Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection.

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/ß-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of ß-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, ß-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted ß-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This ß-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by ß-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

The Transcription Factor Bhlhe40 Programs Mitochondrial Regulation of Resident CD8+ T Cell Fitness and Functionality.

Tissue-resident memory CD8+ T (Trm) cells share core residency gene programs with tumor-infiltrating lymphocytes (TILs). However, the transcriptional, metabolic, and epigenetic regulation of Trm cell and TIL development and function is largely undefined. Here, we found that the transcription factor Bhlhe40 was specifically required for Trm cell and TIL development and polyfunctionality. Local PD-1 signaling inhibited TIL Bhlhe40 expression, and Bhlhe40 was critical for TIL reinvigoration following anti-PD-L1 blockade. Mechanistically, Bhlhe40 sustained Trm cell and TIL mitochondrial fitness and a functional epigenetic state. Building on these findings, we identified an epigenetic and metabolic regimen that promoted Trm cell and TIL gene signatures associated with tissue residency and polyfunctionality. This regimen empowered the anti-tumor activity of CD8+ T cells and possessed therapeutic potential even at an advanced tumor stage in mouse models. Our results provide mechanistic insights into the local regulation of Trm cell and TIL function.

Tissue-resident memory T cells and lung immunopathology.

Rapid reaction to microbes invading mucosal tissues is key to protect the host against disease. Respiratory tissue-resident memory T (TRM ) cells provide superior immunity against pathogen infection and/or re-infection, due to their presence at the site of pathogen entry. However, there has been emerging evidence that exuberant TRM -cell responses contribute to the development of various chronic respiratory conditions including pulmonary sequelae post-acute viral infections. In this review, we have described the characteristics of respiratory TRM cells and processes underlying their development and maintenance. We have reviewed TRM -cell protective functions against various respiratory pathogens as well as their pathological activities in chronic lung conditions including post-viral pulmonary sequelae. Furthermore, we have discussed potential mechanisms regulating the pathological activity of TRM cells and proposed therapeutic strategies to alleviate TRM -cell-mediated lung immunopathology. We hope that this review provides insights toward the development of future vaccines or interventions that can harness the superior protective abilities of TRM cells, while minimizing the potential for immunopathology, a particularly important topic in the era of coronavirus disease 2019 (COVID-19) pandemic.

Inhibition of stearoyl-CoA desaturases suppresses follicular help T- and germinal center B- cell responses.

Stearoyl-CoA desaturases (SCD) are endoplasmic reticulum (ER)-associated enzymes that catalyze the synthesis of the monounsaturated fatty acids (MUFAs). As such, SCD play important roles in maintaining the intracellular balance between saturated fatty acid (SFAs) and MUFAs. The roles of SCD in CD4+ T-helper cell responses are currently unexplored. Here, we have found that murine and human follicular helper T (TFH ) cells express higher levels of SCD compared to non-TFH cells. Further, the expression of SCD in TFH cells is dependent on the TFH lineage-specification transcription factor BCL6. We found that the inhibition of SCD impaired TFH cell maintenance and shifted the balance between TFH and follicular regulatory T (TFR ) cells in the spleen. Consequently, SCD inhibition dampened germinal center B-cell responses following influenza immunization. Mechanistically, we found that SCD inhibition led to increased ER stress and enhanced TFH cell apoptosis in vitro and in vivo. These results reveal a possible link between fatty acid metabolism and cellular and humoral responses induced by immunization or potentially, autoimmunity.

Neonatal hyperoxia promotes asthma-like features through IL-33-dependent ILC2 responses.

BACKGROUND: Premature infants often require oxygen supplementation and, therefore, are exposed to oxidative stress. Following oxygen exposure, preterm infants frequently develop chronic lung disease and have a significantly increased risk of asthma. OBJECTIVE: We sought to identify the underlying mechanisms by which neonatal hyperoxia promotes asthma development. METHODS: Mice were exposed to neonatal hyperoxia followed by a period of room air recovery. A group of mice was also intranasally exposed to house dust mite antigen. Assessments were performed at various time points for evaluation of airway hyperresponsiveness, eosinophilia, mucus production, inflammatory gene expression, and TH and group 2 innate lymphoid cell (ILC2) responses. Sera from term- and preterm-born infants were also collected and levels of IL-33 and type 2 cytokines were measured. RESULTS: Neonatal hyperoxia induced asthma-like features including airway hyperresponsiveness, mucus hyperplasia, airway eosinophilia, and type 2 pulmonary inflammation. In addition, neonatal hyperoxia promoted allergic TH responses to house dust mite exposure. Elevated IL-33 levels and ILC2 responses were observed in the lungs most likely due to oxidative stress caused by neonatal hyperoxia. IL-33 receptor signaling and ILC2s were vital for the induction of asthma-like features following neonatal hyperoxia. Serum IL-33 levels correlated significantly with serum levels of IL-5 and IL-13 but not IL-4 in preterm infants. CONCLUSIONS: These data demonstrate that an axis involving IL-33 and ILC2s is important for the development of asthma-like features following neonatal hyperoxia and suggest therapeutic potential for targeting IL-33, ILC2s, and oxidative stress to prevent and/or treat asthma development related to prematurity.

Persistent B Cell-Derived MHC Class II Signaling Is Required for the Optimal Maintenance of Tissue-Resident Helper T Cells.

Emerging studies have identified the critical roles of tissue-resident memory CD8+ T (TRM) and B (BRM) cells in the protection against mucosal viral infections, but the underlying mechanisms regulating robust development of TRM and BRM cells remain incompletely understood. We have recently shown that tissue-resident helper CD4+ T (TRH) cells, developed following influenza virus infection, function to sustain the optimal maintenance of TRM and BRM cells at the mucosal surface. In this study, we have explored the cellular and molecular cues modulating lung TRH persistence after influenza infection in C57BL/6 mice. We found that TRH cells were colocalized in tertiary lymphoid structures (TLSs) with local B cells. Abolishing TLSs or the depletion of B cells impaired lung TRH cell numbers. Of note, we found that persistent TCR signaling is needed for the maintenance of TRH cells after the clearance of infectious influenza virus. Furthermore, selective ablation of B cell-derived MHC class II resulted in partial reduction of lung TRH cell number after influenza infection. Our findings suggest that the interaction between lung-resident TRH cells and B cells, along with persistent Ag stimulation, is required to maintain TRH cells after respiratory viral infection.

Establishment of a Dual-Vector System for Gene Delivery Utilizing Prototype Foamy Virus.

Foamy viruses (FVs) are generally recognized as non-pathogenic, often causing asymptomatic or mild symptoms in infections. Leveraging these unique characteristics, FV vectors hold significant promise for applications in gene therapy. This study introduces a novel platform technology using a pseudo-virus with single-round infectivity. In contrast to previous vector approaches, we developed a technique employing only two vectors, pcHFV lacking Env and pCMV-Env, to introduce the desired genes into target cells. Our investigation demonstrated the efficacy of the prototype foamy virus (PFV) dual-vector system in producing viruses and delivering transgenes into host cells. To optimize viral production, we incorporated the codon-optimized Env (optEnv) gene in pCMV-Env and the Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element (WPRE) at the 3' end of the transgene in the transfer vector. Consequently, the use of optEnv led to a significant enhancement in transgene expression in host cells. Additionally, the WPRE exhibited an enhancing effect. Furthermore, the introduced EGFP transgene was present in host cells for a month. In an effort to expand transgene capacity, we further streamlined the viral vector, anticipating the delivery of approximately 4.3 kbp of genes through our PFV dual-vector system. This study underscores the potential of PFVs as an alternative to lentiviruses or other retroviruses in the realm of gene therapy.

Proximal immune-epithelial progenitor interactions drive chronic tissue sequelae post COVID-19.

The long-term physiological consequences of SARS-CoV-2, termed Post-Acute Sequelae of COVID-19 (PASC), are rapidly evolving into a major public health concern. The underlying cellular and molecular etiology remain poorly defined but growing evidence links PASC to abnormal immune responses and/or poor organ recovery post-infection. Yet, the precise mechanisms driving non-resolving inflammation and impaired tissue repair in the context of PASC remain unclear. With insights from three independent clinical cohorts of PASC patients with abnormal lung function and/or viral infection-mediated pulmonary fibrosis, we established a clinically relevant mouse model of post-viral lung sequelae to investigate the pathophysiology of respiratory PASC. By employing a combination of spatial transcriptomics and imaging, we identified dysregulated proximal interactions between immune cells and epithelial progenitors unique to the fibroproliferation in respiratory PASC but not acute COVID-19 or idiopathic pulmonary fibrosis (IPF). Specifically, we found a central role for lung-resident CD8+ T cell-macrophage interactions in maintaining Krt8hi transitional and ectopic Krt5+ basal cell progenitors, thus impairing alveolar regeneration and driving fibrotic sequelae after acute viral pneumonia. Mechanistically, CD8+ T cell derived IFN-γ and TNF stimulated lung macrophages to chronically release IL-1ß, resulting in the abnormal accumulation of dysplastic epithelial progenitors and fibrosis. Notably, therapeutic neutralization of IFN-γ and TNF, or IL-1ß after the resolution of acute infection resulted in markedly improved alveolar regeneration and restoration of pulmonary function. Together, our findings implicate a dysregulated immune-epithelial progenitor niche in driving respiratory PASC. Moreover, in contrast to other approaches requiring early intervention, we highlight therapeutic strategies to rescue fibrotic disease in the aftermath of respiratory viral infections, addressing the current unmet need in the clinical management of PASC and post-viral disease.

Proximal immune-epithelial progenitor interactions drive chronic tissue sequelae post COVID-19.

The long-term physiological consequences of SARS-CoV-2, termed Post-Acute Sequelae of COVID-19 (PASC), are rapidly evolving into a major public health concern. The underlying cellular and molecular etiology remain poorly defined but growing evidence links PASC to abnormal immune responses and/or poor organ recovery post-infection. Yet, the precise mechanisms driving non-resolving inflammation and impaired tissue repair in the context of PASC remain unclear. With insights from three independent clinical cohorts of PASC patients with abnormal lung function and/or viral infection-mediated pulmonary fibrosis, we established a clinically relevant mouse model of post-viral lung sequelae to investigate the pathophysiology of respiratory PASC. By employing a combination of spatial transcriptomics and imaging, we identified dysregulated proximal interactions between immune cells and epithelial progenitors unique to the fibroproliferation in respiratory PASC but not acute COVID-19 or idiopathic pulmonary fibrosis (IPF). Specifically, we found a central role for lung-resident CD8+ T cell-macrophage interactions in maintaining Krt8hi transitional and ectopic Krt5+ basal cell progenitors, thus impairing alveolar regeneration and driving fibrotic sequelae after acute viral pneumonia. Mechanistically, CD8+ T cell derived IFN-γ and TNF stimulated lung macrophages to chronically release IL-1ß, resulting in the abnormal accumulation of dysplastic epithelial progenitors and fibrosis. Notably, therapeutic neutralization of IFN-γ and TNF, or IL-1ß after the resolution of acute infection resulted in markedly improved alveolar regeneration and restoration of pulmonary function. Together, our findings implicate a dysregulated immune-epithelial progenitor niche in driving respiratory PASC. Moreover, in contrast to other approaches requiring early intervention, we highlight therapeutic strategies to rescue fibrotic disease in the aftermath of respiratory viral infections, addressing the current unmet need in the clinical management of PASC and post-viral disease.

The Microbiome-Immune Axis Therapeutic Effects in Cancer Treatments.

During the last decades, research and therapeutic methods in cancer treatment have been evolving. As the results, nowadays, cancer patients are receiving several types of treatments, ranging from chemotherapy and radiation therapy to surgery and immunotherapy. In fact, most cancer patients take a combination of current anti-cancer therapies to improve the efficacy of treatment. However, current strategies still cause some side effects to patients, such as pain and depression. Therefore, there is the need to discover better ways to eradicate cancer whilst minimizing side effects. Recently, immunotherapy, particularly immune checkpoint blockade, is rising as an effective anti-cancer treatment. Unlike chemotherapy or radiation therapy, immunotherapy has few side effects and a higher tumor cell removal efficacy depend on cellular immunological mechanisms. Moreover, recent studies suggest that tissue immune responses are regulated by their microbiome composition. Each tissue has their specific microenvironment, which makes their microbiome composition different, particularly in the context of different types of cancer, such as breast, colorectal, kidney, lung, and skin. Herein, we review the current understanding of the relationship of immune responses and tissue microbiome in cancer in both animal and human studies. Moreover, we discuss the cancermicrobiome-immune axis in the context of cancer development and treatment. Finally, we speculate on strategies to control tissue microbiome alterations that may synergistically affect the immune system and impact cancer treatment outcomes.

Respiratory mucosal immunity against SARS-CoV-2 after mRNA vaccination.

SARS-CoV-2 mRNA vaccination induces robust humoral and cellular immunity in the circulation; however, it is currently unknown whether it elicits effective immune responses in the respiratory tract, particularly against variants of concern (VOCs), including Omicron. We compared the SARS-CoV-2 S-specific total and neutralizing antibody responses, and B and T cell immunity, in the bronchoalveolar lavage fluid (BAL) and blood of COVID-19-vaccinated individuals and hospitalized patients. Vaccinated individuals had significantly lower levels of neutralizing antibody against D614G, Delta (B.1.617.2), and Omicron BA.1.1 in the BAL compared with COVID-19 convalescents despite robust S-specific antibody responses in the blood. Furthermore, mRNA vaccination induced circulating S-specific B and T cell immunity, but in contrast to COVID-19 convalescents, these responses were absent in the BAL of vaccinated individuals. Using a mouse immunization model, we demonstrated that systemic mRNA vaccination alone induced weak respiratory mucosal neutralizing antibody responses, especially against SARS-CoV-2 Omicron BA.1.1 in mice; however, a combination of systemic mRNA vaccination plus mucosal adenovirus-S immunization induced strong neutralizing antibody responses not only against the ancestral virus but also the Omicron BA.1.1 variant. Together, our study supports the contention that the current COVID-19 vaccines are highly effective against severe disease development, likely through recruiting circulating B and T cell responses during reinfection, but offer limited protection against breakthrough infection, especially by the Omicron sublineage. Hence, mucosal booster vaccination is needed to establish robust sterilizing immunity in the respiratory tract against SARS-CoV-2, including infection by the Omicron sublineage and future VOCs.

Co-Ordination of Mucosal B Cell and CD8 T Cell Memory by Tissue-Resident CD4 Helper T Cells.

Adaptive cellular immunity plays a major role in clearing microbial invasion of mucosal tissues in mammals. Following the clearance of primary pathogens, memory lymphocytes are established both systemically and locally at pathogen entry sites. Recently, resident memory CD8 T and B cells (TRM and BRM respectively), which are parked mainly in non-lymphoid mucosal tissues, were characterized and demonstrated to be essential for protection against secondary microbial invasion. Here we reviewed the current understanding of the cellular and molecular cues regulating CD8 TRM and BRM development, maintenance and function. We focused particularly on elucidating the role of a novel tissue-resident helper T (TRH) cell population in assisting TRM and BRM responses in the respiratory mucosa following viral infection. Finally, we argue that the promotion of TRH responses by future mucosal vaccines would be key to the development of successful universal influenza or coronavirus vaccines, providing long-lasting immunity against a broad spectrum of viral strains.

T resident helper cells promote humoral responses in the lung.

Influenza is a deadly and costly infectious disease, even during flu seasons when an effective vaccine has been developed. To improve vaccines against respiratory viruses, a better understanding of the immune response at the site of infection is crucial. After influenza infection, clonally expanded T cells take up permanent residence in the lung, poised to rapidly respond to subsequent infection. Here, we characterized the dynamics and transcriptional regulation of lung-resident CD4+ T cells during influenza infection and identified a long-lived, Bcl6-dependent population that we have termed T resident helper (TRH) cells. TRH cells arise in the lung independently of lymph node T follicular helper cells but are dependent on B cells, with which they tightly colocalize in inducible bronchus-associated lymphoid tissue (iBALT). Deletion of Bcl6 in CD4+ T cells before heterotypic challenge infection resulted in redistribution of CD4+ T cells outside of iBALT areas and impaired local antibody production. These results highlight iBALT as a homeostatic niche for TRH cells and advocate for vaccination strategies that induce TRH cells in the lung.

Tissue-resident CD4+ T helper cells assist the development of protective respiratory B and CD8+ T cell memory responses.

Much remains unknown about the roles of CD4+ T helper cells in shaping localized memory B cell and CD8+ T cell immunity in the mucosal tissues. Here, we report that lung T helper cells provide local assistance for the optimal development of tissue-resident memory B and CD8+ T cells after the resolution of primary influenza virus infection. We have identified a population of T cells in the lung that exhibit characteristics of both follicular T helper and TRM cells, and we have termed these cells as resident helper T (TRH) cells. Optimal TRH cell formation was dependent on transcription factors involved in T follicular helper and resident memory T cell development including BCL6 and Bhlhe40. We show that TRH cells deliver local help to CD8+ T cells through IL-21-dependent mechanisms. Our data have uncovered the presence of a tissue-resident helper T cell population in the lung that plays a critical role in promoting the development of protective B cell and CD8+ T cell responses.

Intranasal Vaccination with Outer-Membrane Protein of Orientia tsutsugamushi induces Protective Immunity Against Scrub Typhus.

Scrub typhus develops after the individual is bitten by a trombiculid mite infected with Orientia tsutsugamushi. Since it has been reported that pneumonia is frequently observed in patients with scrub typhus, we investigated whether intranasal (i.n.) vaccination with the outer membrane protein of O. tsutsugamushi (OMPOT) would induce a protective immunity against O. tsutsugamushi infection. It was particular interest that when mice were infected with O. tsutsugamushi, the bacteria disseminated into the lungs, causing pneumonia. The i.n. vaccination with OMPOT induced IgG responses in serum and bronchoalveolar lavage (BAL) fluid. The anti-O. tsutsugamushi IgA Abs in BAL fluid after the vaccination showed a high correlation of the protection against O. tsutsugamushi. The vaccination induced strong Ag-specific Th1 and Th17 responses in the both spleen and lungs. In conclusion, the current study demonstrated that i.n. vaccination with OMPOT elicited protective immunity against scrub typhus in mouse with O. tsutsugamushi infection causing subsequent pneumonia.

Circulating autoreactive proteinase 3+ B cells and tolerance checkpoints in ANCA-associated vasculitis.

BACKGROUNDLittle is known about the autoreactive B cells in antineutrophil cytoplasmic antibody-associated (ANCA-associated) vasculitis (AAV). We aimed to investigate tolerance checkpoints of circulating antigen-specific proteinase 3-reactive (PR3+) B cells.METHODSMulticolor flow cytometry in combination with bioinformatics and functional in vitro studies were performed on baseline samples of PBMCs from 154 well-characterized participants of the RAVE trial (NCT00104299) with severely active PR3-AAV and myeloperoxidase-AAV (MPO-AAV) and 27 healthy controls (HCs). Clinical data and outcomes from the trial were correlated with PR3+ B cells (total and subsets).RESULTSThe frequency of PR3+ B cells among circulating B cells was higher in participants with PR3-AAV (4.77% median [IQR, 3.98%-6.01%]) than in participants with MPO-AAV (3.16% median [IQR, 2.51%-5.22%]) and participants with AAV compared with HCs (1.67% median [IQR, 1.27%-2.16%], P < 0.001 for all comparisons), implying a defective central tolerance checkpoint in patients with AAV. Only PBMCs from participants with PR3-AAV contained PR3+ B cells capable of secreting PR3-ANCA IgG in vitro, proving they were functionally distinct from those of participants with MPO-AAV and HCs. Unsupervised clustering identified subtle subsets of atypical autoreactive PR3+ memory B cells accumulating through the maturation process in patients with PR3-AAV. PR3+ B cells were enriched in the memory B cell compartment of participants with PR3-AAV and were associated with higher serum CXCL13 levels, suggesting an increased germinal center activity. PR3+ B cells correlated with systemic inflammation (C-reactive protein and erythrocyte sedimentation rate, P < 0.05) and complete remission (P < 0.001).CONCLUSIONThis study suggests the presence of defective central antigen-independent and peripheral antigen-dependent checkpoints in patients with PR3-AAV, elucidating the selection process of autoreactive B cells.Trial registrationClinicalTrials.gov NCT00104299.FundingThe Vasculitis Foundation, the National Institute of Allergy and Infectious Diseases of the NIH, and the Mayo Foundation for Education and Research.

Resistin enhances the expansion of regulatory T cells through modulation of dendritic cells.

BACKGROUND: Resistin, a member of adipokine family, is known to be involved in the modulation of immune responses including inflammatory activity. Interestingly, resistin is secreted by adipocytes in mice and rats whereas it is secreted by leukocytes in humans. However, the mechanism behind the effect of resistin on the expansion of regulatory T cells (Tregs) remains poorly understood. Therefore, we examined regulatory effect of resistin on the induction and cellular modification of Tregs. RESULTS: Both protein and mRNA expression of FoxP3, a representative marker of Tregs, increased in a dose-dependent manner when peripheral blood mononuclear cells were treated with resistin. At the same time, resistin had no direct effect on the induction of FoxP3 in CD4+ T cells, suggesting an indirect role through other cells type(s). Since DCs are an important player in the differentiation of T cells, we focused on the role of DCs in the modulation of Tregs by resistin. Resistin suppressed the expression of interferon regulatory factor (IRF)-1 and its target cytokines, IL-6, IL-23p19 and IL-12p40, in DCs. Furthermore, FoxP3 expression is increased in CD4+ T cells when co-cultured with DCs and concomitantly treated with resistin. CONCLUSION: Our results suggest that resistin induces expansion of functional Tregs only when co-cultured with DCs.

Single-cell mass cytometry on peripheral blood identifies immune cell subsets associated with primary biliary cholangitis.

The relationship between primary biliary cholangitis (PBC), a chronic cholestatic autoimmune liver disease, and the peripheral immune system remains to be fully understood. Herein, we performed the first mass cytometry (CyTOF)-based, immunophenotyping analysis of the peripheral immune system in PBC at single-cell resolution. CyTOF was performed on peripheral blood mononuclear cells (PBMCs) from PBC patients (n = 33) and age-/sex-matched healthy controls (n = 33) to obtain immune cell abundance and marker expression profiles. Hierarchical clustering methods were applied to identify immune cell types and subsets significantly associated with PBC. Subsets of gamma-delta T cells (CD3+TCRgd+), CD8+ T cells (CD3+CD8+CD161+PD1+), and memory B cells (CD3-CD19+CD20+CD24+CD27+) were found to have lower abundance in PBC than in control. In contrast, higher abundance of subsets of monocytes and naïve B cells were observed in PBC compared to control. Furthermore, several naïve B cell (CD3-CD19+CD20+CD24-CD27-) subsets were significantly higher in PBC patients with cirrhosis (indicative of late-stage disease) than in those without cirrhosis. Alternatively, subsets of memory B cells were lower in abundance in cirrhotic relative to non-cirrhotic PBC patients. Future immunophenotyping investigations could lead to better understanding of PBC pathogenesis and progression, and also to the discovery of novel biomarkers and treatment strategies.

Tissue-resident CD8+ T cells drive age-associated chronic lung sequelae after viral pneumonia.

Lower respiratory viral infections, such as influenza virus and severe acute respiratory syndrome coronavirus 2 infections, often cause severe viral pneumonia in aged individuals. Here, we report that influenza viral pneumonia leads to chronic nonresolving lung pathology and exacerbated accumulation of CD8+ tissue-resident memory T cells (TRM) in the respiratory tract of aged hosts. TRM cell accumulation relies on elevated TGF-ß present in aged tissues. Further, we show that TRM cells isolated from aged lungs lack a subpopulation characterized by expression of molecules involved in TCR signaling and effector function. Consequently, TRM cells from aged lungs were insufficient to provide heterologous protective immunity. The depletion of CD8+ TRM cells dampens persistent chronic lung inflammation and ameliorates tissue fibrosis in aged, but not young, animals. Collectively, our data demonstrate that age-associated TRM cell malfunction supports chronic lung inflammatory and fibrotic sequelae after viral pneumonia.