Contributions of CD8 T cells to the pathogenesis of mouse adenovirus type 1 respiratory infection

Immunological pathogenesis and treatment progress of adenovirus pneumonia in children

Human adenovirus is an infectious agent that causes respiratory infections in adults and children. It has been found that immunocompromised children are highly susceptible to this pathogen, as it can swiftly evolve into severe pneumonia with multiple sequelae. Due to the lack of immunity in children, the body's response mechanisms to innate and acquired immunity are specialized. We first examined the infection classification and clinical characteristics associated with adenovirus in children. Subsequently, we explored the in-depth understanding of the pathogenic mechanism of adenovirus pneumonia in children, focusing on immunological and cellular biological aspects. Adenovirus infection in children can disrupt the balance of the innate immune response, inducing immune cells to secrete an abundance of pro-inflammatory cytokines. This cascade results in a cytokine storm, which triggers an inflammatory response and causes lung tissue damage. As a result, the infection may progress to a severe state, potentially leading to multi-organ failure. Immunocompromised children exhibit impaired immune cell numbers and functions, which affects both the secretion of antibodies to humoral immunity and the immune response of cellular immunity to adenovirus. Lastly, we reviewed the progress in treating adenovirus pneumonia in children. There are many treatments for adenovirus pneumonia in children, which must be personalized based on a thorough assessment to optimize treatment outcomes. Recent advancements in pharmaceutical development have provided new treatment options for children. Immunomodulatory therapy can reduce inflammation in children, while adjuvant therapy can improve respiratory function; however, it can also lead to complications. Further, co-infections increased the complexity of diagnosis and treatment, necessitating dynamic adjustments to treatment regimens. This review could serve as the basis for identifying potential therapeutic approaches to alleviate the symptoms associated with adenovirus infections in children.

Effects of immunoproteasome inhibition on acute respiratory infection with murine hepatitis virus strain 1

The immunoproteasome (IP) is a predominantly inducible component of the ubiquitin proteasome system that plays key roles in multiple aspects of immune function, inflammation, and protein homeostasis. We used murine hepatitis virus strain 1 (MHV-1), a mouse coronavirus, to define the role of IP activity during acute coronavirus respiratory infection. Expression of the β5i subunit of the IP and cytokines that induce IP activity, including IFN-γ, TNF-α, and IFN-β, increased in lungs and livers of CH3/HeJ mice following intranasal infection with MHV-1. IP inhibition using ONX-0914 did not affect MHV-1 replication in bone marrow-derived dendritic cells in vitro. IP inhibition in vivo exacerbated virus-induced weight loss and mortality but had no effect on virus replication in lungs or livers. IP inhibition had minimal effect on virus-induced pulmonary inflammation but led to substantially increased liver pathology, including greater upregulation of pro-inflammatory cytokines and histological evidence of inflammation and necrosis. Those findings were associated with evidence of increased endoplasmic reticulum stress although not with accumulation of ubiquitinated protein. Our results indicate that the IP is a protective host factor during acute MHV-1 infection.

IMPORTANCE

Inflammatory responses triggered by acute infection by respiratory viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) drive morbidity and mortality. Infection of mice with murine hepatitis virus strain 1 (MHV-1), a mouse coronavirus, is a useful model to study the pathogenesis of coronavirus respiratory infections. The immunoproteasome is an inducible component of the ubiquitin proteasome system that is poised to contribute to multiple aspects of immune function, inflammation, and protein homeostasis during an infection. We used the MHV-1 model to define the role of the immunoproteasome in coronavirus pathogenesis. We found that immunoproteasome subunit expression increases in the lungs and the liver during acute MHV-1 respiratory infection. Inhibition of immunoproteasome activity did not affect MHV-1 replication but increased MHV-1-induced weight loss, mortality, and inflammation in lungs and livers. Thus, our findings indicate that the immunoproteasome is a critical protective host factor during coronavirus respiratory infection.

A recombinant virus-like particle vaccine against adenovirus-7 induces a potent humoral response

Adenoviruses (AdVs) cause infections in humans that range from mild to severe, and can cause outbreaks particularly in close contact settings. Several human AdV types have been identified, which can cause a wide array of clinical manifestations. AdV types 4 and 7 (AdV-4 and AdV-7), which are among the most commonly circulating types in the United States, are known to cause acute respiratory disease that can result in hospitalization and rarely, death. Currently, the only vaccines approved for use in humans are live virus vaccines against AdV-4 and AdV-7, though these vaccines are only authorized for use in U.S. military personnel. While they are efficacious, use of these live virus vaccines carries considerable risks of vaccine-associated viral shedding and recombination. Here, we present an alternative vaccination strategy against AdV-7 using the virus-like particle platform (AdVLP-7). We describe the production of stable recombinant AdVLP-7, and demonstrate that AdVLP-7 is structurally analogous to wild-type AdV-7 virions (WT AdV-7). Preclinical immunogenicity studies in mice show that AdVLP-7 elicits a potent humoral immune response, comparable to that observed in mice immunized with WT AdV-7. Specifically, AdVLP-7 induces high titers of antibodies against AdV-7-specific antigens that can effectively neutralize AdV-7.

Adenoviruses in medicine: innocuous pathogen, predator, or partner

The consequences of human adenovirus (HAdV) infections are generally mild. However, despite the perception that HAdVs are harmless, infections can cause severe disease in certain individuals, including newborns, the immunocompromised, and those with pre-existing conditions, including respiratory or cardiac disease. In addition, HAdV outbreaks remain relatively common events and the recent emergence of more pathogenic genomic variants of various genotypes has been well documented. Coupled with evidence of zoonotic transmission, interspecies recombination, and the lack of approved AdV antivirals or widely available vaccines, HAdVs remain a threat to public health. At the same time, the detailed understanding of AdV biology garnered over nearly 7 decades of study has made this group of viruses a molecular workhorse for vaccine and gene therapy applications.

Soluble Receptor for Advanced Glycation End Product Is Involved in the Inflammatory Response of Human Adenovirus-Infected Patients

Human adenovirus (HAdV) infection causes excessive inflammation associated with severe tissue injury, such as pneumonia. The molecules involved in the underlying inflammatory mechanisms remain to be elucidated. Receptor for advanced glycation end product (RAGE) is mainly expressed on immune cells and lung tissues, and it is a key factor in the initiation and development of inflammation. RAGE can be cleaved by metalloprotease 9 (MMP9) to release the extracellular segment, which is named soluble RAGE (sRAGE), into the intercellular space, where it can bind to RAGE ligands and block RAGE activation and subsequent inflammation. In our study, we enrolled HAdV-infected patients and their contacts to examine the relationship between sRAGE and inflammation induced by HAdV infection. The results showed that HAdV infection stimulated inflammatory cytokine secretion, increased such as high mobility group box 1 (HMGB1) levels, and suppressed sRAGE expression. sRAGE levels were significantly different between patients with or without pneumonia. We also found that MMP9 was significantly lower in patients with pneumonia, and it was positively correlated with sRAGE levels over 7 days after disease onset. The mitogen-activated protein kinase (MAPK) pathway is an important immune activation signaling pathway that is regulated by RAGE. We observed the activation of the MAPK pathway in the peripheral blood mononuclear cells (PBMCs) of patients. Negative correlations between sRAGE and phosphorylated JNK and p38 were observed. These results suggest that sRAGE is involved in HAdV-induced inflammatory responses, and might be a potential therapeutic target to alleviate the HAdV-induced excessive inflammation.

Considerations of CD8+ T Cells for Optimized Vaccine Strategies Against Respiratory Viruses

The primary goal of vaccines that protect against respiratory viruses appears to be the induction of neutralizing antibodies for a long period. Although this goal need not be changed, recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have drawn strong attention to another arm of acquired immunity, CD8⁺ T cells, which are also called killer T cells. Recent evidence accumulated during the coronavirus disease 2019 (COVID-19) pandemic has revealed that even variants of SARS-CoV-2 that escaped from neutralizing-antibodies that were induced by either infection or vaccination could not escape from CD8⁺ T cell-mediated immunity. In addition, although traditional vaccine platforms, such as inactivated virus and subunit vaccines, are less efficient in inducing CD8⁺ T cells, newly introduced platforms for SARS-CoV-2, namely, mRNA and adenoviral vector vaccines, can induce strong CD8⁺ T cell-mediated immunity in addition to inducing neutralizing antibodies. However, CD8⁺ T cells function locally and need to be at the site of infection to control it. To fully utilize the protective performance of CD8⁺ T cells, it would be insufficient to induce only memory cells circulating in blood, using injectable vaccines; mucosal immunization could be required to set up CD8⁺ T cells for the optimal protection. CD8⁺ T cells might also contribute to the pathology of the infection, change their function with age and respond differently to booster vaccines in comparison with antibodies. Herein, we overview cutting-edge ideas on CD8⁺ T cell-mediated immunity that can enable the rational design of vaccines for respiratory viruses.

Cytokine Responses to Adenovirus and Adenovirus Vectors

The expression of cytokines and chemokines in response to adenovirus infection is tightly regulated by the innate immune system. Cytokine-mediated toxicity and cytokine storm are known clinical phenomena observed following naturally disseminated adenovirus infection in immunocompromised hosts as well as when extremely high doses of adenovirus vectors are injected intravenously. This dose-dependent, cytokine-mediated toxicity compromises the safety of adenovirus-based vectors and represents a critical problem, limiting their utility for gene therapy applications and the therapy of disseminated cancer, where intravenous injection of adenovirus vectors may provide therapeutic benefits. The mechanisms triggering severe cytokine response are not sufficiently understood, prompting efforts to further investigate this phenomenon, especially in clinically relevant settings. In this review, we summarize the current knowledge on cytokine and chemokine activation in response to adenovirus- and adenovirus-based vectors and discuss the underlying mechanisms that may trigger acute cytokine storm syndrome. First, we review profiles of cytokines and chemokines that are activated in response to adenovirus infection initiated via different routes. Second, we discuss the molecular mechanisms that lead to cytokine and chemokine transcriptional activation. We further highlight how immune cell types in different organs contribute to synthesis and systemic release of cytokines and chemokines in response to adenovirus sensing. Finally, we review host factors that can limit cytokine and chemokine expression and discuss currently available and potential future interventional approaches that allow for the mitigation of the severity of the cytokine storm syndrome. Effective cytokine-targeted interventional approaches may improve the safety of systemic adenovirus delivery and thus broaden the potential clinical utility of adenovirus-based therapeutic vectors.

Mouse Adenovirus Type 1 Persistence Exacerbates Inflammation Induced by Allogeneic Bone Marrow Transplantation

Bone marrow transplantation (BMT) recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus. Human adenovirus persistence in mucosal lymphocytes has been described, but specific cellular reservoirs of persistence and effects of persistence on host responses to unrelated stimuli are not completely understood. We used mouse adenovirus type 1 (MAV-1) to characterize persistence of an adenovirus in its natural host and test the hypothesis that persistence increases complications of bone marrow transplantation (BMT). Following intranasal infection of C57BL/6J mice, MAV-1 DNA was detected in lung, mediastinal lymph nodes, and liver during acute infection at 7 days post infection (dpi), and at lower levels at 28 dpi that remained stable through 150 dpi. Expression of early and late viral transcripts was detected in those organs at 7 dpi but not at later time points. MAV-1 persistence was not affected by deficiency of IFN-γ. We detected no evidence of MAV-1 reactivation in vivo following allogeneic BMT of persistently infected mice. Persistent infection did not substantially affect mortality, weight loss, or pulmonary inflammation following BMT. However, T cell infiltration and increased expression of pro-inflammatory cytokines consistent with graft-versus-host disease (GVHD) were more pronounced in livers of persistently infected BMT mice than in uninfected BMT mice. These results suggest that MAV-1 persists in multiple sites without detectable evidence of ongoing replication. Our results indicate that MAV-1 persistence alters host responses to an unrelated challenge, even in the absence of detectable reactivation. Importance Long-term persistence in an infected host is an essential step in the life cycle of DNA viruses. Adenoviruses persist in their host following acute infection, but the nature of adenovirus persistence remains incompletely understood. Following intranasal infection of mice, we found that MAV-1 persists for a prolonged period in multiple organs, although we did not detect evidence of ongoing replication. Because BMT recipients are at risk for substantial morbidity and mortality from human adenovirus infections, often in the setting of reactivation of persistent virus in the recipient, we extended our findings using MAV-1 infection in a mouse model of BMT. MAV-1 persistence exacerbated GVHD-like inflammation following allogeneic BMT, even in the absence of virus reactivation. This novel finding suggests that adenovirus persistence has consequences, and it highlights the potential for a persistent adenovirus to influence host responses to unrelated challenges.

Changes of Host Immunity Mediated by IFN-γ+ CD8+ T Cells in Children with Adenovirus Pneumonia in Different Severity of Illness

The host immunity of patients with adenovirus pneumonia in different severity of illness is unclear. This study compared the routine laboratory tests and the host immunity of human adenovirus (HAdV) patients with different severity of illness. A co-cultured cell model in vitro was established to verify the T cell response in vitro. Among 140 patients with confirmed HAdV of varying severity, the number of lymphocytes in the severe patients was significantly reduced to 1.91 × 10⁹/L compared with the healthy control (3.92 × 10⁹/L) and the mild patients (4.27 × 10⁹/L). The levels of IL-6, IL-10, and IFN-γ in patients with adenovirus pneumonia were significantly elevated with the severity of the disease. Compared with the healthy control (20.82%) and the stable patients (33.96%), the percentage of CD8⁺ T cells that produced IFN-γ increased to 56.27% in the progressing patients. Adenovirus infection increased the percentage of CD8⁺ T and CD4⁺ T cells that produce IFN-γ in the co-culture system. The hyperfunction of IFN-γ⁺ CD8⁺ T cells might be related to the severity of adenovirus infection. The in vitro co-culture cell model could also provide a usable cellular model for subsequent experiments.

Effects of tumor necrosis factor on viral replication and pulmonary inflammation during acute mouse adenovirus type 1 respiratory infection

CD8 T cells contribute to effective clearance of mouse adenovirus type 1 (MAV-1) and to virus-induced pulmonary inflammation. We characterized effects of a CD8 T cell effector, TNF, on MAV-1 pathogenesis. TNF inhibited MAV-1 replication in vitro. TNF deficiency or immunoneutralization had no effect on lung viral loads or viral gene expression in mice infected intranasally with MAV-1. Absence of TNF delayed virus-induced weight loss and reduced histological evidence of pulmonary inflammation, although concentrations of proinflammatory cytokines and chemokines in bronchoalveolar lavage fluid (BALF) were not significantly affected. BALF concentrations of IL-10 were greater in TNF-deficient mice compared to controls. Our data indicate that TNF is not essential for control of viral replication in vivo, but virus-induced TNF contributes to some aspects of immunopathology and disease. Redundant CD8 T cell effectors and other aspects of immune function are sufficient for antiviral and pro-inflammatory responses to acute MAV-1 respiratory infection.

Murine adenoviruses: tools for studying adenovirus pathogenesis in a natural host

Small laboratory animals are powerful models for investigating in vivo viral pathogenesis of a number of viruses. For adenoviruses (AdVs), however, species-specificity poses limitations to studying human adenoviruses (HAdVs) in mice and other small laboratory animals. Thus, this review covers work on naturally occurring mouse AdVs, primarily mouse adenovirus type 1 (MAdV-1), a member of the species Murine mastadenovirus A. Molecular genetics, virus life cycle, cell and tissue tropism, interactions with the host immune response, persistence, and host genetics of susceptibility are described. A brief discussion of MAdV-2 (member of species Murine mastadenovirus B) and MAdV-3 (member of species Murine mastadenovirus C) is included. We report the use of MAdVs in the development of vectors and vaccines.

Age-Dependent Effects of Immunoproteasome Deficiency on Mouse Adenovirus Type 1 Pathogenesis

Acute respiratory infection with mouse adenovirus type 1 (MAV-1) induces activity of the immunoproteasome, an inducible form of the proteasome that shapes CD8 T cell responses by enhancing peptide presentation by major histocompatibility complex (MHC) class I. We used mice deficient in all three immunoproteasome subunits (triple-knockout [TKO] mice) to determine whether immunoproteasome activity is essential for control of MAV-1 replication or inflammatory responses to acute infection. Complete immunoproteasome deficiency in adult TKO mice had no effect on MAV-1 replication, virus-induced lung inflammation, or adaptive immunity compared to C57BL/6 (B6) controls. In contrast, immunoproteasome deficiency in neonatal TKO mice was associated with decreased survival and decreased lung gamma interferon (IFN-γ) expression compared to B6 controls, although without substantial effects on viral replication, histological evidence of inflammation, or expression of the proinflammatory cytokines tumor necrosis factor alpha and interleukin-1β in lungs or other organs. T cell recruitment and IFN-γ production was similar in lungs of infected B6 and TKO mice. In lungs of uninfected B6 mice, we detected low levels of immunoproteasome subunit mRNA and protein that increased with age. Immunoproteasome subunit expression was lower in lungs of adult IFN-γ-deficient mice compared to B6 controls. Together, these results demonstrate developmental regulation of the immunoproteasome that is associated with age-dependent differences in MAV-1 pathogenesis.IMPORTANCE MAV-1 infection is a useful model to study the pathogenesis of an adenovirus in its natural host. Host factors that control MAV-1 replication and contribute to inflammation and disease are not fully understood. The immunoproteasome is an inducible component of the ubiquitin proteasome system that shapes the repertoire of peptides presented by MHC class I to CD8 T cells, influences other aspects of T cell survival and activation, and promotes production of proinflammatory cytokines. We found that immunoproteasome activity is dispensable in adult mice. However, immunoproteasome deficiency in neonatal mice increased mortality and impaired IFN-γ responses in the lungs. Baseline immunoproteasome subunit expression in lungs of uninfected mice increased with age. Our findings suggest the existence of developmental regulation of the immunoproteasome, like other aspects of host immune function, and indicate that immunoproteasome activity is a critical protective factor early in life.

Fas activity mediates airway inflammation during mouse adenovirus type 1 respiratory infection

CD8 T cells play a key role in clearance of mouse adenovirus type 1 (MAV-1) from the lung and contribute to virus-induced airway inflammation. We tested the hypothesis that interactions between Fas ligand (FasL) and Fas mediate the antiviral and proinflammatory effects of CD8 T cells. FasL and Fas expression were increased in the lungs of C57BL/6 (B6) mice during MAV-1 respiratory infection. Viral replication and weight loss were similar in B6 and Fas-deficient (lpr) mice. Histological evidence of pulmonary inflammation was similar in B6 and lpr mice, but lung mRNA levels and airway proinflammatory cytokine concentrations were lower in MAV-1-infected lpr mice compared to infected B6 mice. Virus-induced apoptosis in lungs was not affected by Fas deficiency. Our results suggest that the proinflammatory effects of CD8 T cells during MAV-1 infection are mediated in part by Fas activation and are distinct from CD8 T cell antiviral functions.

Mouse adenovirus type 1 infection of adipose tissue

Human adenovirus (HAdV) type 36 seropositivity has been linked to obesity in humans. That link is supported by a small number of studies using HAdV-36 infection of animals that are not natural hosts for HAdVs. In this study, we infected mice with mouse adenovirus type 1 (MAV-1), a mouse pathogen, to determine whether MAV-1 infected adipose tissue and was associated with adipose tissue inflammation and obesity. We detected MAV-1 in adipose tissue during acute MAV-1 infection, but we did not detect virus-induced increases in adipose tissue cytokine expression or histological evidence of adipose tissue inflammation during acute infection. MAV-1 did not persist in adipose tissue at later times, and we did not detect long-term adipose inflammation, increased adipose tissue mass, or body weight in infected mice. Our data indicate that MAV-1 is not associated with obesity in infected mice.