In vitro inhibition of CSFV replication by retroviral vector-mediated RNA interference

Classical swine fever (CSF) is a highly contagious viral disease of pigs which causes major economic losses worldwide. No specific drug is currently available for the effective treatment of CSFV infection. RNA interference (RNAi) technology depends on effective delivery systems, for which several effective vectors have recently been developed. Three retroviral plasmids containing siRNA genes targeting different regions of N(pro) and NS4A have been constructed, and 3 replication-incompetent retroviral vectors have been produced in the human embryo kidney cell line GP2-293 by retroviral plasmid transfection. PK-15 cells were then infected with these replication-incompetent retroviral vectors and screened for siRNA stably expressing PK-15 cell clones. Growth of CSFV in such siRNA stably expressing cell clones resulted in a 186-fold reduction in viral genome copies and, at 72 h post-infection, only a small % of cells showed infection by indirect immunofluorescence microscopy, and effective inhibition of virus replication persisted for up to 120 h. Retroviral vector-mediated RNAi can therefore be used to study the specific function of viral genes associated with CSFV replication and may have potential therapeutic application.