BACKGROUNDSuicide gene therapy is a widely used molecular treatment for head and neck cancer. In this study, we try to use the method of homogenous recombination in bacteria to clone thymidine kinase gene (tk)-a kind of suicide gene to adenovirus backbone vectors for the construction of replication-defective adenoviruses.

METHODSpAdTrack-CMV/tk was constructed through subclone of a restriction endonuclease fragment including thymidine kinase gene from plasmid pCMV-tk to another plasmid pAdTrack-CMV, and then co-transfected with supercoiled pAdEasy-1, which was an adenoviral backbone vector except for deletions of E1 and E3, to competent E. coli BJ5183 for homogenous recombination using electroporation procedure. With the same method, pAdTrack-CMV was also co-transformed with pAdEasy-1 for homogenous recombination in BJ5183. Identified with restriction endonuclease PacI and polymerase chain reaction (PCR), plasmids pAd-GFP/tk and pAd-GFP were successfully constructed. Each of them was digested with PacI and sequently transfected into human embryo kidney 293 cells (HEK293) using Lipofectamine 2000.

RESULTSComet-like adenovirus-producing foci of Ad-GFP/tk and Ad-GFP were observed after 5 to 7 days of cell culture. After twelve days of packaging, the replication-defective adenoviruses were collected. Identified with PCR, thymidine kinase gene was successfully constructed into Ad-GFP/tk.

CONCLUSIONThe replication-defective adenoviruses containing thymidine kinase can be constructed more easily by homogenous recombination in bacteria than conventional techniques.