Nanoparticles in biomedicine: new insights from plant viruses

In recent years there has been an outburst of interest regarding the employment of nanoparticles for biomedical applications. Among the different types, such as metallic, organic, biological and hybrid systems, virus based nanoparticles have become a popular field of research. Viruses are able to form organized structures by molecular self assembly of repetitive building blocks, which implies non covalent interactions of protein monomers to form the quaternary structure of viral capsids. Plant virus based systems, in particular, are among the most advanced and exploited for their potential use as bioinspired structured nanomaterials and nanovectors. Plant viruses have a size particularly suitable for nanoscale applications and can offer several advantages. In fact, they are structurally uniform, robust, biodegradable and easy to produce. Moreover, many are the examples regarding functionalization of plant virus based nanoparticles by means of modification of their external surface and by loading cargo molecules into their internal cavity. This plasticity in terms of nanoparticles engineering is the ground on which multivalency, payload containment and targeted delivery can be fully exploited. This review aims primarily to summarize the most important plant virus based nanoparticles systems through their recent applications in biomedicine, such as epitope display for vaccine development and targeted delivery for diagnosis or therapy. In addition, their production in the most commonly used plant propagation and expression systems will be also reviewed.