Neurovirulent flavivirus can be attenuated in mice by incorporation of neuron-specific microRNA recognition elements into viral genome.

Engineering viruses by inserting microRNA (miRNA) recognition elements (MREs) into the 3'-untranslated region (3'-UTR) of viral RNA can efficiently restrict viral tissue tropism. We used the mosquito-borne Japanese encephalitis virus (JEV) to investigate whether endogenous neuron-specific microRNA-124 (miR-124) could be used to restrict viral neurotropism and, consequently, diminish the neurovirulence of JEV in mice. To recover a neuron-restricted JEV, we inserted 2 copies of a perfectly matched MRE specific to miR-124 into the 3'-UTR to create infectious JEV recombinant RP-124PT (rRP-124PT). The effect of rRP-124PT was attenuated in infected mice as compared with MRE mutant and parental strains, both of which were lethal to challenged mice. Immunization with rRP-124PT appeared to elicit full protective immunity against subsequent JEV lethal challenge. We found neurons of the central nervous system critical targets for infection by JEV, which directly causes lethal encephalitis. The silencing of JEV rRP-124PT in mice by miR-124 illustrates that endogenous miRNA can readily recognize and interact with the 3'-UTR of naturally occurring genomic/mRNAs lacking a polyadenylated tail. Inserting MREs into viral RNA may facilitate further study of flaviviral pathogenesis involving tissue tropism and suggest an additional layer of biosafety for the rational design of safe flavivirus vaccines.