A self-assembling nanoparticle: Implications for the development of thermostable vaccine candidates

Multifaceted therapeutic applications of biomimetic nanovaccines

The development of vaccines has had a crucial role in preventing and controlling infectious diseases on a global scale. Innovative formulations of biomimetic vaccines inspired by natural defense mechanisms combine long-term antigen stability, immunogenicity, and targeted delivery with sustained release. Types of biomimetic nanoparticle (NP) include bacterial outer membrane vesicles (OMVs), cell membrane-decorated NPs, liposomes, and exosomes. These approaches have shown potential for cancer immunotherapy, and in antibacterial and antiviral applications. Despite current challenges, nanovaccines have immense potential to transform disease prevention and treatment, promising therapeutic approaches for the future. In this review, we highlight recent advances in biomimetic vaccine design, mechanisms of action, and clinical applications, emphasizing their role in personalized medicine, targeted drug delivery, and immunomodulation.

Spike 1 trimer, a nanoparticle vaccine against porcine epidemic diarrhea virus induces protective immunity challenge in piglets

Porcine epidemic diarrhea virus (PEDV) is considered the cause for porcine epidemic diarrhea (PED) outbreaks and hefty losses in pig farming. However, no effective commercial vaccines against PEDV mutant strains are available nowadays. Here, we constructed three native-like trimeric candidate nanovaccines, i.e., spike 1 trimer (S1-Trimer), collagenase equivalent domain trimer (COE-Trimer), and receptor-binding domain trimer (RBD-Trimer) for PEDV based on Trimer-Tag technology. And evaluated its physical properties and immune efficacy. The result showed that the candidate nanovaccines were safe for mice and pregnant sows, and no animal death or miscarriage occurred in our study. S1-Trimer showed stable physical properties, high cell uptake rate and receptor affinity. In the mouse, sow and piglet models, immunization of S1-Trimer induced high-level of humoral immunity containing PEDV-specific IgG and IgA. S1-Trimer-driven mucosal IgA responses and systemic IgG responses exhibited high titers of virus neutralizing antibodies (NAbs) in vitro. S1-Trimer induced Th1-biased cellular immune responses in mice. Moreover, the piglets from the S1-Trimer and inactivated vaccine groups displayed significantly fewer microscopic lesions in the intestinal tissue, with only one and two piglets showing mild diarrhea. The viral load in feces and intestines from the S1-Trimer and inactivated vaccine groups were significantly lower than those of the PBS group. For the first time, our data demonstrated the protective efficacy of Trimer-Tag-based nanovaccines used for PEDV. The S1-Trimer developed in this study was a competitive vaccine candidate, and Trimer-Tag may be an important platform for the rapid production of safe and effective subunit vaccines in the future.

Self-Assembling E2-Based Nanoparticles Improve Vaccine Thermostability and Protective Immunity against CSFV

Classical swine fever virus (CSFV) is a highly contagious pathogen causing significant economic losses in the swine industry. Conventional inactivated or attenuated live vaccines for classical swine fever (CSF) are effective but face biosafety concerns and cannot distinguish vaccinated animals from those infected with the field virus, complicating CSF eradication efforts. It is noteworthy that nanoparticle (NP)-based vaccines resemble natural viruses in size and antigen structure, and offer an alternative tool to circumvent these limitations. In this study, we developed an innovative vaccine delivery scaffold utilizing self-assembled mi3 NPs, which form stable structures carrying the CSFV E2 glycoprotein. The expressed yeast E2-fused protein (E2-mi3 NPs) exhibited robust thermostability (25 to 70 °C) and long-term storage stability at room temperature (25 °C). Interestingly, E2-mi3 NPs made with this technology elicited enhanced antigen uptake by RAW264.7 cells. In a rabbit model, the E2-mi3 NP vaccine against CSFV markedly increased CSFV-specific neutralizing antibody titers. Importantly, it conferred complete protection in rabbits challenged with the C-strain of CSFV. Furthermore, we also found that the E2-mi3 NP vaccines triggered stronger cellular (T-lymphocyte proliferation, CD8+ T-lymphocytes, IFN-γ, IL-2, and IL-12p70) and humoral (CSFV-specific neutralizing antibodies, CD4+ T-lymphocytes, and IL-4) immune responses in pigs than the E2 vaccines. To sum up, these structure-based, self-assembled mi3 NPs provide valuable insights for novel antiviral strategies against the constantly infectious agents.

Accurate location of two conserved linear epitopes of PEDV utilizing monoclonal antibodies induced by S1 protein nanoparticles

Porcine Epidemic diarrhea virus (PEDV), which can result in severe vomiting, diarrhea, dehydration and death in newborn piglets, poses a great threat to the pig industry around the world. The S1 subunit of S protein is crucial for triggering neutralizing antibodies binding to the receptor. Based on the advantages of high immunogenicity and precise assembly of nanoparticles, the mi3 nanoparticles and truncated S1 protein were assembled by the SpyTag/SpyCatcher system and then expressed in HEK293F cells, whereafter high-efficiency monoclonal antibodies (mAbs) were produced and identified. The obtained five mAbs can bind to various genotypes of PEDV, including a mAb (12G) which can neutralize G1 and G2 genotypes of PEDV in vitro. By further identification of monoclonal antibody target sequences, 507FNDHSF512 and 553LFYNVTNSYG562 were first identified as B-cell linear epitopes, in which 553LFYNVTNSYG562 was a neutralizing epitope. Alanine scans identified the key amino acid sites of two epitopes. Moreover, the results of multiple sequence alignment analysis showed that these two epitopes were highly conserved in various subtype variants. In brief, these findings can serve as a basis for additional research of PEDV and prospective resources for the creation of later detection and diagnostic techniques.

Self-Assembling Nanovaccine Fused with Flagellin Enhances Protective Effect against Foot-and-Mouth Disease Virus

Nanovaccines based on self-assembling nanoparticles (NPs) can show conformational epitopes of antigens and they have high immunogenicity. In addition, flagellin, as a biological immune enhancer, can be fused with an antigen to considerably enhance the immune effect of antigens. In improving the immunogenicity and stability of a foot-and-mouth disease virus (FMDV) antigen, novel FMDV NP antigens were prepared by covalently coupling the VP1 protein and truncated flagellin containing only N-terminus D0 and D1 (N-terminal aa 1-99, nFLiC) with self-assembling NPs (i301). The results showed that the fusion proteins VP1-i301 and VP1-i301-nFLiC can assemble into NPs with high thermal tolerance and stability, obtain high cell uptake efficiency, and upregulate marker molecules and immune-stimulating cytokines in vitro. In addition, compared with monomeric VP1 antigen, high-level cytokines were stimulated with VP1-i301 and VP1-i301-nFLiC nanovaccines in guinea pigs, to provide clinical protection against viral infection comparable to an inactivated vaccine. This study provides new insight for the development of a novel FMD vaccine.

Nanovaccines: Merits, and diverse roles in boosting antitumor immune responses

An attractive type of cancer immunotherapy is cancer therapeutic vaccines that induce antitumor immunity effectively. Although supportive results in the recent vaccine studies, there are still numerous drawbacks, such as poor stability, weak immunogenicity and strong toxicity, to be tackled for promoting the potency and durability of antitumor efficacy. NPs (Nanoparticles)-based vaccines offer unique opportunities to breakthrough the current bottleneck. As a rule, nanovaccines are new the generations of vaccines that use NPs as carriers and/or adjuvants. Several advantages of nanovaccines are constantly explored, including optimal nanometer size, high stability, plenty of antigen loading, enhanced immunogenicity, tunable antigen presentation, more retention in lymph nodes and promote patient compliance by a lower frequency of dosing. Here, we summarized the merits and highlight the diverse role nanovaccines play in improving antitumor responses.

A modular and self-adjuvanted multivalent vaccine platform based on porcine circovirus virus-like nanoparticles

BACKGROUND

Virus-like particles (VLPs) are supramolecular structures composed of multiple protein subunits and resemble natural virus particles in structure and size, making them highly immunogenic materials for the development of next-generation subunit vaccines. The orderly and repetitive display of antigenic epitopes on particle surface allows efficient recognition and cross-link by B cell receptors (BCRs), thereby inducing higher levels of neutralizing antibodies and cellular immune responses than regular subunit vaccines. Here, we present a novel multiple antigen delivery system using SpyCatcher/Spytag strategy and self-assembled VLPs formed by porcine circovirus type 2 (PCV2) Cap, a widely used swine vaccine in solo.

RESULTS

Cap-SC, recombinant Cap with a truncated SpyCatcher polypeptide at its C-terminal, self-assembled into 26-nm VLPs. Based on isopeptide bonds formed between SpyCatcher and SpyTag, classical swine fever virus (CSFV) E2, the antigen of interest, was linked to SpyTag and readily surface-displayed on SpyCatcher decorated Cap-SC via in vitro covalent conjugation. E2-conjugated Cap VLPs (Cap-E2 NPs) could be preferentially captured by antigen presenting cells (APCs) and effectively stimulate APC maturation and cytokine production. In vivo studies confirmed that Cap-E2 NPs elicited an enhanced E2 specific IgG response, which was significantly higher than soluble E2, or the admixture of Cap VLPs and E2. Moreover, E2 displayed on the surface did not mask the immunodominant epitopes of Cap-SC VLPs, and Cap-E2 NPs induced Cap-specific antibody levels and neutralizing antibody levels comparable to native Cap VLPs.

CONCLUSION

These results demonstrate that this modularly assembled Cap-E2 NPs retains the immune potential of Cap VLP backbone, while the surface-displayed antigen significantly elevated E2-induced immune potency. This immune strategy provides distinctly improved efficacy than conventional vaccine combination. It can be further applied to the development of dual or multiple nanoparticle vaccines to prevent co-infection of PCV2 and other swine pathogens.

The truncated form of flagellin (tFlic) provides the 2dCap subunit vaccine with better immunogenicity and protective effects in mice

Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus-associated diseases, and it causes substantial economic losses in the swine industry each year. It is crucial to develop an effective vaccine against the circulating strain PCV2d, which is prone to substantial degrees of mutation. In this study, a truncated form of flagellin (tFlic: 85-111 aa) was inserted into the C-terminal sequence of 2dCap, and Western blotting results showed that recombinant Cap-tFlic VLPs were successfully expressed. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) data indicated that purified recombinant Cap-tFlic fusion proteins existed in the form of polymers and that tFlic could not affect the formation and internalization of VLPs. Integrated Cap-tFlic VLPs induced the expression of antigen presentation-related factors (MHC-II and CD86) by bone marrow-derived dendritic cells (BM-DCs), and the expression of TLR5-related factors (TNF-α) was dramatically elevated. Mice intramuscularly immunized with Cap-tFlic VLPs exhibited significantly higher levels of Cap-specific antibodies and neutralizing antibodies than mice immunized with wild-type Cap VLPs. The data obtained in the current study indicate that Cap-tFlic may be a candidate for a subunit vaccine against PCV2 in the future.

The Development of Classical Swine Fever Marker Vaccines in Recent Years

Classical swine fever (CSF) is a severe disease that has caused serious economic losses for the global pig industry and is widely prevalent worldwide. In recent decades, CSF has been effectively controlled through compulsory vaccination with a live CSF vaccine (C strain). It has been successfully eradicated in some countries or regions. However, the re-emergence of CSF in Japan and Romania, where it had been eradicated, has brought increased attention to the disease. Because the traditional C-strain vaccine cannot distinguish between vaccinated and infected animals (DIVA), this makes it difficult to fight CSF. The emergence of marker vaccines is considered to be an effective strategy for the decontamination of CSF. This paper summarizes the progress of the new CSF marker vaccine and provides a detailed overview of the vaccine design ideas and immunization effects. It also provides a methodology for the development of a new generation of vaccines for CSF and vaccine development for other significant epidemics.

Targeted Delivery of Nanovaccine to Dendritic Cells via DC-Binding Peptides Induces Potent Antiviral Immunity in vivo

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Conclusion

Nanoparticle and virus-like particle vaccine approaches against SARS-CoV-2

The global spread of coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has provoked an urgent need for prophylactic measures. Several innovative vaccine platforms have been introduced and billions of vaccine doses have been administered worldwide. To enable the creation of safer and more effective vaccines, additional platforms are under development. These include the use of nanoparticle (NP) and virus-like particle (VLP) technology. NP vaccines utilize self-assembling scaffold structures designed to load the entire spike protein or receptor-binding domain of SARS-CoV-2 in a trimeric configuration. In contrast, VLP vaccines are genetically modified recombinant viruses that are considered safe, as they are generally replication-defective. Furthermore, VLPs have indigenous immunogenic potential due to their microbial origin. Importantly, NP and VLP vaccines have shown stronger immunogenicity with greater protection by mimicking the physicochemical characteristics of SARS-CoV-2. The study of NP- and VLP-based coronavirus vaccines will help ensure the development of rapid-response technology against SARS-CoV-2 variants and future coronavirus pandemics.