Viral vectors are scientific tools used to insert genes into cells. During a process known as transduction, the desired genes are delivered into the cells after. Viral vectors can be manufactured in an organism (in vivo) or in culture (in vitro) and a variety of viruses are commonly used to transduce cells, including adenovirus, lentivirus, retrovirus, and herpes simplex virus. Viral vectors are used as targeted gene therapies and in vaccine development.