“Cardiac gene therapy” has been a thing for years.

But it hasn’t really been a thing in patients.

The history is honestly pretty brutal.

Mydicar (intracoronary AAV1-SERCA2a) failed CUPID-2 in 2015.

Various AAV cardiac programs hit safety walls.

Doses are tricky because the heart is a big muscle that requires a lot of vector.

Antibody pre-existence is high.

Manufacturing is hard.

You know the drill.

So Tenaya Therapeutics dropping a late-breaking ASGCT presentation with one-year follow-up data from their first cohort of TN-401 patients matters more than the press release headline suggests.

TN-401 is an AAV9-based gene replacement therapy delivering a functional copy of PKP2 to cardiomyocytes. The indication is PKP2-associated arrhythmogenic right ventricular cardiomyopathy – a genetic disease that causes the right ventricle to progressively fibrose and produce life-threatening arrhythmias.

This affects roughly 70,000 people in the US and there are no disease-modifying therapies. Just a heart monitor and management.

Phase 1b/2 data at ASGCT 2026 will include one-year follow-up from the first cohort enrolled in late 2024 plus early data from a second cohort.

They didn’t include any specifics in the announcement (and I’m not going to ASGCT so someone is going to have to TELL ME what the data looks like), but this is the first chance to see whether AAV9 gene replacement actually does anything durable for cardiac muscle disease.

Tenaya’s lead program TN-201 (for MYBPC3 hypertrophic cardiomyopathy) did show signs of working at AHA 2025.

They reported detectable vector DNA in heart tissue, transgene RNA expression, and rising MyBP-C protein levels in treated patients, with deeper responses over time.

Cohort 1 follow-up data continues to look good. That’s an encouraging precedent for what TN-401 might show in PKP2-ARVC.

Also, the company has built infrastructure most cardiac gene therapy players don’t have.

They have an in-house manufacturing facility producing AAV at 1000L scale using a baculovirus-Sf9 system, which is good because the cardiac dose for AAV9 is high – 3E13 to 6E13 vg/kg in the RIDGE-1 trial – and supply is the rate-limiter for everyone else.

The thing to watch at ASGCT: do the Cohort 1 patients show measurable changes in cardiac structure, function, or arrhythmia burden at 12 months?

Look for things like Plakophilin-2 protein levels in cardiac biopsies. Reduced T-wave inversions or PVC burden? Anything that suggests the gene replacement is doing real biological work in the right tissue at the right dose.

If the data is clean, TN-401 is the leading edge of an entirely new category… cardiac gene therapy that actually does something. If it’s noisy or absent, the field’s confidence in AAV9 cardiac delivery takes another hit.

Either way, this is the one means a lot for the cardiac gene therapy space.