AAV9 immunogenicity as a scalability trap. PROJECT OPTIMUS to boot. The anti-AAV9 titer cutoff of ≤1:50 reflects a real immunological constraint: patients with prior AAV9 exposure mount a neutralizing immune response that reduces transduction efficiency and risks severe inflammation. https://www.sciencedirect.com/science/article/pii/S1359644626001571?dgcid=authorhttps://lnkd.in/g2YVjCDb
Pre-existing anti-AAV9 antibodies are present in roughly 30–50% of the general population, with the exact rate depending on age, geography, and assay methodology.(p19) The immediate consequence is that a meaningful proportion of otherwise eligible ALS patients will be excluded from treatment on serologic grounds alone. Applying that 30–50% background seroprevalence range directly to the ALS population – absent ALS-specific serosurvey data, which do not yet exist – implies that roughly one-third to one-half of otherwise trial-eligible patients could be excluded by the ≤1:50 titer cutoff alone, before any other eligibility criterion is applied. This figure should be treated as an extrapolation from general-population data rather than a population-specific estimate.

A related and distinct consideration is that patients who receive an irreversible, single-administration gene therapy are typically excluded from participating in essentially all other clinical trials thereafter, because of the permanent nature of the intervention. This constrains the eligible patient pool through a mechanism separate from AAV9 seroconversion: prior participation in any gene therapy trial – AAV9-based or otherwise – will limit eligibility for subsequent studies regardless of a patient’s current anti-AAV9 titer.

The longer-term scalability consideration compounds both effects. Because AAV-based gene therapies proliferate across neuromuscular indications, seroconversion rates among potential ALS patients could plausibly rise with successive exposures from other therapeutic programs, although this trend has not yet been directly measured in the ALS population and should be treated as a hypothesis rather than an established trajectory. Celosia’s commercial forecasts should model this dynamic explicitly; a therapy that works but can only be administered to a diminishing fraction of eligible patients is not, on its own, a durable therapeutic platform.

Dose optimization and regulatory imperatives

Although the KOANEWA trial follows a conventional Phase Ib safety design, its long-term success will likely hinge on adopting more rigorous dose-optimization strategies to mitigate the risks inherent to irreversible gene therapy. Figure 3 contrasts the limitations of the traditional ‘accelerated’ pipeline with an optimized framework modeled after oncological dose-selection principles, highlighting the necessity of data-driven target engagement for central nervous system (CNS) gene therapies.