AAV Tropism for Salivary Gland Tissues

The salivary glands are highly attractive targets for gene therapy because they are isolated, easily accessible (via the mouth), and can function as “bioreactors” to secrete therapeutic proteins into either the saliva or the bloodstream.

Unlike most organs, the success of salivary gland transduction depends heavily on retrograde cannulation (injecting through the duct) rather than systemic injection.

Serotype	Target Cells	Transduction Efficiency	Best Use Case	Key Features
AAV2	Ductal Cells	High	Radiation-induced dry mouth	The clinical “pioneer.” Used to deliver hAQP1 to help surviving ductal cells secrete fluid.
AAVrh10	Acinar Cells	Very High	Primary gland repair	A natural primate strain that out-transduces AAV2 in acinar cells (the cells that actually make saliva).
AAV44.9	Acinar Cells	Very High	Systemic protein secretion	A novel natural isolate that shows robust and stable long-term expression in acinar cells.
AAV5	Ductal & Acinar	Moderate/High	Chronic gland disease	Shows broad expression across the gland, though often requires higher titers than AAVrh10.
BAAV	Mesenchymal	High	Developmental research	Bovine AAV uniquely targets the supportive connective tissue rather than the epithelial cells.
AAV8	General Gland	Moderate	Global expression	Effective for general gland transduction, but often shows high “leakage” to the liver if not delivered locally.
AAV9	General Gland	Moderate	Multi-organ targeting	While great for the heart/CNS, it is less specialized for salivary glands compared to AAVrh10 or AAV2.

Key Cell Types in the Salivary Glands

Understanding the difference between these two cell types is vital for deciding on a serotype:

• Acinar Cells: The “factories” that produce and secrete primary saliva. AAVrh10 and AAV44.9 are the best at targeting these.
• Ductal Cells: The “pipes” that modify the saliva and transport it to the mouth. AAV2 is highly effective at targeting these, which is why it’s used for Aquaporin-1 (AQP1) therapy to turn these “pipes” into “secreting units.”

Delivery: The Retrograde Advantage

The most effective way to target salivary glands is Retrograde Duct Cannulation.

1. A tiny tube (cannula) is inserted into the salivary duct in the cheek (Stensen’s duct) or under the tongue (Wharton’s duct).
2. The AAV is infused directly into the gland.
3. Benefit: This uses much lower doses of virus, avoids the liver entirely, and bypasses the blood-brain barrier.

Tissue-Specific Promoters

To ensure the gene only turns on in the specific parts of the gland:

• AMY1C (Amylase): Restricts expression to Acinar Cells.
• KLK1 (Kallikrein): Restricts expression to Ductal Cells.
• CMV / RSV: Broad, ubiquitous promoters often used in the salivary gland because the organ is so isolated that “off-target” spread is minimal.