Search

Human respiratory syncytial virus (RSV) is the leading cause of respiratory tract infections in humans. A well-known challenge in the development of a live attenuated RSV vaccine is that interferon (IFN)-mediated antiviral responses are strongly suppressed by RSV nonstructural proteins which, in turn, dampens the subsequent adaptive immune responses. Here, we discovered a novel strategy to enhance innate and adaptive immunity to RSV infection. Specifically, we found that recombinant RSVs deficient in viral RNA N6-methyladenosine (m6A) and RSV grown in m6A methyltransferase (METTL3)-knockdown cells induce higher expression of RIG-I, bind more efficiently to RIG-I, and enhance RIG-I ubiquitination and IRF3 phosphorylation compared to wild-type virion RNA, leading to enhanced type I IFN production. Importantly, these m6A-deficient RSV mutants also induce a stronger IFN response in vivo, are significantly attenuated, induce higher neutralizing antibody and T cell immune responses in mice and provide complete protection against RSV challenge in cotton rats. Collectively, our results demonstrate that inhibition of RSV RNA m6A methylation enhances innate immune responses which in turn promote adaptive immunity. Author summary: RSV is the most important cause of upper and lower respiratory tract infection of infants, young children, immunocompromised individuals, and the elderly. Despite major efforts, no vaccine is available for RSV. A live attenuated vaccine is one of the most promising vaccine approaches for RSV. However, a major problem is that natural RSV infection does not induce long-lived protection. The reason likely lies in its NS1 and NS2 proteins' strong inhibition of type I interferon (IFN) induction, which impairs subsequent adaptive immunity. We found that RSV RNA contains N6-methyladenosine (m6A) and that recombinant RSVs lacking m6A methylation induce significantly higher type I IFN in cell culture and in mice compared to the parental RSV. Despite the fact that these m6A-deficient RSVs are significantly attenuated, they induce higher RSV-specific antibody and T cell immune responses in mice and provide complete protection against RSV challenge in cotton rats. Thus, m6A-deficient RSVs are more immunogenic than the parental RSV, highlighting that suppression of viral RNA m6A methylation is a novel strategy to enhance innate immunity which, in turn, enhances adaptive immunity. [ABSTRACT FROM AUTHOR]

Maternal antibodies inhibit seroconversion and the generation of measles virus (MeV)-specific antibodies (both neutralizing and non-neutralizing antibodies) after vaccination whereas T cell responses are usually unaffected. The lack of seroconversion leaves individuals susceptible to vaccine-preventable infections. Inhibition of antibody secretion is due to the inhibition of B cells through a cross-link of the B cell receptor with the inhibitory FccIIB receptor (CD32) by maternal antibody/vaccine complexes. Here, we demonstrate that a combination of TLR-3 and TLR-9 agonists induces synergistically higher levels of type I interferon in vitro and in vivo than either agonist alone. The synergistic action of TLR-3 and TLR-9 agonists is based on a feedback loop through the interferon receptor. Finally, we have identified CD21 as a potential receptor for interferon α on B cells which contributes to interferon a-mediated activation of B cells in the presence of maternal antibodies. The combination leads to complete restoration of B cell and antibody responses after immunization in the presence of inhibitory MeV-specific IgG. The strong stimulatory action of type I interferon is due to the fact that type I interferon uses not only the interferon receptor but also CD21 as a functional receptor for B cell activation. [ABSTRACT FROM AUTHOR]