Complementation of helper-dependent adenoviral vectors: size effects and titer fluctuations.

The complementation of adenoviral vectors with large deletions in the viral genome was studied. The helper adenovirus used to complement these vectors contains a partial deletion of the packaging signal and the E1 region substituted by the lacZ gene. The effect of vector size on packaging efficiency was analysed in 293 cells using decreasingly shorter vectors expressing GFP from a CMV enhancer-beta-actin promoter. Vectors with longer genomes propagated more efficiently than shorter ones. Vectors containing only the packaging signal and the ITRs of Ad5, having all the viral genes replaced with unrelated sequences packaged as efficiently as vectors of the same size containing adenoviral DNA instead of exogenous DNA. The amounts of helper and vector produced in coinfected 293 cells exhibited the typical cycling fluctuation observed during serial propagation of a virus with defective interfering particles.