Yaba-Like Disease Virus: an Alternative Replicating Poxvirus Vector for Cancer Gene Therapy

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Abstract
Vaccinia virus is being investigated as a replicating vector for tumor-directed gene therapy. However, the majority of cancer patients have preformed immunologic reactivity against vaccinia virus, as a result of smallpox vaccination, which may limit its use as a vector. The Yaba-like disease (YLD) virus was investigated here as an alternative, replicating poxvirus for cancer gene therapy. We have demonstrated that the YLD virus does not cross-react with vaccinia virus antibodies, and it replicates efficiently in human tumor cells. YLD virus can be expanded and purified to high titer in CV-1 cells under conditions utilized for vaccinia virus. The YLD virus RNA polymerase was able to express genes regulated by a synthetic promoter designed for use in orthopoxviruses. We sequenced the YLD virus TK gene and created a shuttle plasmid, which allowed the recombination of the green fluorescent protein (GFP) gene into the YLD virus. In a murine model of ovarian cancer, up to 38% of cells in the tumor expressed the GFP transgene 12 days after intraperitoneal virus delivery. YLD virus has favorable characteristics as a vector for cancer gene therapy, and this potential should be explored further.