Postsurgical assessment and long-term safety of recombinant adeno-associated virus-mediated gene transfer into the retinas of dogs and primates

Objective: To evaluate, in dogs and primates, the short-term effects of subretinal injection and the safety of long-term recombinant adeno-associated virus (rAAV)mediated transgene expression with respect to retinal morphology and function. Methods: Subretinal delivery of rAAV (serotype 2, 4, or 5) was performed unilaterally in 14 beagles and 9 macaques. Postsurgical condition was evaluated during a 2-month follow-up study. Three dogs and I primate were examined for the long-term study. Green fluorescent protein expression was monitored by fluorescent retinal imaging. Retinal anatomy and function were assessed by angiography and electroretinography, respectively. Results: Transgene expression was observed in 20 of 23 subretinally injected animals (both with and without vitrectomy). We did not detect an inflammatory response in any of the 23 treated subjects. In the long-term study, transgene expression was detected at the latest points evaluated: 36 months for the rAAV-2-injected dog, 24 months for the rAAV-4 and rAAV-5 dogs, and more than 18 months for the rAAV-4-injected primate. Angiography examinations were performed and showed no retinal abnormalities. Functional evaluation showed normal electroretinographic amplitude responses that were similar to those of the noninjected contralateral eyes. Conclusions: Subretinal injection of the rAAV vector in dogs and primates is a safe procedure with no perioperative complications and a high rate of successful retinal gene transfer. The retinal anatomy and function remained unchanged, despite persistent transgene expression up to 36 months postinjection with rAAV-2, -4, or -5. Additionally, we observed no other adverse effects, such as tumor formation due to possible insertional mutagenesis. These short- and long-term studies on rAAV transgene expression using large animals are encouraging for the prospects of ocular gene therapy applications in humans. Clinical Relevance: These short- and long-term studies on rAAV transgene expression using large animals are encouraging for the prospects of ocular gene therapy applications in humans.