Comparative Transduction Profiling of Four Intravenously Delivered AAV Capsids in the Neonatal Murine Nervous System

Background: Selecting the most efficient and specific adeno-associated virus (AAV) capsids for gene delivery to the nervous system via minimally invasive routes is critical to gene therapy advancement. While AAV9, rAAV2-retro, AAV-PHP.eB, and AAV-MacpnS1 have demonstrated significant central nervous system (CNS) transduction ability after systemic delivery, their tropism, efficiency, and safety profiles in a developmentally relevant model have yet to be systematically compared. This study comparatively evaluated four capsids after intravenous administration in neonatal C57BL/6 mice. Methods: Transgene expression was quantitatively assessed across multiple CNS regions, as well as in the heart and liver. Associated biochemical indicators of hepatic stress were also evaluated. Results: The resulting transduction profiles were distinct and capsid-specific. Both AAV9 and AAV-MacpnS1 induced widespread CNS transduction and robust peripheral organ expression. However, AAV-MacpnS1-neuronal tropism in the thalamus was superior, and it was also associated with the most prominent biochemical indicators of hepatic stress. In contrast, rAAV2-retro was remarkably specific to the medulla and spinal motor neurons, demonstrating a valuable safety profile. AAV-PHP.eB achieved broad cellular transduction in the spinal cord, but it was the least specific towards cholinergic motor neurons. Furthermore, transduction in DRG neurons using AAV9 and AAV-MacpnS1 was efficient, but that using rAAV2-retro or AAV-PHP.eB was not. Conclusions: These findings provide an "atlas-like" comparative framework that clearly outlines the strengths and limitations of each vector. They also offer valuable guidance on selecting the most suitable AAV capsid for fundamental neuroscience applications and for developing targeted gene therapies, particularly for neurodevelopmental and motor neuron disorders, where intravenous administration in the early stages of life is a promising strategy.