Abstract: This invention generally relates to the field of somatic gene therapy. The invention provides a nucleic acid construct comprising a transgene encoding a therapeutic protein, a tetracycline-responsive aptazyme sequence, and inverted terminal repeats (ITRs). The nucleic acid construct can be transferred to a subject in need thereof in the form of a viral vector, in particular an adeno-associated virus (AAV) vector. The Tet-responsive aptazyme sequence allows for a tightly controlled expression of the transgene in the subject, thereby avoiding toxic side effects. The nucleic acid construct and the viral vectors comprising same are particularly useful in the treatment of proliferative diseases like cancer.