Protection against Rift Valley fever virus infection in mice upon administration of interferon-inducing RNA transcripts from the FMDV genome

In this work we have addressed the effect of synthetic, non-infectious, RNA transcripts, mimicking structural domains of the non-coding regions (NCRs) of the foot-and-mouth disease virus (FMDV) genome on the infection of mice with Rift Valley fever virus (RVFV). Groups of 5 mice were inoculated intraperitoneally (i.p.) with 200 μg of synthetic RNA resembling the 5′-terminal S region, the internal ribosome entry site (IRES) or the 3′-NCR of the FMDV genome. RNA inoculation was performed 24 h before (−24 h), 24 h after (+24 h) or simultaneously to the challenge with a lethal dose of RVFV. Administration of the IRES RNA afforded higher survival rates than administration of S or 3′NCR transcripts either at −24 h or +24 h after challenge. In contrast, when RNA inoculation and viral challenge were performed simultaneously, all mice survived in both IRES- and 3′NCR-inoculated groups, with an 80% survival in mice receiving the S RNA. Among survivors, a complete correlation between significant anti-RVFV circulating antibody titers and resistance to a second lethal challenge with the virus was observed, supporting a limited viral replication in the RNA-inoculated animals upon the first challenge. All three RNA transcripts were able to induce the production of systemic antiviral and pro-inflammatory cytokines. These data show that triggering of intracellular pathogen sensing pathways constitutes a promising approach towards development of novel RVF preventive or therapeutic strategies.