Persistent postnatal transgene expression in both muscle and liver after fetal injection of recombinant adenovirus

Background/Purpose: Immune responses to both vector and transgene antigens have limited the efficacy of postnatal gene therapy. We hypothesize that th e fetal period may offer immunologic and developmental advantages for succe ssful gene therapy. in this study we examined the efficacy, persistence, an d immunologic effects of recombinant adenovirus after intramuscular deliver y into fetal mice. Methods: E1-deleted adenovirus (AdCMVlacZ) containing the beta-galactosidas e marker gene was used for injection. Fetal Balb/c mice (14 to 15 days' ges tation) were injected with AdCMVlacZ in 10-mu L volume in either the should er or hindlimb musculature. Animals were killed at 18 to 20 days' gestation and up to 4 months postnatally for analysis of transgene expression and ad enoviral genome persistence. Results: Fetuses were injected with doses of AdCMVlacZ from 1 X 10(8) to 2 X 10(10) viral particles (n = 80). Optimal survival rate was 83% at 18 to 2 0 days' gestation and 55% at 4 weeks of age using a dose of 1 x 10(9) parti cles. Expression of beta-galactosidasae at 18 to 20 days localized to multi ple muscle groups surrounding the site of injection, as well as bone marrow stroma, liver, lung, and dorsal root ganglia. Persistent muscle and liver transgene expression was observed for as long as 16 and 8 weeks, respective ly, after injection. The pattern of liver expression was confined to discre te foci of hepatocytes, which appeared to increase in size in older animals . No histological evidence of muscle or liver inflammation was observed at any time after injection. No neutralizing antibodies were observed postnata lly. Conclusions: Our results confirm that gene therapy in the fetus may be adva ntageous. Distribution of vector in the fetus at the site of injection is c learly broader than in the adult setting. Furthermore, the absence of immun e response and persistence of transgene expression suggests that feta I exp osure to foreign transgene and vector antigens may induce tolerance. Althou gh we have not proven genomic integration, the histological appearance of t ransgene expression in the liver supports this conclusion. By understanding the mechanisms that underlie persistent transgene expression, fetal gene t herapy may become a feasible strategy for the treatment of fatal genetic di seases. Copyright (C) 1999 by W.B. Saunders Company.