The use of animal virus-like particles (VLPs) as vectors for the delivery of genes to mammalian cells has been explored for many years. Plant viruses are almost without exception “just” genetic material (DNA or RNA) surrounded by a shell composed of the capsid protein (CP) – with no membrane envelope. Plant-derived VLPs have not been used for direct gene delivery and expression. There have been no attempts to use a spherical plant viral capsid to deliver heterologous genes for expression in mammalian cells, even though there are several independent demonstrations of the internalization of plant virus by cells.
In light of there being no direct demonstration of spherical plant viruses disassembling and thereby releasing their contents in animal cells, this paper asks the question: Can heterologous genes in spherical plant VLPs be made available to a mammalian cell and their protein products synthesized?
Getting RNA into cells is a major barrier to future theraputic approaches, so robust systems are urgently needed.
Reconstituted plant viral capsids can release genes to mammalian cells. Virology. 19 April 2013 doi: 10.1016/j.virol.2013.03.001
The nucleocapsids of many plant viruses are significantly more robust and protective of their RNA contents than those of enveloped animal viruses. In particular, the capsid protein (CP) of the plant virus Cowpea Chlorotic Mottle Virus (CCMV) is of special interest because it has been shown to spontaneously package, with high efficiency, a large range of lengths and sequences of single-stranded RNA molecules. In this work we demonstrate that hybrid virus-like particles, assembled in vitro from CCMV CP and a heterologous RNA derived from a mammalian virus (Sindbis), are capable of releasing their RNA in the cytoplasm of mammalian cells. This result establishes the first step in the use of plant viral capsids as vectors for gene delivery and expression in mammalian cells. Furthermore, the CCMV capsid protects the packaged RNA against nuclease degradation and serves as a robust external scaffold with many possibilities for further functionalization and cell targeting.