Antibodies | Computationally Designed Headless Influenza Hemagglutinin Antigens for Modular Universal Nanoparticle Vaccine Development

This study systematically optimized the stability and expression efficiency of influenza hemagglutinin (HA) stem domain antigens through a combined strategy of computational design and experimental validation, providing a scalable, modular antigen platform for developing universal influenza vaccines that elicit broad neutralizing antibody responses, offering significant inspiration for the vaccine development field.

 

Literature Overview

The article titled 'Computational Design and Expression of Headless Influenza Hemagglutinin Antigens Toward a Modular Universal Nanoparticle Vaccine,' published in the journal Antibodies, systematically explores how to design stable, soluble headless influenza hemagglutinin (HA) trimeric antigens using computational methods and achieve high-level mammalian expression. The study focuses on overcoming the immunosubdominance of conserved stem epitopes in native HA antigens caused by the immunodominant head domain, proposing a stabilization strategy based on a novel collagen XV (CXV) trimerization domain that significantly improves antigen expression yield and structural integrity. The authors further validate the broad applicability of this design across multiple subtypes, laying the foundation for constructing chimeric nanoparticle vaccines covering a wide range of influenza strains.

Background Knowledge

Influenza virus causes significant global morbidity and mortality each year, and the high variability of its surface antigen HA is the primary reason for the limited effectiveness (10–60%) of current seasonal vaccines. Although the head domain of HA undergoes frequent mutations, several relatively conserved epitopes exist in its stem region, which can be recognized by broadly neutralizing antibodies (bnAbs). However, these conserved epitopes are immunosubdominant in native HA due to factors including B-cell negative selection, low precursor B-cell frequency, glycan shielding, immune imprinting, and immunodominance interference from the head domain. Therefore, vaccine strategies targeting the HA stem must overcome immunogenicity bottlenecks by removing the immunodominant head domain to redirect immune responses toward conserved epitopes. This study's approach lies in using computational modeling to guide antigen design, combining it with a novel trimerization domain to enhance stability and enable high-yield soluble expression, thereby providing standardized antigen units for constructing modular universal vaccines.

 

 

Research Methods and Experiments

The authors employed a computational protein design strategy, constructing headless HA antigens based on known HA structures (e.g., PDB 3ZTJ), replacing the traditional T4 bacteriophage foldon trimerization domain with the human collagen XV (CXV) domain. They used AlphaFold2 for structure prediction and assessed stability via molecular dynamics (MD) simulations. Antigens were transiently expressed in HEK293F cells, purified using HisTrap affinity chromatography, and analyzed for purity and oligomeric state by SDS-PAGE and SEC-HPLC. Additionally, the authors tested CXV homologs from different species (e.g., zebrafish, phage hyaluronidase) to evaluate sequence compatibility. To support subsequent nanoparticle display, some antigens were C-terminally fused with SpyTag sequences for covalent coupling to mi3 nanoparticles expressing SpyCatcher. The experiments covered H1, H3, H5, and eight additional subtypes (H2, H6, H7, H9, H10, H13, H16, H17), with principal component analysis (PCA) used to assess the representativeness of selected strains within the influenza antigenic space.

Key Conclusions and Perspectives

• All designed headless HA antigens formed stable trimeric structures in AlphaFold2 predictions, with MD simulations showing backbone RMSD stabilized around ~2 Å, indicating good thermodynamic stability. This supports that HA stem antigens can achieve correct folding through computational design, providing a theoretical basis for subsequent experimental expression.
• Experimental expression results showed that the H3-CXVH design yielded 9.8 mg in a 30 mL culture, with SEC-HPLC revealing a predominant trimer peak, demonstrating that this strategy enables high-yield soluble expression. This finding suggests that protein expression systems must balance structural stability and secretion efficiency, with mammalian systems being more favorable for correct folding.
• The antigens retained their trimeric state after SpyTag fusion, indicating that the tag does not disrupt antigen conformation, thus providing a flexible covalent coupling pathway for constructing multivalent nanoparticle vaccines. This result offers guidance for nanoparticle vaccine platform development.
• Soluble expression was still achieved using non-human CXV domains (e.g., zebrafish), suggesting future potential to avoid immunogenicity risks associated with human proteins and enhance vaccine safety. This strategy opens new avenues for optimizing vaccine safety.
• Successful expression across 11 HA subtypes, combined with PCA analysis showing coverage of current circulating strains (sequence similarity 72–84%), indicates the platform's broad applicability and supports the construction of diverse mosaic nanoparticle vaccines. This achievement directly advances modular antigen design for universal influenza vaccines.

Research Significance and Prospects

This study provides a standardized, scalable antigen design framework for universal influenza vaccine development. By applying computation-guided structural optimization and novel trimerization domains, it solves previous issues of unstable expression and low yield in headless HA antigens, significantly enhancing translational potential. This modular design allows flexible assembly of antigens from different subtypes onto nanoparticles, potentially enhancing the induction efficiency of broadly neutralizing antibodies through multivalent display.

Future work could include animal immunization studies to evaluate the immunogenicity and cross-protection of mosaic nanoparticles in mice or non-human primates. Additionally, further antigen optimization—such as introducing glycan masking or site-directed mutations—could reduce potential autoreactivity. Moreover, this platform could be extended to the design of conserved antigens for other viruses (e.g., coronaviruses), promoting the development of broad-spectrum antiviral vaccines.

 

 

Conclusion

This study successfully developed a class of high-yield, structurally stable headless influenza hemagglutinin antigens by integrating computational modeling, molecular dynamics simulations, and experimental validation, providing key antigen components for constructing modular universal nanoparticle vaccines. The strategy effectively addresses the immunosubdominance of conserved stem epitopes by removing the immunodominant head domain and stabilizing the trimeric conformation, thereby redirecting immune responses toward broadly neutralizing epitopes. From a translational perspective, this antigen platform demonstrates excellent scalability and production compatibility, suitable for rapid response to emerging influenza variants. Combined with existing nanoparticle display technologies, this research lays a solid foundation for achieving long-lasting, broad protection with universal influenza vaccines, potentially significantly reducing the frequency of seasonal vaccinations and enhancing pandemic preparedness. This work not only advances influenza vaccine innovation but also provides a paradigm applicable to vaccine design against other variable viruses.

 

Victor Ovchinnikov and Martin Karplus. Computational Design and Expression of Headless Influenza Hemagglutinin Antigens Toward a Modular Universal Nanoparticle Vaccine. Antibodies.