Toca 511 (vocimagene amiretrorepvec) is an RRV carrying a modified yeast-derived cytosine deaminase gene (CD) that integrates into the tumor cell genome and converts systemically delivered pro-drug, 5-fluorocytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) [124]. The gene discussed is CTLA4; the disease is neoplasm.