AAV Tropism for Liver Tissues

The liver is one of the most common targets for gene therapy because it acts as a “bioreactor,” producing proteins (like clotting factors) that are secreted into the bloodstream.

While AAV8 is the most famous liver-targeting serotype in animal models, research has shown that AAV3B and certain engineered variants like LK03 are often more effective at “unlocking” human liver cells.

Serotype	Target Cells	Transduction Efficiency	Best Use Case	Key Features
AAV8	Hepatocytes	Very High	Liver-directed therapy (Animal)	The “gold standard” for mice/NHPs; 3–4x more efficient than AAV2 in the liver.
AAV3B	Hepatocytes	High (Human)	Human liver therapy	Specifically uses the Human Hepatocyte Growth Factor Receptor (hHGFR) to enter cells.
AAV5	Hepatocytes	High	Hemophilia B	Used in Hemgenix; shows lower pre-existing immunity in the general population.
AAVrh74	Hepatocytes	High	Hemophilia B	Used in Beqvez; a rhesus-derived serotype with high systemic potency.
AAV2	Hepatocytes	Moderate	General research	The first serotype used for liver trials, but requires higher doses than AAV8 or AAV5.
AAV-LK03	Hepatocytes	Ultra High	Synthetic / Humanized	A “shuffled” capsid (97% like AAV3B) engineered to target human liver cells 10x better than AAV8.
AAV-DJ	Hepatocytes	Very High	In vitro & In vivo	A synthetic chimera of 8 serotypes; extremely potent but highly susceptible to human antibodies.

Species Differences: The “Mouse vs. Human” Trap

One of the most important lessons in liver gene therapy is that what works in mice may not work in humans.

• AAV8 is incredibly efficient in mice, often transducing nearly 100% of the liver.
• AAV3B and LK03 are significantly more efficient than AAV8 when used on human hepatocytes (often tested in “humanized” mouse models).

Liver-Specific Promoters

To ensure that your gene is only expressed in the liver (and not in the heart or brain if the virus leaks into the bloodstream), researchers use specific promoters:

• LP1: A small, potent promoter often used in Hemophilia trials.
• hAAT (Human Alpha-1 Antitrypsin): A very common promoter that restricts expression strictly to hepatocytes.
• TBG (Thyroxine-binding Globulin): Known for being exceptionally “quiet” in non-liver tissues, reducing the risk of off-target effects.

Delivery Route

For the liver, the Intravenous (IV) route is standard. Because the liver filters the blood, it naturally “catches” a large percentage of the AAV particles as they circulate, especially those with an affinity for galactose (like AAV9) or heparin sulfate (like AAV2).