Mucosal Immunization with Recombinant Adenovirus Encoding Soluble Globular Head of Hemagglutinin Protects Mice Against Lethal Influenza Virus Infection

Influenza virus is one of the major sources of respiratory tract infection. Due to antigenic drift in surface glycoproteins the virus causes annual epidemics with severe morbidity and mortality. Although hemagglutinin (HA) is one of the highly variable surface glycoproteins of the influenza virus, it remains the most attractive target for vaccine development against seasonal influenza infection because antibodies generated against HA provide virus neutralization and subsequent protection against the virus infection. Combination of recombinant adenovirus (rAd) vector-based vaccine and mucosal administration is a promising regimen for safe and effective vaccination against influenza. In this study, we constructed rAd encoding the globular head region of HA from A/Puerto Rico/8/34 virus as vaccine candidate. The rAd vaccine was engineered to express high level of the protein in secreted form. Intranasal or sublingual immunization of mice with the rAd-based vaccine candidates induced significant levels of sustained HA-specific mucosal IgA and IgG. When challenged with lethal dose of homologous virus, the vaccinated mice were completely protected from the infection. The results demonstrate that intranasal or sublingual vaccination with HA-encoding rAd elicits protective immunity against infection with homologous influenza virus. This finding underlines the potential of our recombinant adenovirus-based influenza vaccine candidate for both efficacy and rapid production.

Sublingual Delivery of Vaccines for the Induction of Mucosal Immunity

The mucosal surfaces are constantly exposed to incoming pathogens which can cause infections that result in severe morbidity and/or mortality. Studies have reported that mucosal immunity is important for providing protection against these pathogens and that mucosal vaccination is effective in preventing local infections. For many years, the sublingual mucosa has been targeted to deliver immunotherapy to treat allergic hypersensitivities. However, the potential of vaccine delivery via sublingual mucosal has received little attention until recently. Recent studies exploring such potential have documented the safety and effectiveness of sublingual immunization, demonstrating the ability of sublingual immunization to induce both systemic and mucosal immune responses against a variety of antigens, including soluble proteins, inter particulate antigens, and live-attenuated viruses. This review will summarize the recent findings that address the promising potential of sublingual immunization in proving protection against various mucosal pathogens.

The Bacterial Surface Expression of SARS Viral Epitope using Salmonella typhi Cytolysin A

The cytolysin A (ClyA) is a 34 kDa pore-forming cytotoxic protein and expressed by some enteric bacteria including Salmonella typhi. This toxin is transported on the bacterial surface and secreted without posttranslational modification. Using the surface display of ClyA, the expression vectors for 193-aa immunogenic antigen of spike protein (termed S1E) from severe acute respiratory syndrome coronavirus (SARS-CoV) were constructed. The vectors carried a gene encoding S. typhi ClyA conjugated to S1E at the C terminus (termed ClyA-S1E) and asd gene in pGEM-T and pBR322, named pGApLCS1E and pBApLCS1E, respectively. An asd-mutated E. coli transformed with these vectors could grow without diaminopimelic acid (DAP), indicating that they were stably maintained in such mutants. ClyA-S1E recombinant proteins from these vectors were expressed on the surface of the attenuated S. typhimurium deficient of global virulence gene regulator, ppGpp. However, they did not show the hemolytic activity on the blood agar plate and cytotoxicity against HeLa cells. To examine whether bacteria expressing ClyA-S1E induced the immune response against S1E, S. typhimurium deficient of ppGpp and Asd was transformed with these vectors and orally immunized in mice. In the western blotting against GST-conjugated S1E using the immunized mouse sera, it was shown that the significant band was detected in the mouse serum by the bacteria transformed with pGApLCS1E but not with pBApLCS1E. It indicates that the immune response producing antibody was dependent on the expression level of ClyA-S1E. Therefore, ClyA delivery system can be used for SARS vaccine development.

Efficient Induction of Th1-type Immune Responses to Hepatitis B Virus Antigens by DNA Prime-Adenovirus Boost

BACKGROUND: Chronic infection with hepatitis B virus (HBV) affects about 350 million people worldwide, which have a high risk of development of cirrhosis and hepatocellular carcinoma. Treatment of chronic HBV infection relies on IFN-alpha or lamivudine. However, interferon-alpha is effective in only about 30% of patients. Also, the occurrence of escape mutations limits the usage of lamivudine. Therefore, the development and evaluation of new compounds or approaches are urgent. METHODS: We comparatively evaluated DNA and adenoviral vaccines expressing HBV antigens, either alone or in combined regimens, for their ability to elicit Th1-type immune responses in Balb/c mice which are believed to be suited to resolve HBV infection. The vaccines were tested with or without a genetically engineered IL-12 (mIL-12 N220L) which was shown to enhance sustained Th1-type immune responses in HCV E2 DNA vaccine. RESULTS: Considering the Th1-type cytokine secretion and the IgG2a titers, the strongest Th1-type immune response was elicited by the DNA prime-adenovirus boost regimen in the presence of mIL-12 N220L. In addition, the codelivery of mIL-12 N220L modulated differentially the immune responses by different vaccination regimens. CONCLUSION: Our results suggest that the DNA prime-adenovirus boost regimen in the presence of mIL-12 N220L may be the best candidate for HBV vaccine therapy of the regimens tested in this study and will be worthwhile being evaluated in chronic HBV patients.