AAV gene therapy is essentially one-shot. After the first dose, the immune system generates neutralizing antibodies (NAbs) against the viral capsid. These NAbs persist for years thanks to memory B cells. A second dose of the same serotype gets neutralized before it reaches target cells.
This is not a hypothetical concern. Patients seropositive for anti-AAV antibodies are excluded from most clinical trials. And 30-60% of the general population already has pre-existing anti-AAV immunity from childhood wild-type AAV exposure.
For STRC gene therapy, this creates a specific problem. If the first dose does not achieve sufficient transduction, there is no second chance with the same vector. This is where the delivery vehicle choice becomes critical.
Neutralizing antibody titer over time after intracochlear AAV administration (seronegative patient). Cochlear immune privilege reduces systemic response by ~30% compared to IV delivery.
Percentage of population with pre-existing neutralizing antibodies by AAV serotype:
Pediatric (<5 years): 20-30% (lower than adults)
Boutin et al. 2010, Calcedo et al. 2015
| Property | AAV | LNP | Exosome |
|---|---|---|---|
| First-dose efficiency | 60-90% | 10-50% | 5-20% |
| Immune response | Strong: IgG NAbs + memory B cells | Innate only (complement). No memory | Minimal (autologous) |
| Re-dosing | Extremely difficult (same serotype) | Every 2-4 weeks | Anytime |
| Seroprevalence barrier | 30-60% excluded | 0% | 0% |
| Cochlear advantage | Partial immune privilege | Repeatable compensates lower per-dose | Natural barrier crossing |
| Clinical readiness | Phase 1/2 (for OTOF) | Preclinical (cochlear), approved (COVID) | In vivo (mice) + 1st human trial |
Three new capsids emerged in 2025 with potentially superior OHC transduction. The current STRC preclinical work (Boston) uses AAV9-PHP.eB, which turns out to have poor OHC tropism in adult mice.
| Capsid | OHC | IHC | Notes |
|---|---|---|---|
| WAC19-1 | ~2M× enrichment | TBD | Peptide-modified AAV1, directed evolution |
| AAV-S | 50-75% | ~100% | From AAV9, neonatal mice + NHPs |
| Anc80L65 | 62% | 41% | Ancestral, lowest seroprevalence |
| AAV9-PHP.eB | 17% | 21% | Used in current STRC work (Boston) |
| AAV2.7m8 | Excellent | Moderate | Engineered, ~25% seroprevalence |
WAC19-1 data is from peptide display on AAV1 backbone, 3 rounds of in vivo directed evolution via posterior semicircular canal injection. ~2 million-fold enrichment for cochlear cells. AAV-S generated from AAV9 random library.
Acta Oto-Laryngologica (2025) found that different AAV serotypes trigger different macrophage activation patterns in the cochlea. Promoter choice also affects immunogenicity. This is distinct from the systemic NAb response: even if a patient is seronegative, the local innate immune response in the cochlea could reduce transduction efficiency or damage hair cells.
Our immune model covers NAb kinetics and seroprevalence but not this innate inflammatory component. This may affect capsid and promoter selection beyond just transduction efficiency.
Five dual-AAV trials for OTOF deafness reported results by late 2025:
Regeneron DB-OTO (CHORD): 11/12 children with clinically meaningful improvement. 3 achieved normal hearing. NEJM, October 2025.
Eli Lilly AK-OTOF: 11-year-old, deaf for 10+ years. All frequencies restored within 30 days.
Sensorion AUDIOGENE: 5 patients dosed, early auditory responses observed.
These target OTOF (IHCs), not STRC (OHCs). Different cell type, different protein biology. But the AAV delivery platform and surgical approach are validated in human cochlea.
Single-vector mini-STRC has a higher probability of success on the first (and possibly only) AAV dose. Dual-vector full STRC wastes half the dose on each vector, then loses another 70-80% to failed recombination.
The hybrid strategy from our delivery model (AAV surgery for base coverage + LNP top-up via sonoporation) directly addresses the re-dosing problem. AAV provides high initial transduction. LNP provides indefinite maintenance doses without immune barrier.
For pediatric patients like Misha (age 4), anti-AAV seroprevalence is lower (20-30%). This is a timing advantage that diminishes with age as children encounter wild-type AAV.
Cochlear immune privilege is real but incomplete. The blood-perilymph barrier is weaker than the blood-brain barrier. Local AAV delivery to the cochlea generates lower systemic NAb responses than intravenous delivery, but still sufficient to block re-dosing with the same serotype. The 30% reduction factor is estimated from comparative studies of intraocular vs systemic AAV delivery in NHPs (Timmers 2022). Direct cochlear NAb kinetics data in humans does not yet exist. Note: any computational modeling of NAb-AAV capsid interactions via AF3 should be interpreted with caution — Li et al. (2026) showed that AF3 systematically underperforms on antigen-antibody complexes due to the structurally plastic, rapidly evolving nature of immune interfaces (CDR-H3 loop variability, atypical residue usage at paratopes).