Adenoviral vectors have the potential to be extremely valuable tools for human gene therapy. It has been used to infect many mammalian cell types (both replicative and non-replicative) for high expression of the recombinant protein. Recombinant adenoviruses are especially useful for gene transfer and protein expression in cell lines. During adenovirus vector production, particles may be generated which are replication competent through recombination with host sequences or by contamination.