaining TCF1 expression. Some TCF1-expressing cells in DLNs acquired an alternative, follicular helper-like fate. Modeled differentiation experiments in vitro suggested that unequal PI3K/mechanistic target of rapamycin signaling drives intraclonal cell fate heterogeneity. Asymmetric division enables self-renewal to be coupled to production of differentiated CD4+ effector T cells during clonal selection.

Pauken, K. E., et al. (2016). "Epigenetic stability of exhausted T cells limits durability of reinvigoration by PD-1 blockade." Science.

                  Blocking PD-1 can re-invigorate exhausted CD8 T cells (TEX) and improve control of chronic infections and cancer. However, whether blocking PD-1 can reprogram TEX into durable memory T cells (TMEM) is unclear. We found that re-invigoration of TEX in mice by PD-L1 blockade caused minimal memory development. After blockade, re-invigorated TEX became re-exhausted if antigen remained high, and failed to become TMEM upon antigen clearance. TEX acquired an epigenetic profile distinct from effector (TEFF) and TMEM cells that was minimally remodeled following PD-L1 blockade. This suggests TEX are a distinct lineage of CD8 T cells. Nevertheless, PD-1 pathway blockade resulted in transcriptional rewiring and re-engagement of effector circuitry in the TEX epigenetic landscape. These data indicate that epigenetic fate inflexibility may limit current immunotherapies.

Pollizzi, K. N., et al. (2016). "Asymmetric inheritance of mTORC1 kinase activity during division dictates CD8(+) T cell differentiation." Nat Immunol 17(6): 704-711.

                  The asymmetric partitioning of fate-determining proteins has been shown to contribute to the generation of CD8(+) effector and memory T cell precursors. Here we demonstrate the asymmetric partitioning of mTORC1 activity after the activation of naive CD8(+) T cells. This results in the generation of two daughter T cells, one of which shows increased mTORC1 activity, increased glycolytic activity and increased expression of effector molecules. The other daughter T cell has relatively low mTORC1 activity and increased lipid metabolism, expresses increased amounts of anti-apoptotic molecules and subsequently displays enhanced long-term survival. Mechanistically, we demonstrate a link between T cell antigen receptor (TCR)-induced asymmetric expression of amino acid transporters and RagC-mediated translocation of mTOR to the lysosomes. Overall, our data provide important insight into how mTORC1-mediated metabolic reprogramming affects the fate decisions of T cells.

Pulko, V., et al. (2016). "Human memory T cells with a naive phenotype accumulate with aging and respond to persistent viruses." Nat Immunol.

                  The number of naive T cells decreases and susceptibility to new microbial infections increases with age. Here we describe a previously unknown subset of phenotypically naive human CD8+ T cells that rapidly secreted multiple cytokines in response to persistent viral antigens but differed transcriptionally from memory and effector T cells. The frequency of these CD8+ T cells, called ‘memory T cells with a naive phenotype’ (TMNP cells), increased with age and after severe acute infection and inversely correlated with the residual capacity of the immune system to respond to new infections with age. CD8+ TMNP cells represent a potential new target for the immunotherapy of persistent infections and should be accounted for and subtracted from the naive pool if truly naive T cells are needed to respond to antigens.

Quach, H., et al. (2016). "Genetic Adaptation and Neandertal Admixture Shaped the Immune System of Human Populations." Cell 167(3): 643-656.e617.

                  Humans differ in the outcome that follows exposure to life-threatening pathogens, yet the extent of population differences in immune responses and their genetic and evolutionary determinants remain undefined. Here, we characterized, using RNA sequencing, the transcriptional response of primary monocytes from Africans and Europeans to bacterial and viral stimuli-ligands activating Toll-like receptor pathways (TLR1/2, TLR4, and TLR7/8) and influenza virus-and mapped expression quantitative trait loci (eQTLs). We identify numerous cis-eQTLs that contribute to the marked differences in immune responses detected within and between populations and a strong trans-eQTL hotspot at TLR1 that decreases expression of pro-inflammatory genes in Europeans only. We find that immune-responsive regulatory variants are enriched in population-specific signals of natural selection and show that admixture with Neandertals introduced regulatory variants into European genomes, affecting preferentially responses to viral challenges. Together, our study uncovers evolutionarily important determinants of differences in host immune responsiveness between human populations.

Quinn, K. M., et al. (2016). "Heightened self-reactivity associated with selective survival, but not expansion, of naive virus-specific CD8+ T cells in aged mice." Proc Natl Acad Sci U S A 113(5): 1333-1338.

                  In advanced age, decreased CD8(+) cytotoxic T-lymphocyte (CTL) responses to novel pathogens and cancer is paralleled by a decline in the number and function of naive CTL precursors (CTLp). Although the age-related fall in CD8(+) T-cell numbers is well established, neither the underlying mechanisms nor the extent of variation for different epitope specificities have been defined. Furthermore, naive CD8(+) T cells expressing high levels of CD44 accumulate with age, but it is unknown whether this accumulation reflects their preferential survival or an age-dependent driver of CD8(+) T-cell proliferation. Here, we track the number and phenotype of four influenza A virus (IAV)-specific CTLp populations in naive C57BL/6 (B6) mice during aging, and compare T-cell receptor (TCR) clonal diversity for the CD44hi and CD44lo subsets of one such population. We show differential onset of decline for several IAV-specific CD8(+) T-cell populations with advanced age that parallel age-associated changes in the B6 immunodominance hierarchy, suggestive of distinct impacts of aging on different epitope-specific populations. Despite finding no evidence of clonal expansions in an aged, epitope-specific TCR repertoire, nonrandom alterations in TCR usage were observed, along with elevated CD5 and CD8 coreceptor expression. Collectively, these data demonstrate that naive CD8(+) T cells expressing markers of heightened self-recognition are selectively retained, but not clonally expanded, during aging.

Reese, T. A., et al. (2016). "Sequential Infection with Common Pathogens Promotes Human-like Immune Gene Expression and Altered Vaccine Response." Cell Host Microbe 19(5): 713-719

                  Immune responses differ between laboratory mice and humans. Chronic infection with viruses and parasites are common in humans, but are absent in laboratory mice, and thus represent potential contributors to inter-species differences in immunity. To test this, we sequentially infected laboratory mice with herpesviruses, influenza, and an intestinal helminth and compared their blood immune signatures to mock-infected mice before and after vaccination against yellow fever virus (YFV-17D). Sequential infection altered pre- and post-vaccination gene expression, cytokines, and antibodies in blood. Sequential pathogen exposure induced gene signatures that recapitulated those seen in blood from pet store-raised versus laboratory mice, and adult versus cord blood in humans. Therefore, basal and vaccine-induced murine immune responses are altered by infection with agents common outside of barrier facilities. This raises the possibility that we can improve mouse models of vaccination and immunity by selective microbial exposure of laboratory animals to mimic that of humans.

Renkema, K. R., et al. (2016). "IL-4 sensitivity shapes the peripheral CD8+ T cell pool and response to infection." J Exp Med.

                  Previous studies have revealed that a population of innate memory CD8+ T cells is generated in response to IL-4, first appearing in the thymus and bearing high expression levels of Eomesodermin (Eomes) but not T-bet. However, the antigen specificity and functional properties of these cells is poorly defined. In this study, we show that IL-4 regulates not only the frequency and function of innate memory CD8+ T cells, but also regulates Eomes expression levels and functional reactivity of naive CD8+ T cells. Lack of IL-4 responsiveness attenuates the capacity of CD8+ T cells to mount a robust response to lymphocytic choriomeningitis virus infection, with both quantitative and qualitative effects on effector and memory antigen-specific CD8+ T cells. Unexpectedly, we found that, although numerically rare, memory phenotype CD8+ T cells in IL-4Ralpha-deficient mice exhibited enhanced reactivity after in vitro and in vivo stimulation. Importantly, our data revealed that these effects of IL-4 exposure occur before, not during, infection. Together, these data show that IL-4 influences the entire peripheral CD8+ T cell pool, influencing expression of T-box transcription factors, functional reactivity, and the capacity to respond to infection. These findings indicate that IL-4, a canonical Th2 cell cytokine, can sometimes promote rather than impair Th1 cell-type immune responses.

Rubelt, F., et al. (2016). "Individual heritable differences result in unique cell lymphocyte receptor repertoires of naive and antigen-experienced cells." Nat Commun 7: 11112.

                  The adaptive immune system’s capability to protect the body requires a highly diverse lymphocyte antigen receptor repertoire. However, the influence of individual genetic and epigenetic differences on these repertoires is not typically measured. By leveraging the unique characteristics of B, CD4(+) T and CD8(+) T-lymphocyte subsets from monozygotic twins, we quantify the impact of heritable factors on both the V(D)J recombination process and on thymic selection. We show that the resulting biases in both V(D)J usage and N/P addition lengths, which are found in naive and antigen experienced cells, contribute to significant variation in the CDR3 region. Moreover, we show that the relative usage of V and J gene segments is chromosomally biased, with approximately 1.5 times as many rearrangements originating from a single chromosome. These data refine our understanding of the heritable mechanisms affecting the repertoire, and show that biases are evident on a chromosome-wide level.

Saito, T., et al. (2016). "Two FOXP3(+)CD4(+) T cell subpopulations distinctly control the prognosis of colorectal cancers." Nat Med 22(6): 679-684.

                  CD4(+) T cells that express the forkhead box P3 (FOXP3) transcription factor function as regulatory T (Treg) cells and hinder effective immune responses against cancer cells. Abundant Treg cell infiltration into tumors is associated with poor clinical outcomes in various types of cancers. However, the role of Treg cells is controversial in colorectal cancers (CRCs), in which FOXP3(+) T cell infiltration indicated better prognosis in some studies. Here we show that CRCs, which are commonly infiltrated by suppression-competent FOXP3(hi) Treg cells, can be classified into two types by the degree of additional infiltration of FOXP3(lo) nonsuppressive T cells. The latter, which are distinguished from FOXP3(+) Treg cells by non-expression of the naive T cell marker CD45RA and instability of FOXP3, secreted inflammatory cytokines. Indeed, CRCs with abundant infiltration of FOXP3(lo) T cells showed significantly better prognosis than those with predominantly FOXP3(hi) Treg cell infiltration. Development of such inflammatory FOXP3(lo) non-Treg cells may depend on secretion of interleukin (IL)-12 and transforming growth factor (TGF)-beta by tissues and their presence was correlated with tumor invasion by intestinal bacteria, especially Fusobacterium nucleatum. Thus, functionally distinct subpopulations of tumor-infiltrating FOXP3(+) T cells contribute in opposing ways to determining CRC prognosis. Depletion of FOXP3(hi) Treg cells from tumor tissues, which would augment antitumor immunity, could thus be used as an effective treatment strategy for CRCs and other cancers, whereas strategies that locally increase the population of FOXP3(lo) non-Treg cells could be used to suppress or prevent tumor formation.

Schenkel, J. M., et al. (2016). "IL-15-Independent Maintenance of Tissue-Resident and Boosted Effector Memory CD8 T Cells." J Immunol 196(9): 3920-3926.

                  IL-15 regulates central and effector memory CD8 T cell (TCM and TEM, respectively) homeostatic proliferation, maintenance, and longevity. Consequently, IL-15 availability hypothetically defines the carrying capacity for total memory CD8 T cells within the host. In conflict with this hypothesis, previous observations demonstrated that boosting generates preternaturally abundant TEM that increases the total quantity of memory CD8 T cells in mice. In this article, we provide a potential mechanistic explanation by reporting that boosted circulating TEM do not require IL-15 for maintenance. We also investigated tissue-resident memory CD8 T cells (TRM), which protect nonlymphoid tissues from reinfection. We observed up to a 50-fold increase in the total magnitude of TRM in mouse mucosal tissues after boosting, suggesting that the memory T cell capacity in tissues is flexible and that TRM may not be under the same homeostatic regulation as primary central memory CD8 T cells and TEM Further analysis identified distinct TRM populations that depended on IL-15 for homeostatic proliferation and survival, depended on IL-15 for homeostatic proliferation but not for survival, or did not depend on IL-15 for either process. These observations on the numerical regulation of T cell memory indicate that there may be significant heterogeneity among distinct TRM populations and also argue against the common perception that developing vaccines that confer protection by establishing abundant TEM and TRM will necessarily erode immunity to previously encountered pathogens as the result of competition for IL-15.

Song, J., et al. (2016). "Donor-derived exosomes induce specific regulatory T cells to suppress immune inflammation in the allograft heart." Sci Rep 7: 20077.

                  To inhibit the immune inflammation in the allografts can be beneficial to organ transplantation. This study aims to induce the donor antigen specific regulatory T cells (Treg cell) inhibit the immune inflammation in the allograft heart. In this study, peripheral exosomes were purified from the mouse serum. A heart transplantation mouse model was developed. The immune inflammation of the allograft heart was assessed by histology and flow cytometry. The results showed that the donor antigen-specific T helper (Th)2 pattern inflammation was observed in the allograft hearts; the inflammation was inhibited by immunizing the recipient mice with the donor-derived exosomes. Purified peripheral exosomes contained integrin MMP1a; the latter induced CD4(+) T cells to express Fork head protein-3 and transforming growth factor (TGF)-beta via inhibiting the Th2 transcription factor, GATA binding protein 3, in CD4(+) T cells. Administration with the donor-derived exosomes significantly prolonged the allograft heart survival. We conclude that the donor-derived peripheral exosomes have the capacity to inhibit the immune inflammation in the allograft heart via inducing specific Treg cells, implicating that administration with the donor-derived exosomes may be beneficial to cardiac transplantation.

Swamy, M., et al. (2016). "A Cholesterol-Based Allostery Model of T Cell Receptor Phosphorylation." Immunity 44(5): 1091-1101.

                  Signaling through the T cell receptor (TCR) controls adaptive immune responses. Antigen binding to TCRalphabeta transmits signals through the plasma membrane to induce phosphorylation of the CD3 cytoplasmic tails by incompletely understood mechanisms. Here we show that cholesterol bound to the TCRbeta transmembrane region keeps the TCR in a resting, inactive conformation that cannot be phosphorylated by active kinases. Only TCRs that spontaneously detached from cholesterol could switch to the active conformation (termed primed TCRs) and then be phosphorylated. Indeed, by modulating cholesterol binding genetically or enzymatically, we could switch the TCR between the resting and primed states. The active conformation was stabilized by binding to peptide-MHC, which thus controlled TCR signaling. These data are explained by a model of reciprocal allosteric regulation of TCR phosphorylation by cholesterol and ligand binding. Our results provide both a molecular mechanism and a conceptual framework for how lipid-receptor interactions regulate signal transduction.

Tubo, N. J., et al. (2016). "Most microbe-specific naive CD4(+) T cells produce memory cells during infection." Science 351(6272): 511-514.

                  Infection elicits CD4(+) memory T lymphocytes that participate in protective immunity. Although memory cells are the progeny of naive T cells, it is unclear that all naive cells from a polyclonal repertoire have memory cell potential. Using a single-cell adoptive transfer and spleen biopsy method, we found that in mice, essentially all microbe-specific naive cells produced memory cells during infection. Different clonal memory cell populations had different B cell or macrophage helper compositions that matched effector cell populations generated much earlier in the response. Thus, each microbe-specific naive CD4(+) T cell produces a distinctive ratio of effector cell types early in the immune response that is maintained as some cells in the clonal population become memory cells.

Utzschneider, D. T., et al. (2016). "High antigen levels induce an exhausted phenotype in a chronic infection without impairing T cell expansion and survival." J Exp Med

                  Chronic infections induce T cells showing impaired cytokine secretion and up-regulated expression of inhibitory receptors such as PD-1. What determines the acquisition of this chronic phenotype and how it impacts T cell function remain vaguely understood. Using newly generated recombinant antigen variant-expressing chronic lymphocytic choriomeningitis virus (LCMV) strains, we uncovered that T cell differentiation and acquisition of a chronic or exhausted phenotype depend critically on the frequency of T cell receptor (TCR) engagement and less significantly on the strength of TCR stimulation. In fact, we noted that low-level antigen exposure promotes the formation of T cells with an acute phenotype in chronic infections. Unexpectedly, we found that T cell populations with an acute or chronic phenotype are maintained equally well in chronic infections and undergo comparable primary and secondary expansion. Thus, our observations contrast with the view that T cells with a typical chronic infection phenotype are severely functionally impaired and rapidly transition into a terminal stage of differentiation. Instead, our data unravel that T cells primarily undergo a form of phenotypic and functional differentiation in the early phase of a chronic LCMV infection without inheriting a net survival or expansion deficit, and we demonstrate that the acquired chronic phenotype transitions into the memory T cell compartment.

Wyss, L., et al. (2016). "Affinity for self antigen selects Treg cells with distinct functional properties." Nat Immunol.

                  The manner in which regulatory T cells (Treg cells) control lymphocyte homeostasis is not fully understood. We identified two Treg cell populations with differing degrees of self-reactivity and distinct regulatory functions. We found that GITRhiPD-1hiCD25hi (Triplehi) Treg cells were highly self-reactive and controlled lympho-proliferation in peripheral lymph nodes. GITRloPD-1loCD25lo (Triplelo) Treg cells were less self-reactive and limited the development of colitis by promoting the conversion of CD4+ Tconv cells into induced Treg cells (iTreg cells). Although Foxp3-deficient (Scurfy) mice lacked Treg cells, they contained Triplehi-like and Triplelo-like CD4+ T cells zsuper> T cells infiltrated the skin, whereas Scurfy TripleloCD4+ T cells induced colitis and wasting disease. These findings indicate that the affinity of the T cell antigen receptor for self antigen drives the differentiation of Treg cells into distinct subsets with non-overlapping regulatory activities.


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