In vitro-synthesized infectious RNA as an attenuated live vaccine in a flavivirus model

Live virus vaccines have in many cases proven to be an extremely effective tool for the prevention of viral diseases(1,2). However, the production of conventional live vaccines in eu; karyotic cell cultures has many disadvant ages, including the potential for contamination with adventitious agents(3) and genetic alterations during propagation, making it necessary to do exte nsive testing before distribution(4,5). Based on results obtained with a fl avivirus(6) (tick-borne encephalitis virus) in an experimental animal syste m, we propose a novel live attenuated virus vaccination strategy consisting of the application of in vitro-synthesized infectious RNA instead of the l ive virus itself. When administered using the GeneGun, less than 1 ng of RN A was required to initiate replication of virus that was attenuated by a sp ecifically engineered deletion(7) and this induced a protective immunity in laboratory mice. Because this approach uses RNA, it does not have the pote ntial drawbacks of DNA vaccines(8-10) and thus combines the advantages of c onventional live virus vaccines(1,2) (for example, mimicking natural infect ion and inducing long-lasting immunity) with those of nucleic acid-based va ccines(2,8,11,12) (for example, ease of production without a requirement fo r eukaryotic cell culture, stability and purity).