Adenovirus type 35, but not type 5, stimulates NK cell activation via plasmacytoid dendritic cells and TLR9 signaling

Cell entry and innate sensing shape adaptive immune responses to adenovirus-based vaccines

Nonreplicating adenovirus-based vectors have been successfully implemented as prophylactic vaccines against infectious viral diseases and induce protective cellular and humoral responses. Differences in the mechanisms of cellular entry or endosomal escape of these vectors contribute to differences in innate immune sensing between adenovirus species. Innate immune responses to adenovirus-based vaccines, such as interferon signaling, have been reported to affect the development of adaptive responses in preclinical studies, although limited data are available in humans. Understanding the mechanisms of these early events is critical for the development of vaccines that elicit effective and durable adaptive immune responses while maintaining an acceptable reactogenicity profile.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Characteristics of Lung Microbiota in Children's Refractory Mycoplasma pneumoniae Pneumonia Coinfected with Human Adenovirus B

Background

Both M. pneumoniae and human adenovirus (HAdV) are common causative agents of lower respiratory tract infection in children; nonetheless, the lung microbiota in patients with coinfection of HAdV and M. pneumoniae remain unexplored.

Methods

Thirty-two children, diagnosed with refractory M. pneumoniae pneumonia (RMPP), entered into the one-year study from July 1, 2019 to June 30, 2020. Among them, twenty-one entered into the M. pneumoniae monoinfection (MP) group and eleven entered into the M. pneumoniae and HAdV coinfection (MP&ADV) group. The characteristics of the clinical findings were examined, and the lung microbiota was analyzed by metagenomic next generation sequencing (mNGS).

Results

Eleven patients in the MP&ADV group were coinfected with human mastadenovirus species B. The fever days lasted for significantly longer periods in the MP&ADV group than in the MP group (P < 0.05). The percentage of CD16⁺CD56⁺ cells was significantly higher in the MP&ADV group than that in the MP group (P < 0.05). There were no significant differences in α-diversity between the MP and MP&ADV groups, but the β-diversity was clearly higher in the MP&ADV group than that in the MP group (P < 0.05). At the microbial level, the top phylum of the MP BALF microbiota was Tenericutes; in contrast, it was Preplasmiviricota in the MP&ADV BALF. There were significant differences in the relative abundance of Tenericutes and Preplasmiviricota between the two groups (P < 0.001). There was a strong positive correlation between human mastadenovirus B and fever days, M. pneumoniae and level of IgA, and a strong negative correlation between Mycoplasma pneumoniae and PCT.

Conclusions

In RMPP, the BALF microbiota in children with mono M. pneumoniae infection was simpler than those with coinfection with human mastadenovirus B. Prolonged fever days were associated with human mastadenovirus B coinfection.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

Imbalance in the ratio of CpG and polyG contributes to impaired interferon-α expression

The secretion of interferon-α (IFN-α) is impaired during hepatitis B virus (HBV) infection. DNA sequences purified from distinct viruses, for example, HBV versus members of Herpesviridae, have been shown to differ in their IFN-α signaling properties. The present study found that DNA from HBV inhibited, while DNA from members of Herpesviridae induced, the expression of IFN-α. Furthermore, stimulatory cytosine-phosphate-guanosine (CpG) sequences derived from these DNA viruses could induce the secretion of IFN-α, while inhibitory guanosine-rich oligodeoxynucleoti (polyG) oligonucleotide sequences derived from these DNA viruses could inhibit CpG-induced IFN-α secretion. Using a computational analysis of genomic DNA sequences, the discrimination between the genomes of HBV and those of other DNA viruses that can also cause inflammation of the liver is based on different frequencies of the CpG and polyG motifs. The underrepresentation of stimulatory CpG motifs and overrepresentation of inhibitory polyG motifs were documented in HBV genomes, whereas the DNA from other viral genomes displayed the opposite trend. Moreover, it was demonstrated that HBV could suppress the activation of IFN-α via its own DNA through the high proportion of polyG motifs. To our knowledge, this is the first demonstration of a specific role for polyG motifs in the inhibition of the IFN-α response following DNA virus infection.

Memory-Like NK Cells: Remembering a Previous Activation by Cytokines and NK Cell Receptors

Natural Killer (NK) cells are cytotoxic innate lymphoid cells serving at the front line against infection and cancer. In inflammatory microenvironments, multiple soluble and contact-dependent signals modulate NK cell responsiveness. Besides their innate cytotoxic and immunostimulatory activity, it has been uncovered in recent years that NK cells constitute a heterogeneous and versatile cell subset. Persistent memory-like NK populations that mount a robust recall response were reported during viral infection, contact hypersensitivity reactions, and after stimulation by pro-inflammatory cytokines or activating receptor pathways. In this review, we highlight recent findings on the generation, functionality, and clinical applicability of memory-like NK cells and describe common features in comparison to other recent concepts of memory NK cells. Understanding of these features will facilitate the conception and design of novel NK cell-based immunotherapies.

Blood Coagulation Factor X Exerts Differential Effects on Adenovirus Entry into Human Lymphocytes

It has been proposed that blood coagulation factors, principally factor X (FX), enhance the uptake of human adenovirus type 5 (Ad5) into cultured epithelial cells by bridging the viral hexon capsid protein and cell-surface heparan sulphate proteoglycans (HSPGs). We studied the effects of FX on Ad transduction of lymphoid cell lines (NK92MI, a natural killer cell line; Daudi, a B-cell line and Jurkat, a T-cell line) as well as primary peripheral blood lymphocytes (PBL) and HeLa epithelial cells using either replication-deficient Ad5, or a derivative in which the Ad5 fiber was replaced with that of another Ad type, Ad35, termed Ad5F35. PBL and NK92MI were resistant to Ad5 transduction. Transduction of Jurkat and Daudi cells by Ad5 was reduced by FX but without discernible effects on cell-surface Ad5 binding. FX reduced virus binding and transduction of all lymphoid cell lines by Ad5F35, as well as transduction of the T- and Natural Killer (NK)-cell populations of PBL. Flow cytometry analysis showed that all lymphoid cell lines were negative for HSPG components, in contrast to HeLa cells. FX reduced transduction of an HSPG-negative mutant Chinese hamster ovary cell line (CHOpgsA745) by Ad5 and Ad5F35, with Ad5F35 binding also being reduced by FX. These results point to fiber-dependent differences (Ad5 versus Ad35 fiber) in Ad binding to and transduction of human lymphoid and epithelial cells in the presence of FX.

Efficient induction of cross-presentating human B cell by transduction with human adenovirus type 7 vector

Although human autologous B cells represent a promising alternative to dendritic cells (DCs) for easy large-scale preparation, the naive human B cells are always poor at antigen presentation. The safe and effective usage record of human adenovirus type 7 (HAdV7) live vaccines makes it attractive as a promising vaccine vector candidate. To investigate whether HAdV7 vector could be used to induce the human B cells cross-presentation, in the present study, we constructed the E3-defective recombinant HAdV7 vector encoding green fluorescent protein (GFP) and carcinoembryonic antigen (CEA). We demonstrated that naive human B cells can efficiently be transduced, and that the MAPKs/NF-κB pathway can be activated by recombinant HAdV7. We proved that cytokine TNF-α, IL-6 and IL-10, surface molecule MHC class I and the CD86, antigen-processing machinery (APM) compounds ERp57, TAP-1, and TAP-2. were upregulated in HAdV7 transduced human B cells. We also found that CEA-specific IFNγ expression, degranulation, and in vitro and ex vivo cytotoxicities are induced in autologous CD8(+) T cells presensitized by HAd7CEA modified human B cells. Meanwhile, our evidences clearly show that Toll-like receptors 9 (TLR9) antagonist IRS 869 significantly eliminated most of the HAdV7 initiated B cell activation and CD8(+) T cells response, supporting the role and contribution of TLR9 signaling in HAdV7 induced human B cell cross-presentation. Besides a better understanding of the interactions between recombinant HAdV7 and human naive B cells, to our knowledge, the present study provides the first evidence to support the use of HAdV7-modified B cells as a vehicle for vaccines and immunotherapy.

The effect of cidofovir on adenovirus plasma DNA levels in stem cell transplantation recipients without T cell reconstitution

Cidofovir is frequently used to treat life-threatening human adenovirus (HAdV) infections in immunocompromised children after hematopoietic stem cell transplantation (HSCT). However, the antiviral effect irrespective of T cell reconstitution remains unresolved. Plasma HAdV DNA levels were monitored by real-time quantitative PCR during 42 cidofovir treatment episodes for HAdV viremia in 36 pediatric allogeneic HSCT recipients. HAdV load dynamics were related to T and natural killer (NK) cell reconstitution measured by flow cytometry. To evaluate the in vivo antiadenoviral effect of cidofovir, we focused on 20 cidofovir treatment episodes lacking concurrent T cell reconstitution. During 2 to 10 weeks of follow-up in the absence of T cells, HAdV load reduction (n = 7) or stabilization (n = 8) was observed in 15 of 20 treatments. Although HAdV load reduction was always accompanied by NK cell expansion, HAdV load stabilization was measured in 2 children lacking both T and NK cell reconstitution. In cases with T cell reconstitution, rapid HAdV load reduction (n = 14) or stabilization (n = 6) was observed in 20 of 22 treatments. In the absence of T cells, cidofovir treatment was associated with HAdV viremia control in the majority of cases. Although the contribution of NK cells cannot be excluded, cidofovir has the potential to mediate HAdV load stabilization in the time pending T cell reconstitution.

Late endosomal trafficking of alternative serotype adenovirus vaccine vectors augments antiviral innate immunity

Adenovirus (Ad) vaccine vectors have found widespread use as vaccine platforms against multiple infections and cancers, and multiple serotypes have been shown to differ significantly in their biological properties and immune phenotypes. Our laboratory and others have previously described differential innate immune stimulation elicited by various Ad serotypes. Here, we show that Ad serotype 5 (Ad5) traffics rapidly to the nucleus following infection, whereas Ad35 and Ad26 accumulate in late endosomes 2 to 8 h postinfection. Innate immune cytokine elicitation by all Ad serotypes was abrogated by blockade of endosomal acidification, cathepsin B, and caspase 1, suggesting that virus interactions with acid-dependent sensors, such as Toll-like receptor- and cathepsin-dependent inflammasome activation in late endosomes, may trigger innate immunity. These data suggest a mechanism by which Ad vectors from various serotypes differentially trigger innate antiviral pathways via distinct intracellular trafficking to late endosomes.

IMPORTANCE

Adenoviruses (Ad) are widely used for vaccination and gene therapy applications. Importantly, Ad vectors have been shown to differ significantly in their innate immune profiles both in vivo and in vitro. The molecular mechanism that underlies these observed differences has important implications for the development of improved vaccines. In this study, we propose a mechanism in which the degree of late endosomal trafficking of Ad vectors results in differential stimulation of late endosomal pattern recognition receptors.

Circumventing antivector immunity: potential use of nonhuman adenoviral vectors

Adenoviruses are efficient gene delivery vectors based on their ability to transduce a wide variety of cell types and drive high-level transient transgene expression. While there have been advances in modifying human adenoviral (HAdV) vectors to increase their safety profile, there are still pitfalls that need to be further addressed. Preexisting humoral and cellular immunity against common HAdV serotypes limits the efficacy of gene transfer and duration of transgene expression. As an alternative, nonhuman AdV (NHAdV) vectors can circumvent neutralizing antibodies against HAdVs in immunized mice and monkeys and in human sera, suggesting that NHAdV vectors could circumvent preexisting humoral immunity against HAdVs in a clinical setting. Consequently, there has been an increased interest in developing NHAdV vectors for gene delivery in humans. In this review, we outline the recent advances and limitations of HAdV vectors for gene therapy and describe examples of NHAdV vectors focusing on their immunogenicity, tropism, and potential as effective gene therapy vehicles.

Type I interferon-dependent activation of NK cells by rAd28 or rAd35, but not rAd5, leads to loss of vector-insert expression

Vaccines constructed from rare-serotype recombinant adenovirus vectors (rAd) such as rAd serotype 28 (rAd28) and rAd35 are currently being explored as alternatives to rAd5-based vaccines because they circumvent the problems with pre-existing immunity that complicate the effectiveness of rAd5 vaccines. However, previous work has demonstrated that the immunogenicity of rAd28 and rAd35 is substantially lower than rAd5. Here we show that rAd28 and rAd35 increase apoptosis of antigen presenting cells (APCs), such as monocytes, relative to rAd5 and mock infected controls. APCs undergoing apoptosis showed an increased loss of vector-insert expression. Loss of vector-insert expression correlated with activation of NK cells, which resulted in apoptosis of co-cultured monocytes. Finally, we show that activation of NK cells is dependent on IFNα which is produced by exposure to rAd28 or rAd35, but not to rAd5. Taken together, these data demonstrate that IFNα-induced activation of NK cells leads to increased monocyte apoptosis and subsequent vector-insert loss. This may be a possible mechanism that results in reduced immunogenicity of rAd28 and rAd35-based vectors.

Adenoviruses types, cell receptors and local innate cytokines in adenovirus infection

Adenovirus is a common infectious pathogen in both children and adults. It is a significant cause of morbidity in immunocompetent people living in crowded living conditions and of mortality in immunocompromised hosts. It has more recently become a popular vehicle for gene therapy applications. The host response to wild-type infection and gene therapy vector exposure involves both virus entry receptor and the innate immune systems. Cell-mediated recognition of viruses via capsid components has received significant attention, principally thought to be regulated by the coxsackievirus-adenovirus receptor (CAR), CD46, integrins and heparin sulfate-containing proteoglycans. Antiviral innate immune responses are initiated by the infected cell, which activates the interferon response to block viral replication, while simultaneously releasing chemokines to attract neutrophils and NK cells. This review discusses the innate immune response primarily during wild-type adenovirus infection because this serves as the basis for understanding the response during both natural infection and exposure to adenovirus vectors.

CpG-depleted adeno-associated virus vectors evade immune detection

Due to their efficient transduction potential, adeno-associated virus (AAV) vectors are leading candidates for gene therapy in skeletal muscle diseases. However, immune responses toward the vector or transgene product have been observed in preclinical and clinical studies. TLR9 has been implicated in promoting AAV-directed immune responses, but vectors have not been developed to circumvent this barrier. To assess the requirement of TLR9 in promoting immunity toward AAV-associated antigens following skeletal muscle gene transfer in mice, we compared immunological responses in WT and Tlr9-deficient mice that received an AAV vector with an immunogenic capsid, AAVrh32.33. In Tlr9-deficient mice, IFN-γ T cell responses toward capsid and transgene antigen were suppressed, resulting in minimal cellular infiltrate and stable transgene expression in target muscles. These findings suggest that AAV-directed immune responses may be circumvented by depleting the ligand for TLR9 (CpG sequences) from the vector genome. Indeed, we found that CpG-depleted AAVrh32.33 vectors could establish persistent transgene expression, evade immunity, and minimize infiltration of effector cells. Thus, CpG-depleted AAV vectors could improve outcome of clinical trials of gene therapy for skeletal muscle disease.