A Universal Plug-and-Display Vaccine Carrier Based on HBsAg VLP to Maximize Effective Antibody Response

Column-free purification and coating of SpyCatcher protein on ELISA wells generates universal solid support for capturing of SpyTag-fusion protein from the non-purified condition

•Spy Tag-Protein covalent interaction is rapid and specific method for protein immobilization.•Column free purification of SpyCatcher protein enables develop a universal solid support for SpyTag protein purification.•This method is highly simple and applicable to other proteins.

Novel ssRNA phage VLP platform for displaying foreign epitopes by genetic fusion

Virus-like particles (VLPs) can be used as efficient carriers of various antigens and therefore serve as attractive tools in vaccine development. Although VLPs of different viruses can be used, VLPs of ssRNA phages have convincing advantages due to their unique properties, including efficient protein production in bacterial and yeast expression systems, low production cost and easy and fast purification. Currently, the range of ssRNA phage VLPs is limited. In particular, this is true for VLPs that tolerate insertions at the N- and C-termini of the coat protein. It is therefore necessary to find new alternatives within the known ssRNA phage VLP range. From previous studies, we found approximately 80 new VLPs forming ssRNA phage coat proteins. In the current study, we attached a model peptide to the N- and C-termini of coat proteins. As a model peptide, we used a triple repeat of 23 N-terminal residues of the ectodomain of the influenza M2 protein, used previously in the development of the flu vaccine. Examining 43 novel phage coat proteins for the ability to form chimeric VLPs, we found ten new promising candidates for further vaccine design, five of which were tolerant to insertions at both the N- and C-termini. Furthermore, we demonstrate that most of the chimeric VLPs have good antigenic properties as judged from their reactivity with anti-M2 antibodies.

A Platform Incorporating Trimeric Antigens into Self-Assembling Nanoparticles Reveals SARS-CoV-2-Spike Nanoparticles to Elicit Substantially Higher Neutralizing Responses than Spike Alone

Antigens displayed on self-assembling nanoparticles can stimulate strong immune responses and have been playing an increasingly prominent role in structure-based vaccines. However, the development of such immunogens is often complicated by inefficiencies in their production. To alleviate this issue, we developed a plug-and-play platform using the spontaneous isopeptide-bond formation of the SpyTag:SpyCatcher system to display trimeric antigens on self-assembling nanoparticles, including the 60-subunit Aquifex aeolicus lumazine synthase (LuS) and the 24-subunit Helicobacter pylori ferritin. LuS and ferritin coupled to SpyTag expressed well in a mammalian expression system when an N-linked glycan was added to the nanoparticle surface. The respiratory syncytial virus fusion (F) glycoprotein trimer - stabilized in the prefusion conformation and fused with SpyCatcher - could be efficiently conjugated to LuS-SpyTag or ferritin-SpyTag, enabling multivalent display of F trimers with prefusion antigenicity. Similarly, F-glycoprotein trimers from human parainfluenza virus-type 3 and spike-glycoprotein trimers from SARS-CoV-2 could be displayed on LuS nanoparticles with decent yield and antigenicity. Notably, murine vaccination with the SARS-CoV-2 spike-LuS nanoparticles elicited ~25-fold higher neutralizing responses, weight-per-weight relative to spike alone. The versatile platform described here thus allows for multivalent plug-and-play presentation on self-assembling nanoparticles of trimeric viral antigens, with SARS-CoV-2 spike-LuS nanoparticles inducing particularly potent neutralizing responses.

Incorporation of a Novel CD4+ Helper Epitope Identified from Aquifex aeolicus Enhances Humoral Responses Induced by DNA and Protein Vaccinations

CD4+ T cells play an important role in the maturation of the antibody responses. Conjugation of identified CD4+ T cell helper epitope to the target antigen has been developed as a strategy to enhance vaccine-induced humoral immunity. In this work, we reported the identification of a novel HLA-IAb helper epitope LS-3 from Aquifex aeolicus. In silico analysis predicted this epitope to have high binding affinity to common human HLA alleles and have complementary binding coverage to the established PADRE epitope. Introduction of HLA-IAb knockout mutations to the LS-3 epitope significantly attenuated humoral responses induced by a vaccine containing this epitope. Finally, engineered fusion of the epitope to a model antigen, influenza hemagglutinin, significantly improved both binding and hemagglutination inhibition antibody responses in mice receiving DNA or protein vaccines. In summary, LS-3 and additional identified CD4+ helper epitopes may be further explored to improve vaccine responses in translational studies.

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Identification of a novel CD4+ helper epitope, LS-3, from Aquifex aeolicus

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In silico analysis predicts high binding affinity of LS-3 to human HLA-DR alleles

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Fusing LS-3 to antigen enhances humoral response by vaccinations

Advantages and Prospects of Tag/Catcher Mediated Antigen Display on Capsid-Like Particle-Based Vaccines

Capsid-like particles (CLPs) are multimeric, repetitive assemblies of recombinant viral capsid proteins, which are highly immunogenic due to their structural similarity to wild-type viruses. CLPs can be used as molecular scaffolds to enable the presentation of soluble vaccine antigens in a similar structural format, which can significantly increase the immunogenicity of the antigen. CLP-based antigen display can be obtained by various genetic and modular conjugation methods. However, these vary in their versatility as well as efficiency in achieving an immunogenic antigen display. Here, we make a comparative review of the major CLP-based antigen display technologies. The Tag/Catcher-AP205 platform is highlighted as a particularly versatile and efficient technology that offers new qualitative and practical advantages in designing modular CLP vaccines. Finally, we discuss how split-protein Tag/Catcher conjugation systems can help to further propagate and enhance modular CLP vaccine designs.