Over the past decade, researchers have found that neural stem cells (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.