Liang Deng

Modified Vaccinia Virus Ankara Triggers Type I IFN Production in Murine Conventional Dendritic Cells via a cGAS/STING-Mediated Cytosolic DNA-Sensing Pathway

Modified vaccinia virus Ankara (MVA) is an attenuated poxvirus that has been engineered as a vaccine against infectious agents and cancers. Our goal is to understand how MVA modulates innate immunity in dendritic cells (DCs), which can provide insights to vaccine design. In this study, using murine bone marrow-derived dendritic cells, we assessed type I interferon (IFN) gene induction and protein secretion in response to MVA infection. We report that MVA infection elicits the production of type I IFN in murine conventional dendritic cells (cDCs), but not in plasmacytoid dendritic cells (pDCs). Transcription factors IRF3 (IFN regulatory factor 3) and IRF7, and the positive feedback loop mediated by IFNAR1 (IFN alpha/beta receptor 1), are required for the induction. MVA induction of type I IFN is fully dependent on STING (stimulator of IFN genes) and the newly discovered cytosolic DNA sensor cGAS (cyclic guanosine monophosphate-adenosine monophosphate synthase). MVA infection of cDCs triggers phosphorylation of TBK1 (Tank-binding kinase 1) and IRF3, which is abolished in the absence of cGAS and STING. Furthermore, intravenous delivery of MVA induces type I IFN in wild-type mice, but not in mice lacking STING or IRF3. Treatment of cDCs with inhibitors of endosomal and lysosomal acidification or the lysosomal enzyme Cathepsin B attenuated MVA-induced type I IFN production, indicating that lysosomal enzymatic processing of virions is important for MVA sensing. Taken together, our results demonstrate a critical role of the cGAS/STING-mediated cytosolic DNA-sensing pathway for type I IFN induction in cDCs by MVA. We present evidence that vaccinia virulence factors E3 and N1 inhibit the activation of IRF3 and the induction of IFNB gene in MVA-infected cDCs.

Vaccinia Virus Infection Attenuates Innate Immune Responses and Antigen Presentation by Epidermal Dendritic Cells

ABSTRACT Langerhans cells (LCs) are antigen-presenting cells in the skin that play sentinel roles in host immune defense by secreting proinflammatory molecules and activating T cells. Here we studied the interaction of vaccinia virus with XS52 cells, a murine epidermis-derived dendritic cell line that serves as a surrogate model for LCs. We found that vaccinia virus productively infects XS52 cells, yet this infection displays an atypical response to anti-poxvirus agents. Whereas adenosine N1-oxide blocked virus production and viral protein synthesis during a synchronous infection, cytosine arabinoside had no effect at concentrations sufficient to prevent virus replication in BSC40 monkey kidney cells. Vaccinia virus infection of XS52 cells not only failed to elicit the production of various cytokines, including tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-10, IL-12 p40, alpha interferon (IFN-α), and IFN-γ, it actively inhibited the production of proinflammatory cytokines TNF-α and IL-6 by XS52 cells in response to exogenous lipopolysaccharide (LPS) or poly(I:C). Infection with a vaccinia virus mutant lacking the E3L gene resulted in TNF-α secretion in the absence of applied stimuli. Infection of XS52 cells or BSC40 cells with the ΔE3L virus, but not wild-type vaccinia virus, triggered proteolytic decay of IκBα. These results suggest a novel role for the E3L protein as an antagonist of the NF-κB signaling pathway. ΔE3L-infected XS52 cells secreted higher levels of TNF-α and IL-6 in response to LPS and poly(I:C) than did cells infected with the wild-type virus. XS52 cells were productively infected by a vaccinia virus mutant lacking the K1L gene. ΔK1L-infected cells secreted higher levels of TNF-α and IL-6 in response to LPS than wild-type virus-infected cells. Vaccinia virus infection of primary LCs harvested from mouse epidermis was nonpermissive, although a viral reporter protein was expressed in the infected LCs. Vaccinia virus infection of primary LCs strongly inhibited their capacity for antigen-specific activation of T cells. Our results highlight suppression of the skin immune response as a feature of orthopoxvirus infection.

Identification of Novel Antipoxviral Agents: Mitoxantrone Inhibits Vaccinia Virus Replication by Blocking Virion Assembly

ABSTRACT The bioterror threat of a smallpox outbreak in an unvaccinated population has mobilized efforts to develop new antipoxviral agents. By screening a library of known drugs, we identified 13 compounds that inhibited vaccinia virus replication at noncytotoxic doses. The anticancer drug mitoxantrone is unique among the inhibitors identified in that it has no apparent impact on viral gene expression. Rather, it blocks processing of viral structural proteins and assembly of mature progeny virions. The isolation of mitoxantrone-resistant vaccinia strains underscores that a viral protein is the likely target of the drug. Whole-genome sequencing of mitoxantrone-resistant viruses pinpointed missense mutations in the N-terminal domain of vaccinia DNA ligase. Despite its favorable activity in cell culture, mitoxantrone administered intraperitoneally at the maximum tolerated dose failed to protect mice against a lethal intranasal infection with vaccinia virus.

Vaccinia Virus Subverts a Mitochondrial Antiviral Signaling Protein-Dependent Innate Immune Response in Keratinocytes through Its Double-Stranded RNA Binding Protein, E3

ABSTRACT Skin keratinocytes provide a first line of defense against invading microorganisms in two ways: (i) by acting as a physical barrier to pathogen entry and (ii) by initiating a vigorous innate immune response upon sensing danger signals. How keratinocytes detect virus infections and generate antiviral immune responses is not well understood. Orthopoxviruses are dermatotropic DNA viruses that cause lethal disease in humans. Virulence in animal models depends on the virus-encoded bifunctional Z-DNA/double-stranded RNA (dsRNA)-binding protein E3. Here, we report that infection of mouse primary keratinocytes with a vaccinia ΔE3L mutant virus triggers the production of beta interferon (IFN-β), interleukin-6 (IL-6), CCL4, and CCL5. None of these immune mediators is produced by keratinocytes infected with wild-type vaccinia virus. The dsRNA-binding domain of E3 suffices to prevent activation of the innate immune response. ΔE3L induction of IFN-β, IL-6, CCL4, and CCL5 secretion requires mitochondrial antiviral signaling protein (MAVS; an adaptor for the cytoplasmic viral RNA sensors RIG-I and MDA5) and the transcription factor IRF3. IRF3 phosphorylation is induced in keratinocytes infected with ΔE3L, an event that depends on MAVS. The response of keratinocytes to ΔE3L is unaffected by genetic ablation of Toll-like receptor 3 (TLR3), TRIF, TLR9, and MyD88.

Binding-Pocket and Lid-Region Substitutions Render Human STING Sensitive to the Species-Specific Drug DMXAA.

SUMMARY The drug DMXAA (5,6-dimethylxanthenone-4-acetic acid) showed therapeutic promise against solid tumors in mouse models but subsequently failed in human clinical trials. DMXAA was later discovered to activate mouse, but not human, STING, an adaptor protein in the cyclic dinucleotide cGAMP-mediated signaling pathway, inducing type I interferon expression. To facilitate the development of compounds that target human STING, we combined structural, biophysical, and cellular assays to study mouse and human chimeric proteins and their interaction with DMXAA. We identified a single substitution (G230I) that enables a DMXAA-induced conformational transition of hSTING from an inactive “open” to an active “closed” state. We also identified a substitution within the binding pocket (Q266I) that cooperates with G230I and the previously identified S162A binding-pocket point substitution, rendering hSTING highly sensitive to DMXAA. These findings should facilitate the reciprocal engineering of DMXAA analogs that bind and stimulate wild-type hSTING and their exploitation for vaccine-adjuvant and anti-cancer drug development.

Innate Immune Response of Human Plasmacytoid Dendritic Cells to Poxvirus Infection Is Subverted by Vaccinia E3 via Its Z-DNA/RNA Binding Domain

Plasmacytoid dendritic cells (pDCs) play important roles in antiviral innate immunity by producing type I interferon (IFN). In this study, we assess the immune responses of primary human pDCs to two poxviruses, vaccinia and myxoma virus. Vaccinia, an orthopoxvirus, was used for immunization against smallpox, a contagious human disease with high mortality. Myxoma virus, a Leporipoxvirus, causes lethal disease in rabbits, but is non-pathogenic in humans. We report that myxoma virus infection of human pDCs induces IFN-α and TNF production, whereas vaccinia infection does not. Co-infection of pDCs with myxoma virus plus vaccinia blocks myxoma induction effects. We find that heat-inactivated vaccinia (Heat-VAC; by incubating the virus at 55°C for 1 h) gains the ability to induce IFN-α and TNF in primary human pDCs. Induction of IFN-α in pDCs by myxoma virus or Heat-VAC is blocked by chloroquine, which inhibits endosomal acidification required for TLR7/9 signaling, and by inhibitors of cellular kinases PI3K and Akt. Using purified pDCs from genetic knockout mice, we demonstrate that Heat-VAC-induced type I IFN production in pDCs requires the endosomal RNA sensor TLR7 and its adaptor MyD88, transcription factor IRF7 and the type I IFN feedback loop mediated by IFNAR1. These results indicate that (i) vaccinia virus, but not myxoma virus, expresses inhibitor(s) of the poxvirus sensing pathway(s) in pDCs; and (ii) Heat-VAC infection fails to produce inhibitor(s) but rather produces novel activator(s), likely viral RNA transcripts that are sensed by the TLR7/MyD88 pathway. Using vaccinia gene deletion mutants, we show that the Z-DNA/RNA binding domain at the N-terminus of the vaccinia immunomodulatory E3 protein is an antagonist of the innate immune response of human pDCs to poxvirus infection and TLR agonists. The myxoma virus ortholog of vaccinia E3 (M029) lacks the N-terminal Z-DNA/RNA binding domain, which might contribute to the immunostimulating properties of myxoma virus.

Intratumoral delivery of inactivated modified vaccinia virus Ankara (iMVA) induces systemic antitumor immunity via STING and Batf3-dependent dendritic cells.

Inactivated vaccinia virus induces antitumor immunity that can overcome resistance to checkpoint inhibitors. A viral STING operation for tumors The immune response to viruses can be harnessed to attack tumors. Here, Dai et al. demonstrate that inactivated modified vaccinia virus Ankara (iMVA) can induce antitumor responses in two different models of cancer in mice. This effect relied on both Batf3-dependent dendritic cells and the cGAS-STING cytosolic DNA-sensing pathway. Moreover, intratumor injection of iMVA overcame tumor resistance to checkpoint inhibitors. Viral-induced innate immune responses may therefore tip the scale to successful cancer immunotherapy. Advanced cancers remain a therapeutic challenge despite recent progress in targeted therapy and immunotherapy. Novel approaches are needed to alter the tumor immunosuppressive microenvironment and to facilitate the recognition of tumor antigens that leads to antitumor immunity. Poxviruses, such as modified vaccinia virus Ankara (MVA), have potential as immunotherapeutic agents. We show that infection of conventional dendritic cells (DCs) with heat- or ultraviolet-inactivated MVA leads to higher levels of interferon induction than MVA alone through the cGAS (cyclic guanosine monophosphate–adenosine monophosphate synthase)–STING cytosolic DNA-sensing pathway. Intratumoral injection of inactivated MVA (iMVA) was effective and generated adaptive antitumor immunity in murine melanoma and colon cancer models. iMVA-induced antitumor therapy was less effective in STING- or Batf3-deficient mice than in wild-type mice, indicating that both cytosolic DNA sensing and Batf3-dependent CD103+/CD8α+ DCs are essential for iMVA immunotherapy. The combination of intratumoral delivery of iMVA and systemic delivery of immune checkpoint blockade generated synergistic antitumor effects in bilateral tumor implantation models as well as in a unilateral large established tumor model. Our results suggest that inactivated vaccinia virus could be used as an immunotherapeutic agent for human cancers.

White paper on microbial anti-cancer therapy and prevention

In this White Paper, we discuss the current state of microbial cancer therapy. This paper resulted from a meeting (‘Microbial Based Cancer Therapy’) at the US National Cancer Institute in the summer of 2017. Here, we define ‘Microbial Therapy’ to include both oncolytic viral therapy and bacterial anticancer therapy. Both of these fields exploit tumor-specific infectious microbes to treat cancer, have similar mechanisms of action, and are facing similar challenges to commercialization. We designed this paper to nucleate this growing field of microbial therapeutics and increase interactions between researchers in it and related fields. The authors of this paper include many primary researchers in this field. In this paper, we discuss the potential, status and opportunities for microbial therapy as well as strategies attempted to date and important questions that need to be addressed. The main areas that we think will have the greatest impact are immune stimulation, control of efficacy, control of delivery, and safety. There is much excitement about the potential of this field to treat currently intractable cancer. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other biological or small molecule drugs. By better understanding and controlling these mechanisms, we will create new therapies that will become integral components of cancer care.

Abstract B031: Heat-inactivated modified vaccinia virus ankara induces type I IFN and antitumor immunity via the cytosolic DNA-sensing pathway

Type I interferon (IFN), well known for its antiviral activity, is a critical component of cancer immune surveillance through its direct actions on cancer cells as well as on tumor microenvironment. Advanced melanoma remains a therapeutic challenge despite recent progress in targeted therapy and immunotherapy. Novel approaches are needed to alter the tumor immune suppressive microenvironment and to facilitate the recognition of tumor antigens that leads to antitumor immunity. Poxviruses are cytosolic DNA viruses that have been investigated as oncolytic and immunotherapeutic agents. We recently reported that the highly attenuated modified vaccinia virus Ankara (MVA), a safe vaccine for smallpox, triggers type I IFN production in conventional dendritic cells (cDCs) via the cytosolic DNA sensor cGAS and its adaptor STING, and that it requires transcription factors IRF3 and IRF7. Here we show that infection of cDCs with heat-inactivated MVA leads to higher levels of IFN induction than MVA. This induction is also mediated by the cytosolic DNA-sensing pathway cGAS/STING/IRF3/IRF7. In addition, we found that intratumoral injection of Heat-MVA caused tumor eradication in a murine B16 melanoma model as well as the generation of adaptive anti-tumor immunity. Furthermore, Heat-MVA-induced anti-tumor therapy is less effective in STING, IRF7, or Batf3-deficient mice than in wild-type mice, indicating that both the innate immune-sensing pathway and CD8α+DCs are essential for Heat-MVA-based immunotherapy. Lastly, the combination of intratumoral delivery of Heat-MVA with systemic delivery of anti-CTLA-4, PD-1 or PD-L1 antibodies achieved enhanced efficacy in tumor eradication and survival than Heat-MVA alone. Our results have strong implications for the development of poxvirus-based cancer immunotherapeutics as well novel strategies to overcome resistance to immune checkpoint blockade therapy. Citation Format: Peihong Dai, Weiyi Wang, Cristian Serna-Tamayo, Dimitriy Zamarin, Stewart Shuman, Taha Merghoub, Jedd D. Wolchok, Liang Deng. Heat-inactivated modified vaccinia virus ankara induces type I IFN and antitumor immunity via the cytosolic DNA-sensing pathway. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B031.

Abstract A007: Intratumoral delivery of inactivated vaccinia virus is more efficacious than live oncolytic vaccinia virus in murine bilateral tumor implantation models

Poxviruses are large cytoplasmic DNA viruses that have potentials as vaccine vectors and oncolytic agents. Although almost all of the oncolytic vaccinia viruses that are being investigated in clinical trials are replication competent, it is still unclear how these viruses exert antitumor immunologic effects, and whether viral replication is even necessary to achieve systemic antitumor efficacy. In this study, we compared therapeutic efficacy of the intratumoral delivery of the live, attenuated, replication competent oncolytic vaccinia virus expressing mGM-CSF (VC-TK−-mGM-CSF)vs. its heat-inactivated counterpart (iVC-TK−-mGM-CSF) in two bilateral tumor implantation models- B16-F10 murine melanoma and MC38 colon adenocarcinoma. We found that intratumoral injection of inactivated virus exerted stronger systemic antitumor effects than the live virus. FACS analyses of tumor infiltrating immune cells revealed that intratumoral injection of iVC-TK−-mGM-CSF lead to increased percentages and numbers of activating effector CD8+ and CD4+ T cells and reduced percentages and numbers of CD4+Foxp3+ regulatory T cells in the non-injected tumors compared with intratumoral delivery of the live virus. Infection of bone marrow-derived dendritic cells (DCs) with iVC-TK−-mGM-CSF induced type I IFN and proinflammatory cytokine and chemokine production and DC maturation, whereas the live virus did not. Taken together, our results demonstrate that intratumoral delivery of inactivated vaccina virus is safer and more efficacious than live oncolytic vaccinia virus expressing mGM-CSF in two murine bilateral tumor implantation models. Our findings have important implications for the design of poxviral-based immunotherapeutics for patients with metastatic cancers. Note: This abstract was not presented at the conference. Citation Format: Weiyi Wang, Peihong Dai, Ning Yang, Stewart Shuman, Taha Merghoub, Jedd D. Wolchok, Liang Deng. Intratumoral delivery of inactivated vaccinia virus is more efficacious than live oncolytic vaccinia virus in murine bilateral tumor implantation models [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A007.