Ferritin as a Platform for Creating Antiviral Mosaic Nanocages: Prospects for Treating COVID-19

Ferritin nanoparticles significantly enhance the immune response to the African swine fever virus p34 protein

BACKGROUND

African swine fever (ASF) is a highly contagious disease, and the core-shell protein p34 is an important antigen that can induce immune responses. The use of ferritin nanoparticles for the orderly and repetitive display of antigens on the particle surface can improve the immunogenicity of subunit vaccines. Here, we used the SpyCatcher/Spytag system to conjugate ferritin nanoparticles with the p34 protein (F-p34).

RESULTS

The N-terminus of ferritin was conjugated to a truncated SpyCatcher (SC-ferritin). The antigen of ASFV p34 was linked to SpyTag (p34-ST). SC-Ferritin and p34-ST were expressed in E. coli and purified via CaptoTM Core 700 and Ni-NTA columns, respectively. Based on the isopeptide bonds formed between SpyCatcher and SpyTag, p34 linked to SpyTag was readily surface-displayed on SC-ferritin via in vitro covalent conjugation (F-p34). F-p34 can be taken up by bone marrow dendritic cells (BMDCs) and effectively stimulate BMDC maturation. Compared with the monomeric p34 protein, in vivo studies confirmed that the recombinant F-p34 nanoparticle can induce more robust T-cell responses and stronger specific IgG antibody responses against ASFV. Moreover, F-p34 can increase serum cytokines, which is also significantly greater than that of the p34 protein. These results indicate that the recombinant nanoparticles can induce not only humoral immune responses but also cellular immune responses. In addition, there were no significant pathological changes in the heart, liver, spleen, lung or kidney tissue sections of the mice immunized with F-p34, demonstrating that the recombinant nanoparticles exhibit favorable histocompatibility or safety.

CONCLUSIONS

These results demonstrate that we successfully designed a recombinant plasmid and obtained a recombinant protein through the prokaryotic expression system of E. coli. The covalently coupled recombinant F-p34 nanoparticles significantly increased the antigenicity of p34 and contributed to research on African swine fever subunit vaccines.

Ferritin: Significance in viral infections

As an indispensable trace element, iron is essential for many biological processes. Increasing evidence has shown that virus infection can perturb iron metabolism and play a role in the occurrence and development of viral infection-related diseases. Ferritin plays a crucial role in maintaining the body's iron homoeostasis. It is an important protein to stabilise the iron balance in cells. Ferritin is a 24-mer hollow iron storage protein composed of two subunits: ferritin heavy chain and ferritin light chain. It was reported that ferritin is not only an intra-cellular iron storage protein, but also a pathogenic mediator that enhances the inflammatory process and stimulates the further inflammatory pathway, which is a key member of the vicious pathogenic cycle to perpetuate. Ferritin exerts immuno-suppressive and pro-inflammatory functions during viral infection. In this review, we describe in detail the basic information of ferritin in the first section, including its structural features, the regulation of ferritin. In the second part, we focus on the role of ferritin in viral infection-related diseases and the molecular mechanisms by which viral infection regulates ferritin. The last section briefly outlines the potential of ferritin in antiviral therapy. Given the importance of iron and viral infection, understanding the role of ferritin during viral infection helps us understand the relationship between iron metabolic dysfunction and viral infection, which provides a new direction for the development of antiviral therapeutic drugs.

Ferritin nanocages as efficient nanocarriers and promising platforms for COVID-19 and other vaccines development

BACKGROUND

The development of safe and effective vaccines against SARS-CoV-2 and other viruses with high antigenic drift is of crucial importance to public health. Ferritin is a well characterized and ubiquitous iron storage protein that has emerged not only as a useful nanoreactor and nanocarrier, but more recently as an efficient platform for vaccine development.

SCOPE OF REVIEW

This review discusses ferritin structure-function properties, self-assembly, and novel bioengineering strategies such as interior cavity and exterior surface modifications for cargo encapsulation and delivery. It also discusses the use of ferritin as a scaffold for biomedical applications, especially for vaccine development against influenza, Epstein-Barr, HIV, hepatitis-C, Lyme disease, and respiratory viruses such as SARS-CoV-2. The use of ferritin for the synthesis of mosaic vaccines to deliver a cocktail of antigens that elicit broad immune protection against different viral variants is also explored.

MAJOR CONCLUSIONS

The remarkable stability, biocompatibility, surface functionalization, and self-assembly properties of ferritin nanoparticles make them very attractive platforms for a wide range of biomedical applications, including the development of vaccines. Strong immune responses have been observed in pre-clinical studies against a wide range of pathogens and have led to the exploration of ferritin nanoparticles-based vaccines in multiple phase I clinical trials.

GENERAL SIGNIFICANCE

The broad protective antibody response of ferritin nanoparticles-based vaccines demonstrates the usefulness of ferritin as a highly promising and effective approaches for vaccine development.