988. Effect of Lentiviral Promoter and Fetal Route of Administration on Transgene Biodistribution and Expression in Rhesus Monkeys (Macaca mulatta)

Fetal gene transfer is a promising therapy for the correction of pathology associated with inherited or acquired diseases, however information on the optimal conditions for gene transfer is limited. In this study, we have determined the effect of the time of gene transfer and route of administration on the efficiency of this approach. Fetal rhesus monkeys were injected intraperitoneal (IP) at 40 (N=4) or 60 (N=4) days of gestation (term 165±10 days) with 2 × 107 HIV-1-derived lentiviral vector particles/fetus (HIV/VSV-G/MND/EGFP) and gene marking and expression was assessed in multiple tissues (cerebrum, trachea, esophagus, thymus, lung, heart, pericardium, thorax, lymph nodes, liver, spleen, pancreas, kidneys, adrenals, gonads, stomach, colon, diaphragm, omentum, peritoneum, bone marrow) using quantitative real-time PCR. Results were compared to lentiviral vector gene transfer using the intrahepatic (IH) (N=4) and intraportal (Ipo) (N=4) routes of administration. Analysis revealed that gene transfer at 40 days gestation resulted in high gene marking in omentum (18%), peritoneum (1%) and diaphragm (5%) with levels up to 400-fold higher than in other abdominal organs. The amount of gene expression highly correlated (P < 0.0001) with the extent of gene transduction within the peritoneal cavity. We obtained similar vector biodistribution at 60 days gestation, and no significant differences in the amount of gene transfer (P < 0.005) were found between the groups. However, gene transfer and expression at 40 versus 60 days gestation in nonabdominal tissues were 3 - 20 and 4 - 400 - fold higher, respectively. When comparing IH to IP gene delivery, a similar vector biodistribution was found with no significant differences on the extent of gene transfer (P < 0.05) in all tissues examined. In contrast, Ipo administration resulted in a reduction of vector spread and a 200-fold reduction in the level of gene marking when compared to the IP route of administration. In conclusion, definition of the conditions at the time of fetal transfer will further shape the feasibility and safety of this approach for the treatment of human disease.