Modified vaccinia virus Ankara triggers type I IFN production in murine conventional dendritic cells via a cGAS/STING-mediated cytosolic DNA-sensing pathway

Mpox virus poxin-schlafen fusion protein suppresses innate antiviral response by sequestering STAT2

Mpox virus (MPXV) has to establish efficient interferon (IFN) antagonism for effective replication. MPXV-encoded IFN antagonists have not been fully elucidated. In this study, the IFN antagonism of poxin-schlafen (PoxS) fusion gene of MPXV was characterized. MPXV PoxS was capable of decreasing cGAS-produced 2'3'-cGAMP, like its ortholog poxin of vaccinia virus, which is the first known cytosolic nuclease that hydrolyses the 3'-5' bond of 2'3'-cyclic GMP-AMP (cGAMP). However, MPXV PoxS did not suppress cGAS-STING-mediated type I IFN production. Instead, MPXV PoxS antagonized basal and type I IFN-induced expression of IFN-stimulated genes such as OAS1, SAMD9, SAMD9L, ISG15, ISG56 and IFIT3. Consistently, MPXV PoxS inhibited both basal and type I IFN-stimulated activity of interferon-stimulated response elements, but did not affect activation of IFN-γ-activated sites. Mechanistically, MPXV PoxS interacted with STAT2 and sequestered it in the cytoplasm. Both the viral schlafen fusion and the active site of 2'3'-cGAMP nuclease were required for STAT2 sequestration and consequent suppression of IFN-stimulated gene expression. MPXV PoxS conferred resistance to the suppression of MPXV replication by type I IFN. Taken together, our findings suggested that MPXV PoxS counteracts host antiviral response by sequestering STAT2 to circumvent basal and type I IFN-induced expression of antiviral genes.

MPXV infection activates cGAS-STING signaling and IFN-I treatment reduces pathogenicity of mpox in CAST/EiJ mice and rhesus macaques

The recent mpox outbreak underscores the urgent need for more accessible vaccines and treatments. However, the mpox virus (MPXV) clade IIb exhibits milder virulence and fails to develop typical pathological characteristics in mouse models. Herein, we found that CAST/EiJ mice infected intraperitoneally with MPXV clade IIb exhibited more efficient viral replication and experienced splenomegaly. Additionally, MPXV infection triggers the phosphorylation of stimulator of interferon genes (STING), TANK-binding kinase 1 (TBK1), and interferon regulatory factor 3 (IRF3) in ex vivo bone marrow-derived macrophages from mice and promotes the transcription of interferon (IFN)-β via the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-STING pathway. Notably, IFN-β treatment significantly reduced viral replication and alleviated splenomegaly in MPXV-infected CAST/EiJ mice. In rhesus macaques, the clinically approved pegylated IFN alpha-2b treatment markedly reduced the severity of MPXV infection by alleviating skin lesions and lowering plasma viremia. These findings demonstrate that MPXV clade IIb activates the cGAS-STING pathway and highlight the potential of type I interferon (IFN-I) treatment in CAST/EiJ mice and rhesus macaques for mpox.

Double-stranded RNA orbivirus disrupts the DNA-sensing cGAS-sting axis to prevent type I IFN induction

Cyclic GMP-AMP synthase (cGAS) is a DNA sensing cellular receptor that induces IFN-I transcription in response to pathogen and host derived cytosolic DNA and can limit the replication of some RNA viruses. Some viruses have nonetheless evolved mechanisms to antagonize cGAS sensing. In this study, we evaluated the interaction between Bluetongue virus (BTV), the prototypical dsRNA virus of the Orbivirus genus and the Sedoreoviridae family, and cGAS. We found mitochondrial damage and DNA accumulation in the cytoplasm of infected cells. In addition, we show that BTV infection blocks DNA-induced IFN-I transcription and that virus infection prevents DNA sensing by inducing cGAS and STING degradation. We identify BTV-NS3 as the viral protein responsible for cGAS degradation, showing that NS3 physically interacts with cGAS and induces its degradation through an autophagy-dependent mechanism. Taken together, these findings identify for the first time a mechanism by which a dsRNA virus interferes with a DNA sensing pathway to evade the innate immune response.

DNA PAMPs as Molecular Tools for the cGAS-STING Signaling Pathways

Beyond its role as the bearer of genetic material, DNA also plays a crucial role in the activation phase of innate immunity. Pathogen recognition receptors (PRRs) and their homologs, pathogen-associated molecular patterns (PAMPs), form the foundation for driving innate immune activation and the induction of immune responses during infection. In the context of DNA viruses or bacterial infections, specific DNA sequences are recognized and bound by DNA sensors, marking the DNA as a PAMP for host recognition and subsequent activation of innate immunity. The primary DNA sensor pathway known to date is cGAS-STING, which can induce Type I interferons (IFN) and innate immune responses against viruses and bacteria. Additionally, the cGAS-STING pathway has been identified to mediate functions in autophagy and senescence. Herein, we introduce methods for using DNA PAMPs as molecular tools to study the role of cGAS-STING and its signaling pathway in regulating innate immunity, both in vitro and in vivo.

MVA-based SARS-CoV-2 vaccine candidates encoding different spike protein conformations induce distinct early transcriptional responses which may impact subsequent adaptive immunity

Introduction

Vaccine platforms such as viral vectors and mRNA can accelerate vaccine development in response to newly emerging pathogens, as demonstrated during the COVID-19 pandemic. However, the differential effects of platform and antigen insert on vaccine immunogenicity remain incompletely understood. Innate immune responses induced by viral vector vaccines are suggested to have an adjuvant effect for subsequent adaptive immunity. Integrating data on both innate and adaptive immunity, systems vaccinology approaches can improve the understanding of vaccine-induced immune mechanisms.

Methods

Two vaccine candidates against SARS-CoV-2, both based on the viral vector Modified Vaccinia virus Ankara (MVA) and encoding the native (MVA-SARS-2-S) or prefusion-stabilized spike protein (MVA-SARS-2-ST), were evaluated in phase 1 clinical trials (ClinicalTrials.gov: NCT04569383, NCT04895449). Longitudinal dynamics of innate and early adaptive immune responses induced by vaccination in SARS-CoV-2-naïve individuals were analyzed based on transcriptome and flow cytometry data, in comparison to the licensed ChAd and mRNA vaccines.

Results

Compared to MVA-SARS-2-S, MVA-SARS-2-ST (encoding the prefusion-stabilized spike protein) induced a stronger transcriptional activation early after vaccination, as well as higher virus neutralizing antibodies. Positive correlations were observed between innate and adaptive immune responses induced by a second MVA-SARS-2-ST vaccination. MVA-, ChAd- and mRNA-based vaccines induced distinct immune signatures, with the overall strongest transcriptional activation as well as monocyte and circulating T follicular helper (cTFH) cell responses induced by ChAd.

Discussion

Our findings suggest a potential impact of the spike protein conformation not only on adaptive but also on innate immune responses. As indicated by positive correlations between several immune parameters induced by MVA-SARS-2-ST, the distinct transcriptional activation early after vaccination may be linked to the induction of classical monocytes and activation of cTFH1 cells, which may in turn result in the superior adaptive immunogenicity of MVA-SARS-2-ST, compared to MVA-SARS-2-S. Overall, our data demonstrate that both the vaccine platform and antigen insert can affect innate immune responses and subsequent vaccine immunogenicity in humans.

Cytoplasmic DNA and AIM2 inflammasome in RA: where they come from and where they go?

Rheumatoid arthritis is a chronic autoimmune disease of undetermined etiology characterized by symmetric synovitis with predominantly destructive and multiple joint inflammation. Cytoplasmic DNA sensors that recognize protein molecules that are not themselves or abnormal dsDNA fragments play an integral role in the generation and perpetuation of autoimmune diseases by activating different signaling pathways and triggering innate immune signaling pathways and host defenses. Among them, melanoma deficiency factor 2 (AIM2) recognizes damaged DNA and double-stranded DNA and binds to them to further assemble inflammasome, initiating the innate immune response and participating in the pathophysiological process of rheumatoid arthritis. In this article, we review the research progress on the source of cytoplasmic DNA, the mechanism of assembly and activation of AIM2 inflammasome, and the related roles of other cytoplasmic DNA sensors in rheumatoid arthritis.

The unique immune evasion mechanisms of the mpox virus and their implication for developing new vaccines and immunotherapies

Mpox is an infectious and contagious zoonotic disease caused by the mpox virus (MPXV), which belongs to the genus Orthopoxvirus. Since 2022, MPXV has posed a significant threat to global public health. The emergence of thousands of cases across the Western Hemisphere prompted the World Health Organization to declare an emergency. The extensive coevolutionary history of poxviruses with humans has enabled these viruses to develop sophisticated mechanisms to counter the human immune system. Specifically, MPXV employs unique immune evasion strategies against a wide range of immunological elements, presenting a considerable challenge for treatment, especially following the discontinuation of routine smallpox vaccination among the general population. In this review, we start by discussing the entry of the mpox virus and the onset of early infection, followed by an introduction to the mechanisms by which the mpox virus can evade the innate and adaptive immune responses. Two caspase-1 inhibitory proteins and a PKR escape-related protein have been identified as phylogenomic hubs involved in modulating the immune environment during the MPXV infection. With respect to adaptive immunity, mpox viruses exhibit unique and exceptional T-cell inhibition capabilities, thereby comprehensively remodeling the host immune environment. The viral envelope also poses challenges for the neutralizing effects of antibodies and the complement system. The unique immune evasion mechanisms employed by MPXV make novel multi-epitope and nucleic acid-based vaccines highly promising research directions worth investigating. Finally, we briefly discuss the impact of MPXV infection on immunosuppressed patients and the current status of MPXV vaccine development. This review may provide valuable information for the development of new immunological treatments for mpox.

Poxin-deficient poxviruses are sensed by cGAS prior to genome replication

Poxviruses are dsDNA viruses infecting a wide range of cell types, where they need to contend with multiple host antiviral pathways, including DNA and RNA sensing. Accordingly, poxviruses encode a variety of immune antagonists, most of which are expressed early during infection from within virus cores before uncoating and genome release take place. Amongst these antagonists, the poxvirus immune nuclease (poxin) counteracts the cyclic 2'3'-GMP-AMP (2'3'-cGAMP) synthase (cGAS)/stimulator of interferon genes DNA sensing pathway by degrading the immunomodulatory cyclic dinucleotide 2'3'-cGAMP, the product of activated cGAS. Here, we use poxviruses engineered to lack poxin to investigate how virus infection triggers the activation of STING and its downstream transcription factor interferon-responsive factor 3 (IRF3). Our results demonstrate that poxin-deficient vaccinia virus (VACV) and ectromelia virus (ECTV) induce IRF3 activation in primary fibroblasts and differentiated macrophages, although to a lower extent in VACV compared to ECTV. In fibroblasts, IRF3 activation was detectable at 10 h post-infection (hpi) and was abolished by the DNA replication inhibitor cytosine arabinoside (AraC), indicating that the sensing was mediated by replicated genomes. In macrophages, IRF3 activation was detectable at 4 hpi, and this was not affected by AraC, suggesting that the sensing in this cell type was induced by genomes released from incoming virions. In agreement with this, macrophages expressing short hairpin RNA (shRNA) against the virus uncoating factor D5 showed reduced IRF3 activation upon infection. Collectively, our data show that the viral genome is sensed by cGAS prior to and during genome replication, but immune activation downstream of it is effectively suppressed by poxin. Our data also support the model where virus uncoating acts as an immune evasion strategy to simultaneously cloak the viral genome and allow the expression of early immune antagonists.

The monkeypox virus-host interplays

Monkeypox virus (MPXV) is a DNA virus belonging to the Orthopoxvirus genus within the Poxviridae family which can cause a zoonotic infection. The unexpected non-endemic outbreak of mpox in 2022 is considered as a new global threat. It is imperative to take proactive measures, including enhancing our understanding of MPXV's biology and pathogenesis, and developing novel antiviral strategies. The host immune responses play critical roles in defensing against MPXV infection while the virus has also evolved multiple strategies for immune escape. This review summarizes the biological features, antiviral immunity, immune evasion mechanisms, pathogenicity, and prevention strategies for MPXV.

cGAS activation in classical dendritic cells causes autoimmunity in TREX1-deficient mice

Detection of cytosolic DNA by the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway provides immune defense against pathogens and cancer but can also cause autoimmunity when overactivated. The exonuclease three prime repair exonuclease 1 (TREX1) degrades DNA in the cytosol and prevents cGAS activation by self-DNA. Loss-of-function mutations of the TREX1 gene are linked to autoimmune diseases such as Aicardi-Goutières syndrome, and mice deficient in TREX1 develop lethal inflammation in a cGAS-dependent manner. In order to determine the type of cells in which cGAS activation drives autoinflammation, we generated conditional cGAS knockout mice on the Trex1-/- background. Here, we show that genetic ablation of the cGAS gene in classical dendritic cells (cDCs), but not in macrophages, was sufficient to rescue Trex1-/- mice from all observed disease phenotypes including lethality, T cell activation, tissue inflammation, and production of antinuclear antibodies and interferon-stimulated genes. These results show that cGAS activation in cDC causes autoinflammation in response to self-DNA accumulated in the absence of TREX1.

Exploring the chemical space for potential inhibitors against cell surface binding protein of Mpox virus using molecular fingerprint based screening approach

Mpox virus is the latest member of the Poxviridae family of which small pox virus is a member. Monekypox virus has led to thousands of infections across the globe. Poxvirus gains entry into the cell making use of glycosaminoglycans like chondroitin sulphate and heparan sulphate. The interaction of the Mpox virus protein E8L also called cell surface binding protein is crucial for host cell attachment, membrane fusion and viral entry into the host cell leading to establishment of infection thus making this protein a very attractive therapeutic target. In this study we have tried to utilize the chondroitin sulphate binding groove present in the protein and identify molecules which are structurally similar to chondroitin sulphate. These molecules can thus occupy the same pocket but with a better binding affinity than chondroitin sulphate in order to outcompete the latter molecule from binding to the E8L protein and thus prevent it from performing its function. This study may pave the way for development of highly efficient therapeutics against the Mpox virus and further curb its infective potential.Communicated by Ramaswamy H. Sarma.

Multi-omics characterization of the monkeypox virus infection

Multiple omics analyzes of Vaccinia virus (VACV) infection have defined molecular characteristics of poxvirus biology. However, little is known about the monkeypox (mpox) virus (MPXV) in humans, which has a different disease manifestation despite its high sequence similarity to VACV. Here, we perform an in-depth multi-omics analysis of the transcriptome, proteome, and phosphoproteome signatures of MPXV-infected primary human fibroblasts to gain insights into the virus-host interplay. In addition to expected perturbations of immune-related pathways, we uncover regulation of the HIPPO and TGF-β pathways. We identify dynamic phosphorylation of both host and viral proteins, which suggests that MAPKs are key regulators of differential phosphorylation in MPXV-infected cells. Among the viral proteins, we find dynamic phosphorylation of H5 that influenced the binding of H5 to dsDNA. Our extensive dataset highlights signaling events and hotspots perturbed by MPXV, extending the current knowledge on poxviruses. We use integrated pathway analysis and drug-target prediction approaches to identify potential drug targets that affect virus growth. Functionally, we exemplify the utility of this approach by identifying inhibitors of MTOR, CHUK/IKBKB, and splicing factor kinases with potent antiviral efficacy against MPXV and VACV.

Vaccinia Virus: Mechanisms Supporting Immune Evasion and Successful Long-Term Protective Immunity

Vaccinia virus is the most successful vaccine in human history and functions as a protective vaccine against smallpox and monkeypox, highlighting the importance of ongoing research into vaccinia due to its genetic similarity to other emergent poxviruses. Moreover, vaccinia's ability to accommodate large genetic insertions makes it promising for vaccine development and potential therapeutic applications, such as oncolytic agents. Thus, understanding how superior immunity is generated by vaccinia is crucial for designing other effective and safe vaccine strategies. During vaccinia inoculation by scarification, the skin serves as a primary site for the virus-host interaction, with various cell types playing distinct roles. During this process, hematopoietic cells undergo abortive infections, while non-hematopoietic cells support the full viral life cycle. This differential permissiveness to viral replication influences subsequent innate and adaptive immune responses. Dendritic cells (DCs), key immune sentinels in peripheral tissues such as skin, are pivotal in generating T cell memory during vaccinia immunization. DCs residing in the skin capture viral antigens and migrate to the draining lymph nodes (dLN), where they undergo maturation and present processed antigens to T cells. Notably, CD8+ T cells are particularly significant in viral clearance and the establishment of long-term protective immunity. Here, we will discuss vaccinia virus, its continued relevance to public health, and viral strategies permissive to immune escape. We will also discuss key events and populations leading to long-term protective immunity and remaining key gaps.

DNA-PKcs is required for cGAS/STING-dependent viral DNA sensing in human cells

To mount an efficient interferon response to virus infection, intracellular pattern recognition receptors (PRRs) sense viral nucleic acids and activate anti-viral gene transcription. The mechanisms by which intracellular DNA and DNA viruses are sensed are relevant not only to anti-viral innate immunity, but also to autoinflammation and anti-tumour immunity through the initiation of sterile inflammation by self-DNA recognition. The PRRs that directly sense and respond to viral or damaged self-DNA function by signaling to activate interferon regulatory factor (IRF)-dependent type one interferon (IFN-I) transcription. We and others have previously defined DNA-dependent protein kinase (DNA-PK) as an essential component of the DNA-dependent anti-viral innate immune system. Here, we show that DNA-PK is essential for cyclic GMP-AMP synthase (cGAS)- and stimulator of interferon genes (STING)-dependent IFN-I responses in human cells during stimulation with exogenous DNA and infection with DNA viruses.

The poxvirus F17 protein counteracts mitochondrially orchestrated antiviral responses

Poxviruses are unusual DNA viruses that replicate in the cytoplasm. To do so, they encode approximately 100 immunomodulatory proteins that counteract cytosolic nucleic acid sensors such as cGAMP synthase (cGAS) along with several other antiviral response pathways. Yet most of these immunomodulators are expressed very early in infection while many are variable host range determinants, and significant gaps remain in our understanding of poxvirus sensing and evasion strategies. Here, we show that after infection is established, subsequent progression of the viral lifecycle is sensed through specific changes to mitochondria that coordinate distinct aspects of the antiviral response. Unlike other viruses that cause extensive mitochondrial damage, poxviruses sustain key mitochondrial functions including membrane potential and respiration while reducing reactive oxygen species that drive inflammation. However, poxvirus replication induces mitochondrial hyperfusion that independently controls the release of mitochondrial DNA (mtDNA) to prime nucleic acid sensors and enables an increase in glycolysis that is necessary to support interferon stimulated gene (ISG) production. To counter this, the poxvirus F17 protein localizes to mitochondria and dysregulates mTOR to simultaneously destabilize cGAS and block increases in glycolysis. Our findings reveal how the poxvirus F17 protein disarms specific mitochondrially orchestrated responses to later stages of poxvirus replication.

Activating neutrophils by co-administration of immunogenic recombinant modified vaccinia virus Ankara and granulocyte colony-stimulating factor for the treatment of malignant peripheral nerve sheath tumor

Malignant peripheral nerve sheath tumor (MPNST) is a rare, aggressive soft-tissue sarcoma with a poor prognosis and is insensitive to immune checkpoint blockade (ICB) therapy. Loss-of-function of the histone modifying polycomb repressive complex 2 (PRC2) components, EED or SUZ12, is one of the main mechanisms of malignant transformation. In a murine model of MPNST, PRC2-loss tumors have an "immune desert" phenotype and intratumoral (IT) delivery immunogenic modified vaccinia virus Ankara (MVA) sensitized the PRC2-loss tumors to ICB. Here we show that IT MQ833, a second-generation recombinant modified vaccinia virus Ankara virus, results in neutrophil recruitment and activation and neutrophil-dependent tumor killing in the MPNST model. MQ833 was engineered by deleting three viral immune evasion genes, E5R, E3L, and WR199, and expressing three transgenes, including the two membrane-bound Flt3L and OX40L, and IL-12 with an extracellular matrix anchoring signal. Furthermore, we explored strategies to enhance anti-tumor effects of MQ833 by co-administration of granulocyte colony-stimulating factor (G-CSF).

The common H232 STING allele shows impaired activities in DNA sensing, susceptibility to viral infection, and in monocyte cell function, while the HAQ variant possesses wild-type properties

Different innate immune pathways converge to Stimulator of interferon genes (STING) and trigger type I interferon responses after recognition of abnormal nucleic acids in the cells. This non-redundant function renders STING a major player in immunosurveillance, and an emerging target for cancer and infectious diseases therapeutics. Beyond somatic mutations that often occur in cancer, the human gene encoding STING protein, TMEM173 (STING1), holds great genetic heterogeneity; R232, HAQ (R71H-G230A-R293Q) and H232 are the most common alleles. Although some of these alleles are likely to be hypomorphic, their function is still debated, due to the available functional assessments, which have been performed in biased biological systems. Here, by using genetic background-matched models, we report on the functional evaluation of R232, HAQ and H232 variants on STING function, and on how these genotypes affect the susceptibility to clinically relevant viruses, thus supporting a potential contributing cause to differences in inter-individual responses to infections. Our findings also demonstrate a novel toll-like receptor-independent role of STING in modulating monocytic cell function and differentiation into macrophages. We further supported the interplay of STING1 variants and human biology by demonstrating how monocytes bearing the H232 allele were impaired in M1/M2 differentiation, interferon response and antigen presentation. Finally, we assessed the response to PD-1 inhibitor in a small cohort of melanoma patients stratified according to STING genotype. Given the contribution of the STING protein in sensing DNA viruses, bacterial pathogens and misplaced cancer DNA, these data may support the development of novel therapeutic options for infectious diseases and cancer.

Intraperitoneal administration of a modified vaccinia virus Ankara confers single-chain interleukin-12 expression to the omentum and achieves immune-mediated efficacy against peritoneal carcinomatosis

BACKGROUND

Peritoneal carcinomatosis is an advanced stage of cancer in which the disease has spread to the peritoneal cavity. In order to restore antitumor immunity subverted by tumor cells in this location, we evaluated intraperitoneal administrations of modified vaccinia virus Ankara (MVA) engineered to express single-chain interleukin 12 (scIL-12) to increase antitumor immune responses.

METHODS

MVA encoding scIL-12 (MVA.scIL-12) was evaluated against peritoneal carcinomatosis models based on intraperitoneal engraftment of tumor cells. CD8-mediated immune responses, elucidated antitumor efficacy, and safety were evaluated following intravenous, intratumoral, or intraperitoneal administration of the viral vector. The immune response was measured by ELISpot (enzyme-linked immunosorbent spot), RNA sequencing, flow cytometry, intravital microscopy, and depletion of lymphocyte subsets with monoclonal antibodies. Safety was assessed by body-weight follow-up and blood testing. Tissue tropism on intravenous or intraperitoneal administration was assessed by bioluminescence analysis using a reporter MVA encoding luciferase.

RESULTS

Intraperitoneal or locoregional administration, but not other routes of administration, resulted in a potent immune response characterized by increased levels of tumor-specific CD8+ T lymphocytes with the ability to produce both interferon-γ and tumor necrosis factor-α. The antitumor immune response was detectable not only in the peritoneal cavity but also systemically. As a result of intraperitoneal treatment, a single administration of MVA.scIL-12 encoding scIL-12 completely eradicated MC38 tumors implanted in the peritoneal cavity and also protected cured mice from subsequent subcutaneous rechallenges. Bioluminescence imaging using an MVA encoding luciferase revealed that intraperitoneal administration targets transgene to the omentum. The omentum is considered a key tissue in immune protection of the peritoneal cavity. The safety profile of intraperitoneal administration was also better than that following intravenous administration since no weight loss or hematological toxicity was observed when the vector was locally delivered into the peritoneal cavity.

CONCLUSION

Intraperitoneal administration of MVA vectors encoding scIL-12 targets the omentum, which is the tissue where peritoneal carcinomatosis usually begins. MVA.scIL-12 induces a potent tumor-specific immune response that often leads to the eradication of experimental tumors disseminated to the peritoneal cavity.

The effect of Toll-like receptor agonists on the immunogenicity of MVA-SARS-2-S vaccine after intranasal administration in mice

Background and aims

Modified Vaccinia virus Ankara (MVA) represents a promising vaccine vector for respiratory administration to induce protective lung immunity including tertiary lymphoid structure, the bronchus-associated lymphoid tissue (BALT). However, MVA expressing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein (MVA-SARS-2-S) required prime-boost administration to induce high titers of anti-Spike antibodies in serum and bronchoalveolar lavage (BAL). As the addition of adjuvants enables efficient tailoring of the immune responses even to live vaccines, we tested whether Toll-like receptor (TLR)-agonists affect immune responses induced by a single dose of intranasally applied MVA-SARS-2-S.

Methods

We intranasally immunized C57BL/6 mice with MVA-SARS-2-S vaccine in the presence of either TLR3 agonist polyinosinic polycytidylic acid [poly(I:C)], TLR4 agonist bacterial lipopolysaccharide (LPS) from Escherichia coli, or TLR9 agonist CpG oligodeoxynucleotide (CpG ODN) 1826. At different time-points after immunization, we analyzed induced immune responses using flow cytometry, immunofluorescent microscopy, and ELISA.

Results

TLR agonists had profound effects on MVA-SARS-2-S-induced immune responses. At day 1 post intranasal application, the TLR4 agonist significantly affected MVA-induced activation of dendritic cells (DCs) within the draining bronchial lymph nodes, increasing the ratio of CD11b+CD86+ to CD103+CD86+ DCs. Nevertheless, the number of Spike-specific CD8+ T cells within the lungs at day 12 after vaccination was increased in mice that received MVA-SARS-2-S co-administered with TLR3 but not TLR4 agonists. TLR9 agonist did neither significantly affect MVA-induced DC activation nor the induction of Spike-specific CD8+ T cells but reduced both number and size of bronchus-associated lymphoid tissue. Surprisingly, the addition of all TLR agonists failed to boost the levels of Spike-specific antibodies in serum and bronchoalveolar lavage.

Conclusions

Our study indicates a potential role of TLR-agonists as a tool to modulate immune responses to live vector vaccines. Particularly TLR3 agonists hold a promise to potentiate MVA-induced cellular immune responses. On the other hand, additional research is necessary to identify optimal combinations of agonists that could enhance MVA-induced humoral responses.

The parapoxvirus Orf virus inhibits dsDNA-mediated type I IFN expression via STING-dependent and STING-independent signalling pathways

Type I interferons (IFNs) are critical in the host defence against viruses. They induce hundreds of interferon-stimulated genes (ISGs) many of which have an antiviral role. Poxviruses induce IFNs via their pathogen-associated molecular patterns, in particular, their genomic DNA. In a majority of cell types, dsDNA is detected by a range of cytoplasmic DNA sensors that mediate type I IFN expression via stimulator of interferon genes (STING). Orf virus (ORFV) induces cutaneous pustular skin lesions and is the type species of the Parapoxvirus genus within the Poxviridae family. The aim of this study was to investigate whether ORFV modulates dsDNA-induced type I IFN expression via STING-dependent signalling pathways in human dermal fibroblasts (hNDF) and THP-1 cells. We showed that ORFV infection of these cell types treated with poly(dA:dT) resulted in strong inhibition of expression of IFN-β. In hNDFs, we showed using siRNA knock-down that STING was essential for type I IFN induction. IFN-β expression was further reduced when both STING and RIG-I were knocked down. In addition, HEK293 cells that do not express STING or Toll-like receptors also produce IFN-β following stimulation with poly(dA:dT). The 5' triphosphate dsRNA produced by RNA polymerase III specifically results in the induction of type I IFNs through the RIG-I receptor. We showed that ORFV infection resulted in strong inhibition of IFN-β expression in HEK293 cells stimulated with poly(dA:dT). Overall, this study shows that ORFV potently counteracts the STING-dependent and STING-independent IFN response by antagonizing dsDNA-activated IFN signalling pathways.

OX40L-expressing recombinant modified vaccinia virus Ankara induces potent antitumor immunity via reprogramming Tregs

Effective depletion of immune suppressive regulatory T cells (Tregs) in the tumor microenvironment without triggering systemic autoimmunity is an important strategy for cancer immunotherapy. Modified vaccinia virus Ankara (MVA) is a highly attenuated, non-replicative vaccinia virus with a long history of human use. Here, we report rational engineering of an immune-activating recombinant MVA (rMVA, MVA∆E5R-Flt3L-OX40L) with deletion of the vaccinia E5R gene (encoding an inhibitor of the DNA sensor cyclic GMP-AMP synthase, cGAS) and expression of two membrane-anchored transgenes, Flt3L and OX40L. Intratumoral (IT) delivery of rMVA (MVA∆E5R-Flt3L-OX40L) generates potent antitumor immunity, dependent on CD8+ T cells, the cGAS/STING-mediated cytosolic DNA-sensing pathway, and type I IFN signaling. Remarkably, IT rMVA (MVA∆E5R-Flt3L-OX40L) depletes OX40hi regulatory T cells via OX40L/OX40 interaction and IFNAR signaling. Single-cell RNA-seq analyses of tumors treated with rMVA showed the depletion of OX40hiCCR8hi Tregs and expansion of IFN-responsive Tregs. Taken together, our study provides a proof-of-concept for depleting and reprogramming intratumoral Tregs via an immune-activating rMVA.

IL-7 producing immunotherapy improves ex vivo T cell functions of immunosenescent patients, especially post hip fracture

Following acute stress such as trauma or sepsis, most of critically ill elderly patients become immunosuppressed and susceptible to secondary infections and enhanced mortality. We have developed a virus-based immunotherapy encoding human interleukin-7 (hIL-7) aiming at restoring both innate an adaptative immune homeostasis in these patients. We assessed the impact of this encoded hIL-7 on the ex vivo immune functions of T cells from PBMC of immunosenescent patients with or without hip fracture. T-cell ex vivo phenotyping was characterized in terms of senescence (CD57), IL-7 receptor (CD127) expression, and T cell differentiation profile. Then, post stimulation, activation status, and functionality (STAT5/STAT1 phosphorylation and T cell proliferation assays) were evaluated by flow cytometry. Our data show that T cells from both groups display immunosenescence features, express CD127 and are activated after stimulation by virotherapy-produced hIL-7-Fc. Interestingly, hip fracture patients exhibit a unique functional ability: An important T cell proliferation occurred compared to controls following stimulation with hIL-7-Fc. In addition, stimulation led to an increased naïve T cell as well as a decreased effector memory T cell proportions compared to controls. This preliminary study indicates that the produced hIL-7-Fc is well recognized by T cells and initiates IL-7 signaling through STAT5 and STAT1 phosphorylation. This signaling efficiently leads to T cell proliferation and activation and enables a T cell "rejuvenation." These results are in favor of the clinical development of the hIL-7-Fc expressing virotherapy to restore or induce immune T cell responses in immunosenescent hip fracture patients.

The prospective outcome of the monkeypox outbreak in 2022 and characterization of monkeypox disease immunobiology

A new threat to global health re-emerged with monkeypox's advent in early 2022. As of November 10, 2022, nearly 80,000 confirmed cases had been reported worldwide, with most of them coming from places where the disease is not common. There were 53 fatalities, with 40 occurring in areas that had never before recorded monkeypox and the remaining 13 appearing in the regions that had previously reported the disease. Preliminary genetic data suggest that the 2022 monkeypox virus is part of the West African clade; the virus can be transmitted from person to person through direct interaction with lesions during sexual activity. It is still unknown if monkeypox can be transmitted via sexual contact or, more particularly, through infected body fluids. This most recent epidemic's reservoir host, or principal carrier, is still a mystery. Rodents found in Africa can be the possible intermediate host. Instead, the CDC has confirmed that there are currently no particular treatments for monkeypox virus infection in 2022; however, antivirals already in the market that are successful against smallpox may mitigate the spread of monkeypox. To protect against the disease, the JYNNEOS (Imvamune or Imvanex) smallpox vaccine can be given. The spread of monkeypox can be slowed through measures such as post-exposure immunization, contact tracing, and improved case diagnosis and isolation. Final Thoughts: The latest monkeypox epidemic is a new hazard during the COVID-19 epidemic. The prevailing condition of the monkeypox epidemic along with coinfection with COVID-19 could pose a serious condition for clinicians that could lead to the global epidemic community in the form of coinfection.

Armored modified vaccinia Ankara in cancer immunotherapy

Cancer immunotherapy relies on unleashing the patient´s immune system against tumor cells. Cancer vaccines aim to stimulate both the innate and adaptive arms of immunity to achieve durable clinical responses. Some roadblocks for a successful cancer vaccine in the clinic include the tumor antigen of choice, the adjuvants employed to strengthen antitumor-specific immune responses, and the risks associated with enhancing immune-related adverse effects in patients. Modified vaccinia Ankara (MVA) belongs to the family of poxviruses and is a versatile vaccine platform that combines several attributes crucial for cancer therapy. First, MVA is an excellent inducer of innate immune responses leading to type I interferon secretion and induction of T helper cell type 1 (Th1) immune responses. Second, it elicits robust and durable humoral and cellular immunity against vector-encoded heterologous antigens. Third, MVA has enormous genomic flexibility, which allows for the expression of multiple antigenic and costimulatory entities. And fourth, its replication deficit in human cells ensures a excellent safety profile. In this review, we summarize the current understanding of how MVA induces innate and adaptive immune responses. Furthermore, we will give an overview of the tumor-associated antigens and immunomodulatory molecules that have been used to armor MVA and describe their clinical use. Finally, the route of MVA immunization and its impact on therapeutic efficacy depending on the immunomodulatory molecules expressed will be discussed.

Vaccinia E5 is a major inhibitor of the DNA sensor cGAS

The DNA sensor cyclic GMP-AMP synthase (cGAS) is critical in host antiviral immunity. Vaccinia virus (VACV) is a large cytoplasmic DNA virus that belongs to the poxvirus family. How vaccinia virus antagonizes the cGAS-mediated cytosolic DNA-sensing pathway is not well understood. In this study, we screened 80 vaccinia genes to identify potential viral inhibitors of the cGAS/Stimulator of interferon gene (STING) pathway. We discovered that vaccinia E5 is a virulence factor and a major inhibitor of cGAS. E5 is responsible for abolishing cGAMP production during vaccinia virus (Western Reserve strain) infection of dendritic cells. E5 localizes to the cytoplasm and nucleus of infected cells. Cytosolic E5 triggers ubiquitination of cGAS and proteasome-dependent degradation via interacting with cGAS. Deleting the E5R gene from the Modified vaccinia virus Ankara (MVA) genome strongly induces type I IFN production by dendritic cells (DCs) and promotes DC maturation, and thereby improves antigen-specific T cell responses.

Human monkeypox infection threat: A comprehensive overview

BACKGROUND

In addition to the COVID-19 waves, the globe is recently facing global monkeypox (MPX) outbreak. As the daily confirmed cases of MPX infection across epidemic and nonepidemic countries are increasing, taking measures to control global pandemic remains crucial. Therefore, this review aimed to provide fundamental knowledge for the prevention and control of future outbreaks of this emerging epidemic.

METHODS

The review was conducted using PubMed and Google Scholar databases; the search terms used were "monkeypox," "MPX tropism," "replication signaling of MPX," "biology and pathogenicity of MPX," "diagnosis of MPX," "treatment of MPX," "prevention of MPX," etc. The update epidemic data were collected from the websites of the World Health Organization (WHO), United States Centers for Disease Control and Prevention (CDC), and Africa Center for Disease Control and Prevention (ADCC). High-quality research results published in authoritative journals were summarized and preferred cited. Excluding all duplicates, non-English published references, and irrelevant literature, totally 1,436 articles were assessed for eligibility.

RESULTS

It is still difficult to diagnose the patient as MPX simply based on clinical manifestations; therefore, under this situation, employing polymerase chain reaction (PCR) technology to provide confirmed evidence for the diagnosis of MPX seems to be the preferred and indispensable strategy. The treatment approach for MPX infection is mainly symptomatic and supportive; anti-smallpox virus drugs including tecovirimat, cidofovir, and brincidofovir can be employed in severe cases. Timely identification and isolation of confirmed cases, cutting off dissemination routes, and vaccination of close contacts are effective measures to control MPX. Also, smallpox vaccines (JYNNEOS, LC16m8, and ACAM2000) can be under consideration due to their immunological cross-protection among Orthopoxvirus. Nevertheless, given the low quality and scarcity of relevant evidence of current antiviral drugs and vaccines, deeply seeking for the MAPK/ERK, PAK-1, PI3K/Akt signaling, and other pathways involved in MPX invasion may provide potential targets for the treatment, prevention, and control of the epidemic.

CONCLUSIONS

In response to the current MPX epidemic, the development of vaccines and antiviral drugs against MPX, as well as the rapid and precise diagnostic methods are still urgently needed. Sound monitoring and detection systems should be established to limit the rapid spread of MPX worldwide.

Complexing CpG adjuvants with cationic liposomes enhances vaccine-induced formation of liver TRM cells

Tissue resident memory T cells (T_RM cells) can provide effective tissue surveillance and can respond rapidly to infection. Vaccination strategies aimed at generating T_RM cells have shown promise against a range of pathogens. We have previously shown that the choice of adjuvant critically influences CD8⁺ T_RM cell formation in the liver. However, the range of adjuvants tested was limited. Here, we assessed the ability of a broad range of adjuvants stimulating membrane (TLR4), endosomal (TLR3, TLR7 and TLR9) and cytosolic (cGAS, RIG-I) pathogen recognition receptors for their capacity to induce CD8⁺ T_RM formation in a subunit vaccination model. We show that CpG oligodeoxynucleotides (ODN) remain the most efficient inducers of liver T_RM cells among all adjuvants tested. Moreover, their combination with the cationic liposome DOTAP further enhances the potency, particularly of the class B ODN CpG 1668 and the human TLR9 ligand CpG 2006 (CpG 7909). This study informs the design of efficient liver T_RM-based vaccines for their potential translation.

CRISPR-mediated rapid arming of poxvirus vectors enables facile generation of the novel immunotherapeutic STINGPOX

Poxvirus vectors represent versatile modalities for engineering novel vaccines and cancer immunotherapies. In addition to their oncolytic capacity and immunogenic influence, they can be readily engineered to express multiple large transgenes. However, the integration of multiple payloads into poxvirus genomes by traditional recombination-based approaches can be highly inefficient, time-consuming and cumbersome. Herein, we describe a simple, cost-effective approach to rapidly generate and purify a poxvirus vector with multiple transgenes. By utilizing a simple, modular CRISPR/Cas9 assisted-recombinant vaccinia virus engineering (CARVE) system, we demonstrate generation of a recombinant vaccinia virus expressing three distinct transgenes at three different loci in less than 1 week. We apply CARVE to rapidly generate a novel immunogenic vaccinia virus vector, which expresses a bacterial diadenylate cyclase. This novel vector, STINGPOX, produces cyclic di-AMP, a STING agonist, which drives IFN signaling critical to the anti-tumor immune response. We demonstrate that STINGPOX can drive IFN signaling in primary human cancer tissue explants. Using an immunocompetent murine colon cancer model, we demonstrate that intratumoral administration of STINGPOX in combination with checkpoint inhibitor, anti-PD1, promotes survival post-tumour challenge. These data demonstrate the utility of CRISPR/Cas9 in the rapid arming of poxvirus vectors with therapeutic payloads to create novel immunotherapies.

Heat-inactivated modified vaccinia virus Ankara boosts Th1 cellular and humoral immunity as a vaccine adjuvant

Protein or peptide-based subunit vaccines have generated excitement and renewed interest in combating human cancer or COVID-19 outbreak. One major concern for subunit vaccine application is the weak immune responses induced by protein or peptides. Developing novel and effective vaccine adjuvants are critical for the success of subunit vaccines. Here we explored the potential of heat-inactivated MVA (heat-iMVA) as a vaccine adjuvant. Heat-iMVA dramatically enhances T cell responses and antibodies responses, mainly toward Th1 immune responses when combined with protein or peptide-based immunogen. The adjuvant effect of Heat-iMVA is stronger than live MVA and is dependent on the cGAS/STING-mediated cytosolic DNA-sensing pathway. In a therapeutic vaccination model based on tumor neoantigen peptide vaccine, Heat-iMVA significantly extended the survival and delayed tumor growth. When combined with SARS-CoV-2 spike protein, Heat-iMVA induced more robust spike-specific antibody production and more potent neutralization antibodies. Our results support that Heat-iMVA can be developed as a safe and potent vaccine adjuvant for subunit vaccines against cancer or SARS-CoV-2.

Monkeypox: disease epidemiology, host immunity and clinical interventions

Monkeypox virus (MPXV), which causes disease in humans, has for many years been restricted to the African continent, with only a handful of sporadic cases in other parts of the world. However, unprecedented outbreaks of monkeypox in non-endemic regions have recently taken the world by surprise. In less than 4 months, the number of detected MPXV infections has soared to more than 48,000 cases, recording a total of 13 deaths. In this Review, we discuss the clinical, epidemiological and immunological features of MPXV infections. We also highlight important research questions and new opportunities to tackle the ongoing monkeypox outbreak.

Pattern Recognition Receptors of Nucleic Acids Can Cause Sublethal Activation of the Mitochondrial Apoptosis Pathway during Viral Infection

The mitochondrial apoptosis pathway has the function to kill the cell, but recent work shows that this pathway can also be activated to a sublethal level, where signal transduction can be observed but the cell survives. Intriguingly, this signaling has been shown to contribute to inflammatory activity of epithelial cells upon infection with numerous agents. This suggests that microbial recognition can generate sublethal activity in the mitochondrial apoptosis pathway. Because this recognition is achieved by pattern recognition receptors (PRRs), it also implies that PRR signals are linked to the mitochondrial apoptosis apparatus. We here test this hypothesis during infection of epithelial cells with modified vaccinia virus Ankara (MVA). MVA recognition is achieved through receptors specific for nucleic acids, and we present evidence that the three receptors, Toll-like receptor 3 (TLR3), RIG-I/MDA5, and cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING), are involved in this signaling. When stimulated directly by specific ligands, all three receptors could trigger sublethal apoptosis signals. During infection with MVA, sublethal apoptosis signals were unmasked in X-linked IAP (XIAP)-deficient cells, where apoptosis induction was observed. Deletion of any of the three signaling adapters, TRIF, MAVS, and STING, reduced the DNA damage response, a sensitive measure of sublethal apoptosis signals. Our results suggest that PRRs signal via mitochondria, where they generate sublethal signals through the BCL-2-family, which may contribute to the response to infectious agents. IMPORTANCE A contribution of the mitochondrial apoptosis apparatus, in the absence of cell death, to the reaction of nonprofessional immune cells to viruses is suggested to play a role as a broad alert system of an infected cell: the apoptosis system can be activated by many upstream signals and could therefore act as a central coordinator of viral recognition. The proapoptotic activity of PRRs has been documented in multiple situations, but this activity seems too low to be meaningful, and a physiological significance of such activity is not immediately obvious. This work suggests the alternative interpretation that PRRs do not have the primary function to induce apoptosis but to trigger sublethal signals in the apoptosis system. A number of lines of recent research suggest that mitochondria contribute to cellular reactions, and this pathway may be a way of triggering an early host response.

Regulation of cGAS/STING signaling and corresponding immune escape strategies of viruses

Innate immunity is the first line of defense against invading external pathogens, and pattern recognition receptors (PRRs) are the key receptors that mediate the innate immune response. Nowadays, there are various PRRs in cells that can activate the innate immune response by recognizing pathogen-related molecular patterns (PAMPs). The DNA sensor cGAS, which belongs to the PRRs, plays a crucial role in innate immunity. cGAS detects both foreign and host DNA and generates a second-messenger cGAMP to mediate stimulator of interferon gene (STING)-dependent antiviral responses, thereby exerting an antiviral immune response. However, the process of cGAS/STING signaling is regulated by a wide range of factors. Multiple studies have shown that viruses directly target signal transduction proteins in the cGAS/STING signaling through viral surface proteins to impede innate immunity. It is noteworthy that the virus utilizes these cGAS/STING signaling regulators to evade immune surveillance. Thus, this paper mainly summarized the regulatory mechanism of the cGAS/STING signaling pathway and the immune escape mechanism of the corresponding virus, intending to provide targeted immunotherapy ideas for dealing with specific viral infections in the future.

Tumor-intrinsic PRC2 inactivation drives a context-dependent immune-desert microenvironment and is sensitized by immunogenic viruses

Immune checkpoint blockade (ICB) has demonstrated clinical success in "inflamed" tumors with substantial T cell infiltrates, but tumors with an immune-desert tumor microenvironment (TME) fail to benefit. The tumor cell-intrinsic molecular mechanisms of the immune-desert phenotype remain poorly understood. Here, we demonstrated that inactivation of the polycomb-repressive complex 2 (PRC2) core components embryonic ectoderm development (EED) or suppressor of zeste 12 homolog (SUZ12), a prevalent genetic event in malignant peripheral nerve sheath tumors (MPNSTs) and sporadically in other cancers, drove a context-dependent immune-desert TME. PRC2 inactivation reprogramed the chromatin landscape that led to a cell-autonomous shift from primed baseline signaling-dependent cellular responses (e.g., IFN-γ signaling) to PRC2-regulated developmental and cellular differentiation transcriptional programs. Further, PRC2 inactivation led to diminished tumor immune infiltrates through reduced chemokine production and impaired antigen presentation and T cell priming, resulting in primary resistance to ICB. Intratumoral delivery of inactivated modified vaccinia virus Ankara (MVA) enhanced tumor immune infiltrates and sensitized PRC2-loss tumors to ICB. Our results identify molecular mechanisms of PRC2 inactivation-mediated, context-dependent epigenetic reprogramming that underline the immune-desert phenotype in cancer. Our studies also point to intratumoral delivery of immunogenic viruses as an initial therapeutic strategy to modulate the immune-desert TME and capitalize on the clinical benefit of ICB.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

Regulation of the Innate Immune Response during the Human Papillomavirus Life Cycle

High-risk human papillomaviruses (HR HPVs) are associated with multiple human cancers and comprise 5% of the human cancer burden. Although most infections are transient, persistent infections are a major risk factor for cancer development. The life cycle of HPV is intimately linked to epithelial differentiation. HPVs establish infection at a low copy number in the proliferating basal keratinocytes of the stratified epithelium. In contrast, the productive phase of the viral life cycle is activated upon epithelial differentiation, resulting in viral genome amplification, high levels of late gene expression, and the assembly of virions that are shed from the epithelial surface. Avoiding activation of an innate immune response during the course of infection plays a key role in promoting viral persistence as well as completion of the viral life cycle in differentiating epithelial cells. This review highlights the recent advances in our understanding of how HPVs manipulate the host cell environment, often in a type-specific manner, to suppress activation of an innate immune response to establish conditions supportive of viral replication.

Disruption of the cGAS/STING axis does not impair sensing of MVA in BHK21 cells

Modified vaccinia Ankara (MVA) is an attenuated strain of vaccinia virus (VACV), a dsDNA virus that replicates its genome in the cytoplasm and as a result is canonically sensed by the cyclic GMP-AMP synthase (cGAS) and its downstream stimulator of interferon genes (STING). MVA has a highly restricted host range due to major deletions in its genome including inactivation of immunomodulatory genes, only being able to grow in avian cells and the hamster cell line BHK21. Here we studied the interplay between MVA and the cGAS/STING DNA in this permissive cell line and determined whether manipulation of this axis could impact MVA replication and cell responses. We demonstrate that BHK21 cells retain a functional cGAS/STING axis that responds to canonical DNA sensing agonists, upregulating interferon stimulated genes (ISGs). BHK21 cells also respond to MVA, but with a distinct ISG profile. This profile remains unaltered after CRISPR/Cas9 knock-out editing of STING and ablation of cytosolic DNA responses, indicating that MVA responses are independent of the cGAS/STING axis. Furthermore, infection by MVA diminishes the ability of BHK21 cells to respond to exogenous DNA suggesting that MVA still encodes uncharacterised inhibitors of DNA sensing. This suggests that using attenuated strains in permissive cell lines may assist in identification of novel host-virus interactions that may be of relevance to disease or the therapeutic applications of poxviruses.

Pseudocowpox virus, a novel vector to enhance the therapeutic efficacy of antitumor vaccination

Objective

Antitumor viral vaccines, and more particularly poxviral vaccines, represent an active field for clinical development and translational research. To improve the efficacy and treatment outcome, new viral vectors are sought, with emphasis on their abilities to stimulate innate immunity, to display tumor antigens and to induce a specific T‐cell response.

Methods

We screened for a new poxviral backbone with improved innate and adaptive immune stimulation using IFN‐α secretion levels in infected PBMC cultures as selection criteria. Assessment of virus effectiveness was made in vitro and in vivo.

Results

The bovine pseudocowpox virus (PCPV) stood out among several poxviruses for its ability to induce significant secretion of IFN‐α. PCPV produced efficient activation of human monocytes and dendritic cells, degranulation of NK cells and reversed MDSC‐induced T‐cell suppression, without being offensive to activated T cells. A PCPV‐based vaccine, encoding the HPV16 E7 protein (PCPV‐E7), stimulated strong antigen‐specific T‐cell responses in TC1 tumor‐bearing mice. Complete regression of tumors was obtained in a CD8⁺ T‐cell‐dependent manner after intratumoral injection of PCPV‐E7, followed by intravenous injection of the cancer vaccine MVA‐E7. PCPV also proved active when injected repeatedly intratumorally in MC38 tumor‐bearing mice, generating tumor‐specific T‐cell responses without encoding a specific MC38 antigen. From a translational perspective, we demonstrated that PCPV‐E7 effectively stimulated IFN‐γ production by T cells from tumor‐draining lymph nodes of HPV⁺‐infected cancer patients.

Conclusion

We propose PCPV as a viral vector suitable for vaccination in the field of personalised cancer vaccines, in particular for heterologous prime‐boost regimens.

Single Immunization with Recombinant ACAM2000 Vaccinia Viruses Expressing the Spike and the Nucleocapsid Proteins Protects Hamsters against SARS-CoV-2-Caused Clinical Disease

Increasing cases of SARS-CoV-2 breakthrough infections from immunization with current spike protein-based COVID-19 vaccines highlight the need to develop alternative vaccines using different platforms and/or antigens. In this study, we expressed SARS-CoV-2 spike and nucleocapsid proteins based on a novel vaccinia virus (VACV) ACAM2000 platform (rACAM2000). In this platform, the vaccinia virus host range and immunoregulatory gene E3L was deleted to make the virus attenuated and to enhance innate immune responses, and another host range gene, K3L, was replaced with a poxvirus ortholog gene, taterapox virus 037 (TATV037), to make virus replication competent in both hamster and human cells. Following a single intramuscular immunization, the rACAM2000 coexpressing the spike and nucleocapsid proteins induced significantly improved protection against SARS-CoV-2 challenge in comparison to rACAM2000 expressing the individual proteins in a hamster model, as shown by reduced weight loss and shorter recovery time. The protection was associated with reduced viral loads, increased neutralizing antibody titer, and reduced neutrophil-to-lymphocyte ratio. Thus, our study demonstrates that rACAM2000 expressing a combination of the spike and nucleocapsid antigens is a promising COVID-19 vaccine candidate, and further studies will investigate if the rACAM2000 vaccine candidate can induce a long-lasting immunity against infection by SARS-CoV-2 variants of concern. IMPORTANCE Continuous emergence of SARS-CoV-2 variants which cause breakthrough infection from the immunity induced by current spike protein-based COVID-19 vaccines highlights the need for new generations of vaccines that will induce long-lasting immunity against a wide range of the variants. To this end, we investigated the protective efficacy of the recombinant COVID-19 vaccine candidates based on a novel VACV ACAM2000 platform, in which an immunoregulatory gene, E3L, was deleted and both the SARS-CoV-2 spike (S) and nucleocapsid (N) antigens were expressed. Thus, it is expected that the vaccine candidate we constructed should be more immunogenic and safer. In the initial study described in this work, we demonstrated that the vaccine candidate expressing both the S and N proteins is superior to the constructs expressing an individual protein (S or N) in protecting hamsters against SARS-CoV-2 challenge after a single-dose immunization, and further investigation against different SARS-CoV-2 variants will warrant future clinical evaluations.

Biochemistry, Cell Biology, and Pathophysiology of the Innate Immune cGAS-cGAMP-STING Pathway

In the decade since the discovery of the innate immune cyclic GMP-AMP synthase (cGAS)- 2'3'-cyclic GMP-AMP (cGAMP)- stimulator of interferon genes (STING) pathway, its proper activation and dysregulation have been rapidly implicated in many aspects of human disease. Understanding the biochemical, cellular, and regulatory mechanisms of this pathway is critical to developing therapeutic strategies that either harness it to boost defense or inhibit it to prevent unwanted inflammation. In this review, we first discuss how the second messenger cGAMP is synthesized by cGAS in response to double-stranded DNA and cGAMP's subsequent activation of cell-type-dependent STING signaling cascades with differential physiological consequences. We then review how cGAMP as an immunotransmitter mediates tightly controlled cell-cell communication by being exported from producing cells and imported into responding cells via cell-type-specific transporters. Finally, we review mechanisms by which the cGAS-cGAMP-STING pathway responds to different sources of mislocalized double-stranded DNA in pathogen defense, cancer, and autoimmune diseases. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Second Messenger 2'3'-cyclic GMP-AMP (2'3'-cGAMP):Synthesis, transmission, and degradation

Cyclic GMP-AMP synthase (cGAS) senses foreign DNA to produce 2'3'-cyclic GMP-AMP (2'3'-cGAMP). 2'3'-cGAMP is a second messenger that binds and activates the adaptor protein STING, which triggers the innate immune response. As a STING agonist, the small molecule 2'3'-cGAMP plays pivotal roles in antiviral defense and has adjuvant applications, and anti-tumor effects. 2'3'-cGAMP and its analogs are thus putative targets for immunotherapy and are currently being testedin clinical trials to treat solid tumors. However, several barriers to further development have emerged from these studies, such as evidence of immune and inflammatory side-effects, poor pharmacokinetics, and undesirable biodistribution. Here, we review the status of 2'3'-cGAMP research and outline the role of 2'3'-cGAMP in immune signaling, adjuvant applications, and cancer immunotherapy, as well as various 2'3'-cGAMP detection methods.

Single Immunization of a Vaccine Vectored by a Novel Recombinant Vaccinia Virus Affords Effective Protection Against Respiratory Syncytial Virus Infection in Cotton Rats

Respiratory syncytial virus (RSV) is a leading cause of respiratory infections worldwide and disease management measures are hampered by the lack of a safe and effective vaccine against the infection. We constructed a novel recombinant RSV vaccine candidate based on a deletion mutant vaccinia virus platform, in that the host range genes E3L and K3L were deleted (designated as VACVΔE3LΔK3L) and a poxvirus K3L ortholog gene was used as a marker for the rapid and efficient selection of recombinant viruses. The safety of the modified vaccinia virus was investigated by intranasal administration of BALB/c mice with the modified vaccinia vector using a dose known to be lethal in the wild-type Western Reserve. Only a minor loss of body weight by less than 5% and mild pulmonary inflammation were observed, both of which were transient in nature following nasal administration of the high-dose modified vaccinia virus. In addition, the viruses were cleared from the lung in 2 days with no viral invasions of the brain and other vital organs. These results suggest that the virulence of the virus has been essentially abolished. We then investigated the efficiency of the vector for the delivery of vaccines against RSV through comparison with another RSV vaccine delivered by the widely used Modified Vaccinia virus Ankara (MVA) backbone. In the cotton rats, we found a single intramuscular administration of VACVΔE3LΔK3L-vectored vaccine elicited immune responses and protection at a level comparable to the MVA-vectored vaccine against RSV infection. The distinct features of this novel VACV vector, such as an E3L deletion for attenuation and a K3L ortholog for positive selection and high efficiency for vaccine delivery, could provide unique advantages to the application of VACV as a platform for vaccine development.

Elucidating mechanisms of antitumor immunity mediated by live oncolytic vaccinia and heat-inactivated vaccinia

Background

Viral-based immunotherapy can overcome resistance to immune checkpoint blockade (ICB) and fill the unmet needs of many patients with cancer. Oncolytic viruses (OVs) are defined as engineered or naturally occurring viruses that selectively replicate in and kill cancer cells. OVs also induce antitumor immunity. The purpose of this study was to compare the antitumor effects of live oncolytic vaccinia viruses versus the inactivated versions and elucidate their underlying immunological mechanisms.

Methods

We engineered a replication-competent, oncolytic vaccinia virus (OV-GM) by inserting a murine GM-CSF gene into the thymidine kinase locus of a mutant vaccinia E3L∆83N, which lacks the Z-DNA-binding domain of vaccinia virulence factor E3. We compared the antitumor effects of intratumoral (IT) delivery of live OV-GM versus heat-inactivated OV-GM (heat-iOV-GM) in a murine B16-F10 melanoma bilateral implantation model. We also generated vvDD, a well-studied oncolytic vaccinia virus, and compared the antitumor effects of live vvDD vs heat-inactivated vvDD (heat-ivvDD) in a murine A20 B-cell lymphoma bilateral tumor implantation model.

Results

Heat-iOV-GM infection of dendritic cells (DCs) and tumor cells in vitro induced type I interferon and proinflammatory cytokines and chemokines, whereas live OV-GM did not. IT live OV-GM was less effective in generating systemic antitumor immunity compared with heat-iOV-GM. Similar to heat-iOV-GM, the antitumor effects of live OV-GM also require Batf3-dependent CD103⁺ dendritic cells. When combined with systemic delivery of ICB, IT heat-iOV-GM was more effective in eradicating tumors, compared with live OV-GM. IT heat-ivvDD was also more effective in treating murine A20 B-cell lymphoma, compared with live vvDD.

Conclusions

Tumor lysis induced by the replication of oncolytic vaccinia virus has a limited effect on the generation of systemic antitumor immunity. The activation of Batf3-dependent CD103⁺ DCs is critical for antitumor effects induced by both live OV-GM and heat-iOV-GM, with the latter being more potent than live OV-GM in inducing innate and adaptive immunity in both locally injected and distant, non-injected tumors. We propose that evaluations of both innate and adaptive immunity, induced by IT oncolytic viral immunotherapy at injected and non-injected tumors, should be included as potential biomarkers for host responses to viral therapy.

Activation of interferon regulatory factor 3 by replication-competent vaccinia viruses improves antitumor efficacy mediated by T cell responses

Recently, oncolytic vaccinia viruses (VACVs) have shown their potential to provide for clinically effective cancer treatments. The reason for this clinical usefulness is not only the direct destruction of infected cancer cells but also activation of immune responses directed against tumor antigens. For eliciting a robust antitumor immunity, a dominant T helper 1 (Th1) cell differentiation of the response is preferred, and such polarization can be achieved by activating the Toll-like receptor 3 (TLR3)-interferon regulatory factor 3 (IRF3) signaling pathway. However, current VACVs used as oncolytic viruses to date still encode several immune evasion proteins involved in the inhibition of this signaling pathway. By inactivating genes of selected regulatory virus proteins, we aimed for a candidate virus with increased potency to activate cellular antitumor immunity but at the same time with a fully maintained replicative capacity in cancer cells. The removal of up to three key genes (C10L, N2L, and C6L) from VACV did not reduce the strength of viral replication, both in vitro and in vivo, but resulted in the rescue of IRF3 phosphorylation upon infection of cancer cells. In syngeneic mouse tumor models, this activation translated to enhanced cytotoxic T lymphocyte (CTL) responses directed against tumor-associated antigens and neo-epitopes and improved antitumor activity.

Single-cell analysis reveals divergent responses of human dendritic cells to the MVA vaccine

Modified vaccinia Ankara (MVA) is a live, attenuated human smallpox vaccine and a vector for the development of new vaccines against infectious diseases and cancer. Efficient activation of the immune system by MVA partially relies on its encounter with dendritic cells (DCs). MVA infection of DCs leads to multiple outcomes, including cytokine production, activation of costimulatory molecules for T cell stimulation, and cell death. Here, we examined how these diverse responses are orchestrated in human DCs. Single-cell analyses revealed that the response to MVA infection in DCs was limited to early viral gene expression. In response to the early events in the viral cycle, we found that DCs grouped into three distinct clusters. A cluster of infected cells sensed the MVA genome by the intracellular innate immunity pathway mediated by cGAS, STING, TBK1, and IRF3 and subsequently produced inflammatory cytokines. In response to these cytokines, a cluster of noninfected bystander cells increased costimulatory molecule expression. A separate cluster of infected cells underwent caspase-dependent apoptosis. Induction of apoptosis persisted after inhibition of innate immunity pathway mediators independently of previously described IRF-dependent or replication-dependent pathways and was a response to early MVA gene expression. Together, our study identified multiple mechanisms that underlie the interactions of MVA with human DCs.

Type I interferon mediated induction of somatostatin leads to suppression of ghrelin and appetite thereby promoting viral immunity in mice

Loss of appetite (anorexia) is a typical behavioral response to infectious diseases that often reduces body weight. Also, anorexia can be observed in cancer and trauma patients, causing poor quality of life and reduced prospects of positive therapeutic outcomes. Although anorexia is an acute symptom, its initiation and endocrine regulation during antiviral immune responses are poorly understood. During viral infections, plasmacytoid dendritic cells (pDCs) produce abundant type I interferon (IFN-I) to initiate first-line defense mechanisms. Here, by targeted ablation of pDCs and various in vitro and in vivo mouse models of viral infection and inflammation, we identified that IFN-I is a significant driver of somatostatin (SST). Consequently, SST suppressed the hunger hormone ghrelin that led to severe metabolic changes, anorexia, and rapid body weight loss. Furthermore, during vaccination with Modified Vaccinia Ankara virus (MVA), the SST-mediated suppression of ghrelin was critical to viral immune response, as ghrelin restrained the production of early cytokines by natural killer (NK) cells and pDCs, and impaired the clonal expansion of CD8⁺ T cells. Thus, the hormonal modulation of ghrelin through SST and the cytokine IFN-I is fundamental for optimal antiviral immunity, which comes at the expense of calorie intake.

Battle Royale: Innate Recognition of Poxviruses and Viral Immune Evasion

Host pattern recognition receptors (PRRs) sense pathogen-associated molecular patterns (PAMPs), which are molecular signatures shared by different pathogens. Recognition of PAMPs by PRRs initiate innate immune responses via diverse signaling pathways. Over recent decades, advances in our knowledge of innate immune sensing have enhanced our understanding of the host immune response to poxviruses. Multiple PRR families have been implicated in poxvirus detection, mediating the initiation of signaling cascades, activation of transcription factors, and, ultimately, the expression of antiviral effectors. To counteract the host immune defense, poxviruses have evolved a variety of immunomodulators that have diverse strategies to disrupt or circumvent host antiviral responses triggered by PRRs. These interactions influence the outcomes of poxvirus infections. This review focuses on our current knowledge of the roles of PRRs in the recognition of poxviruses, their elicited antiviral effector functions, and how poxviral immunomodulators antagonize PRR-mediated host immune responses.

Innate Immune Sensing of Viruses and Its Consequences for the Central Nervous System

Viral infections remain a global public health concern and cause a severe societal and economic burden. At the organismal level, the innate immune system is essential for the detection of viruses and constitutes the first line of defense. Viral components are sensed by host pattern recognition receptors (PRRs). PRRs can be further classified based on their localization into Toll-like receptors (TLRs), C-type lectin receptors (CLR), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), NOD-like receptors (NLRs) and cytosolic DNA sensors (CDS). TLR and RLR signaling results in production of type I interferons (IFNα and -β) and pro-inflammatory cytokines in a cell-specific manner, whereas NLR signaling leads to the production of interleukin-1 family proteins. On the other hand, CLRs are capable of sensing glycans present in viral pathogens, which can induce phagocytic, endocytic, antimicrobial, and pro- inflammatory responses. Peripheral immune sensing of viruses and the ensuing cytokine response can significantly affect the central nervous system (CNS). But viruses can also directly enter the CNS via a multitude of routes, such as the nasal epithelium, along nerve fibers connecting to the periphery and as cargo of infiltrating infected cells passing through the blood brain barrier, triggering innate immune sensing and cytokine responses directly in the CNS. Here, we review mechanisms of viral immune sensing and currently recognized consequences for the CNS of innate immune responses to viruses.

Injection site vaccinology of a recombinant vaccinia-based vector reveals diverse innate immune signatures

Poxvirus systems have been extensively used as vaccine vectors. Herein a RNA-Seq analysis of intramuscular injection sites provided detailed insights into host innate immune responses, as well as expression of vector and recombinant immunogen genes, after vaccination with a new multiplication defective, vaccinia-based vector, Sementis Copenhagen Vector. Chikungunya and Zika virus immunogen mRNA and protein expression was associated with necrosing skeletal muscle cells surrounded by mixed cellular infiltrates. The multiple adjuvant signatures at 12 hours post-vaccination were dominated by TLR3, 4 and 9, STING, MAVS, PKR and the inflammasome. Th1 cytokine signatures were dominated by IFNγ, TNF and IL1β, and chemokine signatures by CCL5 and CXCL12. Multiple signatures associated with dendritic cell stimulation were evident. By day seven, vaccine transcripts were absent, and cell death, neutrophil, macrophage and inflammation annotations had abated. No compelling arthritis signatures were identified. Such injection site vaccinology approaches should inform refinements in poxvirus-based vector design.

Poxvirus vector systems have been widely developed for vaccine applications. Despite considerable progress, so far only one recombinant poxvirus vectored vaccine has to date been licensed for human use, with ongoing efforts seeking to enhance immunogenicity whilst minimizing reactogenicity. The latter two characteristics are often determined by early post-vaccination events at the injection site. We therefore undertook an injection site vaccinology approach to analyzing gene expression at the vaccination site after intramuscular inoculation with a recombinant, multiplication defective, vaccinia-based vaccine. This provided detailed insights into inter alia expression of vector-encoded immunoregulatory genes, as well as host innate and adaptive immune responses. We propose that such injection site vaccinology can inform rational vaccine vector design, and we discuss how the information and approach elucidated herein might be used to improve immunogenicity and limit reactogenicity of poxvirus-based vaccine vector systems.