Systemic Elimination ofde novoCapsid Protein Synthesis from Replication-Competent AAV Contamination in the Liver

Abstract

The capsid protein synthesis in targeted tissues resulting from residual contaminating replication-competent adeno-associated virus particles (rcAAV) remains a concern for hazardous immune responses that shut down the factor IX expression in the hemophilia B clinical trial. To systematically reduce/eliminate the effects of potential contaminating rcAAV particles, we designed a novel adeno-associated virus (AAV) helper (pH22mir) with a microRNA binding cassette containing multiple copies of liver-specific (hsa-mir-122) and hematopoietic-specific (has-mir-142-3p) sequences to specifically control cap gene expression. In 293 cells, the rep and cap gene from pH22mir functioned similarly to that of conventional helper pH22. The vector yields and compositions from pH22mir and pH22 were indistinguishable. The performance of vector produced in this new system was comparable to that of similar vectors produced by conventional methods. In the human hepatic cell line, the capsid expression was reduced significantly from cap-mir cassette driven by a cytomegalovirus promoter. In the liver, 99.9% of capsid expression could be suppressed and no cap expression could be detected by western blot. In summary, we demonstrated a new concept in reducing de novo capsid synthesis in the targeted tissue. This strategy may not only help AAV vectors in controlling undesirable capsid gene expression, but can also be adopted for lentiviral or adenoviral vector production. Replication-competent adeno-associated viral particles (rcAAV) are an undesirable contaminant of vector preparations that may affect transgene expression or elicit a hazardous immune response. In this study, Yuan and colleagues have designed a recombinant AAV (rAAV) vector production system to tightly control AAV rep and capsid activity from rcAAV particles. According to the authors, this new method does not have any effects on rAAV yield or affect rAAV vector performance and is compatible with all current rAAV production systems.