Optimal designs of an HA-based DNA vaccine against H7 subtype influenza viruses

Immunogenicity and biodistribution of lipid nanoparticle formulated self-amplifying mRNA vaccines against H5 avian influenza

This study reports on the immunogenicity and biodistribution of H5 hemagglutinin (HA)-based self-amplifying (sa) mRNA vaccines in mice. Four sa-mRNA vaccines encoding either a secreted full-length HA, a secreted HA head domain, a secreted HA stalk domain, or a full-length membrane-anchored HA were investigated. All vaccines elicited an adaptive immune response. However, the full-length HA sa-RNA vaccines demonstrated superior performance compared to head and stalk domain vaccines. The antibody titers positively correlated with the vaccine dose. Cellular immune responses and antigen-specific IgA antibodies in the lungs were also observed. The comparison of the sa-mRNA vaccines encoding the secreted and membrane-anchored full-length HA revealed that anchoring of the HA to the membrane significantly enhanced the antibody and cellular responses. In addition to the injection site, the intramuscularly injected sa-mRNA-LNPs were also detected in the draining lymph nodes, spleen, and to a lesser extent, in the lung, kidney, liver, and heart.

Soluble PD-1-based vaccine targeting MUC1 VNTR and survivin improves anti-tumor effect

Soluble PD-1 (sPD1) can bind with ligands PD-L1/PD-L2 on the surface of dendritic cells (DCs). Therefore, a sPD1 vaccine fused with an immunogen can increase T cell activation against cancer. Here, we constructed a MUC1 and survivin (MS) combination gene tumor vaccine expressing MS fused with soluble PD-1 (sPD1/MS). To investigate whether the sPD1/MS fusion vaccine could enhance tumor-specific immune responses, its immunogenicity and anti-tumor activity were examined after intramuscular immunization in mice. Compared with the MS DNA vaccine, the specific cytolysis rate of the sPD1/MS fusion DNA vaccine was increased from 21.64% to 34.77%. Moreover, the sPD1/MS vaccine increased the tumor suppression rate from 17.18% to 30.96% and prolonged survival from 6.96% to 19.44% in a murine colorectal cancer model. Combining the sPD1/MS vaccine with oxaliplatin improved the tumor suppression rate to 74.71% in the murine colorectal cancer model. The sPD1/MS vaccine could also exert a good anti-tumor effect, increasing the tumor infiltrated CD8⁺ T cells by 6.5-fold (from 0.10% to 0.65%) in the murine lung cancer model. In conclusion, the sPD1/MS vaccine showed good immunogenicity and anti-tumor effect by activating lymphocytes effectively.

Inactivated H7 Influenza Virus Vaccines Protect Mice despite Inducing Only Low Levels of Neutralizing Antibodies

Avian influenza viruses of the H7 hemagglutinin (HA) subtype present a significant public health threat, as evidenced by the ongoing outbreak of human A(H7N9) infections in China. When evaluated by hemagglutination inhibition (HI) and microneutralization (MN) assays, H7 viruses and vaccines are found to induce lower level of neutralizing antibodies (nAb) than do their seasonal counterparts, making it difficult to develop and evaluate prepandemic vaccines. We have previously shown that purified recombinant H7 HA appear to be poorly immunogenic in that they induce low levels of HI and MN antibodies. In this study, we immunized mice with whole inactivated reverse genetics reassortant (RG) viruses expressing HA and neuraminidase (NA) from 3 different H7 viruses [A/Shanghai/2/2013(H7N9), A/Netherlands/219/2003(H7N7), and A/New York/107/2003(H7N2)] or with human A(H1N1)pdm09 (A/California/07/2009-like) or A(H3N2) (A/Perth16/2009) viruses. Mice produced equivalent titers of antibodies to all viruses as measured by enzyme-linked immunosorbent assay (ELISA). However, the antibody titers induced by H7 viruses were significantly lower when measured by HI and MN assays. Despite inducing very low levels of nAb, H7 vaccines conferred complete protection against homologous virus challenge in mice, and the serum antibodies directed against the HA head region were capable of mediating protection. The apparently low immunogenicity associated with H7 viruses and vaccines may be at least partly related to measuring antibody titers with the traditional HI and MN assays, which may not provide a true measure of protective immunity associated with H7 immunization. This study underscores the need for development of additional correlates of protection for prepandemic vaccines.IMPORTANCE H7 avian influenza viruses present a serious risk to human health. Preparedness efforts include development of prepandemic vaccines. For seasonal influenza viruses, protection is correlated with antibody titers measured by hemagglutination inhibition (HI) and virus microneutralization (MN) assays. Since H7 vaccines typically induce low titers in HI and MN assays, they have been considered to be poorly immunogenic. We show that in mice H7 whole inactivated virus vaccines (WIVs) were as immunogenic as seasonal WIVs, as they induced similar levels of overall serum antibodies. However, a larger fraction of the antibodies induced by H7 WIV was nonneutralizing in vitro Nevertheless, the H7 WIV completely protected mice against homologous viral challenge, and antibodies directed against the HA head were the major contributor toward immune protection. Vaccines against H7 avian influenza viruses may be more effective than HI and virus neutralization assays suggest, and such vaccines may need other methods for evaluation.

A cGAS-Independent STING/IRF7 Pathway Mediates the Immunogenicity of DNA Vaccines

It has been known since the discovery of DNA vaccines >20 y ago that DNA vaccines can function as adjuvants. Our recent study reported the involvement of Aim2 as the sensor of DNA vaccines in eliciting Ag-specific Ab responses. Our findings indicated the presence of previously unrecognized innate immune response pathways in addition to the TLR9 pathway, which is mainly activated by the CpG motifs of DNA vaccines. Our data further demonstrated the requirement of type I IFN in DNA vaccine-induced immune responses via the Aim2 pathway, but the exact downstream molecular mechanism was not characterized. In the present study, we investigated the roles of the putative DNA sensor cyclic GMP-AMP synthase (cGas), as well as the downstream IFN regulatory factors (IRF) 3 and 7 in type I IFN induction and Ag-specific immune responses elicited by DNA vaccination. Our results showed that DNA vaccine-induced, Irf7-dependent signaling, as part of the Sting pathway, was critical for generation of both innate cytokine signaling and Ag-specific B and T cell responses. In contrast, Irf3 was not as critical as expected in this pathway and, more surprisingly, immune responses elicited by DNA vaccines were not cGas-dependent in vivo. Data from this study provide more details on the innate immune mechanisms involved in DNA vaccination and further enrich our understanding on the potential utility of DNA vaccines in generating Ag-specific immune responses.

Efficient vaccine against pandemic influenza: combining DNA vaccination and targeted delivery to MHC class II molecules

There are two major limitations to vaccine preparedness in the event of devastating influenza pandemics: the time needed to generate a vaccine and rapid generation of sufficient amounts. DNA vaccination could represent a solution to these problems, but efficacy needs to be enhanced. In a separate line of research, it has been established that targeting of vaccine molecules to antigen-presenting cells enhances immune responses. We have combined the two principles by constructing DNA vaccines that encode bivalent fusion proteins; these target hemagglutinin to MHC class II molecules on antigen-presenting cells. Such DNA vaccines rapidly induce hemagglutinin-specific antibodies and T cell responses in immunized mice. Responses are long-lasting and protect mice against challenge with influenza virus. In a pandemic situation, targeted DNA vaccines could be produced and tested within a month. The novel DNA vaccines could represent a solution to pandemic preparedness in the advent of novel influenza pandemics.

Identification of Aim2 as a sensor for DNA vaccines

Recent human study data have re-established the value of DNA vaccines, especially in priming high-level Ag-specific Ab responses, but also raised questions about the mechanisms responsible for such effects. Whereas previous reports have shown involvement of downstream signaling molecules in the innate immune system, the current study investigated the role of absent in melanoma 2 (Aim2) as a sensor for DNA vaccines. The Aim2 inflammasome directs maturation of the proinflammatory cytokines IL-1β and IL-18 and an inflammatory form of cell death called pyroptosis. Both the humoral and cellular Ag-specific adaptive responses were significantly reduced in Aim2-deficient mice in an IL-1β/IL-18-independent manner after DNA vaccination. Surprisingly, Aim2-deficient mice also exhibited significantly lower levels of IFN-α/β at the site of injection. These results indicate a previously unreported link between DNA vaccine-induced pyroptotic cell death and vaccine immunogenicity that is instrumental in shaping the Ag-specific immune response to DNA vaccines.

A single immunization with modified vaccinia virus Ankara-based influenza virus H7 vaccine affords protection in the influenza A(H7N9) pneumonia ferret model

Since the first reports in early 2013, >440 human cases of infection with avian influenza A(H7N9) have been reported including 122 fatalities. After the isolation of the first A(H7N9) viruses, the nucleotide sequences became publically available. Based on the coding sequence of the influenza virus A/Shanghai/2/2013 hemagglutinin gene, a codon-optimized gene was synthesized and cloned into a recombinant modified vaccinia virus Ankara (MVA). This MVA-H7-Sh2 viral vector was used to immunize ferrets and proved to be immunogenic, even after a single immunization. Subsequently, ferrets were challenged with influenza virus A/Anhui/1/2013 via the intratracheal route. Unprotected animals that were mock vaccinated or received empty vector developed interstitial pneumonia characterized by a marked alveolitis, accompanied by loss of appetite, weight loss, and heavy breathing. In contrast, animals vaccinated with MVA-H7-Sh2 were protected from severe disease.

Profiles of acute cytokine and antibody responses in patients infected with avian influenza A H7N9

The influenza A H7N9 virus outbreak in Eastern China in the spring of 2013 represented a novel, emerging avian influenza transmission to humans. While clinical and microbiological features of H7N9 infection have been reported in the literature, the current study investigated acute cytokine and antibody responses in acute H7N9 infection. Between March 27, 2013 and April 23, 2013, six patients with confirmed H7N9 influenza infection were admitted to Drum Tower Hospital, Nanjing, China. Acute phase serum cytokine profiles were determined using a high-throughput multiplex assay. Daily H7 hemagglutinin (HA)-specific IgG, IgM, and IgA responses were monitored by ELISA. Neutralizing antibodies specific for H7N9 viruses were determined against a pseudotyped virus expressing the novel H7 subtype HA antigen. Five cytokines (IL-6, IP-10, IL-10, IFNγ, and TNFα) were significantly elevated in H7N9-infected patients when compared to healthy volunteers. Serum H7 HA-specific IgG, as well as IgM and IgA responses, were detected within 8 days of disease onset and increased in a similar pattern during acute infection. Neutralizing antibodies developed shortly after the appearance of binding antibody responses and showed similar kinetics as a fraction of the total H7 HA-specific IgG responses. H7N9 infection resulted in hallmark serum cytokine increases, which correlated with fever and disease persistence. The novel finding of simultaneous development of IgG, IgM, and IgA responses in acute H7N9 infection points to the potential for live influenza viruses to elicit fast and potent protective antibodies to limit the infection.