A Sendai Virus-Derived RNA Agonist of RIG-I as a Virus Vaccine Adjuvant

Pattern recognition receptors (PRR) sense certain molecular patterns uniquely expressed by pathogens. Retinoic-acid-inducible gene I (RIG-I) is a cytosolic PRR that senses viral nucleic acids and induces innate immune activation and secretion of type I interferons (IFNs). Here, using influenza vaccine antigens, we investigated the consequences of activating the RIG-I pathway for antigen-specific adaptive immune responses. We found that mice immunized with influenza vaccine antigens coadministered with 5=ppp-double-stranded RNA (dsRNA), a RIG-I ligand, developed robust levels of hemagglutination-inhibiting antibodies, enhanced germinal center reaction, and T follicular helper cell responses. In addition, RIG-I activation enhanced antibody affinity maturation and plasma cell responses in the draining lymph nodes, spleen, and bone marrow and conferred protective immunity against virus challenge. Importantly, activation of the RIG-I pathway was able to reduce the antigen requirement by 10-to 100-fold in inducing optimal influenza-specific cellular and humoral responses, including protective immunity. The effects induced by 5=ppp-dsRNA were significantly dependent on type I IFN and IPS-1 (an adapter protein downstream of the RIG-I pathway) signaling but were independent of the MyD88-and TLR3-mediated pathways. Our results show that activation of the RIG-I-like receptor pathway programs the innate immunity to achieve qualitatively and quantitatively enhanced protective cellular adaptive immune responses even at low antigen doses, and this indicates the potential utility of RIG-I ligands as molecular adjuvants for viral vaccines. IMPORTANCEThe recently discovered RNA helicase family of RIG-I-like receptors (RLRs) is a critical component of host defense mechanisms responsible for detecting viruses and triggering innate antiviral cytokines that help control viral replication and dissemination. In this study, we show that the RLR pathway can be effectively exploited to enhance adaptive immunity and protective immune memory against viral infection. Our results show that activation of the RIG-I pathway along with influenza vaccination programs the innate immunity to induce qualitatively and quantitatively superior protective adaptive immunity against pandemic influenza viruses. More importantly, RIG-I activation at the time of vaccination allows induction of robust adaptive responses even at low vaccine antigen doses. These results highlight the potential utility of exploiting the RIG-I pathway to enhance viralvaccine-specific immunity and have broader implications for designing better vaccines in general.

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Activation of the RIG-I Pathway during Influenza Vaccination Enhances the Germinal Center Reaction, Promotes T Follicular Helper Cell Induction, and Provides a Dose-Sparing Effect and Protective Immunity

Kulkarni

Rasheed

Bhaumik

et al. 2014

“…We previously demonstrated that the 5=pppRNA sequence can be rationally modified to maximize the RIG-I response, leading to high expression of many proinflammatory and antiviral genes (24). Among the PRR-stimulating adjuvants, 5=pppRNA molecules, TLR agonists, defective interfering RNA produced by Sendai virus, and baculovirus-based vaccination vectors have all been utilized as adjuvants in several vaccine formulations, yielding promising data in preclinical studies (35,(43)(44)(45)(46)(47). Unfortunately, widespread implementation of PRR-based adjuvants in vaccines has been hampered by safety concerns, as infections and innate responses can sometimes be linked to autoimmune diseases (15).…”

Section: Discussionmentioning

confidence: 99%

Enhanced Influenza Virus-Like Particle Vaccination with a Structurally Optimized RIG-I Agonist as Adjuvant

Beljanski

Chiang

Kirchenbaum

et al. 2015

The molecular interaction between viral RNA and the cytosolic sensor RIG-I represents the initial trigger in the development of an effective immune response against infection with RNA viruses, resulting in innate immune activation and subsequent induction of adaptive responses. In the present study, the adjuvant properties of a sequence-optimized 5=-triphosphate-containing RNA (5=pppRNA) RIG-I agonist (termed M8) were examined in combination with influenza virus-like particles (VLP) (M8-VLP) expressing H5N1 influenza virus hemagglutinin (HA) and neuraminidase (NA) as immunogens. In combination with VLP, M8 increased the antibody response to VLP immunization, provided VLP antigen sparing, and protected mice from a lethal challenge with H5N1 influenza virus. M8-VLP immunization also led to long-term protective responses against influenza virus infection in mice. M8 adjuvantation of VLP increased endpoint and antibody titers and inhibited influenza virus replication in lungs compared with approved or experimental adjuvants alum, AddaVax, and poly(I·C). Uniquely, immunization with M8-VLP stimulated a T H 1-biased CD4 T cell response, as determined by increased T H 1 cytokine levels in CD4 T cells and increased IgG2 levels in sera. Collectively, these data demonstrate that a sequence-optimized, RIG-I-specific agonist is a potent adjuvant that can be utilized to increase the efficacy of influenza VLP vaccination and dramatically improve humoral and cellular mediated protective responses against influenza virus challenge. IMPORTANCEThe development of novel adjuvants to increase vaccine immunogenicity is an important goal that seeks to improve vaccine efficacy and ultimately prevent infections that endanger human health. This proof-of-principle study investigated the adjuvant properties of a sequence-optimized 5=pppRNA agonist (M8) with enhanced capacity to stimulate antiviral and inflammatory gene networks using influenza virus-like particles (VLP) expressing HA and NA as immunogens. Vaccination with VLP in combination with M8 increased anti-influenza virus antibody titers and protected animals from lethal influenza virus challenge, highlighting the potential clinical use of M8 as an adjuvant in vaccine development. Altogether, the results describe a novel immunostimulatory agonist targeted to the cytosolic RIG-I sensor as an attractive vaccine adjuvant candidate that can be used to increase vaccine efficacy, a pressing issue in children and the elderly population.

“…Thus, RNA replicon-based vaccines are amplified in the cells of the vaccinated hosts, permitting the expression of the vaccine antigen, without generating virus particles. Furthermore, in the process of amplification of their genomes, RNA replicons engage pattern recognition receptors in the host cell, adjuvanting the responses to the encoded immunogen (45)(46)(47). Although both mRNA-and replicon RNA-based vaccines were shown to elicit antigen-specific antibody and cellular immune responses against several pathogens (44,(48)(49)(50)(51), the self-amplifying nature of replicon-based vaccines is likely to result in higher levels of antigen expression and in a more effective engagement of innate immune responses than mRNA-based vaccine candidates.…”

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confidence: 99%

Induction of Broad-Based Immunity and Protective Efficacy by Self-amplifying mRNA Vaccines Encoding Influenza Virus Hemagglutinin

Brazzoli

Magini

Bonci

et al. 2016

134

130

Seasonal influenza is a vaccine-preventable disease that remains a major health problem worldwide, especially in immunocompromised populations. The impact of influenza disease is even greater when strains drift, and influenza pandemics can result when animal-derived influenza virus strains combine with seasonal strains. In this study, we used the SAM technology and characterized the immunogenicity and efficacy of a self-amplifying mRNA expressing influenza virus hemagglutinin ( IMPORTANCEIn this study, we describe protective immune responses in mice and ferrets after vaccination with a novel HA-based influenza vaccine. This novel type of vaccine elicits both humoral and cellular immune responses. Although vaccine-specific antibodies are the key players in mediating protection from homologous influenza virus infections, vaccine-specific T cells contribute to the control of heterologous infections. The rapid production capacity and the synthetic origin of the vaccine antigen make the SAM platform particularly exploitable in case of influenza pandemic.