The Co-Transduction Conundrum: Improving Dual rAAV Delivery Through Co-Administration of Capsid Serotypes With Complementary Tropism.

PURPOSE: Recombinant adeno-associated virus (rAAV) vectors are promising tools for the treatment of inherited retinal diseases (IRDs) but have a limited carrying capacity for therapeutic cassettes of up to 4.8 kilobase (kb). To circumvent this limitation, multiple vector approaches have been proposed wherein the transgene cassette is split across two or more rAAV vector genomes. In this study, we examine whether rAAV serotype choice has an effect on co-transduction of retinal cells following subretinal delivery and whether co-transduction represents a rate-limiting step preventing successful large transgene delivery.

METHODS

The rAAV vector serotypes with known photoreceptor affinity (rAAV2/5, rAAV2/8, and rAAV2/9) packaging fluorescent reporter genes (GFP or mCherry) were co-delivered to C57Bl/6J mice via subretinal injection in all combinations of serotype. Two to 3 weeks following injection, confocal scanning laser ophthalmoscopy (cSLO) imaging and immunohistochemistry was used to visualize the extent of transduction and flow cytometry was utilized to quantify co-transduction of retinal cells.

RESULTS

Fluorescent GFP and mCherry transgene expression was observed by in vivo cSLO imaging in all injected eyes. Flow cytometry showed that the highest rate of co-transduction came from co-administration of rAAV2/8.mCherry and rAAV2/9.GFP (87.43 ± 3.84%) with considerable overlap in the expression observed. The lowest rate of co-transduction resulted from the co-delivery of rAAV2/5.mCherry and rAAV2/8.GFP (36.57 ± 4.79%) with cSLO imaging showing minimal overlap in fluorescent expression.

CONCLUSIONS

Utilizing a combination of rAAV capsids with similar cellular tropisms for dual rAAV delivery can result in an increased efficiency of co-transduction but is serotype dependent.

TRANSLATIONAL RELEVANCE: Identification of bottlenecks in rAAV transduction may improve the efficiency of large transgene delivery.