Herpes simplex virus 1 thymidine kinase (HSV-TK) (HSV-TK)

Herpes simplex virus 1 thymidine kinase (HSV-TK) is a viral enzyme widely utilized in gene and cell therapy as a safety switch or suicide gene. In the specific context of FailSafe Cells, the HSV-TK gene is genetically linked to an essential cell-cycle gene (such as CDK1) within pluripotent stem cells, ensuring that the suicide trigger is constitutively expressed in all proliferating progeny (Liang et al., 2018, Nature Communications). The enzyme possesses a unique substrate specificity that allows it to monophosphorylate nucleoside analogs like ganciclovir (GCV) much more efficiently than mammalian thymidine kinases. Once monophosphorylated, endogenous cellular kinases further convert the drug into GCV-triphosphate, which incorporates into nascent DNA strands, leading to DNA polymerase inhibition, double-strand breaks, and subsequent apoptosis (UniProt P03176). This pharmacological safeguard allows for the selective elimination of transplanted cells if they undergo malignant transformation or cause adverse effects such as graft-versus-host disease. Beyond its role in regenerative medicine safety, HSV-TK has been extensively studied in oncology as a method to sensitize tumor cells to antiviral therapy (Fillat et al., 2003, Current Gene Therapy).

Other names

HSV1-TKThymidine kinase 1 (viral)Suicide geneHSV-tkTK_HHV11

HSV-TK phosphorylates the prodrug ganciclovir into ganciclovir monophosphate, which is subsequently converted by host cell kinases into ganciclovir triphosphate; this metabolite acts as a deoxyguanosine triphosphate analog that incorporates into DNA, causing chain termination and apoptosis.