Most strategies for developing virus-resistant transgenic cells and animals are based on the concept of virus-derived resistance, in which dysfunctional virus-derived products are expressed to interfere with the pathogenic process of the virus in transgenic cells or animals. However, these viral protein targeting approaches are limited because they only target specific viruses and are susceptible to viral mutations.
A new paper describes a novel strategy that targets the viral genome rather than virus gene products to generate virus-resistant transgenic cells and animals. A synthetic mini antibody (3D8 scFv), which has both DNase and RNase activities, was expressed in HeLa cells and transgenic mice. The authours found that the transgenic cells and mice acquired complete resistance to two DNA viruses and showed delayed onset of disease symptoms.
The antiviral effects against DNA viruses demonstrated in this study were caused by (1) DNase activity of the antibody in the nucleus, which inhibited DNA replication or RNA transcription and (2) antibody RNase activity in the cytoplasm, which blocked protein translation. This strategy might allow control of a broad spectrum of viruses, including viruses uncharacterized at the molecular level, regardless of their genome type or variations in gene products.
A Nucleic-Acid Hydrolyzing Single Chain Antibody Confers Resistance to DNA Virus Infection in HeLa Cells and C57BL/6 Mice. (2014) PLOS Pathog 10(6): e1004208. doi:10.1371/journal.ppat.1004208
Viral protein neutralizing antibodies have been developed but they are limited only to the targeted virus and are often susceptible to antigenic drift. Here, we present an alternative strategy for creating virus-resistant cells and animals by ectopic expression of a nucleic acid hydrolyzing catalytic 3D8 single chain variable fragment (scFv), which has both DNase and RNase activities. HeLa cells (SCH7072) expressing 3D8 scFv acquired significant resistance to DNA viruses. Virus challenging with Herpes simplex virus (HSV) in 3D8 scFv transgenic cells and fluorescence resonance energy transfer (FRET) assay based on direct DNA cleavage analysis revealed that the induced resistance in HeLa cells was acquired by the nucleic acid hydrolyzing catalytic activity of 3D8 scFv. In addition, pseudorabies virus (PRV) infection in WT C57BL/6 mice was lethal, whereas transgenic mice (STG90) that expressed high levels of 3D8 scFv mRNA in liver, muscle, and brain showed a 56% survival rate 5 days after PRV intramuscular infection. The antiviral effects against DNA viruses conferred by 3D8 scFv expression in HeLa cells as well as an in vivo mouse system can be attributed to the nuclease activity that inhibits viral genome DNA replication in the nucleus and/or viral mRNA translation in the cytoplasm. Our results demonstrate that the nucleic-acid hydrolyzing activity of 3D8 scFv confers viral resistance to DNA viruses in vitro in HeLa cells and in an in vivo mouse system.