Herpes simplex virus thymidine kinase suicide gene system (HSV-TK suicide gene system)

The herpes simplex virus thymidine kinase suicide gene system is a gene therapy approach that utilizes the HSV-TK enzyme as a safety and control mechanism in cellular therapies. HSV-TK, encoded by the herpesvirus gene, is expressed in target cells (such as donor T lymphocytes or tumor cells) via genetic modification. When a non-toxic prodrug (typically ganciclovir) is administered, only cells expressing HSV-TK convert ganciclovir to its active triphosphate form, which is incorporated into DNA during replication and causes DNA damage, leading to apoptotic cell death. This selective killing allows clinicians to ablate problematic therapeutic cells upon demand (such as in graft-versus-host disease, or cancer therapy), increase safety of gene or cell therapy, and exert a bystander effect beneficial in eliminating neighboring tumor cells. The system is extensively validated in preclinical and clinical settings for cancer and variable cellular therapies, but faces challenges including transgene expression efficiency, immune responses, and control of off-target toxicities.

Other names

HSV-TK/ganciclovir systemTK/GCV systemThymidine kinase suicide geneHerpesvirus thymidine kinase gene therapy

The HSV thymidine kinase enzyme phosphorylates the prodrug ganciclovir, converting it to ganciclovir triphosphate, which causes chain termination and DNA strand breaks when incorporated during DNA synthesis in dividing cells, leading to apoptosis. Selective cell killing: Only cells expressing HSV-TK are sensitized to ganciclovir-mediated death. Bystander effect: Cytotoxic metabolites or immune mechanisms also kill adjacent non-transduced cells.