Inactivated Influenza Vaccine That Provides Rapid, Innate-Immune- System-Mediated Protection and Subsequent Long-Term Adaptive Immunity

The continual threat to global health posed by influenza has led to increased efforts to improve the effectiveness of influenza vaccines for use in epidemics and pandemics. We show in this study that formulation of a low dose of inactivated detergent-split influenza vaccine with a Toll-like receptor 2 (TLR2) agonist-based lipopeptide adjuvant (R4Pam2Cys) provides (i) immediate, antigen-independent immunity mediated by the innate immune system and (ii) significant enhancement of antigendependent immunity which exhibits an increased breadth of effector function. Intranasal administration of mice with vaccine formulated with R4Pam2Cys but not vaccine alone provides protection against both homologous and serologically distinct (heterologous) viral strains within a day of administration. Vaccination in the presence of R4Pam2Cys subsequently also induces high levels of systemic IgM, IgG1, and IgG2b antibodies and pulmonary IgA antibodies that inhibit hemagglutination (HA) and neuraminidase (NA) activities of homologous but not heterologous virus. Improved primary virus nucleoprotein (NP)-specific CD8! T cell responses are also induced by the use of R4Pam2Cys and are associated with robust recall responses to provide heterologous protection. These protective effects are demonstrated in wild-type and antibody-deficient animals but not in those depleted of CD8! T cells. Using a contact-dependent virus transmission model, we also found that heterologous virus transmission from vaccinated mice to naive mice is significantly reduced. These results demonstrate the potential of adding a TLR2 agonist to an existing seasonal influenza vaccine to improve its utility by inducing immediate short-term nonspecific antiviral protection and also antigen-specific responses to provide homologous and heterologous immunity

Innate Immune Responses to Influenza Virus Infections in the Upper Respiratory Tract

The innate immune system is the host’s first line of immune defence against any invading pathogen. To establish an infection in a human host the influenza virus must replicate in epithelial cells of the upper respiratory tract. However, there are several innate immune mechanisms in place to stop the virus from reaching epithelial cells. In addition to limiting viral replication and dissemination, the innate immune system also activates the adaptive immune system leading to viral clearance, enabling the respiratory system to return to normal homeostasis. However, an overzealous innate immune system or adaptive immune response can be associated with immunopathology and aid secondary bacterial infections of the lower respiratory tract leading to pneumonia. In this review, we discuss the mechanisms utilised by the innate immune system to limit influenza virus replication and the damage caused by influenza viruses on the respiratory tissues and how these very same protective immune responses can cause immunopathology

Reducing the impact of influenza-associated secondary pneumococcal infections

When administered prophylactically, we show that the Toll-like receptor-2 (TLR-2) agonist PEG-Pam 2 Cys (pegylated-S-(2,3-bis(palmitoyloxy)propyl)cysteine) not only mediates potent anti-viral activity against influenza virus but also reduces the impact of secondary infections with Streptococcus pneumoniae (the pneumococcus) by reducing (i) pulmonary viral and bacterial burdens, (ii) the levels of proinflammatory cytokines that normally accompany influenza and S. pneumoniae secondary infections and (iii) the vascular permeability of the pulmonary tract that can allow bacterial invasion of the blood in mice. We also show that an inactivated detergent-disrupted influenza virus vaccine formulated with the Pam 2 Cys-based adjuvant R 4 -Pam 2 Cys provides the host with both immediate and long-term protection against secondary pneumococcal infections following influenza virus infection through innate and specific immune mechanisms, respectively. Vaccinated animals generated influenza virus-specific immune responses that provided the host with long-term protection against influenza virus and its sequelae. This vaccine, which generates an immediate response, provides an additional countermeasure, which is ideal for use even in the midst of an influenza outbreak

Multi-tasking an inactivated influenza vaccine to provide rapid innate immune- system mediated protection and subsequent long-term adaptive immunity against influenza and secondary pneumococcal infections

The threat to global health posed by influenza warrants continued efforts to improve the protective capability of influenza vaccines particularly against outbreaks of novel strains. Both innate and adaptive immune systems differ in mechanism, specificity and times at which they take effect. The innate immune system responds within hours of exposure to infectious agents while adaptive immunity takes several days to become effective. Here we show, by using a simple lipopeptide-based TLR2 agonist, a low dose of an inactivated detergent-split influenza vaccine can be made to simultaneously stimulate and amplify both systems in animals to provide immediate antigen-independent anti-viral protection mediated by innate immune responses while giving the adaptive immune system time to effect long-term antigen-dependent immunity (Chua et al. 2015). This immediate effect protects against both homologous and serologically distinct heterologous viral strains within a day of administration for up to a week. The enhancement of the adaptive immune response is characterized by the induction of high levels of hemagglutinin and neuraminidase-inhibiting antibodies against homologous virus as well as viral nucleoprotein-specific primary CD8+ T cell responses, which act to reduce disease severity associated with heterologous viral infection and significantly mitigate the severity of infection caused by contact-dependent transmission. Results from the use of antibody deficient and CD8+ T cell depleted animals also indicate that the heterologous immunity bestowed by this vaccine co-formulation is attributed to robust recall T cell-mediated responses. Additionally, we also demonstrate that vaccination can significantly lessen the impact of secondary infections with Streptococcus pneumonia by reducing (i) viral-associated pulmonary bacterial burdens, (ii) levels of pro-inflammatory cytokines that normally accompany co-infection and (iii) the vascular permeability of the pulmonary tract thereby preventing systemic bacterial infection (Mifsud et al. 2015). These protective effects are achieved using a considerably smaller dose of vaccine than is usually required to induce biologically active antibody responses in animals. The value of this cost-effective method coupled with its ease of implementation and conferring of dual functionality on influenza vaccines could be especially beneficial for improving community protection particularly during periods between an outbreak and when a vaccine becomes available or in scenarios when there is imperative for mass vaccination against a strain to which the population is immunologically naïve. References: Chua et al. An inactivated influenza vaccine that provides rapid, innate-mediated protection and subsequent long-term adaptive immunity. mBio (2015). Oct 27; 6 (6). doi: 10.1128/mBio.01024-15 Mifsud et al. Reducing the impact of influenza-associated secondary pneumococcal infections. Immunol Cell Biol (2015) Jul 21. doi:10.1038/icb.2015.71

Evaluating the fitness of PA/I38T-substituted influenza A viruses with reduced baloxavir susceptibility in a competitive mixtures ferret model.

Baloxavir is approved in several countries for the treatment of uncomplicated influenza in otherwise-healthy and high-risk patients. Treatment-emergent viruses with reduced susceptibility to baloxavir have been detected in clinical trials, but the likelihood of widespread occurrence depends on replication capacity and onward transmission. We evaluated the fitness of A/H3N2 and A/H1N1pdm09 viruses with the polymerase acidic (PA) I38T-variant conferring reduced susceptibility to baloxavir relative to wild-type (WT) viruses, using a competitive mixture ferret model, recombinant viruses and patient-derived virus isolates. The A/H3N2 PA/I38T virus showed a reduction in within-host fitness but comparable between-host fitness to the WT virus, while the A/H1N1pdm09 PA/I38T virus had broadly similar within-host fitness but substantially lower between-host fitness. Although PA/I38T viruses replicate and transmit between ferrets, our data suggest that viruses with this amino acid substitution have lower fitness relative to WT and this relative fitness cost was greater in A/H1N1pdm09 viruses than in A/H3N2 viruses