Recombinant, Replication-Defective Adenovirus Gene Transfer Vectors Induce Cell Cycle Dysregulation and Inappropriate Expression of Cyclin Proteins

First-generation adenovirus (Ad) vectors that had been rendered replication defective by removal of the E1 region of the viral genome (ΔE1) or lacking the Ad E3 region in addition to E1 sequences (ΔE1ΔE3) induced G₂ cell cycle arrest and inhibited traverse across G₁/S in primary and immortalized human bronchial epithelial cells. Cell cycle arrest was independent of the cDNA contained in the expression cassette and was associated with the inappropriate expression and increase in cyclin A, cyclin B1, cyclin D, and cyclin-dependent kinase p34^cdc2 protein levels. In some instances, infection with ΔE1 or ΔE1ΔE3 Ad vectors produced aneuploid DNA histogram patterns and induced polyploidization as a result of successive rounds of cell division without mitosis. Cell cycle arrest was absent in cells infected with a second-generation ΔE1Ad vector in which all of the early region E4 except the sixth open reading frame was also deleted. Consequently, E4 viral gene products present in ΔE1 or ΔE1ΔE3 Ad vectors induce G₂ growth arrest, which may pose new and unintended consequences for human gene transfer and gene therapy.