Adeno-associated virus (AAV) vectors are a leading delivery platform for central nervous system (CNS) gene therapy because they combine relatively low pathogenicity, durable transgene expression, and adaptable tissue tropism.[1][2] In neurodegeneration, those properties matter because effective therapy usually depends on getting a therapeutic payload into neurons and glia across the blood-brain barrier or through direct cerebrospinal fluid delivery.[1:1][3] Recent advances in capsid engineering have dramatically improved BBB crossing efficiency, opening new therapeutic possibilities for neurodegenerative diseases.[4]
Adeno-associated virus (AAV) vectors are widely used for CNS gene transfer because they can support long-term expression, can be engineered for cell-type selectivity, and in the case of serotypes such as AAV9 can achieve clinically relevant CNS delivery after systemic administration.[1:2][3:1]
The ~4.7 kb packaging limit constrains cargo size. This necessitates:
| Route | BBB Crossing | Distribution | Invasiveness |
|---|---|---|---|
| Intravenous | Requires engineered capsids | Widespread | Low |
| Intrathecal | Direct to CSF | Leptomeninges, spinal cord | Moderate |
| Intracerebroventricular | Direct to ventricles | Ventricular surfaces | Higher |
| Intraparenchymal | Direct to brain | Local region | Highest |
| Serotype | BBB Crossing | Neuronal Tropism | Key Use |
|---|---|---|---|
| AAV9 | Yes (high) | Excellent | Systemic delivery |
| AAVrh.10 | Yes | Excellent | Broad CNS targeting |
| PHP.B / PHP.eB | Yes (mouse-biased) | Excellent | Research / preclinical |
| AAV2 | Limited | Good | Direct injection |
| AAV5 | Limited | Good | Striatal delivery and HD programs |
The PHP (PHP.B, PHP.eB, PHP.S) family represents a breakthrough in BBB-crossing capsids:
Hematopoietic stem cell-derived capsids (AAVHSC) represent another engineering approach:
An engineered capsid with CNS tropism:
| Company | Focus Programs | Stage |
|---|---|---|
| Voyager Therapeutics | PD, AD, ALS | Phase 1/2 |
| Passage Bio | HD, AD | Preclinical/Phase 1 |
| Prevail Therapeutics | ALS, PD | Acquired by Eli Lilly |
| uniQure | AD, HD | Preclinical/Phase 1 |
| Spark Therapeutics | Inherited retinal disease, CNS | Phase 1/2 |
Multiple AAV gene therapy trials are underway:
| Product | Company | Indication | Year |
|---|---|---|---|
| Luxturna | Spark/Roche | Leber congenital amaurosis | 2017 |
| Zolgensma | Novartis | Spinal muscular atrophy | 2019 |
| Ryplazim | Takeda | Plasminogen deficiency | 2023 |
| Elevidys | Sarepta | Duchenne muscular dystrophy | 2023 |
No AAV therapy is yet FDA approved specifically for a CNS neurodegenerative disease, but the platform has demonstrated regulatory viability in related neurologic indications.[6:1]
The rapid rise of AAV-based therapeutics reflects converging improvements in capsid engineering, promoter design, neurosurgical delivery, and large-scale vector manufacturing. Those advances have turned CNS gene therapy from a purely experimental strategy into a realistic therapeutic platform for neurodegenerative disease programs.[1:9][4:2]
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