AAV Tropism for Lymph Nodes and Immune Cells

In the context of the immune system and lymph nodes, AAV tropism is often discussed in two ways: how the virus naturally avoids the immune system to deliver a gene, or how it can be purposely used to target Antigen-Presenting Cells (APCs) for vaccines and immunotherapy.

Lymph nodes are highly concentrated with B cells, T cells, and Dendritic Cells (DCs). Targeting these cells is notoriously difficult because many natural AAVs have evolved to avoid “alerting” these immune hubs.

Serotype	Target Cells	Tropism Level	Best Use Case	Notes
AAV5	Dendritic Cells (DCs)	High	Vaccine development	Shows significantly higher natural tropism for human and mouse DCs compared to AAV2.
AAVrh74	Lymph Node Tissue	High	Muscle therapy	Naturally isolated from rhesus macaque lymph nodes; excellent for bypassing pre-existing human immunity.
AAV6	Draining Lymph Nodes	Moderate/High	Cancer Immunotherapy	Engineered variants (like S663V) can transduce ~10% of DCs in draining lymph nodes after muscle injection.
AAV1	Dendritic Cells	Moderate	Immune modulation	Better at inducing humoral (antibody) responses than AAV2 when delivered to muscle.
AAV2	B cells / DCs	Low/Moderate	General research	Can transduce DCs ex vivo, but is often neutralized by antibodies in the lymph nodes in vivo.
AAV8	APCs (Systemic)	Low/Moderate	Liver-directed therapy	While it reaches the liver well, it does interact with APCs in the spleen and lymph nodes, often triggering T-cell responses.
AAV-PHP.S	Peripheral Nerves	Moderate	Immune-system interface	While designed for nerves, its systemic spread includes significant interaction with lymphoid tissues.

Why Lymph Node Tropism Matters

1. Vaccine Design: If you want to create a vaccine, you want the AAV to go to the lymph nodes and infect Dendritic Cells. AAV5 and AAV6 are the preferred “natural” choices for this because they are better at showing the “blueprint” of the vaccine to the immune system.
2. Gene Therapy Success: If you are treating a disease like Hemophilia, you want to avoid the lymph nodes. If the AAV infects cells in the lymph nodes, the immune system might create “neutralizing antibodies” that destroy the treatment.
3. The rh74 Discovery: It is a fascinating piece of virology that AAVrh74 was actually discovered inside the lymph nodes of a monkey. This natural “homing” is partly why it is so effective at navigating the primate immune system to reach muscles.

Key Promoters for Immune Cells

To ensure the AAV only works inside the specific immune cells within the lymph node, researchers use:

• CD11c: Targets Dendritic Cells.
• CD19 / CD20: Targets B cells.
• CD3 / CD4: Targets T cells.

The “Drainage” Effect

Most AAVs reach the lymph nodes through lymphatic drainage. If you inject an AAV into the muscle (intramuscular), a portion of the virus naturally flows through the lymphatic vessels to the “draining lymph node” nearby. This is where the immune system first decides whether to attack the virus or ignore it.