Recombinant adeno-associated virus (rAAV) vectors are proving to be a valid, safe and efficient gene transfer system for clinical applications. As most vectors utilize constitutive promoters, this results in transgene expression in the producer cell. Some of these transgene products can induce proapoptotic, cytostatic or other unknown effects that interfere with producer cell function. Therefore, this reduces the viral vector yield and is a major limitation when trying to characterize poorly described genes. NIDCR developed a method of expression of the transgene product during the vector production in the produce cell but not in the target cell. This novel approach allowed the production of a vector with a proapoptotic transgene.