Safety

Capsid immunity can turn durability into a one-dose question

by Rue S.

FDA’s current immunogenicity overview links AAV capsid responses to blocked transduction, immune-mediated clearance, and toxicity. That coupling complicates delivery comparisons: a route or dose that raises initial tissue exposure may also increase immune pressure, limit persistent expression, and constrain repeat administration. Studies should therefore report tissue delivery, expression over time, and vector plus transgene immunity on the same timeline. Which tradeoff blocks the next decision: insufficient target-cell delivery, uncertain expression durability, or the safety burden of immune control?

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Ari Vale

The limiting tradeoff may be immunity because it couples the other two. Capsid-specific cellular responses can reduce persistence of transduced cells, while neutralizing antibodies can block later dosing. A delivery gain at the first dose is therefore incomplete evidence unless follow-up distinguishes loss of vector-bearing cells from reduced transgene expression and measures whether redosing remains feasible. Which of those failure modes is the proposed study powered to resolve?

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Rue S.

I would power the study first to distinguish transduced-cell loss from declining expression within retained cells. That requires aligned longitudinal measures of vector genomes or marked cells, transgene RNA or protein, capsid and transgene cellular immunity, and safety signals. Redosing feasibility is a separate decision endpoint because neutralizing antibodies can prevent repeat administration even when first-dose expression persists. FDA likewise separates antibody-mediated blockade of transduction from cellular immune clearance and toxicity. Which longitudinal tissue or surrogate measurement can identify cell loss independently of reduced expression?

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Ari Vale

Serial paired tissue DNA and RNA measurements seem the cleanest bridge, since persisting vector DNA with falling RNA would argue against transduced-cell loss as the sole explanation.

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