AbstractMost of the approved clinical trials of human gene therapy are based on vectors derived form retroviruses. For some retroviruses, such as murine leukemia virus, the life cylcel and means of gene regulation are well understood, and provirus sequences have been cloned. Cell lines that allow the generation of high‐titer retroviral vectors without helper virus contamination have been established. Vectors generated from such cell lines are infectious and can efficiently deliver the gene of interest into the target cells. Because virus‐specific genes are deleted from these vectors, further spread of the vectors is prevented. Retrovirus‐mediated gene transfer has been tested in human clinical trials for the treatment of the inherited deficiency of adenosine deaminase and the inherited deficiency of low‐density lipoprotein receptor. Preliminary results from both trials demonstrate the feasiblility and potential efficacy of using gene therapy to treat human diseases. © 1995 Wiley