Whilst there are no reported recombinant OVs armed with IDO pathway inhibitors, in human glioma cells infected with either a wild-type oncolytic HSV strain (KOS) or one edited to remove a viral virulence gene (ICP0) designed to counteract the normal IFNγ response (JD05), IFNγ-induced IDO production was found to be almost completely abrogated [182]. This evidence concerns the gene IDO1 and central nervous system cancer.