Antiviral CD8 T-cell Research Articles

Roles of the Fc Receptor γ-Chain in Inducing Protective Immune Responses after Heterologous Vaccination against Respiratory Syncytial Virus Infection.

The roles of the Fc receptor (FcR) in protection or inflammatory disease after respiratory syncytial virus (RSV) vaccination and infection remain unknown. Virus-like particles containing RSV fusion proteins (RSV F-VLPs) induce T-helper type 1 antibody responses and protection against RSV. Heterologous RSV F-VLP prime and formalin-inactivated RSV (FI-RSV) boost vaccination has been reported to be effective in providing protection without inflammatory disease. Here, we investigated whether the FcRγ-chain is important for immune protection by the heterologous F-VLP and FI-RSV vaccination using FcRγ-chain knockout (−/−) mice. RSV F-VLP-primed and FI-RSV-boosted FcRγ −/− mice displayed less protective efficacy, as shown by higher lung viral titers upon RSV challenge, compared to RSV F-VLP-primed and FI-RSV-boosted immunized wild-type mice. RSV F-VLP and FI-RSV immunization induced lower levels of neutralizing activity and interferon-γ-producing CD8 T-cells in the bronchoalveolar lavage cells of FcRγ −/− mice than in those of wild-type mice. In addition, FcRγ −/− mice displayed a trend of enhancing lung histopathology after RSV vaccination and infection. This study suggests that the FcRγ-chain plays an important role in inducing antiviral protection and CD8 T-cell responses in RSV F-VLP prime and FI-RSV boost vaccination after RSV infections.

Lipophagy confers a key metabolic advantage that ensures protective CD8A T-cell responses against HIV-1

ABSTRACT Although macroautophagy/autophagy has been proposed as a critical defense mechanism against HIV-1 by targeting viral components for degradation, its contribution as a catabolic process in providing optimal anti-HIV-1 immunity has never been addressed. The failure to restore proper antiviral CD8A/CD8 T-cell immunity, especially against HIV-1, is still the major limitation of current antiretroviral therapies. Consequently, it is of clinical imperative to provide new strategies to enhance the function of HIV-1-specific CD8A T-cells in patients under antiretroviral treatments (ART). Here, we investigated whether targeting autophagy activity could be an optional solution to make this possible. Our data show that, after both polyclonal and HIV-1-specific activation, CD8A T-cells from ART displayed reduced autophagy-dependent degradation of lysosomal contents when compared to naturally HIV-1 protected elite controllers (EC). We further confirmed in EC, by using specific BECN1 gene silencing and lysosomal inhibitors, the critical role of active autophagy in superior CD8A T-cell protection against HIV-1. More importantly, we found that an IL21 treatment was effective in rescuing the antiviral CD8A T-cell immunity from ART in an autophagy-dependent manner. Finally, we established that IL21-dependent rescue occurred due to the enhanced degradation of endogenous lipids via autophagy, referred to as lipophagy, which fueled the cellular rates of mitochondrial beta-oxidation. In summary, our data show that autophagy/lipophagy can be considered as a therapeutic tool to elicit functional antiviral CD8 T-cell responses. Our results also provide additional insights toward the development of improved T-cell-based prevention and cure strategies against HIV-1. Abbreviations: ART: patients under antiretroviral therapy; BaF: bafilomycin A1; BECN1: beclin 1; CEF: cytomegalo-, Epstein-Barr- and flu-virus peptide pool; Chloro.: chloroquine; EC: elite controllers; FAO: fatty acid beta-oxidation; HIVneg: HIV-1-uninfected control donors; IFNG/IFN-γ: interferon gamma; IL21: interleukin 21; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PBMC: peripheral blood mononuclear cells; SQSTM1: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Vesicular Stomatitis Virus Encoding a Destabilized Tumor Antigen Improves Activation of Anti-tumor T Cell Responses

Enhancing the immunogenicity of tumor-associated antigens would represent a major advance for anti-tumor vaccination strategies. Here, we investigated structure-directed antigen destabilization as a strategy to improve the degradation, immunogenic epitope presentation, and Tcell activation against a vesicularstomatitis virus (VSV)-encoded tumor antigen. We used the crystal structure of the model antigen ovalbumin to identify charge-disrupting amino acid mutations that were predicted to decrease the stability of the protein. One mutation, OVA-C12R, significantly reduced the half-life of the protein and was preferentially degraded in a 26-S proteasomal-dependent manner. The destabilized ovalbumin protein exhibited enhanced presentation of the major histocompatibility complex (MHC) class I immunogenic epitope, SIINFEKL, on the surface of B16F10 cells or murine bone marrow-derived dendritic cells (BMDCs) invitro. Enhanced presentation correlated with better recognition by cognate CD8 OT-I Tcells as measured by activation, proliferation, and effector cytokine production. Finally, VSV encoding the degradation-prone antigen was better able to prime an antigen ovalbumin-specific CD8 Tcell response invivo without altering the anti-viral CD8 Tcell response. Our studies highlight that not only is the choice of antigen in cancer vaccines of importance, but that emphasis should be placed on modifying antigen quality to ensure optimal priming of anti-tumor responses.

PP 4.2 - Enhancement of antiviral CD8 T-cell responses and complete remission of metastatic melanoma in an HIV-1 infected subject treated with pembrolizumab

PP 4.2 - Enhancement of antiviral CD8 T-cell responses and complete remission of metastatic melanoma in an HIV-1 infected subject treated with pembrolizumab

Preferential Small Intestine Homing and Persistence of CD8 T Cells in Rhesus Macaques Achieved by Molecularly Engineered Expression of CCR9 and Reduced Ex Vivo Manipulation.

Adoptive cell transfer (ACT) is a powerful experimental approach to directly study T-cell-mediated immunity in vivo In the rhesus macaque AIDS virus model, infusing simian immunodeficiency virus (SIV)-infected animals with CD8 T cells engineered to express anti-SIV T-cell receptor specificities enables direct experimentation to better understand antiviral T-cell immunity in vivo Limiting factors in ACT experiments include suboptimal trafficking to, and poor persistence in, the secondary lymphoid tissues targeted by AIDS viruses. Previously, we redirected CD8 T cells to B-cell follicles by ectopic expression of the CXCR5 homing protein. Here, we modify peripheral blood mononuclear cell (PBMC)-derived CD8 T cells to express the CCR9 chemokine receptor, which induces preferential homing of the engineered cells to the small intestine, a site of intense early AIDS virus replication and pathology in rhesus macaques. Additionally, we increase in vivo persistence and overall systemic distribution of infused CD8 T cells, especially in secondary lymphoid tissues, by minimizing ex vivo culture/manipulation, thereby avoiding the loss of CD28+/CD95+ central memory T cells by differentiation in culture. These proof-of-principle results establish the feasibility of preferentially localizing PBMC-derived CD8 T cells to the small intestine and enables the direct experimental ACT-based assessment of the potential role of the quality and timing of effective antiviral CD8 T-cell responses to inhibit viral infection and subsequent replication in small intestine CD4 T cells. More broadly, these results support the engineered expression of homing proteins to direct CD8 T cells to target tissues as a means for both experimental and potential therapeutic advances in T-cell immunotherapies, including cancer.IMPORTANCEAdoptive cell transfer (ACT) of T cells engineered with antigen-specific effector properties can deliver targeted immune responses against malignancies and infectious diseases. Current T-cell-based therapeutic ACT relies on circulatory distribution to deliver engineered T cells to their targets, an approach which has proven effective for some leukemias but provided only limited efficacy against solid tumors. Here, engineered expression of the CCR9 homing receptor redirected CD8 T cells to the small intestine in rhesus macaque ACT experiments. Targeted homing of engineered T-cell immunotherapies holds promise to increase the effectiveness of adoptively transferred cells in both experimental and clinical settings.

Abstract B200: Single-cell RNA-sequencing (ScRNA-seq) reveals broad heterogeneity among CD8 T-cells during chronic viral infection and identifies a critical role for CD4 help in promoting the differentiation of a potent cytotoxic CD8 T-cell subset

Abstract During chronic viral infection and cancer, CD8 T-cells undergo a differentiation process commonly referred to as T-cell exhaustion. This process is traditionally defined by a stepwise loss of effector functions, eventually leading to cell death. Despite their inability to completely clear the infection, exhausted T-cells are still necessary for limiting viral replication during infection. Thus, it has been proposed that functional adaptation is a more appropriate term for T-cell exhaustion, as CD8 T-cells may be undergoing a multifaceted process of differentiation to better meet the needs of a chronic infection. In line with this hypothesis, it has recently been demonstrated that CD8 T-cells responding to chronic infection are non-homogenous and can be compartmentalized into at least two major subsets, with a TCF-1+ subset serving as a progenitor population that can give rise to a more terminally exhausted TCF-1- subset. However, whether additional heterogeneity exists among CD8 T-cells responding to persistent infection remains unclear. Here, we used ScRNA-seq to fully characterize the heterogeneity of CD8 T-cells during chronic LCMV Cl13 infection. We identified that several transcriptionally distinct subsets of CD8 T-cells develop during chronic LCMV infection, with 3 particular clusters, Slamf6, Pdcd1, and Cx3cr1 cell subsets dominating the antiviral CD8 T-cell response. Importantly both ScRNA-seq and flow cytometric analyses demonstrated that differential expression of cell surface receptors CX3CR1 and Ly108 (encoded by Slamf6) can distinguish these 3 major T-cell subsets. Notably, Ly108 cells shared similar characteristics to the previously described progenitor population and displayed elevated expression of TCF-1. Conversely, CX3CR1 CD8 T-cells displayed increased expression of killer cell lectin-like receptors Klre1 and Klra9, and the TFs T-bet and Zeb2, whereas CX3CR1-Ly108- (DN) cells exhibited elevated expression of multiple co-inhibitory receptors and the TFs Eomes and Nr4a2. Ex vivo functional analyses further indicated that Ly108 CD8 T-cells exhibit an enhanced capacity to co-produce IFN-γ and TNF-α upon GP33 peptide stimulation, whereas CX3CR1 CD8 T-cells display augmented cytotoxicity against peptide-pulsed targeT-cells. Sc trajectory modeling using Monocle analyses predicted that Ly108 CD8 T-cells give rise to both CX3CR1 and DN subsets, with the DN subset branch appearing closer in pseudotime to the Ly108 progenitor subset. To determine the in vivo differentiation trajectory, proliferative potential, and phenotypic stability of these 3 subsets, we performed adoptive transfer experiments using congenically marked CD8 T-cells. Importantly, and consistent with our Monocle predictions, our results demonstrate that Ly108 CD8 T-cells display robust secondary proliferation and give rise to both CX3CR1 and DN subsets. By contrast, CX3CR1 cells retained high CX3CR1 and T-bet expression and did not differentiate into Ly108 or DN CD8 T-cells. Intriguingly, although the DN subset appeared to be the most phenotypically and functionally exhausted subset, more than half of their progeny acquired high CX3CR1 and T-bet expression, indicating that this subset may not be as terminally differentiated as its CX3CR1 counterpart. Notably, our ScRNA-seq analyses also identified that DN cells displayed the highest levels of IL-21R expression, suggesting a potential role for CD4 help in regulating the differentiation of this subset. Strikingly, depletion of CD4 T-cells or deletion of IL-21R signaling in P14 transgenic CD8 T-cells abrogated the development of the CX3CR1 CD8 subset, indicating a critical role for CD4 help in facilitating the differentiation of exhausted CD8 T-cells into a potent cytotoxic CD8 subset. Collectively, our work supports a new model of CD8 T-cell differentiation during chronic viral infection and has important implications for T-cell-based immunotherapies aimed at treating persistent infections and/or cancer. Citation Format: Ryan Zander, David Schauder, Gang Xin, Christine Nguyen, Xiaopeng Wu, Weiguo Cui. Single-cell RNA-sequencing (ScRNA-seq) reveals broad heterogeneity among CD8 T-cells during chronic viral infection and identifies a critical role for CD4 help in promoting the differentiation of a potent cytotoxic CD8 T-cell subset [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B200.

Bacterial coinfection restrains antiviral CD8 T-cell response via LPS-induced inhibitory NK cells

Infection of specific pathogen-free mice with lymphocytic choriomeningitis virus (LCMV) is a widely used model to study antiviral T-cell immunity. Infections in the real world, however, are often accompanied by coinfections with unrelated pathogens. Here we show that in mice, systemic coinfection with E. coli suppresses the LCMV-specific cytotoxic T-lymphocyte (CTL) response and virus elimination in a NK cell- and TLR2/4-dependent manner. Soluble TLR4 ligand LPS also induces NK cell-mediated negative CTL regulation during LCMV infection. NK cells in LPS-treated mice suppress clonal expansion of LCMV-specific CTLs by a NKG2D- or NCR1-independent but perforin-dependent mechanism. These results suggest a TLR4-mediated immunoregulatory role of NK cells during viral-bacterial coinfections.

A Mitochondrial Checkpoint in Autoimmune Disease

Cell-fate decisions in innate and adaptive immune cells are metabolically regulated and modified by tissue-derived signals, thereby balancing protective and pathogenic immunity. Reporting in Science, Ling etal. (2018) have identified C1q as a mitochondrial activator that suppresses exuberant anti-self and anti-viral CD8 Tcell effector responses to prevent autoimmune disease.

The transcription factor T-bet is regulated by microRNA-155 in murine anti-viral CD8+ T cells via SHIP-1.

Abstract MicroRNAs (miRNAs) are small, single-stranded non-coding RNAs that play essential roles in regulating key cellular processes, and are highly conserved across species. However, the regulatory role of microRNAs in generating effective CD8+ T cell (CTL) responses to viral infection and tumors is only now being elucidated. Microarray miRNA expression profiling identified unique expression patterns of miRNAs in naïve and effector anti-viral CTL. In particular, microRNA-155 was significantly upregulated in effector CTL. Previously, we have demonstrated that miR-155 is essential to CD8+ T cell responses to viral and intracellular bacterial infections. In the present study, we show that miR-155 overexpression in CTL augments anti-viral effector CTL and skews memory CD8+ T cells towards an effector memory phenotype. MiR-155 overexpression resulted in enhanced T-bet expression, which is known to be required for effector CTL and to promote effector memory cell formation. Importantly, we show that the proliferative effect of miR-155 on CD8+ T cells is mediated by T-bet. In CTL, T-bet levels were controlled in vivo by miR-155 via SH2 (Src homology 2)-containing inositol phosphatase-1 (SHIP-1), a known direct target of miR-155. Our studies have revealed an important and unexpected link between miR-155, T-bet transcription factor and SHIP-1 in the context of CTL responses to an in vivo viral infection.

Cytokine-Mediated Regulation of CD8 T-Cell Responses During Acute and Chronic Viral Infection.

The common γ-chain cytokines, interleukin (IL)-2, IL-7, and IL-15, regulate critical aspects of antiviral CD8 T-cell responses. During acute infections, IL-2 controls expansion and differentiation of antiviral CD8 T cells, whereas IL-7 and IL-15 are key cytokines to maintain memory CD8 T cells long term in an antigen-independent manner. On the other hand, during chronic infections, in which T-cell exhaustion is established, precise roles of these cytokines in regulation of antiviral CD8 T-cell responses are not well defined. Nonetheless, administration of IL-2, IL-7, or IL-15 can increase function of exhausted CD8 T cells, and thus can be an attractive therapeutic approach. A new subset of stem-cell-like CD8 T cells, which provides a proliferative burst after programmed cell death (PD)-1 therapy, has been recently described during chronic viral infection. Further understanding of cytokine-mediated regulation of this CD8 T-cell subset will improve cytokine therapies to treat chronic infections and cancer in combination with immune checkpoint inhibitors.

MicroRNA-155 regulates T-bet expression in anti-viral CD8+ T cells

Abstract MicroRNAs (miRNAs) are small, single-stranded non-coding RNAs that play essential roles in regulating key cellular processes, and are highly conserved across species. miRNA are known to regulate immune cells and play an important role in effective CD8+ T cell (CTL) responses to viral infection and tumors. To understand the role of miRNA in CTL responses we performed microarray miRNA expression profiling and identified unique in vivo expression patterns of miRNAs in naïve and effector anti-viral CTL. In particular, miR-155, which we and others previously have demonstrated to regulate CTL responses, was significantly upregulated in effector CTL. We show that further increasing the levels of miR-155 by retroviral overexpression significantly augments anti-viral effector CTL and skews memory CD8+ T cells towards an effector memory phenotype. MiR-155 overexpression resulted in enhanced T-bet expression, which is known to be required for effector CTL and to promote effector memory cell formation. MiR-155 overexpression-induced T-bet expression was required for miR-155 mediated increases in effector CTL. Our studies have revealed an important and unexpected link between miR-155 and T-bet transcription factor in the context of in vivo CTL responses.

Overcoming CD4 Th1 Cell Fate Restrictions to Sustain Antiviral CD8 T Cells and Control Persistent Virus Infection

Viral persistence specifically inhibits CD4 Th1 responses and promotes Tfh immunity, but the mechanisms that suppress Th1 cells and the disease consequences of their loss are unclear. Here, we demonstrate that the loss of CD4 Th1 cells specifically leads to progressive CD8 Tcell decline and dysfunction during viral persistence. Therapeutically reconstituting CD4 Th1 cells restored CD4 Tcell polyfunctionality, enhanced antiviral CD8 Tcell numbers and function, and enabled viral control. Mechanistically, combined interaction of PD-L1 and IL-10 by suppressive dendritic cell subsets inhibited new CD4 Th1 cells in both acute and persistent virus infection, demonstrating an unrecognized suppressive function for PD-L1 in virus infection. Thus, the loss of CD4 Th1 cells is a key event leading to progressive CD8 Tcell demise during viral persistence with important implications for restoring antiviral CD8 Tcell immunity to control persistent viral infection.

CD70 and IFN-1 selectively induce eomesodermin or T-bet and synergize to promote CD8+ T-cell responses.

CD70-mediated stimulation of CD27 is an important cofactor of CD4(+) T-cell licensed dendritic cells (DCs). However, it is unclear how CD70-mediated stimulation of Tcells is integrated with signals that emanate from signal 3 pathways, such as type-1 interferon (IFN-1) and IL-12. We find that while stimulation of CD27 in isolation drives weak Eomesodermin(hi) T-bet(lo) CD8(+) T-cell responses to OVA immunization, profound synergistic expansion is achieved by cotargeting TLR. This cooperativity can substantially boost antiviral CD8(+) T-cell responses during acute infection. Concomitant stimulation of TLR significantly increases per cell IFN-γ production and the proportion of the population with characteristics of short-lived effector cells, yet also promotes the ability to form long-lived memory. Notably, while IFN-1 contributes to the expression of CD70 on DCs, the synergy between CD27 and TLR stimulation is dependent upon IFN-1's effect directly on CD8(+) Tcells, and is associated with the increased expression of T-bet in Tcells. Surprisingly, we find that IL-12 fails to synergize with CD27 stimulation to promote CD8(+) T-cell expansion, despite its capacity to drive effector CD8(+) T-cell differentiation. Together, these data identify complex interactions between signal 3 and costimulatory pathways, and identify opportunities to influence the differentiation of CD8(+) T-cell responses.

Lethal giant larvae‐1 deficiency enhances the CD8+ effector T‐cell response to antigen challenge in vivo

Lethal giant larvae-1 (Lgl-1) is an evolutionary conserved protein that regulates cell polarity in diverse lineages; however, the role of Lgl-1 in the polarity and function of immune cells remains to be elucidated. To assess the role of Lgl-1 in T cells, we generated chimeric mice with a hematopoietic system deficient for Lgl-1. Lgl-1 deficiency did not impair the activation or function of peripheral CD8(+) T cells in response to antigen presentation in vitro, but did skew effector and memory T-cell differentiation. When challenged with antigen-expressing virus or tumor, Lgl-1-deficient mice displayed altered T-cell responses. This manifested in a stronger antiviral and antitumor effector CD8(+) T-cell response, the latter resulting in enhanced control of MC38-OVA tumors. These results reveal a novel role for Lgl-1 in the regulation of virus-specific T-cell responses and antitumor immunity.

Distinct CD4 T-cell effects on primary versus recall CD8 T-cell responses during viral encephalomyelitis.

CD4 T-cell help is not a universal requirement for effective primary CD8 T cells but is essential to generate memory CD8 T cells capable of recall responses. This study examined how CD4 T cells affect primary and secondary anti-viral CD8 T-cell responses within the central nervous system (CNS) during encephalomyelitis induced by sublethal gliatropic coronavirus. CD4 T-cell depletion before infection did not impair peripheral expansion, interferon-γ production, CNS recruitment or initial CNS effector capacity of virus-specific CD8 T cells ex vivo. Nevertheless, impaired virus control in the absence of CD4 T cells was associated with gradually diminished CNS CD8 T-cell interferon-γ production. Furthermore, within the CD8 T-cell population short-lived effector cells were increased and memory precursor effector cells were significantly decreased, consistent with higher T-cell turnover. Transfer of memory CD8 T cells to reduce viral load in CD4-depleted mice reverted the recipient CNS CD8 T-cell phenotype to that in wild-type control mice. However, memory CD8 T cells primed without CD4 T cells and transferred into infected CD4-sufficient recipients expanded less efficiently and were not sustained in the CNS, contrasting with their helped counterparts. These data suggest that CD4 T cells are dispensable for initial expansion, CNS recruitment and differentiation of primary resident memory CD8 T cells as long as the duration of antigen exposure is limited. By contrast, CD4 T cells are essential to prolong primary CD8 T-cell function in the CNS and imprint memory CD8 T cells for recall responses.

Type 1 interferon-induced IL-7 maintains CD8+ T-cell responses and homeostasis by suppressing PD-1 expression in viral hepatitis.

Type 1 interferon (IFN-I) promotes antigen-presenting cell maturation and was recently shown to induce hepatic IL-7 production during infection. Herein, we further explored the underlying mechanisms used by IFN-I to orchestrate antiviral immune responses in the liver. Acute viral hepatitis was induced by i.v. injection of adenovirus (Ad) in IFN-α receptor knockout (IFNAR(-/-)) and control mice. To disrupt signaling, monoclonal antibodies (mAbs) against IL-7 receptor alpha (IL-7Rα) or PD-L1 were i.p. injected. We found that CD8(+) T cells in IFNAR(-/-) mice were less effective than those in control mice. The reduced T-cell function was accompanied by increased levels of PD-1 expression, apoptosis and decreased IFN-γ production. The lack of IFN-I signaling also impaired the expression of accessory molecules in both intrahepatic dendritic cell (DCs) and hepatocytes. PD-L1 was comparably and highly expressed on hepatocytes in both IFNAR(-/-) and control mice. Injection of PD-L1-specific mAb in IFNAR(-/-) mice reversed the compromised immune responses in the liver. Further investigation showed that hepatic IL-7 elevation was less pronounced in IFNAR(-/-) mice compared to the controls. A treatment with recombinant IL-7 suppressed PD-1 expression on CD8(+) T cells in vitro. Accordingly, blocking IL-7R signaling in vivo resulted in increased PD-1 expression on CD8(+) T cells in Ad-infected mice. Collectively, the results suggest that IFN-I-induced hepatic IL-7 production maintains antiviral CD8(+) T-cell responses and homeostasis by suppressing PD-1 expression in acute viral hepatitis.

New insights into the role of the aryl hydrocarbon receptor in the function of CD11c+ cells during respiratory viral infection

The aryl hydrocarbon receptor (AHR) has garnered considerable attention as a modulator of CD4(+) cell lineage development and function. It also regulates antiviral CD8(+) T-cell responses, but via indirect mechanisms that have yet to be determined. Here, we show that during acute influenza virus infection, AHR activation skews dendritic-cell (DC) subsets in the lung-draining lymph nodes, such that there are fewer conventional CD103(+) DCs and CD11b(+) DCs. Sorting DC subsets reveals AHR activation reduces immunostimulatory function of CD103(+) DCs in the mediastinal lymph nodes, and decreases their frequency in the lung. DNA-binding domain Ahr mutants demonstrate that alterations in DC subsets require the ligand-activated AHR to contain its inherent DNA-binding domain. To evaluate the intrinsic role of AHR in DCs, conditional knockouts were created using Cre-LoxP technology, which revealed that AHR in CD11c(+) cells plays a key role in controlling the acquisition of effector CD8(+) T cells in the infected lung. However, AHR within other leukocyte lineages contributes to diminished naïve CD8(+) T-cell activation in the draining lymphoid nodes. These findings indicate DCs are among the direct targets of AHR ligands in vivo, and AHR signaling modifies host responses to a common respiratory pathogen by affecting the complex interplay of multiple cell types.

Interferon Regulatory Factor 4 Sustains CD8+ T Cell Expansion and Effector Differentiation

Upon infection, CD8(+) Tcells undergo a stepwise process of early activation, expansion, and differentiation into effector cells. How these phases are transcriptionally regulated is incompletely defined. Here, we report that interferon regulatory factor 4 (IRF4), dispensable for early CD8(+) Tcell activation, was vital for sustaining the expansion and effector differentiation of CD8(+) Tcells. Mechanistically, IRF4 promoted the expression and function of Blimp1 and T-bet, two transcription factors required for CD8(+) Tcell effector differentiation, and simultaneously repressed genes that mediate cell cycle arrest and apoptosis. Selective ablation of Irf4 in peripheral CD8(+) Tcells impaired antiviral CD8(+) Tcell responses, viral clearance, and CD8(+) Tcell-mediated host recovery from influenza infection. IRF4 expression was regulated by Tcell receptor (TCR) signaling strength via mammalian target of rapamycin (mTOR). Our data reveal that IRF4 translates differential strength of TCR signaling into different quantitative and qualitative CD8(+) Tcell responses.

Negative Regulation of Type I IFN Expression by OASL1 Permits Chronic Viral Infection and CD8+ T-Cell Exhaustion

The type I interferons (IFN-Is) are critical not only in early viral control but also in prolonged T-cell immune responses. However, chronic viral infections such as those of human immunodeficiency virus (HIV) and hepatitis C virus (HCV) in humans and lymphocytic choriomeningitis virus (LCMV) in mice overcome this early IFN-I barrier and induce viral persistence and exhaustion of T-cell function. Although various T-cell-intrinsic and -extrinsic factors are known to contribute to induction of chronic conditions, the roles of IFN-I negative regulators in chronic viral infections have been largely unexplored. Herein, we explored whether 2′–5′ oligoadenylate synthetase-like 1 (OASL1), a recently defined IFN-I negative regulator, plays a key role in the virus-specific T-cell response and viral defense against chronic LCMV. To this end, we infected Oasl1 knockout and wild-type mice with LCMV CL-13 (a chronic virus) and monitored T-cell responses, serum cytokine levels, and viral titers. LCMV CL-13-infected Oasl1 KO mice displayed a sustained level of serum IFN-I, which was primarily produced by splenic plasmacytoid dendritic cells, during the very early phase of infection (2–3 days post-infection). Oasl1 deficiency also led to the accelerated elimination of viremia and induction of a functional antiviral CD8 T-cell response, which critically depended on IFN-I receptor signaling. Together, these results demonstrate that OASL1-mediated negative regulation of IFN-I production at an early phase of infection permits viral persistence and suppresses T-cell function, suggesting that IFN-I negative regulators, including OASL1, could be exciting new targets for preventing chronic viral infection.

ICAM-1–dependent tuning of memory CD8 T-cell responses following acute infection

CD8 T-cell responses are critical for protection against intracellular pathogens and tumors. The induction and properties of these responses are governed by a series of integrated processes that rely heavily on cell-cell interactions. Intercellular adhesion molecule (ICAM)-1 functions to enhance the strength of antigenic stimulation, extend the duration of contact with antigen-presenting cells, and augment cytokine signals, which are all factors that influence peripheral CD8 T-cell differentiation. Although previous studies suggest that ICAM-1 is essential for establishing memory T-cell populations following peptide immunization, the roles of ICAM-1 in antiviral cellular immunity are less well understood. Here we show that, following a prototypic acute viral infection, the formation and maintenance of memory-phenotype CD127(hi), KLRG-1(lo) CD8 T cells does not require ICAM-1. Nevertheless, ICAM-1 expression on nonlymphocytes dictates the phenotypic and functional attributes of the antiviral CD8 T-cell populations that develop and promotes the gradual attrition of residual effector-like CD127(lo), KLRG-1(hi) CD8 T cells during the memory phase of the response. Although memory T cells do emerge and are maintained if ICAM-1 expression is abolished, the secondary proliferative capacity of these T cells is severely curtailed. Collectively, these studies reveal potential dual roles for ICAM-1 in both promoting the decay of effector responses and programming the sensitivity of memory CD8 T cells to secondary stimuli.