Structure comparison of the chimeric AAV2.7m8 vector with parental AAV2

Area of Science:

• Structural Biology
• Virology
• Gene Therapy

Background:

• Adeno-associated virus (AAV) vectors are crucial for gene therapy, particularly for retinal diseases.
• AAV2.7m8 is an engineered AAV variant designed for enhanced retinal transduction via intravitreal injection.
• Understanding structural modifications is key to optimizing AAV vector design.

Purpose of the Study:

• To elucidate the structural differences between the engineered AAV2.7m8 vector and its parental AAV2 serotype.
• To correlate structural changes with the altered antigenic properties and improved tropism of AAV2.7m8.
• To provide insights for future rational design of AAV vectors.

Main Methods:

• Cryo-electron microscopy (cryo-EM) and image reconstruction were employed to determine high-resolution structures.
• Structures of recombinant AAV2.7m8 (rAAV2.7m8) and AAV2 were resolved to 2.91 Å and 3.02 Å, respectively.
• Comparative analysis focused on capsid surface variable region VIII (VR-VIII) and amino acid side-chain configurations.

Main Results:

• The 10-amino acid insertion in AAV2.7m8's VR-VIII was localized, though side-chain details were limited by flexibility.
• Structural comparison revealed distinct side-chain orientations in AAV2.7m8 compared to AAV2, particularly within the modified VR-VIII region.
• These structural variations in VR-VIII, an antigenic epitope, correlate with AAV2.7m8's ability to evade the C37-B monoclonal antibody.

Conclusions:

• The structural basis for AAV2.7m8's altered antigenic profile and enhanced retinal transduction is identified.
• Cryo-EM provides valuable data on the impact of surface peptide insertions on AAV capsid structure.
• Findings support rational design strategies for developing next-generation AAV vectors with tailored tropism and immune evasion properties.