Physiological microbial exposure transiently inhibits mouse lung ILC2 responses to allergens.

Lung group 2 innate lymphoid cells (ILC2s) control the nature of immune responses to airway allergens. Some microbial products, including those that stimulate interferons, block ILC2 activation, but whether this occurs after natural infections or causes durable ILC2 inhibition is unclear. In the present study, we cohoused laboratory and pet store mice as a model of physiological microbial exposure. Laboratory mice cohoused for 2 weeks had impaired ILC2 responses and reduced lung eosinophilia to intranasal allergens, whereas these responses were restored in mice cohoused for ≥2 months. ILC2 inhibition at 2 weeks correlated with increased interferon receptor signaling, which waned by 2 months of cohousing. Reinduction of interferons in 2-month cohoused mice blocked ILC2 activation. These findings suggest that ILC2s respond dynamically to environmental cues and that microbial exposures do not control long-term desensitization of innate type 2 responses to allergens.

Defining Parameters That Modulate Susceptibility and Protection to Respiratory Murine Coronavirus MHV1 Infection.

Patients infected with SARS-CoV-2 experience variable disease susceptibility, and patients with comorbidities such as sepsis are often hospitalized for COVID-19 complications. However, the extent to which initial infectious inoculum dose determines disease outcomes and whether this can be used for immunological priming in a genetically susceptible host has not been completely defined. We used an established SARS-like murine model in which responses to primary and/or secondary challenges with murine hepatitis virus type 1 (MHV-1) were analyzed. We compared the response to infection in genetically susceptible C3H/HeJ mice, genetically resistant C57BL/6J mice, and genetically diverse, variably susceptible outbred Swiss Webster mice. Although defined as genetically susceptible to MHV-1, C3H/HeJ mice displayed decreasing dose-dependent pathological changes in disease severity and lung infiltrate/edema, as well as lymphopenia. Importantly, an asymptomatic dose (500 PFU) was identified that yielded no measurable morbidity/mortality postinfection in C3H/HeJ mice. Polymicrobial sepsis induced via cecal ligation and puncture converted asymptomatic infections in C3H/HeJ and C57BL/6J mice to more pronounced disease, modeling the impact of sepsis as a comorbidity to ß-coronavirus infection. We then used low-dose infection as an immunological priming event in C3H/HeJ mice, which provided neutralizing Ab-dependent, but not circulating CD4/CD8 T cell-dependent, protection against a high-dose MHV-1 early rechallenge. Together, these data define how infection dose, immunological status, and comorbidities modulate outcomes of primary and secondary ß-coronavirus infections in hosts with variable susceptibility.

Sepsis leads to lasting changes in phenotype and function of naïve CD8 T cells.

Sepsis, an amplified immune response to systemic infection, is characterized by a transient cytokine storm followed by chronic immune dysfunction. Consequently, sepsis survivors are highly susceptible to newly introduced infections, suggesting sepsis can influence the function and composition of the naïve CD8 T cell pool and resulting pathogen-induced primary CD8 T cell responses. Here, we explored the extent to which sepsis induces phenotypic and functional changes within the naïve CD8 T cell pool. To interrogate this, the cecal ligation and puncture (CLP) mouse model of polymicrobial sepsis was used. In normal, non-septic mice, we show type-I interferon (IFN I)-mediated signaling plays an important role in driving the phenotypic and functional heterogeneity in the naïve CD8 T cell compartment leading to increased representation of Ly6C+ naïve CD8 T cells. In response to viral infection after sepsis resolution, naïve Ly6C+ CD8 T cells generated more primary effector and memory CD8 T cells with slower conversion to a central memory CD8 T cell phenotype (Tcm) than Ly6C- naïve CD8 T cells. Importantly, as a potent inducer of cytokine storm and IFN I production, sepsis leads to increased representation of Ly6C+ naïve CD8 T cells that maintained their heightened ability to respond (i.e., effector and memory CD8 T cell accumulation and cytokine production) to primary LCMV infection. Lastly, longitudinal analyses of peripheral blood samples obtained from septic patients revealed profound changes in CD8 T cell subset composition and frequency compared to healthy controls. Thus, sepsis has the capacity to alter the composition of naïve CD8 T cells, directly influencing primary CD8 T cell responses to newly introduced infections.

The Calm after the Storm: Implications of Sepsis Immunoparalysis on Host Immunity.

The immunological hallmarks of sepsis include the inflammation-mediated cytokine storm, apoptosis-driven lymphopenia, and prolonged immunoparalysis. Although early clinical efforts were focused on increasing the survival of patients through the first phase, studies are now shifting attention to the long-term effects of sepsis on immune fitness in survivors. In particular, the most pertinent task is deciphering how the immune system becomes suppressed, leading to increased incidence of secondary infections. In this review, we introduce the contribution of numerical changes and functional reprogramming within innate (NK cells, dendritic cells) and adaptive (T cells, B cells) immune cells on the chronic immune dysregulation in the septic murine and human host. We briefly discuss how prior immunological experience in murine models impacts sepsis severity, immune dysfunction, and clinical relevance. Finally, we dive into how comorbidities, specifically autoimmunity and cancer, can influence host susceptibility to sepsis and the associated immune dysfunction.

Inefficient Recovery of Repeatedly Stimulated Memory CD8 T Cells after Polymicrobial Sepsis Induction Leads to Changes in Memory CD8 T Cell Pool Composition.

Long-lasting sepsis-induced immunoparalysis has been principally studied in primary (1°) memory CD8 T cells; however, the impact of sepsis on memory CD8 T cells with a history of repeated cognate Ag encounters is largely unknown but important in understanding the role of sepsis in shaping the pre-existing memory CD8 T cell compartment. Higher-order memory CD8 T cells are crucial in providing immunity against common pathogens that reinfect the host or are generated by repeated vaccination. In this study, we analyzed peripheral blood from septic patients and show that memory CD8 T cells with defined Ag specificity for recurring CMV infection proliferate less than bulk populations of central memory CD8 T cells. Using TCR-transgenic T cells to generate 1° and higher-order (quaternary [4°]) memory T cells within the same host, we demonstrate that the susceptibility and loss of both memory subsets are similar after sepsis induction, and sepsis diminished Ag-dependent and -independent (bystander) functions of these memory subsets equally. Both the 1° and 4° memory T cell populations proliferated in a sepsis-induced lymphopenic environment; however, due to the intrinsic differences in baseline proliferative capacity, expression of receptors (e.g., CD127/CD122), and responsiveness to homeostatic cytokines, 1° memory T cells become overrepresented over time in sepsis survivors. Finally, IL-7/anti-IL-7 mAb complex treatment early after sepsis induction preferentially rescued the proliferation and accumulation of 1° memory T cells, whereas recovery of 4° memory T cells was less pronounced. Thus, inefficient recovery of repeatedly stimulated memory cells after polymicrobial sepsis induction leads to changes in memory T cell pool composition, a notion with important implications in devising strategies to recover the number and function of pre-existing memory CD8 T cells in sepsis survivors.

Natural Microbial Exposure from the Earliest Natural Time Point Enhances Immune Development by Expanding Immune Cell Progenitors and Mature Immune Cells.

Microbial experience fundamentally shapes immunity, particularly during the perinatal period when the immune system is underdeveloped, and novel microbial encounters are common. Most animal models are raised in specific pathogen-free (SPF) conditions with relatively uniform microbial communities. How SPF housing conditions alter early-life immune development relative to natural microbial exposure (NME) has not been thoroughly investigated. In this article, we compare immune development in SPF-raised mice with mice born from immunologically experienced mothers in microbially diverse environments. NME induced broad immune cell expansion, including naive cells, suggesting mechanisms besides activation-induced proliferation contribute to the increase in immune cell numbers. We found NME conditions also expanded immune cell progenitor cell populations in the bone marrow, suggesting microbial experience enhances immune development at the earliest stages of immune cell differentiation. Multiple immune functions characteristically impaired in infants were also enhanced by NME, including T cell memory and Th1 polarization, B cell class switching and Ab production, proinflammatory cytokine expression, and bacterial clearance after Listeria monocytogenes challenge. Collectively, our studies reveal numerous impairments in immune development in SPF conditions relative to natural immune development.

Reduced T Cell Priming in Microbially Experienced "Dirty" Mice Results from Limited IL-27 Production by XCR1+ Dendritic Cells.

Successful vaccination strategies offer the potential for lifelong immunity against infectious diseases and cancer. There has been increased attention regarding the limited translation of some preclinical findings generated using specific pathogen-free (SPF) laboratory mice to humans. One potential reason for the difference between preclinical and clinical findings lies in maturation status of the immune system at the time of challenge. In this study, we used a "dirty" mouse model, where SPF laboratory mice were cohoused (CoH) with pet store mice to permit microbe transfer and immune system maturation, to investigate the priming of a naive T cell response after vaccination with a peptide subunit mixed with polyinosinic-polycytidylic acid and agonistic anti-CD40 mAb. Although this vaccination platform induced robust antitumor immunity in SPF mice, it failed to do so in microbially experienced CoH mice. Subsequent investigation revealed that despite similar numbers of Ag-specific naive CD4 and CD8 T cell precursors, the expansion, differentiation, and recall responses of these CD4 and CD8 T cell populations in CoH mice were significantly reduced compared with SPF mice after vaccination. Evaluation of the dendritic cell compartment revealed reduced IL-27p28 expression by XCR1+ dendritic cells from CoH mice after vaccination, correlating with reduced T cell expansion. Importantly, administration of recombinant IL-27:EBI3 complex to CoH mice shortly after vaccination significantly boosted Ag-specific CD8 and CD4 T cell expansion, further implicating the defect to be T cell extrinsic. Collectively, our data show the potential limitation of exclusive use of SPF mice when testing vaccine efficacy.

NK Cell-Derived IL-10 Supports Host Survival during Sepsis.

The dysregulated sepsis-induced cytokine storm evoked during systemic infection consists of biphasic and interconnected pro- and anti-inflammatory responses. The contrasting inflammatory cytokine responses determine the severity of the septic event, lymphopenia, host survival, and the ensuing long-lasting immunoparalysis state. NK cells, because of their capacity to elaborate pro- (i.e., IFN-γ) and anti-inflammatory (i.e., IL-10) responses, exist at the inflection of sepsis-induced inflammatory responses. Thus, NK cell activity could be beneficial or detrimental during sepsis. In this study, we demonstrate that murine NK cells promote host survival during sepsis by limiting the scope and duration of the cytokine storm. Specifically, NK cell-derived IL-10, produced in response to IL-15, is relevant to clinical manifestations in septic patients and critical for survival during sepsis. This role of NK cells demonstrates that regulatory mechanisms of classical inflammatory cells are beneficial and critical for controlling systemic inflammation, a notion relevant for therapeutic interventions during dysregulated infection-induced inflammatory responses.

Severity of Sepsis Determines the Degree of Impairment Observed in Circulatory and Tissue-Resident Memory CD8 T Cell Populations.

Sepsis reduces the number and function of memory CD8 T cells within the host, contributing to the long-lasting state of immunoparalysis. Interestingly, the relative susceptibility of memory CD8 T cell subsets to quantitative/qualitative changes differ after cecal ligation and puncture (CLP)-induced sepsis. Compared with circulatory memory CD8 T cells (TCIRCM), moderate sepsis (0-10% mortality) does not result in numerical decline of CD8 tissue-resident memory T cells (TRM), which retain their "sensing and alarm" IFN-γ-mediated effector function. To interrogate this biologically important dichotomy, vaccinia virus-immune C57BL/6 (B6) mice containing CD8 TCIRCM and skin TRM underwent moderate or severe (∼50% mortality) sepsis. Severe sepsis led to increased morbidity and mortality characterized by increased inflammation compared with moderate CLP or sham controls. Severe CLP mice also displayed increased vascular permeability in the ears. Interestingly, skin CD103+ CD8 TRM, detected by i.v. exclusion or two-photon microscopy, underwent apoptosis and subsequent numerical loss following severe sepsis, which was not observed in mice that experienced moderate CLP or sham surgeries. Consequently, severe septic mice showed diminished CD8 T cell-mediated protection to localized skin reinfection. Finally, the relationship between severity of sepsis and demise in circulatory versus tissue-embedded memory CD8 T cell populations was confirmed by examining tumor-infiltrating and nonspecific CD8 T cells in B16 melanoma tumors. Thus, sepsis can differentially affect the presence and function of Ag-specific CD8 T cells that reside inside tissues/tumors depending on the severity of the insult, a notion with direct relevance to sepsis survivors and their ability to mount protective memory CD8 T cell-dependent responses to localized Ag re-encounter.

Generation of a Beta-Cell Transplant Animal Model of Diabetes Using CRISPR Technology.

Since insulin deficiency results from pancreatic beta-cell destruction, all type 1 and most type 2 diabetes patients eventually require life-long insulin injections. Insulin gene synthesis could also be impaired due to insulin gene mutations as observed in diabetic patients with MODY 10. At this point, insulin gene therapy could be very effective to recompense insulin deficiency under these circumstances. For this reason, an HIV-based lentiviral vector carrying the insulin gene under the control of insulin promoter (LentiINS) was generated, and its therapeutic efficacy was tested in a beta-cell transplant model lacking insulin produced by CRISPR/Cas9-mediated genetically engineered pancreatic beta cells. To generate an insulin knockout beta-cell transplant animal model of diabetes, a dual gene knockout plasmid system involving CRISPR/Cas9 was transfected into a mouse pancreatic beta cell line (Min6). Fluorescence microscopy and antibiotic selection were utilized to select the insulin gene knockout clones. Transplantation of the genetically engineered pancreatic beta cells under the kidney capsule of STZ-induced diabetic rats revealed LentiINS- but not LentiLacZ-infected Ins2KO cells transiently reduced hyperglycemia similar to that of MIN6 in diabetic animals. These results suggest LentiINS has the potential to functionally restore insulin production in an insulin knockout beta-cell transplant animal model of diabetes.

Toll-like receptor 7 and 8 imidazoquinoline-based agonist/antagonist pairs.

Toll-like receptors (TLRs) 7 and 8 are key targets in the development of immunomodulatory drugs for treating infectious disease, cancer, and autoimmune disorders. These receptors can adopt both agonist and antagonist binding conformations that switch the receptor signal on or off to the downstream production of cytokines. In this study, we examined the effect of simple isomeric substitutions to the C2-butyl group of two imidazoquinoline agonists and evaluated the activity of these analogs using both TLR7 and TLR8 reporter cells and cytokine induction assays. Results are presented showing the C2-isobutyl and C2-cyclopropylmethyl isomers are both mixed TLR7/8 competitive antagonists of the parent agonist [4-Amino-1-(4-(aminomethyl)benzyl)-2-butyl-7-methoxycarbonyl-1H-imidazo[4,5-c]quinoline], indicating the conformation of the dimeric receptor complex is highly sensitive to steric perturbations to the ligand binding pocket. This observation is consistent with prior work demonstrating TLR7 and TLR8 activity is directly correlated to C2-alkyl substitutions that project into a hydrophobic pocket at the dimer interface of the receptor. The close structural relationship of the agonist/antagonist pairs identified here highlights the importance of this pocket in tipping the balance between the agonist and antagonist binding states of the receptor which may have significant ramifications to the design of imidazoquinoline-based immunomodulatory agents.

Immunotherapy for Bladder Cancer: Latest Advances and Ongoing Clinical Trials.

For nearly 50 years, immunotherapy has been used in patients with bladder cancer in the form of Mycobacterium bovis Bacillus Calmette-Guerin (BCG), which is still the first-line therapy for non-muscle invasive disease. However, the remarkable results obtained with checkpoint inhibitor drugs, including Pembrolizumab and Atezolizumab, have fueled the quest to optimize these and other forms of immunotherapy for both non-muscle invasive as well as advanced bladder cancer. In this review we summarize the current state of the rapidly evolving field of immunotherapy in bladder cancer highlighting novel approaches and ongoing trials in this exciting area of research.

New Insights into the Immune System Using Dirty Mice.

The mouse (Mus musculus) is the dominant organism used to investigate the mechanisms behind complex immunological responses because of their genetic similarity to humans and our ability to manipulate those genetics to understand downstream function. Indeed, our knowledge of immune system development, response to infection, and ways to therapeutically manipulate the immune response to combat disease were, in large part, delineated in the mouse. Despite the power of mouse-based immunology research, the translational efficacy of many new therapies from mouse to human is far from ideal. Recent data have highlighted how the naive, neonate-like immune system of specific pathogen-free mice differs dramatically in composition and function to mice living under barrier-free conditions (i.e., "dirty" mice). In this review, we discuss major findings to date and challenges faced when using dirty mice and specific areas of immunology research that may benefit from using animals with robust and varied microbial exposure.

Lentivirus Mediated Pancreatic Beta-Cell-Specific Insulin Gene Therapy for STZ-Induced Diabetes.

Autoimmune destruction of pancreatic beta cells is the characteristic feature of type 1 diabetes mellitus. Consequently, both short- and intermediate-acting insulin analogs are under development to compensate for the lack of endogenous insulin gene expression. Basal insulin is continuously released at low levels in response to hepatic glucose output, while post-prandial insulin is secreted in response to hyperglycemia following a meal. As an alternative to multiple daily injections of insulin, glucose-regulated insulin gene expression by gene therapy is under development to better endure postprandial glucose excursions. Controlled transcription and translation of proinsulin, presence of glucose-sensing machinery, prohormone convertase expression, and a regulated secretory pathway are the key features unique to pancreatic beta cells. To take advantage of these hallmarks, we generated a new lentiviral vector (LentiINS) with an insulin promoter driving expression of the proinsulin encoding cDNA to sustain pancreatic beta-cell-specific insulin gene expression. Intraperitoneal delivery of HIV-based LentiINS resulted in the lowering of fasting plasma glucose, improved glucose tolerance and prevented weight loss in streptozoticin (STZ)-induced diabetic Wistar rats. However, the combinatorial use of LentiINS and anti-inflammatory lentiviral vector (LentiVIP) gene therapy was required to increase serum insulin to a level sufficient to suppress non-fasting plasma glucose and diabetes-related inflammation.

Lentiviral gene therapy vectors encoding VIP suppressed diabetes-related inflammation and augmented pancreatic beta-cell proliferation.

Type 1 diabetes (T1DM) is an autoimmune condition in which the immune system attacks and destroys insulin-producing beta cells in the pancreas leading to hyperglycemia. Vasoactive intestinal peptide (VIP) manifests insulinotropic and anti-inflammatory properties, which are useful for the treatment of diabetes. Because of its limited half-life due to DPP-4-mediated degradation, constant infusions or multiple injections are needed to observe any therapeutic benefit. Since gene therapy has the potential to treat genetic diseases, an HIV-based lentiviral vector carrying VIP gene (LentiVIP) was generated to provide a stable VIP gene expression in vivo. The therapeutic efficacy of LentiVIP was tested in a multiple low-dose STZ-induced animal model of T1DM. LentiVIP delivery into diabetic animals reduced hyperglycemia, improved glucose tolerance, and prevented weight loss. Also, a decrease in serum CRP levels, and serum oxidant capacity, but an increase in antioxidant capacity were observed in LentiVIP-treated animals. Restoration of islet cell mass was correlated with an increase in pancreatic beta-cell proliferation. These beneficial results suggest the therapeutic effect of LentiVIP is due to the repression of diabetes-induced inflammation, its insulinotropic properties, and VIP-induced beta-cell proliferation.

CD8+ T cells mediate ultraviolet A-induced immunomodulation in a model of extracorporeal photochemotherapy.

Extracorporeal photochemotherapy (ECP) that takes advantage of the immunomodulatory effects of UV light has been extensively used for many years for the treatment of several T cell-mediated diseases, including graft-versus-host disease (GvHD) and systemic scleroderma. Immune mechanisms that lead to the establishment of T cell tolerance in ECP-treated patients remain poorly known. In this study, we have tested the effect of UV/psoralen-treated BM-derived dendritic cells, referred to as ECP-BMDCs on the outcome of an antigen-specific T cell-mediated reaction, that is, contact hypersensitivity (CHS), which is mediated by CD8+ effector T cells (CD8+ Teff ). The intravenous (i.v.) injection of antigen-pulsed ECP-BMDCs in recipient C57BL/6 mice induced specific CD8+ T cells endowed with immunomodulatory properties (referred to as CD8+ TECP ), which prevented the priming of CD8+ Teff and the development of CHS, independently of conventional CD4+ regulatory T cells. CD8+ TECP mediated tolerance by inhibiting the migration and functions of skin DC and subsequently the priming of CD8+ Teff . CD8+ TECP displayed none of the phenotypes of the usual CD8+ T regulatory cells described so far. Our results reveal an underestimated participation of CD8+ T cells to ECP-induced immunomodulation that could explain the therapeutic effects of ECP in T cell-mediated diseases.

Cutting Edge: Polymicrobial Sepsis Has the Capacity to Reinvigorate Tumor-Infiltrating CD8 T Cells and Prolong Host Survival.

Malignancy increases sepsis incidence 10-fold and elevates sepsis-associated mortality. Advances in treatment have improved survival of cancer patients shortly after sepsis, but there is a paucity of information on how sepsis impacts cancer growth, development, and prognosis. To test this, cecal ligation and puncture surgery was performed on B16 melanoma-bearing mice to show that sepsis has detrimental effects in hosts with advanced tumors, leading to increased mortality. Surprisingly, mice experiencing cecal ligation and puncture-induced sepsis earlier during tumor development exhibited CD8 T cell-dependent attenuation of tumor growth. Sepsis-resistant CD8 tumor-infiltrating T cells showed increased in vivo activation, effector IFN-γ cytokine production, proliferation, and expression of activation/inhibitory PD-1/LAG-3 receptors because of a sepsis-induced liberation of tumor Ags. Sepsis-reinvigorated CD8 tumor-infiltrating T cells were also amenable to (anti-PD-L1/LAG-3) checkpoint blockade therapy, further prolonging cancer-associated survival in sepsis survivors. Thus, sepsis has the capacity to improve tumor-specific CD8 T cell responses, leading to better cancer prognosis and increased survival.

Sepsis-Induced State of Immunoparalysis Is Defined by Diminished CD8 T Cell-Mediated Antitumor Immunity.

Patients who survive sepsis experience long-term immunoparalysis characterized by numerical and/or functional lesions in innate and adaptive immunity that increase the host's susceptibility to secondary complications. The extent to which tumor development/growth is affected in sepsis survivors remains unknown. In this study, we show cecal ligation and puncture (CLP) surgery renders mice permissive to increased B16 melanoma growth weeks/months after sepsis induction. CD8 T cells provide partial protection in this model, and tumors from sepsis survivors had a reduced frequency of CD8 tumor-infiltrating lymphocytes (TILs) concomitant with an increased tumor burden. Interestingly, the postseptic environment reduced the number of CD8 TILs with high expression of activating/inhibitory receptors PD-1 and LAG-3 (denoted PD-1hi) that define a tumor-specific CD8 T cell subset that retain some functional capacity. Direct ex vivo analysis of CD8 TILs from CLP hosts showed decreased proliferation, IFN-γ production, and survival compared with sham counterparts. To increase the frequency and/or functional capacity of PD-1hi CD8 TILs in tumor-bearing sepsis survivors, checkpoint blockade therapy using anti-PD-L1/anti-LAG-3 mAb was administered before or after the development of sepsis-induced lesions in CD8 TILs. Checkpoint blockade did not reduce tumor growth in CLP hosts when therapy was administered after PD-1hi CD8 TILs had become reduced in frequency and/or function. However, early therapeutic intervention before lesions were observed significantly reduced tumor growth to levels seen in nonseptic hosts receiving therapy. Thus, sepsis-induced immunoparalysis is defined by diminished CD8 T cell-mediated antitumor immunity that can respond to timely checkpoint blockade, further emphasizing the importance of early cancer detection in hosts that survive sepsis.

Cytomegalovirus Evades TRAIL-Mediated Innate Lymphoid Cell 1 Defenses.

Cytomegalovirus (CMV) establishes a lifelong infection facilitated, in part, by circumventing immune defenses mediated by tumor necrosis factor (TNF)-family cytokines. An example of this is the mouse CMV (MCMV) m166 protein, which restricts expression of the TNF-related apoptosis-inducing ligand (TRAIL) death receptors, promoting early-phase replication. We show here that replication of an MCMV mutant lacking m166 is also severely attenuated during viral persistence in the salivary glands (SG). Depleting group I innate lymphoid cells (ILCs) or infecting Trail-/- mice completely restored persistent replication of this mutant. Group I ILCs are comprised of two subsets, conventional natural killer cells (cNK) and tissue-resident cells often referred to as innate lymphoid type I cells (ILC1). Using recently identified phenotypic markers to discriminate between these two cell types, their relative expression of TRAIL and gamma interferon (IFN-γ) was assessed during both early and persistent infection. ILC1 were found to be the major TRAIL expressers during both of these infection phases, with cNK expressing very little, indicating that it is ILC1 that curtail replication via TRAIL in the absence of m166-imposed countermeasures. Notably, despite high TRAIL expression by SG-resident ILC1, IFN-γ production by both ILC1 and cNK was minimal at this site of viral persistence. Together these results highlight TRAIL as a key ILC1-utilized effector molecule that can operate in defense against persistent infection at times when other innate control mechanisms may be muted and highlight the importance for the evolution of virus-employed countermeasures.IMPORTANCE Cytomegalovirus (a betaherpesvirus) is a master at manipulating immune responses to promote its lifelong persistence, a result of millions of years of coevolution with its host. Using a one-of-a-kind MCMV mutant unable to restrict expression of the TNF-related apoptosis-inducing ligand death receptors (TRAIL-DR), we show that TRAIL-DR signaling significantly restricts both early and persistent viral replication. Our results also reveal that these defenses are employed by TRAIL-expressing innate lymphoid type I cells (ILC1) but not conventional NK cells. Overall, our results are significant because they show the key importance of viral counterstrategies specifically neutralizing TRAIL effector functions mediated by a specific, tissue-resident subset of group I ILCs.