Comparative efficacy of virus like particle (VLP) vaccine of foot-and-mouth-disease virus (FMDV) type O adjuvanted with poly I:C or CpG in guinea pigs.

Foot-and-mouth disease (FMD) is one of the most contagious and economically important diseases of cloven-hoofed livestock. Currently used inactivated FMD vaccines have short lived immunity besides risk of handling live virus. We studied recombinant FMD virus like particles (VLPs) encoded by FMDV type O/IND/R2/75 polyprotein genes expressed in Sf9 cells and adjuvanted with CpG or Poly I:C in inducing protective immune response in guinea pigs. Guinea pigs immunized with VLP + CpG vaccine had shown markedly higher cell mediated immunity (CMI) in comparison to the conventional vaccine group as evident from higher levels of IgG2 than IgG1. Although the humoral response was less in VLP + CpG compared to conventional vaccine, the lymphocyte stimulation index was more in VLP + CpG compared to conventional and VLP + Poly I:C vaccine groups. Finally the challenge experiments on 28 and 56 dpv had shown 75% protection in VLP + CpG immunized guinea pigs primary and boosted animals, while 50% and 62% protection in VLP + Poly I:C in primary and boosted animals, respectively. In conclusion, CpG adjuvant was found to be superior followed by ISA206 and Poly I:C in eliciting protection in VLP based FMD vaccines in guinea pigs.

Intranasal Vaccination with a Respiratory-Syncytial-Virus-Based Virus-like Particle Displaying the G Protein Conserved Region Induces Severe Weight Loss and Pathology upon Challenge with Wildtype Respiratory Syncytial Virus.

Respiratory syncytial virus (RSV) is a major cause of severe respiratory tract disease worldwide, and a pediatric vaccine is not available. We generated a filamentous RSV-based virus-like particle (VLP) that presents the central conserved region of the attachment protein G. This was achieved by co-expressing the matrix protein, phosphoprotein, nucleoprotein, and a hybrid fusion protein in which the F ectodomain was replaced with the G central region (GCR). The latter is relatively conserved and contains a receptor binding site and hence is a logical vaccine target. The immunogenicity and efficacy of the resulting VLP, termed VLP-GCR, were examined in mice using intranasal application without adjuvant. VLP-GCR induced substantial anti-N antibody levels but very low anti-G antibody levels, even after three vaccinations. In contrast, a VLP presenting prefusion-stabilized fusion (preF) protein instead of GCR induced both high anti-F and anti-nucleoprotein antibody levels, suggesting that our GCR antigen was poorly immunogenic. Challenge of VLP-GCR-vaccinated mice caused increased weight loss and lung pathology, and both VLPs induced mucus in the lungs. Thus, neither VLP is suitable as a vaccine for RSV-naive individuals. However, VLP-preF enhanced the proportion of preF antibodies and could serve as a multi-antigen mucosal booster vaccine in the RSV-experienced population.

Enhancing Anti-G Antibody Induction by a Live Single-Cycle Prefusion F-Expressing RSV Vaccine Improves In Vitro and In Vivo Efficacy.

The human respiratory syncytial virus (RSV) is a major cause of severe respiratory tract disease, and a vaccine is not available. We previously reported a novel live vaccine expressing prefusion-stabilized fusion protein (preF) in place of the native F protein (RSV-preFΔCT). As preF is non-functional, RSV-preFΔCT was amplified in a production line expressing a functional substitute, and exhibited a single-cycle replication phenotype, which holds several unique potential advantages. RSV-preFΔCT prevented shedding and lung pathology after viral challenge in mice, but induced low levels of anti-attachment protein (G) antibodies (Abs). Given the significant contributions of anti-G Abs toward disease prevention, we generated modifications to RSV-preFΔCT in an effort to induce higher anti-G Ab levels. The Ab levels were monitored after the prime-boost vaccination of mice with modified vaccines. The most successful modification for enhancing induced anti-G Abs was seen with the placement of G in the first genome position. This vaccine also reduced the pathology after challenge with a high dose of wt RSV, and outperformed the sera from wt RSV-vaccinated mice in in vitro neutralization. Thus, raising the anti-G Ab levels induced by RSV-preFΔCT enhanced efficacy in vitro and in vivo, and constitutes an important next step in developing a live, single-cycle, efficacious vaccine for the human population.

A live single-cycle RSV vaccine expressing prefusion F protein.

Live-attenuated Respiratory syncytial virus (RSV) vaccines given intranasally have potential to provide comprehensive protection, including lung-resident immunity. It has however proven challenging to impart both sufficient safety and efficacy in a vaccine. To achieve the latter, we used a trans-complementing approach to generate live single-cycle RSV vaccines expressing the prefusion form (preF) of the viral fusion protein (F), either membrane-anchored or secreted. Both viruses were tested for their ability to induce a protective immune response in mice after intranasal prime-boost vaccination. The secreted preF vaccine failed to induce a protective response. The anchored preF vaccine induced anti-preF antibodies and antiviral T cells, and protected mice from lung pathology and viral shedding after challenge. Neither vaccine induced anti-G antibodies, for reasons unknown. In spite of the latter and single-cycle replication, the membrane-anchored preF vaccine was protective and demonstrates potential for development of an efficacious live vaccine with a stable safety phenotype.