AdrA as a Potential Immunomodulatory Candidate for STING-Mediated Antiviral Therapy That Required Both Type I IFN and TNF-α Production

Inhibition Effect of STING Agonist SR717 on PRRSV Replication

The porcine reproductive and respiratory syndrome virus (PRRSV) belongs to the Arteriviridae family and is a single-stranded, positively stranded RNA virus. The currently available PRRSV vaccines are mainly inactivated and attenuated vaccines, yet none of the commercial vaccines can provide comprehensive, long-lasting, and effective protection against PRRSV. SR717 is a pyridazine-3-carboxamide compound, which is commonly used as a non-nucleoside STING agonist with antitumor and antiviral activities. Nevertheless, there is no evidence that SR717 has any antiviral effects against PRRSV. In this study, a dose-dependent inhibitory effect of SR717 was observed against numerous strains of PRRSV using qRT-PCR, IFA, and WB methods. Furthermore, SR717 was found to stimulate the production of anti-viral molecules and trigger the activation of the signaling cascade known as the stimulator of interferon genes (STING) pathway, which contributed to hindering the reproduction of viruses by a certain margin. Collectively, these results indicate that SR717 is capable of inhibiting PRRSV infection in vitro and may have potential as an antiviral drug against PRRSV.

Lymph node-targeted STING agonist nanovaccine against chronic HBV infection

Chronic hepatitis B virus (HBV) infection is a global health problem that substantially increases the risk of developing liver disease. The development of a novel strategy to induce anti-HB seroconversion and achieve a long-lasting immune response against chronic HBV infection remains challenging. Here, we found that chronic HBV infection affected the signaling pathway involved in STING-mediated induction of host immune responses in dendritic cells (DCs) and then generated a lymph node-targeted nanovaccine that co-delivered hepatitis B surface antigen (HBsAg) and cyclic diguanylate monophosphate (c-di-GMP) (named the PP-SG nanovaccine). The feasibility and efficiency of the PP-SG nanovaccine for CHB treatment were evaluated in HBV-carrier mice. Serum samples were analyzed for HBsAg, anti-HBs, HBV DNA, and alanine aminotransferase levels, and liver samples were evaluated for HBV DNA and RNA and HBcAg, accompanied by an analysis of HBV-specific cellular and humoral immune responses during PP-SG nanovaccine treatment. The PP-SG nanovaccine increased antigen phagocytosis and DC maturation, efficiently and safely eliminated HBV, achieved a long-lasting immune response against HBV reinjection, and disrupted chronic HBV infection-induced immune tolerance, as characterized by the generation and multifunctionality of HBV-specific CD8+ T and CD4+ T cells and the downregulation of immune checkpoint molecules. HBV-carrier mice immunized with the PP-SG nanovaccine achieved partial anti-HBs seroconversion. The PP-SG nanovaccine can induce sufficient and persistent viral suppression and achieve anti-HBs seroconversion, rendering it a promising vaccine candidate for clinical chronic hepatitis B therapy.

The dual function of cGAS-STING signaling axis in liver diseases

Numerous liver diseases, such as nonalcoholic fatty liver disease, hepatitis, hepatocellular carcinoma, and hepatic ischemia-reperfusion injury, have been increasingly prevalent, posing significant threats to global health. In recent decades, there has been increasing evidence linking the dysregulation of cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING)-related immune signaling to liver disorders. Both hyperactivation and deletion of STING can disrupt the immune microenvironment dysfunction, exacerbating liver disorders. Consequently, there has been a surge in research investigating medical agents or mediators targeting cGAS-STING signaling. Interestingly, therapeutic manipulation of the cGAS-STING pathway has yielded inconsistent and even contradictory effects on different liver diseases due to the distinct physiological characteristics of intrahepatic cells that express and respond to STING. In this review, we comprehensively summarize recent advancements in understanding the dual roles of the STING pathway, highlighting that the benefits of targeting STING signaling depend on the specific types of target cells and stages of liver injury. Additionally, we offer a novel perspective on the suitability of STING agonists and antagonists for clinical assessment. In conclusion, STING signaling remains a highly promising therapeutic target, and the development of STING pathway modulators holds great potential for the treatment of liver diseases.

Exosome co-delivery of a STING agonist augments immunogenicity elicited by CVB3 VP1 vaccine via promoting antigen cross-presentation of CD8 + DCs

The induction of a robust CD8+ T cell response is critical for the success of an antiviral vaccine. In this study, we incorporated a STING agonist (SA) 2'3'-cGAMP into a previously developed exosome-based CVB3 viral myocarditis vaccine (Exo-VP1) to enhance its ability to induce CD8+ T cell responses and immunoprotection. Our results showed that compared to free SA adjuvant, exosome-mediated co-delivery (ExoSA-VP1) significantly enhanced SA uptake by dendritic cells (DCs) and more potently stimulated DC maturation. Immunization of mice showed that the ExoSA-VP1 vaccine-induced higher levels of CVB3-specific T cell proliferation and cytotoxicity, significantly increased the percentage of IFN-γ+CD8+ rather than CD4+ T cells, effectively reduced cardiac viral loads, attenuated myocarditis and improved survival in mice compared to the previous Exo-VP1 vaccine. Further investigation showed that ExoSA-VP1 significantly increased both the percentage and antigen cross-presentation capacity of splenic CD8+ DCs. Depletion of these CD8+ DCs by cytochrome C administration nearly abolished the advantage of ExoSA-VP1 in dominantly inducing IFN-γ+CD8+ cytotoxic T lymphocyte (CTL) production in immunized mice. Taken together, our results demonstrated the potential of ExoSA-VP1 as a promising candidate for anti-CVB3 vaccines and provide insights into immune-enhancing strategies aiming at augmenting antigen cross-presentation by DCs and enhancing potent CTL responses.

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.

The deletion of yeaJ gene facilitates Escherichia coli escape from immune recognition

Mammary gland-derived Escherichia coli (E. coli) is an important pathogen causing dairy cow mastitis. Mammary gland mucosal immunity against infectious E. coli mainly depends on recognition of pathogen-associated molecular patterns by innate receptors. Stimulator of interferon (IFN) gene (STING) has recently been the dominant mediator in reacting to bacterial intrusion and preventing inflammatory disorders. In this study, we firstly proved that diguanylate cyclase YeaJ relieves mouse mammary gland pathological damage by changing E. coli phenotypic and host STING-dependent innate immunity response. YeaJ decreases mammary gland circular vacuoles, bleeding and degeneration in mice. In addition, YeaJ participates in STING-IRF3 signaling to regulate inflammation in vivo. While in vitro, YeaJ decreases damage to macrophages (RAW264.7) but not to mouse mammary epithelial cells (EpH4-Ev). Consistent with the results in mouse mammary gland, yeaJ significantly activates STING/TBK1/IRF3 pathway in RAW264.7 as well. In conclusion, the deletion of yeaJ gene facilitates E. coli NJ17 escape from STING-dependent innate immunity recognition in vitro and in vivo. This study highlights a novel role for YeaJ in E. coli infection, which provides a better understanding of host-bacteria interactions and potential prophylactic strategies for infections. IMPORTANCE E. coli is the etiological agent of environmental mastitis in dairy cows, which cause massive financial losses worldwide. However, the pathophysiological role of yeaJ in the interaction between E. coli and host remains unclear. We found that YeaJ significantly influences various biological characteristics and suppresses severe inflammatory response as well as greater damage. YeaJ alleviates damage to macrophages (RAW264.7) and mouse mammary gland. Moreover, these effects of YeaJ are achieved at least partial by mediating the STING-IRF3 signaling pathway. In conclusion, the deletion of yeaJ gene facilitates E. coli NJ17 escape from STING-dependent innate immunity recognition in vitro and in vivo. This study is the basis for further research to better understand host-bacteria interactions and provides potential prophylactic strategies for infections.

HBsAg Dampened STING Associated Activation of NK Cells in HBeAg-Negative CHB Patients

NK cells play crucial roles in defending against persistent HBV. However, NK cells present dysfunction in chronic hepatitis B virus (CHB) infection, and the associated mechanism is still not fully understood. Except for the regulatory receptors, NK cells could also be regulated by the surface and intracellular pattern recognition receptors (PRRs). In the present study, we found that the level of the adaptor of DNA sensor STING in NK cells was significantly decreased in HBeAg-negative CHB patients, and it was positively associated with the degranulation ability of NK cells. Compared to NK cells from healthy donors, NK cells from HBeAg-negative CHB patients displayed a lower responsiveness to cGAMP stimulation. Further investigation showed that HBsAg could inhibit the STING expression in NK cells and suppress the response of NK cells to cGAMP. Significantly, STAT3 was identified to be a transcription factor that directly regulated STING transcription by binding to the promoter. In addition, STAT3 positively regulated the STING associated IFN-α response of NK cells. These findings suggested that STING is an important adaptor in NK cell recognition and activation, while HBsAg disturbs NK cell function by the STAT3-STING axis, providing a new mechanism of NK disability in HBeAg-negative CHB infection.