Modulation of Antigen Display on PapMV Nanoparticles Influences Its Immunogenicity

Convenient Auto-Processing Vector Based on Bamboo Mosaic Virus for Presentation of Antigens Through Enzymatic Coupling

We have developed a new binary epitope-presenting CVP platform based on bamboo mosaic virus (BaMV) by using the sortase A (SrtA)-mediated ligation technology. The reconstructed BaMV genome harbors two modifications: 1) a coat protein (CP) with N-terminal extension of the tobacco etch virus (TEV) protease recognition site plus 4 extra glycine (G) residues as the SrtA acceptor; and 2) a TEV protease coding region replacing that of the triple-gene-block proteins. Inoculation of such construct, pKB5G, on Nicotiana benthamiana resulted in the efficient production of filamentous CVPs ready for SrtA-mediated ligation with desired proteins. The second part of the binary platform includes an expression vector for the bacterial production of donor proteins. We demonstrated the applicability of the platform by using the recombinant envelope protein domain III (rEDIII) of Japanese encephalitis virus (JEV) as the antigen. Up to 40% of the BaMV CP subunits in each CVP were loaded with rEDIII proteins in 1 min. The rEDIII-presenting BaMV CVPs (BJLPET5G) could be purified using affinity chromatography. Immunization assays confirmed that BJLPET5G could induce the production of neutralizing antibodies against JEV infections. The binary platform could be adapted as a useful alternative for the development and mass production of vaccine candidates.

Influenza vaccine: progress in a vaccine that elicits a broad immune response

INTRODUCTION

The licensed seasonal influenza vaccines predominantly induce neutralizing antibodies against immunodominant hypervariable epitopes of viral surface proteins, with limited protection against antigenically distant influenza viruses. Strategies have been developed to improve vaccines' performance in terms of broadly reactive and long-lasting immune response induction.

AREAS COVERED

We have summarized the advancements in the development of cross-protective influenza vaccines and discussed the challenges in evaluating them in preclinical and clinical trials. Here, the literature regarding the current stage of development of universal influenza vaccine candidates was reviewed.

EXPERT OPINION

Although various strategies aim to redirect adaptive immune responses from variable immunodominant to immunosubdominant antigens, more conserved epitopes are being investigated. Approaches that improve antibody responses to conserved B cell epitopes have increased the protective efficacy of vaccines within a subtype or phylogenetic group of influenza viruses. Vaccines that elicit significant levels of T cells recognizing highly conserved viral epitopes possess a high cross-protective potential and may cover most circulating influenza viruses. However, the development of T cell-based universal influenza vaccines is challenging owing to the diversity of MHCs in the population, unpredictable degree of immunodominance, lack of adequate animal models, and difficulty in establishing T cell immunity in humans.

ABBREVIATIONS

cHA: chimeric HA; HBc: hepatitis B virus core protein; HA: hemagglutinin; HLA: human leucocyte antigen; IIV: inactivated influenza vaccine; KLH: keyhole limpet hemocyanin; LAH: long alpha helix; LAIV: live attenuated influenza vaccine; M2e: extracellular domain of matrix 2 protein; MHC: major histocompatibility complex; mRNA: messenger ribonucleic acid; NA: neuraminidase; NS1: non-structural protein 1; qNIV: quadrivalent nanoparticle influenza vaccine; T_RM: tissue-resident memory T cells; VE: vaccine effectiveness; VLP: virus-like particles; VSV: vesicular stomatitis virus.

A Replicating Viral Vector Greatly Enhances Accumulation of Helical Virus-Like Particles in Plants

The production of plant helical virus-like particles (VLPs) via plant-based expression has been problematic with previous studies suggesting that an RNA scaffold may be necessary for their efficient production. To examine this, we compared the accumulation of VLPs from two potexviruses, papaya mosaic virus and alternanthera mosaic virus (AltMV), when the coat proteins were expressed from a replicating potato virus X- based vector (pEff) and a non-replicating vector (pEAQ-HT). Significantly greater quantities of VLPs could be purified when pEff was used. The pEff system was also very efficient at producing VLPs of helical viruses from different virus families. Examination of the RNA content of AltMV and tobacco mosaic virus VLPs produced from pEff revealed the presence of vector-derived RNA sequences, suggesting that the replicating RNA acts as a scaffold for VLP assembly. Cryo-EM analysis of the AltMV VLPs showed they had a structure very similar to that of authentic potexvirus particles. Thus, we conclude that vectors generating replicating forms of RNA, such as pEff, are very efficient for producing helical VLPs.