Objective: Our objective was to create transgenic mammals using systemic delivery of adeno-associated virus serotype 9 (AAV2/9).

Background: The adeno-associated virus serotype 9 (AAV2/9) crosses the blood brain barrier, is capable of transducing developing cells and neurons after intravenous injection in many species, and mediates a long-term stable transduction. Ability to transduce brain decreases over time, being maximum at P1 and decreasing dramatically by P10 already suggesting a developmental period in which AAV2/9 transduction has maximal efficacy. While P1 is an attractive (and easily accessible) time point, in utero gene delivery has clearly demonstrated that a wide transduction of neurons is possible at embryonic stages compatible with the development of the targeted area.

Methods: To test this hypothesis, we injected intracerebroventricularly (i.c.v.) high-titer bolus of AAV2/9 carrying either mutant human α-synuclein (A53T) or enhanced green fluorescent protein (EGFP) under the synapsin or CMV immediate enhancer/β-actin (CAG) promoter respectively, at embryonic day 16.5 for rat and around 100 days fetal age for monkeys under ultrasound imaging guidance. Animals after birth have then been behaviourally followed-up and were terminated at regular interval to access the brain pathology.

Results: We characterized the regional distribution of GFP immunopositivity in brain structures and peripheral organs. We observed transduction of neurons in most regions of the brain – i.e. within hippocampus, thalamus, spinal cord, striatum, globus pallidus, substantia nigra, choroid plexus, cerebellum, and cortex- 25 days after injection in rats. Moreover, the efficacy of transduction seems dependent on the brain structure. Transduction of mutated α-synuclein was then characterized as was defined the specific brain lesions in both rats and monkeys.

Conclusions: Overall, these results indicate that an engineered AAV serotype 9 variant (scAAV9) injected in utero in rats or rhesus macaques results in efficient, neuronal and widespread transduction of the brain. Altogether, this proof of concept study could facilitate and offer unique opportunities for modelling brain diseases in rats and rhesus macaques by targeting mutant genes with tissue-specific gene expression, not mentioning future clinical applications for in vivo correction of monogenic diseases or abnormalities in humans.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/in-utero-delivery-of-scaav9-mediates-widespread-brain-transduction-in-rats-and-monkeys-towards-new-models-of-parkinsons-disease/