Briefing Document — Testing for Replication Competent Retrovirus (RCR)/Lentivirus (RCL) in Retroviral and Lentiviral Vector Based Gene Therapy Products — Revisiting Current FDA Recommendations

Vectors derived from retroviruses, such as MLV-based gammaretroviral vectors, have been used to introduce therapeutic genes into target cells in various clinical gene transfer applications (Hu and Pathak 2000). The stable integration of the vector provides the theoretical potential for long term therapeutic gene expression and may offer persistent beneficial clinical effects in treated patients. Lentiviral based vectors, such as HIV-1 based vectors, have also been used in clinical trials over the last few years. Lentiviral vectors are able to transduce non-dividing cells more efficiently and therefore may also be used for transduction of more quiescent or more differentiated cells or tissue types (Fassati 2006).