Long-term luciferase expression monitored by bioluminescence imaging after adeno-associated Virus-Mediated fetal gene delivery in rhesus monkeys (Macaca mulatta)

The safety and efficiency of fetal adeno-associated virus (AAV) gene delivery in rhesus monkeys and long-term monitoring of transgene expression by bioluminescence imaging (BLI) were evaluated. Early second-trimester fetal monkeys were administered AAV2/5, AAV2/9, or AAV2/10 vector supernatant preparations expressing firefly luciferase under the control of the cytomegalovirus promoter, using an intrathoracic (n=6) or intramyocardial (n=6) approach and established ultrasound-guided techniques. Postnatal BLI was performed monthly up to 6 months postnatal age (n=12) and then every 3 months thereafter to monitor transgene expression up to 24 months postnatal age (27 months after gene transfer; n=6). All AAV serotypes showed greater than 1.0×10⁹ photons/sec at all time points evaluated with limited biodistribution to nontargeted anatomical sites. The highest levels of bioluminescence (photons per second) observed were noted with AAV2/9 and AAV2/10 when the three vector constructs were compared. To correlate in vivo findings at the tissue level, specimens were collected from selected animals and analyzed. Three-dimensional reconstruction showed that firefly luciferase expression was consistent with imaging and morphometric measures. These findings suggest that (1) high levels of AAV-mediated firefly luciferase expression can be found after fetal AAV gene transfer and without any evidence of adverse effects; (2) the intercostal muscles, myocardium, and muscular component of the diaphragm of developing fetuses are readily transduced with AAV2/5, AAV2/9, or AAV2/10; and (3) postnatal outcomes and long-term luciferase expression can be effectively monitored by BLI in young rhesus monkeys.