Distribution of retroviral vectors and vector producer cells using two routes of administration in rats

The clinical use of retroviral vector producer cells (VPCs) to deliver retr oviral vectors efficiently to target cells has been investigated as a metho d to increase efficiency of gene delivery, presumably as a result of contin ued vector production in vivo. Studies were conducted in rats to evaluate t he distribution of vector to distal organs and tissues as measured by trans duction. Rats were treated with two doses of VPCs using two routes of admin istration: (1) subcutaneous injection, chosen to maximize both the dose and exposure of animals, thereby enabling identification of potential target o rgans under worst-case conditions; and (2) direct injection into brain pare nchyma, chosen to mimic the intended clinical route of administration and p rovide an estimate of risk to patients receiving this therapy. Twelve organ s or tissues were collected 7 days after administration of VPCs and analyze d by PCR for the presence of vector and vector producer cell sequences. Vec tor was detected most frequently at the site of injection by either route o f administration. Less frequently, vector was detected in draining lymph no des at the higher dose only using either route of injection. Single specime ns of lung and contralateral skin were positive for vector following subcut aneous administration only. Vector was detected in gonadal tissue from a si ngle low-dose male following subcutaneous administration, but this finding was not reproduced in any high-dose male or any males injected intracerebra lly. In contrast, VPCs were detected only at the site of administration. Th e frequency of detection of VPCs 7 days after administration was higher whe n rats were injected by the intracerebral route. Based on these studies, ge ne transfer to distal organs or gonadal tissue following intracerebral admi nistration of VPCs is not considered to be a risk to patients undergoing re troviral Vector gene therapy for the treatment of brain cancer (glioblastom a multiforme; GBM).