A high throughput in vivo model for testing delivery and antiviral effects of siRNAs in vertebrates

Despite the promise of small interfering RNAs (siRNAs) in antiviral therapy, few in vivo studies of them as inhibitors of viral replication and disease have been published, a lack that is most probably due to problems with obtaining successful delivery. Here we introduce a novel in vivo model composed of small juvenile rainbow trout and a fish pathogenic virus to analyze the delivery and antiviral effects of formulated siRNAs. Intraperitoneally (IP) injected siRNAs formulated in polycationic liposomes, and to a lesser degree naked siRNAs, primarily entered free IP cells, including macrophage-like cells. Uptake in these cells correlated with antiviral activity, seen as reduced mortality of virus-challenged fish. However, protection at the disease level was not dependent upon which of three tested siRNAs was used, and protection correlated with up-regulation of an interferon (IFN)-related gene in the liver, indicating a systemic IFN response. The results emphasize the compromise in using transfection reagents for improved uptake of siRNAs, where these reagents also increase the risk of the siRNAs ending up in a cellular compartment in which stimulation of nonspecific anti-viral defence mechanisms will be initiated.