Reconstituted plant viral capsids can release genes to mammalian cells.

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.