Herpes simplex virus type 1 thymidine kinase mutant 2 (HSV1-TK Mut2)

Herpes simplex virus type 1 thymidine kinase mutant 2 (HSV1-TK Mut2) is an engineered viral enzyme used as a suicide gene or safety switch in cell-based therapies, most notably in allogeneic T-cell transplants [1, 2]. The enzyme's primary biological function is the phosphorylation of nucleosides; however, it is specifically utilized for its ability to convert non-toxic nucleoside analog prodrugs, such as ganciclovir, into cytotoxic metabolites [3, 6]. When ganciclovir is administered, HSV1-TK Mut2 phosphorylates it to ganciclovir monophosphate, which is then further processed by host cellular kinases into ganciclovir triphosphate [1, 3]. This active metabolite acts as a potent DNA polymerase inhibitor and chain terminator, inducing apoptosis in the cells expressing the enzyme [3, 9]. This system is clinically employed in therapies like Zalmoxis to provide a kill switch that allows for the selective elimination of donor T cells if they cause severe graft-versus-host disease (GvHD) [2, 5]. By enabling the controlled destruction of engineered cells, HSV1-TK Mut2 enhances the safety profile of adoptive immunotherapy and gene therapy applications [7, 11]. The Mut2 variant specifically features modifications, such as the removal of cryptic splice sites, to ensure stable and high-level expression in human cells [3, 11]. This target represents a critical tool in the management of complications arising from advanced cellular medicinal products [4, 10].

Other names

HSV-TK Mut2MM-TKSuicide geneHerpes simplex virus 1 thymidine kinase (mutated)HSV1-TK

The enzyme acts as a suicide gene by phosphorylating the prodrug ganciclovir into a monophosphate form, which is subsequently converted by host cell kinases into a toxic triphosphate that inhibits DNA synthesis and induces apoptosis.