Cerepro harnesses an adenovirus, a type of virus which carries its DNA in double-stranded form, to transmit a gene responsible for the production of a protein called thymidine kinase.

This paper introduce the differences in thymidine kinase (tk) isoenzymes and the relation of them to cancer and cell cycle as well as the progress of gene-therapy of cancer based on tk gene.

Thymidine kinase gene is found in herpes simplex virus.