Mammalian Cell-Derived Respiratory Syncytial Virus-Like Particles Protect the Lower as well as the Upper Respiratory Tract

Abstract

Globally, Respiratory Syncytial Virus (RSV) is a leading cause of bronchiolitis and pneumonia in children less than one year of age and in USA alone, between 85,000 and 144,000 infants are hospitalized every year. To date, there is no licensed vaccine. We have evaluated vaccine potential of mammalian cell-derived native RSV virus-like particles (RSV VLPs) composed of the two surface glycoproteins G and F, and the matrix protein M. Results of in vitro testing showed that the VLPs were functionally assembled and immunoreactive, and that the recombinantly expressed F protein was cleaved intracellularly similarly to the virus-synthesized F protein to produce the F1 and F2 subunits; the presence of the F1 fragment is critical for vaccine development since all the neutralizing epitopes present in the F protein are embedded in this fragment. Additional in vitro testing in human macrophage cell line THP-1 showed that both virus and the VLPs were sensed by TLR-4 and induced a Th1-biased cytokine response. Cotton rats vaccinated with RSV VLPs adjuvanted with alum and monophosphoryl lipid A induced potent neutralizing antibody response, and conferred protection in the lower as well as the upper respiratory tract based on substantial virus clearance from these sites. To the best of our knowledge, this is the first VLP/virosome vaccine study reporting protection of the lower as well as the upper respiratory tract: Prevention from replication in the nose is an important consideration if the target population is infants < 6 months of age. This is because continued virus replication in the nose results in nasal congestion and babies at this age are obligate nose breathers. In conclusion, these results taken together suggest that our VLPs show promise to be a safe and effective vaccine for RSV.

The Respiratory Syncytial Virus Phosphoprotein, Matrix Protein, and Fusion Protein Carboxy-Terminal Domain Drive Efficient Filamentous Virus-Like Particle Formation

“…As multiple host factors are likely involved in hRSV VLP assembly, host species and/or cell-type-specific differences for optimal VLP production may come into play and will have to be analyzed and optimized, depending on the cell culture system of choice. A recent paper reported that immunogenic VLPs were isolated from HEK293 cells coexpressing the M, G, and F proteins (58). Our present work would predict that in the absence of P, coalescence of M, F, and G proteins and VLP formation are not optimal and that the efficiency could be enhanced by including P. However, the systems are not readily compared, as the VLPs produced by M-G-F coexpression were spherical and were harvested at a much later time point from suspensions of HEK293 cells at ultrahigh g force, whereas we focused on cell-associated filamentous VLPs at an earlier time point to avoid potential morphological changes associated with purification, as well as excessive cell lysis and/or death.…”

Progress in the development of virus-like particle vaccines against respiratory viruses

“…RSV VLP vaccination of mice induced neutralizing antibodies, correlating with reducing lung viral loads and protection in mice after RSV challenge infection [101]. RSV VLPs composed of RSV G, F, M proteins elicited high titers of IgG antibody responses to homologous RSV A2 and heterologous RSV B strain challenge [102]. Mammalian cell-derived RSV VLP vaccines adjuvanted with combination of alum and monophosphoryl lipid A induced higher levels of IgG titers than non-adjuvanted VLPs [102].…”

“…RSV F VLPs displayed a range of size distribution at approximate 80-100 nm in diameter, whereas G-VLPs were similar but somewhat more heterogeneous in size [101]. RSV VLPs were also reported to be generated by transfection of mammalian HEK293 cells with three types of expression plasmids, containing codon optimized RSV-G, F and M proteins [102]. RSV VLPs appear to mimic native RSV in morphology and structure, as examined by transmission electron microscopy.…”

“…RSV VLPs composed of RSV G, F, M proteins elicited high titers of IgG antibody responses to homologous RSV A2 and heterologous RSV B strain challenge [102]. Mammalian cell-derived RSV VLP vaccines adjuvanted with combination of alum and monophosphoryl lipid A induced higher levels of IgG titers than non-adjuvanted VLPs [102].…”

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.…”