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Updated: Jun 11, 2025
Direct Intrathecal Injection of Recombinant Adeno-associated Viruses in Adult Mice
Published on: February 15, 2019
Expression-based selection identifies a microglia-tropic AAV capsid for direct and CSF routes of administration in
Miguel C Santoscoy1,2,3, Paula Espinoza1,2,3, Killian S Hanlon1,2,3,4
1Department of Neurology, Massachusetts General Hospital, Boston, MA, 02115.
Abstract:
Microglia are critical innate immune cells of the brain. In vivo targeting of microglia using gene-delivery systems is crucial for studying brain physiology and developing gene therapies for neurodegenerative diseases and other brain disorders such as NeuroAIDS. Historically, microglia have been extremely resistant to transduction by viral vectors, including adeno-associated virus (AAV) vectors. Recently, there has been some progress demonstrating the feasibility and potential of using AAV to transduce microglia after direct intraparenchymal vector injection. Data suggests that combining specific AAV capsids with microglia-specific gene expression cassettes to reduce neuron off-targeting will be key. However, no groups have developed AAV capsids for microglia transduction after intracerebroventricular (ICV) injection. The ICV route of administration has advantages such as increased brain biodistribution while avoiding issues related to systemic injection. Here, we performed an in vivo selection using an AAV peptide display library that enables recovery of capsids that mediate transgene expression in microglia. Using this approach, we identified a capsid, MC5, which mediated enhanced transduction of microglia after ICV injection compared to AAV9. Furthermore, MC5 enhanced both the efficiency (85%) and specificity (93%) of transduction compared to a recently described evolved AAV9 capsid for microglia targeting after direct injection into the brain parenchyma. Exploration of the use of MC5 in a mouse models of Alzheimer's disease revealed transduced microglia surrounding and within plaques. Overall, our results demonstrate that the MC5 capsid is a useful gene transfer tool to target microglia in vivo by direct and ICV routes of administration.
Insights
Researchers developed a new adeno-associated virus (AAV) capsid, MC5, for efficiently targeting microglia in the brain. This novel vector shows promise for gene therapy in neurological disorders like Alzheimer's disease.
Area of Science:
- Neuroscience
- Immunology
- Gene Therapy
Background:
- Microglia are key brain immune cells vital for neurological research and treating brain disorders.
- Targeting microglia with gene delivery, particularly adeno-associated virus (AAV) vectors, is challenging due to their resistance to transduction.
- Intracerebroventricular (ICV) injection offers advantages for brain-wide AAV delivery, but specific microglia-targeting capsids for this route are lacking.
Purpose of the Study:
- To develop and characterize novel AAV capsids for efficient microglia transduction via the ICV route.
- To enhance the specificity and efficiency of microglia gene transfer for potential therapeutic applications.
- To evaluate the efficacy of the developed capsid in a mouse model of Alzheimer's disease.
Main Methods:
- An in vivo selection strategy using an AAV peptide display library was employed to identify microglia-targeting capsids.
- The AAV MC5 capsid was identified and characterized for its transduction efficiency and specificity after ICV injection.
- Comparative analysis of MC5 against AAV9 and an evolved AAV9 capsid was performed.
- MC5's utility was assessed in a mouse model of Alzheimer's disease.
Main Results:
- A novel AAV capsid, MC5, was identified that demonstrates enhanced microglia transduction after ICV administration compared to AAV9.
- MC5 achieved 85% transduction efficiency and 93% specificity in microglia, outperforming a previously described evolved AAV9 capsid.
- Transduced microglia were observed surrounding and within amyloid plaques in an Alzheimer's disease mouse model, indicating MC5's potential in disease contexts.
Conclusions:
- The MC5 capsid represents a significant advancement as a gene transfer tool for targeting microglia in vivo.
- MC5 facilitates efficient and specific microglia transduction via both direct intraparenchymal and ICV administration routes.
- This discovery holds promise for advancing gene therapy strategies for neurodegenerative diseases and other brain disorders affecting microglia.
