Progress on Respiratory Syncytial Virus Vaccine Development and Evaluation Methods

Abstract

Respiratory syncytial virus (RSV) remains a significant global health threat, especially to infants, the elderly, and immunocompromised individuals. This review comprehensively explores the progress in RSV vaccine development, the immune evaluation methods, and immunological surrogate. The RSV fusion (F) protein, a primary target for vaccine development, has been engineered in prefusion conformation to elicit potent neutralizing antibodies, while the attachment (G) glycoprotein and other immunogens are also being explored to broaden immune responses. Advances in diverse vaccine platforms, ranging from live attenuated and protein subunit vaccines to cutting-edge mRNA- and nanoparticle-based formulations, highlight the field's progress, yet challenges in balancing safety, immunogenicity, and durability persist. Central to these efforts is the identification and validation of immunological surrogates, which may serve as critical benchmarks for vaccine efficacy. Neutralizing antibody titers, multifunctional T cell responses, and B cell memory have emerged as key correlates of protection. However, the feasibility of these surrogates depends on their ability to predict clinical outcomes across diverse populations and settings. While neutralizing antibodies block the virus directly, T cell responses are essential for clearing infected cells and preventing severe disease, and B cell memory ensures long-term immunity. Integrating these immunological markers into a cohesive framework requires standardized assays, robust clinical validation, and an in-depth understanding of RSV-induced immune response.

Keywords: immunological surrogates; respiratory syncytial virus; vaccine evaluation; vaccines.

Figure 1

Schematic structure and genome of RSV. (A) The virion consists of envelope, matrix and nucleocapsid. The viral envelope is a lipid bilayer containing the fusion (F) and attachment (G) proteins, embedded with small hydrophobic (SH) protein. Beneath the envelope is the matrix protein (M). Inside the envelope, a helical nucleocapsid encapsulates the viral RNA genome, formed by the nucleoprotein (N) and associated with the phosphoprotein (P) and large RNA polymerase (L). (B) The viral genome contains genes encoding 11 proteins: the above-mentioned structural proteins F, G, SH, M, N, P and L proteins, and non-structural protein (NS1, NS2) and second matrix protein (M2-1, M2-2).

Figure 2

Schematic illustration of RSV life cycle. The lifecycle of RSV initiates with attachment and entry into host cells, mediated by the viral glycoproteins. The G protein engages specific host cell receptors, such as heparan sulphate proteoglycan (HSPG) or CX3CR1, facilitating viral docking. Subsequently, the F protein binds to nucleolin and orchestrates membrane fusion, enabling the release of the ribonucleoprotein (RNP) complex into the cytoplasm, where viral replication and transcription are catalyzed by the RNA-dependent RNA polymerase. Following replication, viral components are transported to the cell membrane, where they assemble into progeny virions. These mature particles, enveloped by a host-derived lipid bilayer, eventually egress from the cell surface.

Figure 3

Antigenic sites on the pre-F (left) and post-F (right) structures of the RSV trimeric F protein, along with the neutralizing capabilities. The surface representation of the protein colored in gray was generated from the Protein Data Bank (PDB) code 4JHW (pre-F) and PDB code 3RKI (post-F), and the antigenic sites labelled with site Ø in red, site V in orange, site III in cyan, site IV in blue, site II in green, and site I in magenta are highlighted on the surface.

Figure 4

Aspects of vaccine-induced immune response and key technologies applied for vaccine immunological evaluation. Immunogenicity evaluation mainly includes evaluation of humoral, mainly neutralizing, antibodies, and cellular immunity, including the T cell response and B cell evaluation. Neutralizing antibodies (NAbs) are the most important indicator of immunogenicity, and different standardized and high-throughput technologies for NAb measurement have been utilized. T cell responses are usually measured by the quantification of antigen-specific T cells and the presence of different phenotypes of T cells. Memory B cell evaluation is mainly based on single-cell VDJ sequencing. BCR diversity and CDR3 quantification may indicate humoral immune reserve for immunogens, which may set criteria for screening immunogenic candidates.