Novel Respiratory Syncytial Virus-Like Particle Vaccine Composed of the Postfusion and Prefusion Conformations of the F Glycoprotein

Abstract

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants and children and represents an important global health burden for the elderly and the immunocompromised. Despite decades of research efforts, no licensed vaccine for RSV is available. We have developed virus-like particle (VLP)-based RSV vaccines assembled with the human metapneumovirus (hMPV) matrix protein (M) as the structural scaffold and the RSV fusion glycoprotein (F) in either the postfusion or prefusion conformation as its prime surface immunogen. Vaccines were composed of postfusion F, prefusion F, or a combination of the two conformations and formulated with a squalene-based oil emulsion as adjuvant. Immunization with these VLP vaccines afforded full protection against RSV infection and prevented detectable viral replication in the mouse lung after challenge. Analyses of lung cytokines and chemokines showed that VLP vaccination mostly induced the production of gamma interferon (IFN-γ), a marker of the Th1-mediated immune response, which is predominantly required for viral protection. Conversely, immunization with a formalin-inactivated RSV (FI-RSV) vaccine induced high levels of inflammatory chemokines and cytokines of the Th2- and Th17-mediated types of immune responses, as well as severe lung inflammation and histopathology. The VLP vaccines showed restricted production of these immune mediators and did not induce severe bronchiolitis or perivascular infiltration as seen with the FI-RSV vaccine. Remarkably, analysis of the serum from immunized mice showed that the VLP vaccine formulated using a combination of postfusion and prefusion F elicited the highest level of neutralizing antibody and enhanced the Th1-mediated immune response.

Adjuvant formulations for virus-like particle (VLP) based vaccines

“…and co-workers [104] have demonstrated that alum played an important role in exacerbating RSV disease after immunization with the FI-RSV when formulated with this adjuvant. Our preclinical studies in a mouse model demonstrated that RS-VLP formulated with AddaVax was well tolerated and lacked the lung inflammation and recruited immune cell infiltrate as compared to the FI-RSV vaccine adjuvanted with alum [100]. We conclude that a squalene oil-based adjuvant may prove to be safe and efficacious in a VLP-based RSV vaccine formulation and an excellent candidate for a successful RSV vaccine.…”

“…MF59 appears to have the ability to upregulate production of cytokines and chemokines which attract APCs to the site of injection increasing antigen uptake and subsequent transport to draining lymph nodes [99]. Our group has developed a novel VLP-based vaccine for respiratory syncytial virus (RSV) formulated with AddaVax (InvivoGen) which is analogous to the MF59 adjuvant [100]. Development of an effective RSV vaccine has been hampered by the harmful results of the first clinical trials performed in the 1960s in young children with a formalin inactivated-RSV vaccine (FI-RSV) adjuvanted with alum.…”

Novel recombinant DNA vaccine candidates for human respiratory syncytial virus: Preclinical evaluation of immunogenicity and protection efficiency

“…46 Both of the F protein forms, particularly the pre-fusion form, induce potent neutralizing antibodies. [47][48][49] The identification and quantitative measurement of both the F protein forms were not investigated in this study because both forms induce powerful immune responses. However, we expect that a mixture of pre-and postfusion forms exist in the transfected cells, with the post-fusion form dominating due to its higher stability.…”

Synthetic Biodegradable Microparticle and Nanoparticle Vaccines against the Respiratory Syncytial Virus

“…Due to their size, they share some properties with NPs; for example, they can enter freely into the lymphatic vessel and reach the draining lymph nodes [9]. Several platforms for producing VLPs have been employed to develop RSV vaccines carrying the F, G and/or M2 proteins, such as insect cells [10,90,91], mammalian cells [11,92,93,94], plant expression system [95,96], bacteria [97,98] and in vitro cell-free systems [8,99]. A variety of VLP-based RSV vaccines has been developed and tested in the last decade.…”

“…The adjuvant effect of particle carriers has been reported for many years. Particle carriers include: nanoparticles (NPs), microparticles (MPs), virosomes [8], virus-like particles (VLPs) [9,10,11,12], emulsions, Immune stimulating complexes (ISCOMs) [13,14] and liposomes [15], which have all been shown to work effectively. This has been attributed to the comparable dimensions to pathogens, which they emulate, and how they are presented to the immune system.…”