Induction of protective immunity against influenza A/Jiangxi-Donghu/346/2013 (H10N8) in mice.

Human infections with A/Jiangxi-Donghu/346/2013 (H10N8) virus have raised concerns about its pandemic potential. In order to develop a vaccine against this virus, the immunogenicity of its haemagglutinin protein was evaluated in mice. Using both whole-virion and recombinant subunit protein vaccines, we showed that two doses of either vaccine elicited neutralizing antibody responses. The protective efficacy of the vaccine-induced responses was assessed using a reverse-genetics-derived H10 reassortant virus on the A/Puerto Rico/8/34 (H1N1) backbone. The reassortant virus replicated efficiently in the respiratory tract of unvaccinated mice whereas vaccinated mice were completely protected from challenge, with no detectable viral load in the lower respiratory tract. Finally, the serum neutralizing antibody responses elicited by the H10 vaccines also exhibited cross-neutralizing activity against three heterologous wild-type H10 viruses. Collectively, these findings demonstrate that different vaccine platforms presenting the H10 haemagglutinin protein induce protective immunity.

An adjuvant for the induction of potent, protective humoral responses to an H5N1 influenza virus vaccine with antigen-sparing effect in mice.

Intramuscular administration of inactivated influenza virus vaccine is the main vaccine platform used for the prevention of seasonal influenza virus infection. In clinical trials, inactivated H5N1 vaccines have been shown to be safe and capable of eliciting immune correlates of protection. However, the H5N1 vaccines are poorly immunogenic compared to seasonal influenza virus vaccines. Needle-free vaccination would be more efficient and economical in a pandemic, and the development of an effective and safe mucosal adjuvant will be an important milestone. A stabilized chemical analog of double-stranded RNA, PIKA, was previously reported to be a potent mucosal adjuvant in a murine model. While PIKA stimulates dendritic cells in vitro, little was known about its receptor and adjuvanting mechanism in vivo. In this study, we demonstrated that the immunostimulatory effect of PIKA resulted in an increased number of mature antigen-presenting cells, with the induction of proinflammatory cytokines at the inoculation site. In addition, coadministration of PIKA with a poorly immunogenic H5N1 subunit vaccine led to antigen sparing and quantitative and qualitative improvements of the immune responses over those achieved with an unadjuvanted vaccine in mice. The adjuvanted vaccine provided protection against lethal challenge with homologous and heterologous H5N1 wild-type viruses. Mice lacking functional TLR3 showed diminished cytokine production with PIKA stimulation, diminished antibody responses, and reduced protective efficacy against wild-type virus challenge following vaccination. These data suggest that TLR3 is important for the optimal performance of PIKA as an adjuvant. With its good safety profile and antigen-sparing effect, PIKA could be an attractive adjuvant for use in future pandemics.

Serological response to trivalent inactivated influenza vaccine in HIV-infected adults in Singapore.

A cohort of 81 HIV-infected participants received seasonal trivalent inactivated influenza vaccine (TIV) and their humoral responses were monitored using hemagglutination inhibition (HAI) assay and enzyme-linked immunosorbent assay (ELISA). Three weeks after the vaccination, the percentage of the cohort that had an HAI titer of >1:40 was 35% (for H1N1), 43% (for H3N2) and 19% (for influenza B). An increase in HAI titer can be achieved by an increase in magnitude of the antibody responses, which can be measured by an increase in ELISA titer; as well as a quality improvement of the antibody responses through increased avidity to the virus. For some individuals, an increase in avidity alone is sufficient to reach the sero-protective titer. Notably, a number of volunteers showed an increase in ELISA titer without a rise in HAI titer. A total of 24 participants (30%) did not show any significant increase in both HAI and ELISA tests after vaccination. Apart from a lower peripheral CD4+ T cell count, the non responders' peripheral blood mononuclear cells (PBMC) also had a higher IL-10 mRNA expression after TIV vaccination ex vivo. Cytokine profiling demonstrated that, apart from a weaker MCP-1 expression in the non-responder group, PBMC from both groups responded comparably to lipopolysaccharide (LPS) stimulation in vitro. Since only 3 participants developed sero-protective titers against all 3 subtypes after vaccination, our study highlights a need to enhance the immunogenicity of the subunit vaccine for this population, potentially through harnessing the innate immunity with an external adjuvant.

Complete protection against lethal challenge of novel H7N9 virus with heterologous inactivated H7 vaccine in mice.

A prototype H7 influenza vaccine constructed based on the H7N7 outbreak in 2003 was tested for the protective efficacy against the novel H7N9 virus in a lethal murine challenge model. Serum samples from vaccinated mice showed significant neutralizing activity against the H7N9 virus and the mice were completely protected with no significant weight loss. The results have direct implications on how to overcome potential vaccine shortage and identify donors for immune sera for passive immunization.

Activation of the innate immune system provides broad-spectrum protection against influenza A viruses with pandemic potential in mice.

The efficacy of a stabilized chemical analog of double-stranded ribonucleic acid (RNA), PIKA, as prophylaxis against infection with 5 different influenza A virus subtypes, including the 2009 swine-origin pandemic H1N1 virus, was evaluated in mice. Intranasal treatment with PIKA resulted in a significant reduction of viral replication in the respiratory tract. The inhibitory effect was mediated by rapid infiltration of immune cells into the lungs, and production of inflammatory cytokines. While TLR3 is important for the optimal production of these inflammatory cytokines, inhibition of viral replication was still observed in TLR3(-/-) mice. In addition, a significant synergistic effect in inhibiting H5N1 virus replication was observed when PIKA was coadministered with oseltamivir. The broad-spectrum protection provided by PIKA makes it an attractive option for prophylaxis from infection with influenza A viruses.

A TLR3 ligand that exhibits potent inhibition of influenza virus replication and has strong adjuvant activity has the potential for dual applications in an influenza pandemic.

The appearance and spread of the H5N1 highly pathogenic avian influenza (HPAI) raise concern of a possible pandemic. Current preventive measures include the development of a pre-pandemic influenza vaccine and stockpiling of neuraminidase inhibitors. However, their benefits can be significantly reduced by mutations in the hemagglutinin or neuraminidase resulting in antigenic changes and the appearance of drug-resistance, respectively. Drugs that target the innate immune system to achieve a 'heightened antiviral' state represent another class of antiviral agents that could contribute to the control and treatment of influenza infection. In this study, PIKA (a stabilized dsRNA) provides broad-spectrum prophylaxis against a number of influenza A viruses. In addition, when PIKA was admixed with influenza vaccine preparations, including a formalin-inactivated whole-virion H5 vaccine, significant adjuvanting effect leading to accelerated viral clearance was observed in a murine model. These biological effects appear to be mediated by the ability of PIKA to promote the maturation of dendritic cells, including up-regulation of co-stimulatory molecules, such as CD80 and CD86, and the induction of various cytokines and chemokines. Toll-like receptor 3 (TLR3) was shown to recognize PIKA in a concentration-dependent manner. The potency and versatility in its activities make PIKA an attractive candidate for use in an influenza pandemic.