Replication competent retrovirus testing (rcr) in the national gene vector biorepository: no evidence of rcr in 1595 post-treatment peripheral blood samples obtained from 60 clinical trials.

The clinical impact of any therapy requires the product be safe and effective. Gammaretroviral vectors pose several unique risks, including inadvertent exposure to replication competent retrovirus (RCR) that can arise during vector manufacture. The US FDA has required patient monitoring for RCR, and the National Gene Vector Biorepository is a NIH resource that has assisted eligible investigators in meeting this requirement. To date, we have found no evidence of RCR in 338 pre-treatment and 1595 post-treatment blood samples from 737 patients associated with 60 clinical trials. Most samples (75%) were obtained within one year of treatment, and samples as far out as 9 years post treatment were analyzed. The majority of trials (93%) were cancer immunotherapy, and 90% of the trials used vector products produced with the PG13 packaging cell line. The data presented here provide further evidence that current manufacturing methods generate RCR-free products and support the overall safety profile of retroviral gene therapy.