ABSTRACT
In nature, viruses appear to be ubiquitous. Most viruses are harmless to humans. Relatively little is known about the viral biosphere. The kingdoms of life, often divided into six types (Animalia, Plantae, Fungi, Protoctista, Monera, and Archea) do not include viruses, which are much smaller and less complex than cells. Most viruses are unknown; known viruses range in size from about 20 to about 400 nm. Based on their size and biological function, viruses are quintessential nanoparticles. They have evolved to invade host cells and to evade cell and organism defenses, ultimately delivering their cargo to cells. Used as tools for biomedicine, viruses could theoretically deliver drugs, other small molecules, proteins, RNA, DNA, or other payloads to targeted cells. However, viruses can also cause an infection or an acute immune reaction that can be fatal. Despite the progress made in the fi eld of adenovirus and other targeting viruses, it may prove impractical to use these mammalian infecting virus vectors for medical applications, due to the potential risks. This is a major reason to consider plant viruses as a potential alternative for biomedical applications. Plant viruses do not infect mammalian cells. On the other hand, they have desirable features that may be harnessed for drug delivery, gene therapy, diagnostic imaging and a range of other biomedical applications. In addition, targeting ability may be added to plant viruses by chemical modifi cation, genetic mutation or adaptor binding proteins to enable certain biomedical applications.
