Gene transfer by retroviral vectors: an overview.

Viruses have evolved to deliver their genetic cargo to cells and, due to the pathogenicity of some viruses, this process has been the subject of a great deal of study. In this respect, retroviruses came to the fore in the early 1900s with the demonstration by Ellermann and Bang and by Rous that chicken leukosis was caused by a virus, now referred to as avian sarcoma/leukosis virus (ASLV). This began a body of work that led to the identification of virus-induced tumors in mammalian species and retroviruses (as they are now called) were identified as the causative agents for a number of pathologies from tumors to acquired immunodefiencey syndrome (AIDS). Retroviruses were characterized as RNA viruses that replicate through a DNA intermediate. The study of retroviruses contributed and led to the elucidation of a number of diverse biological phenomena as the oncogenes carried by these viruses began to be identified as receptors, kinases, and transcription factors (3). The idea that these viruses could be used to ferry a gene of choice, rather than the viral genome, springs from the study of Rous sarcoma virus (RSV).