Just like a doctor adjusts the dose of a medication to the patient's needs, the expression of therapeutic genes, those modified in a person to treat or cure a disease via gene therapy, also needs to be maintained within a therapeutic window. Staying within the therapeutic window is important as too much of the protein could be toxic, and too little could result in a small or no therapeutic effect. Researchers now report on a technology to effectively regulate gene expression, a promising solution to fill this gap in gene therapy clinical applications.