AAV Capsid Evaluation
EXPLORATORYAAV serotype evaluation for SMA gene therapy delivery. 9 capsids scored across motor neuron tropism, BBB crossing, immunogenicity (NAb seroprevalence), manufacturing feasibility, and packaging capacity. Zolgensma uses AAV9 (scAAV9-SMN1).
▶How does AAV capsid scoring work?
Why AAV9 for Zolgensma? AAV9 combines the highest motor neuron tropism (~90%) with efficient BBB crossing in neonates and a proven manufacturing process for clinical-grade production. Pre-existing neutralising antibodies (NAbs) exclude patients with anti-AAV9 titres above 1:50.
Composite Score weights tropism, BBB crossing, immunogenicity, manufacturing, and packaging fit. PHP.eB is mouse-specific (LY6A receptor) and does not translate to primates. AAVrh10 and AAV-B1 are in preclinical evaluation as alternatives.
Delivery Strategies
Proven in >3,000 patients. BBB crossing excellent in neonates (<2 years). One-time IV dose. Manufacturing scaled. NAb screening required.
Limitations: Dose-limiting hepatotoxicity. NAb-positive patients excluded (~47%). Declining BBB crossing with age.
Bypass BBB entirely. Lower dose (less hepatotoxicity). Proven IT route for CNS. AAVhu68 shows strong spinal MN transduction in NHP.
Limitations: Invasive procedure. Distribution may be uneven. Repeat dosing unclear (immune response to capsid).
Lower seroprevalence (~30% vs 47%). Good CNS tropism. Could treat patients excluded from Zolgensma due to anti-AAV9 NAbs.
Limitations: Less clinical data than AAV9. Cross-reactivity possible.
Permanent epigenetic silencing of ISS-N1 — combines CRISPR guide (Phase 6.2) with AAV delivery. Split-intein approach fits dCas9 in 2 AAV vectors.
Limitations: Requires co-transduction of both vectors in same cell. Lower efficiency than single vector. No clinical precedent for CNS split-intein.
SMA is multisystem — motor neurons AND NMJ/muscle affected. AAV9 for neuronal SMN1 + MyoAAV for muscle-specific PLS3 or trophic factors.
Limitations: Two vectors = two manufacturing processes. Additive immune response. Complex regulatory pathway.
Capsid Rankings
| # | Serotype | MN Tropism | BBB | Immunogenicity | Mfg | Packaging | Score | Clinical Precedent |
|---|---|---|---|---|---|---|---|---|
| 1 | PHP.eB | 95% | 95% | 25% | 55% | EXCEED | 0.74 | Preclinical only. Mouse-specific BBB crossing via LY6A receptor. Does NOT translate to NHP/human. |
| 2 | AAV9 | 90% | 85% | 47% | 85% | EXCEED | 0.70 | FDA-approved: Zolgensma (onasemnogene abeparvovec) for SMA Type 1. >3,000 patients treated globally. |
| 3 | AAVrh10 | 82% | 70% | 30% | 75% | EXCEED | 0.67 | Phase 1/2 for CLN2 (Batten disease), GM1 gangliosidosis. No SMA trials yet. |
| 4 | AAVhu68 | 80% | 75% | 35% | 70% | EXCEED | 0.66 | Phase 1/2 for GM1 gangliosidosis (intracisternal). No SMA trials. |
| 5 | AAV-PHP.S | 70% | 20% | 20% | 50% | EXCEED | 0.52 | Preclinical only. Peripheral nervous system tropism. |
| 6 | AAV5 | 40% | 30% | 25% | 90% | EXCEED | 0.49 | FDA-approved: Roctavian (AAV5-FVIII) for hemophilia A. Not used for CNS. |
| 7 | AAV-DJ | 45% | 25% | 40% | 80% | EXCEED | 0.46 | Preclinical only. Shuffled capsid from AAV2/8/9. |
| 8 | AAV1 | 50% | 15% | 55% | 90% | EXCEED | 0.43 | FDA-approved: Glybera (lipoprotein lipase deficiency, withdrawn). Luxturna component. |
| 9 | MyoAAV (2A/4A) | 30% | 10% | 20% | 55% | EXCEED | 0.38 | Preclinical only. Engineered for skeletal muscle. |