ADENO—ASSOCIATED VIRAL VECTORS are derived from parvoviruses and used as a tool for delivering genetic material in gene therapy. Such therapy frequently uses stem cells because of their self—renewing properties, which eliminate the need for repeated delivery of therapeutic genes. Adeno—associated virus (AAV) causes no known illness and triggers only mild immune responses. The virus also infects both dividing and nondividing cells. Because stem cells are often quiescent, or nondividing, for long periods until activation, these vectors could provide a method for delivering therapeutic genes to engineer cells capable of proliferation and repairing damaged tissues and organs. AAV can also integrate into the genome of targeted cells, thus leading to long—term expression. However, the amount of integration is often small, which means the use of ...