Over the past decade, researchers have found that [[neural stem cell]]s (NSCs) migrate toward inflammatory sites, including tumors. This insight has inspired research into genetic engineering of human NSCs to express enzymes such as [[cytosine deaminase]] (CD) and [[thymidine kinase]] (TK). These enzymes enable these cells to convert the nontoxic prodrugs 5-fluorocytosine (5FC) and ganciclovir (GCV) into oncolytic 5-fluorouracil and GCV-triphosphate, respectively.