Paramyxovirus-based production of Rift Valley fever virus replicon particles

Replicon-particle-based vaccines combine the efficacy of live-attenuated vaccines with the safety of inactivated or subunit vaccines. Recently, we developed Rift Valley fever virus (RVFV) replicon particles, also known as nonspreading RVFV (NSR), and demonstrated that a single vaccination with these particles can confer sterile immunity in target animals. NSR particles can be produced by transfection of replicon cells, which stably maintain replicating RVFV S and L genome segments, with an expression plasmid encoding the RVFV glycoproteins, Gn and Gc, normally encoded by the M-genome segment. Here, we explored the possibility to produce NSR with the use of a helper virus. We show that replicon cells infected with a Newcastle disease virus expressing Gn and Gc (NDV-GnGc) were able to produce high levels of NSR particles. In addition, using reverse genetics and site-directed mutagenesis, we were able to create an NDV-GnGc variant that lacks the NDV fusion protein and contains two amino acid substitutions in, respectively, Gn and HN. The resulting virus uses a unique entry pathway that facilitates the efficient production of NSR in a one-component system. The novel system provides a promising alternative for transfection-based NSR production.