Construction of adenoviral vectors

Recombinant adenovirus vectors have proven to be useful tools in facilitating gene transfer. Construction of such vectors requires a knowledge of the adenovirus genome structure and its life cycle. A commonly used recombinant adenovirus involves deletion of the E1 region; such a recombinant is traditionally produced by overlap recombination after cotransfection of 293 cells with a plasmid shuttle vector and a large right-end restriction fragment of viral DNA. The shuttle vector contains a cassette for a transgene placed in region E1 and flanking sequences from adenovirus for recombination. Normally, a high background of parental virus results because of the difficulty in separating right-end restriction fragment length DNA from uncut DNA. This paper describes a negative selection based on the traditional cotransfection method using viral DNA from an E1-deleted adenoviral recombinant that expresses green fluorescent protein (GFP). In situ fluorescent microscopy is used to distinguish the recombinant plaques (white or nonfluorescent) from the parental virus plaques (green or fluorescent). In addition, this system allows for the detection of contaminating parental virus at later stages when production lots of the recombinant vector are being made.