Medical Genetics Besides virus-mediated gene delivery systems there are several nonviral options for gene delivery The simplest method is the direct introduction of therapeutic DNa into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of dNAMedical Genetics Besides virus-mediated gene￾delivery systems, there are several nonviral options for gene delivery. The simplest method is the direct introduction of therapeutic DNA into target cells. This approach is limited in its application because it can be used only with certain tissues and requires large amounts of DNA