New Routes and Opportunities for Modular Construction of Particulate Vaccines: Stick, Click, and Glue

Abstract

Vaccines based on virus-like particles (VLPs) can induce potent B cell responses. Some non-chimeric VLP-based vaccines are highly successful licensed products (e.g., hepatitis B surface antigen VLPs as a hepatitis B virus vaccine). Chimeric VLPs are designed to take advantage of the VLP framework by decorating the VLP with a different antigen. Despite decades of effort, there have been few licensed chimeric VLP vaccines. Classic approaches to create chimeric VLPs are either genetic fusion or chemical conjugation, using cross-linkers from lysine on the VLP to cysteine on the antigen. We describe the principles that make these classic approaches challenging, in particular for complex, full-length antigens bearing multiple post-translational modifications. We then review recent advances in conjugation approaches for protein-based non-enveloped VLPs or nanoparticles, to overcome such challenges. This includes the use of strong non-covalent assembly methods (stick), unnatural amino acids for bio-orthogonal chemistry (click), and spontaneous isopeptide bond formation by SpyTag/SpyCatcher (glue). Existing applications of these methods are outlined and we critically consider the key practical issues, with particular insight on Tag/Catcher plug-and-display decoration. Finally, we highlight the potential for modular particle decoration to accelerate vaccine generation and prepare for pandemic threats in human and veterinary realms.

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

“…VLPs were initially exploited for homologous vaccination [i.e., recombinant hepatitis B surface antigen (HBsAg) VLP vaccine protects against Hepatitis B virus, HPV L1 antigen VLP vaccine against Human papilloma virus (11,12)], and have been increasingly investigated also as carrier for heterologous antigens (13). Various techniques are available to decorate VLPs with the antigen(s) of interest [extensively reviewed by Brune and Howarth (14)], such as genetic fusion, chemical derivatization and conjugation, or plug-and-display decoration. This latter technique is based on the isopeptide bond that spontaneously forms between a peptide and its protein couple, derived from specific domains of certain bacterial proteins (15)(16)(17).…”

Recombinant expression of nanobodies and nanobody-derived immunoreagents

“…In this case bacteria displayed the SpyTag that was available for binding to SpyCatcher-fused anti-GFP antibodies [96]. Of course, the method can be expanded by selecting nanobodies specific for other antigens and could be for instance used to decorate Virus Like-Particles with nanobodies suitable for improving their targeted delivery [97]. Nanobody display was exploited also for preparing Escherichia coli modified as tunable modular platforms for studying cell-cell adhesion and multicellular self-assembly [98].…”

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

“…In addition, these technologies allow for separate recombinant production of antigens in various expression systems, ensuring high quality and correct protein processing before CLP conjugation [39][40][41][42]. The different conjugation systems used for modular CLP vaccine development is described in detail elsewhere [43]. Here, the main techniques are listed in Table 1 to provide a comparative overview of their relative practicality and ability to facilitate a high-quality epitope display.…”