Viruslike particle vaccine induces protection against respiratory syncytial virus infection in mice.

BACKGROUND: Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral death in infants. Despite decades of research with traditional or subunit vaccine approaches, there are no approved RSV vaccines. New approaches are therefore urgently needed to develop effective RSV vaccines. METHODS: We developed viruslike particles (VLPs) consisting of an influenza virus matrix (M1) protein core and RSV-F or -G on the surface. We tested the immunogenicity and vaccine efficacy of these VLPs (RSV-F, RSV-G) in a mouse model. RESULTS: Intramuscular vaccination with RSV-F or RSV-G VLPs elicited IgG2a dominant RSV-specific immunoglobulin G (IgG) antibody responses against RSV-A2 viruses in both serum and lung extract. Mice immunized with VLPs (RSV-F or RSV-G) showed higher viral neutralizing antibodies in vitro and significantly decreased lung virus loads in vivo after live RSV-A2 challenge. RSV-G VLPs showed better protective efficacy than RSV-F VLPs as determined by the levels of lung virus loads and morbidity postchallenge. CONCLUSIONS: This study demonstrates that VLP vaccination provides effective protection against RSV infection. VLPs containing RSV-F and/or RSV-G are potential vaccine candidates against RSV.

Enhanced mucosal immune responses to HIV virus-like particles containing a membrane-anchored adjuvant.

Previously, a modified HIV Env protein with a heterologous membrane anchor was found to be incorporated into HIV virus-like particles (VLPs) at 10-fold-higher levels than those of unmodified Env. To further improve the immunogenicity of such VLPs, membrane-anchored forms of bacterial flagellin (FliC) or a flagellin with a truncated variable region (tFliC) were constructed to be incorporated into the VLPs as adjuvants. HIV-specific immune responses induced by the resulting VLPs were determined in a guinea pig model. The VLPs induce enhanced systemic antibody responses by either systemic or mucosal vaccination and enhanced mucosal immunity by a mucosal immunization route, as demonstrated by high levels of HIV-specific serum IgG and mucosal IgG and IgA. The quality of the antibody responses was also improved, as shown by enhanced neutralization capacity. VLPs incorporating FliC were more effective in inducing systemic responses, while VLPs containing tFliC were more effective in inducing mucosal IgA responses. The IgG titers in sera were found to last for at least 5 months without a significant drop. These results indicate that HIV VLPs incorporating high levels of Env and a molecular adjuvant have excellent potential for further development as a prophylactic HIV vaccine.

Vaccination inducing broad and improved cross protection against multiple subtypes of influenza A virus.

Development of an influenza vaccine that provides broadly cross-protective immunity has been a scientific challenge for more than half a century. This study presents an approach to overcome strain-specific protection by supplementing conventional vaccines with virus-like particles (VLPs) containing the conserved M2 protein (M2 VLPs) in the absence of adjuvants. We demonstrate that an inactivated influenza vaccine supplemented with M2 VLPs prevents disease symptoms without showing weight loss and confers complete cross protection against lethal challenge with heterologous influenza A viruses including the 2009 H1N1 pandemic virus as well as heterosubtypic H3N2 and H5N1 influenza viruses. Cross-protective immunity was long-lived, for more than 7 mo. Immune sera from mice immunized with M2 VLP supplemented vaccine transferred cross protection to naive mice. Dendritic and macrophage cells were found to be important for this cross protection mediated by immune sera. The results provide evidence that supplementation of seasonal influenza vaccines with M2 VLPs is a promising approach for overcoming the limitation of strain-specific protection by current vaccines and developing a universal influenza A vaccine.

Incorporation of membrane-anchored flagellin into influenza virus-like particles enhances the breadth of immune responses.

We have designed a membrane-anchored form of the Toll-like receptor 5 ligand flagellin, the major proinflammatory determinant of enteropathogenic Salmonella, which was found to be glycosylated and expressed on cell surfaces. A chimeric influenza virus-like particle (cVLP) vaccine candidate containing A/PR8/34 (H(1)N(1)) hemagglutinin (HA), matrix protein (M1), and the modified flagellin as a molecular adjuvant was produced. The immunogenicity, including the serum antibody levels and cellular immune responses, and the protective efficacy against homologous and heterologous live virus challenge of the resulting VLPs were tested after intramuscular administration in a mouse model. The results demonstrated that flagellin-containing VLPs elicited higher specific immunoglobulin G (IgG) responses than standard HA and M1 VLPs, indicating the adjuvant effect of flagellin. Enhanced IgG2a and IgG2b but not IgG1 responses were observed with flagellin-containing VLPs, illuminating the activation of Th1 class immunity. The adjuvant effects of flagellin were also reflected by enhanced specific cellular responses revealed by the secretion of cytokines by freshly isolated splenocyte cultures when stimulated with pools of major histocompatibility complex class I or II peptides. When immunized mice were challenged with homologous live PR8 virus, complete protection was observed for both the standard and cVLP groups. However, when a heterosubtypic A/Philippines (H(3)N(2)) virus was used for challenge, all of the standard VLP group lost at least 25% of body weight, reaching the experimental endpoint. In contrast, for the cVLP group, 67% of mice survived the challenge infection. These results reveal that cVLPs designed by incorporating flagellin as a membrane-anchored adjuvant induce enhanced cross-protective heterosubtypic immune responses. They also indicate that such cVLP vaccines are a promising new approach for protection against pandemic influenza viruses.

Delivery of DNA HIV-1 vaccine to the liver induces high and long-lasting humoral immune responses.

The quality of immune responses induced by DNA vaccination depends on the site of DNA administration, the expression, and the properties of the encoded antigen. In the present study, we demonstrate that intravenous hydrodynamic HIV-1 envelope DNA injection resulted in high levels of expression of HIV-1 envelope antigen in the liver. When compared to the administration of DNA by i.n., i.d., i.m., and i.splenic routes, hydrodynamic vaccination induced, upon DNA boosting, levels of HIV-1 envelope-specific antibodies 40-fold higher than those elicited by the other routes tested. Hydrodynamic vaccination with 1 microg DNA induced higher humoral responses than 100 microg DNA given intramuscularly in the prime-boost regimen. High levels of envelope-specific IgG and IgA antibodies were induced in genital tract secretions after two doses of DNA followed by intranasal boosting with recombinant HIV-1 gp120 protein. Furthermore, two doses of 100 microg DNA generated interferon-gamma production in approximately 4.3+/-1.7% of CD8(+) splenocytes after in vitro stimulation with HIV-1 envelope peptides. These results demonstrate that DNA vaccines targeted to tissues with high proteosynthetic activity, such as the liver, results in enhanced immune responses.

Parameters of inhibition of HIV-1 infection by small anionic microbicides.

Sulfonated porphyrins and phthalocyanines have been shown to have anti-HIV activity and are under consideration as microbicides. Both categories of compounds are small negatively charged molecules and both were previously shown to inhibit cell fusion induced by the HIV Env protein and to block binding of gp120 to the CD4 receptor. In the present study we show that these compounds inhibit transmission of cell-associated HIV, inactivate a broad range of HIV-1 primary isolates and are active against DS polyanion-resistant virus. The compounds tested are active over a range of pH values, and possess no detectable activity against normal bacterial flora. These results support the conclusion that anionic tetrapyrroles are promising candidates as microbicides for HIV prevention.