AAV Gene Therapy Trials: Eligibility, Dose and Durability

An adeno-associated virus (AAV) gene therapy announcement can report a single administration, a vector dose and years of planned follow-up. Those facts do not yet answer the investor's question: who was studied, what benefit was measured, and how long was that benefit actually observed?

Use the worksheet below to compare evidence within a disease and development program. The FDA labels provide examples of why patient selection and dose notation matter; they do not establish a ranking between products or a treatment recommendation.

1. Start with the population, not the disease total

Record the trial's inclusion and exclusion criteria before treating its results as applicable to everyone with the disease. Identify genotype, age, disease severity, previous treatment and any vector-antibody testing. Then separate the numbers screened, enrolled, treated and included in the reported analysis. If the report does not disclose a denominator, write UNKNOWN rather than estimating it from a recruitment target.

Two FDA label examples show how specific selection can be:

• LUXTURNA: the indication requires confirmed biallelic RPE65 mutation-associated retinal dystrophy and viable retinal cells, as assessed by the treating physician. A broad retinal-disease population is not the labeled population. FDA label, section 1
• ROCTAVIAN: the label specifies adults with severe hemophilia A, with factor VIII activity below 1 IU/dL, without pre-existing antibodies to AAV5 detected by an FDA-approved test. This is only part of its patient-selection information; other restrictions also apply. FDA label, section 1

For an investigational program, read its own protocol and current registry record. An approved product's label cannot substitute for that trial's eligibility criteria. Keep a potential market-size assumption separate from the population actually studied.

2. Keep dose units and administration context attached

A dose number loses meaning when the unit or route disappears. These label examples use different denominators:

Label example	Dose notation	Administration context
LUXTURNA	1.5 × 10^11 vector genomes (vg) per eye	Subretinal administration
ROCTAVIAN	6 × 10^13 vector genomes (vg) per kilogram	Intravenous infusion

Sources: LUXTURNA section 2.1 and ROCTAVIAN section 2.1.

Per eye and per kilogram are not interchangeable. Preserve the vector, therapeutic payload, target tissue, route and dosing schedule alongside the number. The two rows alone cannot support a conclusion that one product is more effective or safer. They concern different diseases and administrations.

For dose-escalation results, compare cohorts using the same endpoint, assessment time and population definition. If a cohort differs on those dimensions, describe the differences before interpreting a dose-response pattern. A larger number by itself is not an efficacy result.

3. Distinguish planned follow-up from observed durability

A protocol can schedule several years of follow-up while its latest results contain much shorter observation. Record the data cutoff, the number of people assessed at each time point, missing assessments and the outcome measured. A change in a laboratory marker and a change in how a patient functions answer different questions.

FDA's rare-disease gene therapy guidance discusses biomarkers, clinically meaningful endpoints and measures to reduce bias. It also explains why a historical-control comparison requires appropriately matched populations. Use those considerations to inspect the actual comparator, background treatment and assessment method; a single-arm change from baseline does not establish the same comparison as a randomized trial. FDA guidance, sections V.B and V.E

Keep long-term safety monitoring separate from evidence that benefit persists. FDA's 2020 long-term follow-up guidance recommends up to five years for AAV vectors in a risk-based framework, with duration depending on the product and supporting information. That recommendation is neither five years of completed patient observations nor proof of five years of efficacy. A single administration also does not establish a lifelong cure. FDA long-term follow-up guidance, sections V.A and V.C

A worksheet for the next AAV readout

Question	What to record	What remains unproven without it
Who could enter, and who was analyzed?	Eligibility criteria; screened, enrolled, treated and analyzed denominators	Applicability beyond the studied population
What was administered?	Vector and payload; dose with unit; route and schedule	A valid dose comparison
What was compared?	Randomization; control group; blinding; background therapy	Attribution of an observed change to treatment
What was measured?	Prespecified primary endpoint; measurement method; assessment time	The clinical meaning of a reported marker
How long was it observed?	Data cutoff; follow-up distribution; numbers assessed and missing data	Persistence of benefit beyond available observations

Use UNKNOWN for unavailable fields. For registry dates and enrollment types, use the ClinicalTrials.gov reading guide. For the comparator and assessment method, use the open-label versus blinded-trial guide.

Apply the evidence check to a company

The research entry for this article asks you to choose a company, then examines its trial evidence: randomization, comparator, blinding, primary endpoint, missing data and available results. It uses the article as question context and checks current original sources. Keep the worksheet nearby for eligibility, dose and follow-up details; an undisclosed field remains UNKNOWN.

The next research question is concrete: does the available study design and follow-up support the claimed benefit in the studied population, and which assumptions still lack evidence? Company selection and confirming a research run remain separate steps.

Source note: FDA documents linked here were read on October 8, 2026. Label examples illustrate evidence interpretation; check the current label and trial-specific sources before applying them to a live program.