AAV Tropism for Cardiac Tissues

To target the heart, AAV9 is generally considered the “gold standard” because of its high efficiency in cardiomyocytes and its ability to spread throughout the myocardium after a simple systemic injection (IV). However, other serotypes like AAV6 and AAVrh74 are also strong contenders depending on the delivery method.

Serotype	Target Cells	Transduction Efficiency	Best Use Case	Key Features
AAV9	Cardiomyocytes	Very High	Systemic heart targeting	Highest efficiency for cardiomyocytes; can achieve global heart transduction via IV delivery.
AAV6	Cardiomyocytes	Very High	Direct/Local injection	Often outperforms AAV9 when delivered directly into the coronary artery or heart wall.
AAV1	Cardiomyocytes	High	Heart failure therapy	Used in historical trials (like CUPID) for SERCA2a delivery to improve heart contractility.
AAV8	Cardiomyocytes, RPE	High	Systemic delivery	Robust expression but often has very high “leakage” to the liver compared to AAV9.
AAVrh74	Heart & Skeletal Muscle	High	Muscular Dystrophy	Excellent at targeting the heart in the context of whole-body muscle diseases.
AAV5	Vascular Endothelium	Moderate	Blood vessel targeting	Better at targeting the smooth muscle cells and lining of heart vessels than other serotypes.
AAV-M41	Cardiomyocytes	Ultra High	Synthetic / Specificity	A “shuffled” variant engineered to have 10x higher heart specificity and significantly less liver uptake.

Delivery Methods for the Heart

The “strength” of a serotype often changes based on how it is given to the patient or animal model:

1. Intravenous (IV): Best for AAV9. This is non-invasive but requires high doses, as much of the virus will still end up in the liver.
2. Intracoronary (IC): Best for AAV6. The virus is infused directly into the arteries that feed the heart. This allows for lower doses and higher local concentration.
3. Intramyocardial Injection: Direct injection into the heart muscle during surgery. This is the most “targeted” but provides very localized expression (it doesn’t spread through the whole heart).

Cardiac-Specific Promoters

To prevent the virus from expressing your gene in the liver or other “off-target” organs, it is vital to use a heart-specific promoter:

• cTnT (Cardiac Troponin T): The most common promoter to restrict expression strictly to cardiomyocytes.
• α-MHC (Alpha-Myosin Heavy Chain): Another highly potent promoter for specific heart muscle expression.
• Desmin: Targets both cardiac and skeletal muscle (useful for muscular dystrophy research).