RSV Infection Life Cycle and Vaccine Target Discovery

Respiratory Syncytial Virus (RSV) is a global health threat, with high risks for infants under six months and adults over 65. It causes millions of lower respiratory tract infections yearly, including bronchiolitis and pneumonia, leading to hospitalizations and deaths. Understanding RSV's infection life cycle is key to finding effective vaccine targets, as each stage offers intervention opportunities. This review breaks down the virus's life cycle, key proteins, host interactions, and vaccine progress for biomedical researchers.

RSV Fundamentals: Classification, Genome, and Structure

Viral Classification and Genomic Organization

RSV belongs to the Pneumoviridae family, Mononegavirales order, and Orthopneumovirus genus. It has two main subtypes (A and B) that differ in the attachment (G) protein, causing antigenic variation and complicating vaccine development.

The RSV genome is ~15 kb, single-stranded negative-sense RNA, encoding 10 major genes. Six are structural proteins (nucleocapsid N, phosphoprotein P, matrix M, fusion F, attachment G, small hydrophobic SH) critical for assembly, entry, and immune recognition. Four are non-structural proteins (NS1, NS2, M2-1, M2-2) that suppress host immunity and regulate replication. The genome is wrapped in N protein to form a ribonucleoprotein (RNP) complex, which, with P (polymerase cofactor) and L (RNA polymerase) proteins, enables transcription and replication.

The RSV Infection Life Cycle: A Step-by-Step Breakdown

Attachment

The G protein mediates viral attachment to host cells via two receptors:

• CX3CR1: G protein's CX3C motif mimics human chemokine CX3CL1, binding to CX3CR1 on respiratory epithelial and immune cells. This aids attachment and disrupts immune signaling.
• GAGs: G protein's heparin-binding domain (HBD) binds negatively charged glycosaminoglycans (e.g., heparan sulfate) on cells, concentrating viruses for better CX3CR1 interaction.

The F protein may also bind secondary receptor nucleolin to assist attachment.

Fusion

F protein drives membrane fusion, switching from prefusion (preF) to postfusion (postF) conformations. PreF is antigenically critical, exposing neutralizing epitopes. Fusion steps:

1. PreF binds receptors (e.g., nucleolin).
2. Conformational shift reveals a hydrophobic fusion peptide.
3. Peptide inserts into host membrane, bringing viral and host membranes close.
4. Further shifts fuse membranes, releasing the nucleocapsid into the cytoplasm.

Transcription/Replication

Viral inclusion bodies (IBs) in the cytoplasm—formed by N, P, M2-1 proteins—protect RNA synthesis:

• Transcription: L protein makes positive-sense mRNAs (3′ to 5′ order), capped and polyadenylated for translation. M2-1 ensures complete gene transcription.
• Replication: Once enough N/P proteins form, L protein makes full-length positive-sense cRNA, which templates new negative-sense genomic RNA. New genomes are wrapped in N protein for assembly.

Protein Translation

Viral mRNAs are translated in the cytoplasm. F/G proteins are glycosylated in the ER/Golgi for stability. Non-structural proteins (e.g., NS1) suppress host interferon signaling early.

Assembly

At the plasma membrane, M protein links nucleocapsids to F/G/SH proteins (transported from ER/Golgi). New nucleocapsids bind M protein, and glycoproteins cluster at assembly sites.

Budding

M protein forms membrane buds around assembled components. Virions pinch off, releasing infectious RSV. SH protein may aid budding by modifying membrane fluidity.

Fig.1 Schematic Illustration of RSV Life Cycle.^1,2

Critical Surface Glycoproteins and Their Functions

The three surface glycoproteins—F, G, and SH—are central to RSV pathogenesis and are the primary focus for therapeutic development.

F Protein

The F protein is responsible for mediating the critical step of viral-to-cell membrane fusion.

• Key Conformation: The pre-fusion F conformation (Prefusion F) has been identified as the structure possessing the highest activity for inducing neutralizing antibodies.
• Vaccine Significance: The structural resolution of the F protein is a core component of modern vaccine design strategies.

The Attachment (G) Protein

The G protein facilitates the initial attachment of the virus to the host cell.

• Immune Evasion: The G protein contains a central conserved domain (CCD) that includes a CX3C chemokine motif. This motif mimics the host chemokine CX3CL, which is thought to induce immune evasion.
• Cell Binding: The G protein also possesses a Heparin Binding Domain (HBD) which demonstrates high affinity for glycosaminoglycans (GAGs) on the cell surface.

The Small Hydrophobic (SH) Protein

Non-essential in cell culture but modulates host immunity (e.g., inhibiting interferons) in vivo. Including SH in multivalent vaccines (with F/G) induces broader immunity in preclinical tests, though more research is needed.

RSV Vaccine Development Progress

Challenges and Future Directions

Antibody Escape

F protein mutations can reduce vaccine-induced antibody binding. Solutions: target conserved epitopes (e.g., F's fusion peptide) and monitor global RSV sequences.

Older Adults' Immune Responses

Immunosenescence weakens vaccine responses. Strategies: adjuvants (e.g., TLR agonists), prime-boost regimens, and targeting CD8+ T cells.

Global Accessibility

Cold chain needs and high costs limit access in LMICs. Efforts: thermostable formulations, low-cost manufacturing, and global health partnerships.

Technological Advances

• Cryo-EM reveals new preF epitopes.
• RNA structural biology targets conserved genomic domains for antivirals.
• High-throughput sequencing uncovers host-virus interactions to identify new targets.

Conclusion

The complete life cycle of RSV offers multiple potential intervention points. The comprehensive analysis of the viral structure, particularly the prefusion F protein and the GCX3C motif, provides a strong foundation for vaccine development. By integrating structural biology, studies on RNA secondary structure, and host receptor interactions, the research community can accelerate the development of new, broad-spectrum RSV vaccines and therapeutics. This multi-pronged approach is crucial for addressing the pervasive threat of RSV infection worldwide.

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References

1. Deng, Lie, et al. "Progress on respiratory syncytial virus vaccine development and evaluation methods." Vaccines 13.3 (2025): 304. https://doi.org/10.3390/vaccines13030304
2. Distributed under Open Access license CC BY 4.0, without modification.

Created October 2025

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