Targeting non-neuronal cells (glia) in the CNS is often more challenging than targeting neurons, as many natural AAVs are inherently neurotropic. To achieve high glial expression, researchers typically combine a serotype that has a natural affinity for glia with a cell-specific promoter.

The following table details the tropism for astrocytes, oligodendrocytes, and microglia.

Serotype	Cell Target	Transduction Efficiency	Best Use Case	Key Features
AAV5	Astrocytes	Very High	Primary astrocyte targeting	Often cited as the best natural serotype for astroglia; widely used in spinal cord research.
AAV4	Ependyma	High	Ventricular lining	Unique among natural AAVs; targets the ependymal cells lining the brain’s ventricles rather than neurons.
AAV9	Astrocytes	Moderate/High	Systemic glial delivery	Can target astrocytes globally via IV injection, though it often prefers neurons in adult brains.
AAV8	Astrocytes	Moderate	Local glial expression	Efficient in the striatum; shows significant astrocytic transduction when used with a GFAP promoter.
AAVrh43	Astrocytes	High	Glial-focused research	A natural primate serotype that shows a stronger natural preference for glia than AAV8.
Olig001	Oligodendrocytes	Ultra High	Demyelinating diseases	A synthetic variant specifically engineered to target >95% of striatal oligodendrocytes.
AAV-DJ8	Astrocytes	High	Hybrid glial targeting	A synthetic chimera that outperforms AAV9 for astrocyte transduction in certain brain regions.
AAV-MG	Microglia	High	Neuroinflammation	Specifically engineered variant; natural AAVs (1-13) are notoriously poor at infecting microglia.

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Critical Promoters for Glial Specificity

Because natural AAVs like AAV9 can infect both neurons and glia, using a Glial Promoter is essential to ensure your gene doesn’t “leak” into neurons:

• GFAP (Glial Fibrillary Acidic Protein): The most common promoter for targeting astrocytes. Truncated versions like GfaABC1D are often used to fit inside the small AAV genome.
• ALDH1L1: Often considered more specific than GFAP, as it labels a broader population of astrocytes including those that are “non-reactive.”
• MBP (Myelin Basic Protein): Used to restrict expression to oligodendrocytes.
• Iba1 / CD11b: Used to target microglia (though these usually require engineered capsids or specific “shuffled” variants to work effectively).

Summary of Best Choices

• For Astrocytes: Use AAV5 or AAV9 paired with a GFAP promoter.
• For Oligodendrocytes: Use Olig001 (synthetic) or AAV8 with an MBP promoter.
• For Microglia: Avoid natural serotypes; look for specialized engineered capsids like AAV-MG or use Lentiviral vectors, which naturally target myeloid cells more effectively.