There are different reasons to do gene transfer. Perhaps foremost among these reasons is the treatment of diseases using gene transfer to supply patients with therapeutic genes. There are also different ways to transfer genes. Some of these methods involve the use of a vector such as a virus that has been specifically modified so it can take the gene along with it when it enters the cell.
For example, gene transfer may help treat type 1 diabetes (which is due to failure of the pancreas to produce enough insulin). Among the key factors that decide whether the gene for insulin is turned on or off is the gene PDX-1. Using a vector virus the PDX-1 gene has been transferred (into mice) where the gene is expressed by liver cells which now produce insulin. Gene transfer of PDX-1 may reprogram tissues other than the pancreas to make insulin and control the abnormally high blood sugar levels in diabetes.