Virus-like particles: the new frontier of vaccines for animal viral infections

Abstract

Vaccination continues to be the main approach to protect animals from infectious diseases. Until recently, all licensed vaccines were developed using conventional technologies. Subunit vaccines are, however, gaining attention from researchers in the field of veterinary vaccinology, and among these, virus-like particles (VLPs) represent one of the most appealing approaches. VLPs are robust protein cages in the nanometer range that mimic the overall structure of the native virions but lack the viral genome. They are often antigenically indistinguishable from the virus from which they were derived and present important advantages in terms of safety. VLPs can stimulate strong humoral and cellular immune responses and have been shown to exhibit self-adjuvanting abilities. In addition to their suitability as a vaccine for the homologous virus from which they are derived, VLPs can also be used as vectors for the multimeric presentation of foreign antigens. VLPs have therefore shown dramatic effectiveness as candidate vaccines. Here, we review the current status of VLPs as a vaccine technology in the veterinary field, and discuss the potential advantages and challenges of this technology.

Fig. 1

Immunogenic features of a VLP presenting foreign antigens. VLPs incorporate key features that underlay their immunogenicity, safety and vaccine potential: (1) well-defined geometry and remarkable uniformity with repetitive and ordered surface structures; multivalent display and highly ordered structure of VLPs constitute PAMPs motifs common to many pathogens but not to the host that trigger innate immune sensing mechanism. PAMPs can be recognized by TLRs and other PRRs which are present in host cells; (2) particulate and multivalent nature; this feature means that VLPs are efficiently taken up by APCs. Their tendency to be a suitable size for uptake by DCs for processing and presentation by MHC-II and MHC-I (cross-presentation) pathways led to describe VLPs as “self-adjuvanting”; (3) preservation of native antigenic conformation; (4) safety for being non-infectious and non-replicating candidates; VLPs lack the DNA or RNA genome of the virus altogether eliminate any of the risks associated with virus replication, reversion, recombination or re-assortment; (5) higher stability than soluble antigens in extreme environmental conditions; (6) applicability as carriers of foreign epitopes; (7) possibility to follow the Differentiating Infected from Vaccinated Animals (DIVA)-compliance concerns.