Biodistribution of LV-TSTA Transduced Rat Bone Marrow Cells Used for “Ex-vivo” Regional Gene Therapy for Bone Repair

“Ex vivo” regional gene therapy using lentiviral (LV) vectors to over-express bone morphogeneticprotein 2 (BMP-2) is an effective way to enhance bone healing in animal models. Here, weevaluated two different “ex vivo” approaches using either “same day” rat bone marrow cells (SDRBMCs)or cultured rat bone marrow cells (C-RBMCs), both transduced with a LV based two-steptranscriptional activation system overexpressing GFP (LV-TSTA-EGFP), to assess the fate of thetransduced cells and the safety of this approach. The transduced cells were implanted in femoral defects of syngeneic rats.Animals were sacrificed at 4, 14, 28 and 56 days after surgery (n=5 per group). Viral copies were detectable in the defectsite of SD-RBMC group and gradually declined at 8w (5 log decrease compared to 4d). In the C-RBMC animals, therewas a 2-4 log decline in the viral copy numbers at 2w and 4w, but at 8w there was a relative rise (about 100 fold) in thenumber of the viral vectors in the defect site of 4 (out of 5) animals compared to the previous time points. For both genetransfer approaches, the pattern of tissue distribution was non-specific and no histological abnormalities were noted in eithergroup. In summary, we demonstrated that the LV-TSTA transduced cells remain in the defect site for at least 56 days,though the numbers decreased over time. There were no consistent findings of viral copies in internal organs which is encouragingwith respect to the development of this strategy for use in humans.