A versatile papaya mosaic virus (PapMV) vaccine platform based on sortase-mediated antigen coupling

Abstract

BackgroundFlexuous rod-shaped nanoparticles made of the coat protein (CP) of papaya mosaic virus (PapMV) have been shown to trigger innate immunity through engagement of toll-like receptor 7 (TLR7). PapMV nanoparticles can also serve as a vaccine platform as they can increase the immune response to fused peptide antigens. Although this approach shows great potential, fusion of antigens directly to the CP open reading frame (ORF) is challenging because the fused peptides can alter the structure of the CP and its capacity to self assemble into nanoparticles—a property essential for triggering an efficient immune response to the peptide. This represents a serious limitation to the utility of this approach as fusion of small peptides only is tolerated.ResultsWe have developed a novel approach in which peptides are fused directly to pre-formed PapMV nanoparticles. This approach is based on the use of a bacterial transpeptidase (sortase A; SrtA) that can attach the peptide directly to the nanoparticle. An engineered PapMV CP harbouring the SrtA recognition motif allows efficient coupling. To refine our engineering, and to predict the efficacy of coupling with SrtA, we modeled the PapMV structure based on the known structure of PapMV CP and on recent reports revealing the structure of two closely related potexviruses: pepino mosaic virus (PepMV) and bamboo mosaic virus (BaMV). We show that SrtA can allow the attachment of long peptides [Influenza M2e peptide (26 amino acids) and the HIV-1 T20 peptide (39 amino acids)] to PapMV nanoparticles. Consistent with our PapMV structural model, we show that around 30% of PapMV CP subunits in each nanoparticle can be fused to the peptide antigen. As predicted, engineered nanoparticles were capable of inducing a strong antibody response to the fused antigen. Finally, in a challenge study with influenza virus, we show that mice vaccinated with PapMV-M2e are protected from infection.ConclusionsThis technology will allow the development of vaccines harbouring long peptides containing several B and/or T cell epitopes that can contribute to a broad and robust protection from infection. The design can be fast, versatile and can be adapted to the development of vaccines for many infectious diseases as well as cancer vaccines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-017-0289-y) contains supplementary material, which is available to authorized users.

Nanoparticle-Based Vaccines Against Respiratory Viruses

“…These N-nanorings are interesting for intranasal delivery of antigen due to their similarities with respiratory viruses in term of size and structure (sub-nucleocapsid-like superstructures). Other examples of SAPNs as potential nanovaccines against respiratory viruses include the capsid protein of the papaya mosaic virus (PapMV), the purified coronavirus spike protein and ferritin, which are selfassembling proteins that form rod-shaped and nearly spherical nanostructures, respectively (96,(130)(131)(132)(133)(134)(135)(136)(137)(138)(139)(140). Recently, assemblies composed of four tandem copies of M2e and headless HA proteins were prepared and stabilized by sulfosuccinimidyl propionate crosslinking, showing the possibility of generating protein nanoparticles almost entirely composed of the antigens of interest (141).…”

Better Adjuvants for Better Vaccines: Progress in Adjuvant Delivery Systems, Modifications, and Adjuvant–Antigen Codelivery

“…Sortase A is a class of enzyme found in gram-positive bacteria and is associated with protein modification through recognition of specific protein sequences (LPXTG motifs); thus, it can be used for site-directed modification of proteins [115][116][117][118]. Influenza M2e peptide was conjugated with PapMV coat-protein (CP) by Sortase A to obtain an antigen-adjuvant complex with good immune response [119]. In another study, the PapMV CP and full-length influenza nucleoprotein were covalently coupled with Sortase A, and the resulting complex induced stronger cellular and humoral immunity [120].…”

Designs of Antigen Structure and Composition for Improved Protein-Based Vaccine Efficacy

“…As opposed to traditional carbodiimide and maleimide conjugation techniques, click chemistry allows for rapid reaction kinetics, selective ligand attachment, and high yields of successfully utilized attachment sites (253). Sortase-mediated conjugation allows for the highly specific attachment of LPETG(G) tagged molecules to PBV bearing recombinantly inserted multi-glycine stretches, though coupling efficiencies (∼30%) tend to be low when using this technique (254,255). Polyhistidine (pHis) tags are well-known for ability to interact with immobilized metal ions in affinity chromatography applications.…”