ACS Nano | SIRC mRNA Vaccine Combined with CpG-ODN1018 Enhances Protection Against Respiratory Virus Infection

This study provides an innovative strategy for developing combination vaccines against multiple respiratory viruses, particularly demonstrating the critical role of CpG-ODN as an adjuvant in enhancing Th1-biased immune responses, offering significant insights for the field of vaccine development.

 

Literature Overview

The article titled 'Combination mRNA Vaccine Adjuvanted with CpG Oligodeoxynucleotides Enhances Protection against Respiratory Virus Infection,' published in the journal ACS Nano, systematically investigates the design and immunogenicity of an octavalent mRNA vaccine, SIR, and its optimized version, SIRC, targeting SARS-CoV-2, influenza virus, and RSV. By integrating multiple antigens and incorporating the TLR-9 agonist CpG-ODN 1018, the study significantly enhances both humoral and cellular immune responses without triggering immune interference. The vaccine demonstrates excellent protective efficacy in mouse models, providing a feasible solution for addressing the co-circulation of multiple respiratory viruses.

Background Knowledge

Currently, the concurrent transmission of SARS-CoV-2, influenza virus, and RSV leads to frequent severe co-infections worldwide, significantly increasing disease burden and mortality. Although vaccines targeting individual viruses exist, poor immunological persistence and viral mutations necessitate frequent updates to vaccine strains, limiting long-term protection. Additionally, multi-dose vaccination strategies reduce compliance, especially among the elderly and children. Therefore, developing a combination vaccine capable of preventing all three major respiratory viruses is an urgent need. However, traditional inactivated or subunit vaccines struggle with co-expression of multivalent antigens and are prone to immune interference. The mRNA platform, due to its flexibility and rapid response capability, has become an ideal choice. Yet, balancing multi-antigen expression, avoiding competitive inhibition, and inducing strong and durable Th1 immune responses remain key challenges. This study addresses these challenges by designing the SIR vaccine encoding RBD, HAhr, and pre-F antigens, and incorporating the approved adjuvant CpG-ODN, offering a rapidly translatable vaccine development pathway.

 

 

Research Methods and Experiments

The authors developed two vaccines using the mRNA-LNP platform: SIR (containing SARS-CoV-2 RBD, influenza HAhr, and RSV pre-F antigens) and SIRC (SIR plus CpG-ODN 1018 adjuvant). The vaccines were administered via three intramuscular injections in BALB/c mice to evaluate immunogenicity and protective efficacy. Antigen-specific IgG antibody titers were measured by ELISA, neutralizing capacity against multiple pseudoviruses was assessed via neutralization assays, CD4+ and CD8+ T cell responses were analyzed by flow cytometry, and IFN-γ secretion was detected by ELISPOT. Finally, protection against influenza and RSV was validated in challenge experiments. Key experiments included comparing immunogenicity between Lmix and Rmix formulations, verifying the impact of CpG-ODN on mRNA expression kinetics, and systematically evaluating survival rates and lung pathology in mice following heterologous viral challenges.

Key Conclusions and Perspectives

• The SIRC vaccine significantly enhances the IgG2a/IgG1 ratio, indicating a Th1-biased immune response, which promotes antiviral cellular immunity and provides guidance for future adjuvant selection in vaccine development
• SIRC provides complete protection against four influenza subtypes and RSV challenge in mouse models, outperforming monovalent vaccines and SIR, highlighting the importance of adjuvant synergy in multivalent vaccine design
• CpG-ODN significantly increases the frequency of IFN-γ+ T cells and neutralizing antibody titers, demonstrating that TLR-9 agonists can effectively overcome multi-antigen competition, suggesting future mRNA vaccines should integrate immunomodulatory elements
• The vaccine did not induce significant inflammation or tissue damage, indicating that the mRNA-LNP combined with CpG-ODN has favorable safety, supporting its progression into clinical development

Research Significance and Prospects

This study provides an efficient and scalable blueprint for combination vaccines against respiratory infections, particularly suitable for annual vaccination strategies in the elderly and high-risk populations. The SIRC design can be rapidly adapted to emerging SARS-CoV-2 variants or influenza strains, greatly enhancing pandemic preparedness. From a drug development perspective, the incorporation of CpG-ODN offers a standardized adjuvant option for mRNA vaccines, potentially reducing the risk of immune escape. Moreover, the long-lasting memory T cell responses induced by this vaccine suggest it may extend the protective duration and reduce the need for booster doses, which is significant for optimizing immunization schedules.

 

 

Conclusion

This study successfully developed and validated SIRC, an octavalent mRNA combination vaccine that significantly enhances humoral and cellular immune responses against SARS-CoV-2, influenza virus, and RSV through the incorporation of the CpG-ODN adjuvant. The vaccine achieves complete protection in mouse models with good safety and no immune interference. From a translational perspective, SIRC represents a significant advancement in next-generation respiratory vaccines, particularly suitable for seasons with co-circulating multiple viruses. Its modular design allows rapid updates to antigen components in response to viral evolution. More importantly, the application of CpG-ODN provides a replicable adjuvant strategy for the mRNA vaccine platform, potentially improving the immunogenicity of other multivalent vaccines. Future studies should focus on validation in non-human primate models and Phase I clinical trials to advance this candidate vaccine toward practical application, ultimately improving the global defense system against respiratory viral infections.

 

Lingyan Cui, Sibo Zhang, Yarong Zeng, Shaowei Li, and Ningshao Xia. Combination mRNA Vaccine Adjuvanted with CpG Oligodeoxynucleotides Enhances Protection against Respiratory Virus Infection. ACS Nano.