Repeated systemic dosing of AAV vectors in immunocompetent mice after blockade of T-cell costimulatory pathways.

Neutralizing antibodies (NAbs) strongly limit adeno-associated virus (AAV) vector transduction and repeated administration. Previous studies have shown that NAbs induced by AAVs are associated with T and B cell activation and that the B7/CD28 and CD40/CD40L costimulation signaling pathways are involved. CTLA4 and CD40 are vital molecules that participate in the costimulatory pathway. In this study, we evaluated CTLA4-Ig and CD40-Ig immunosuppressive efficacies through AAV and investigated their effects on the feasibility for multiple systemic administrations of AAV vectors. The results showed that a single administration of AAV vector carrying either CTLA4-Ig alone or with CD40-Ig could greatly reduce the level of NAbs. An AAV serotype-specific immune tolerance could be successfully established, which enabled repeated, i.e., second and third, systemic administration of AAV vectors in the same mice. A combination of CTLA4-Ig and CD40-Ig delivered via AAV vectors significantly inhibited T and B cell activations without affecting immune response to the total immunoglobulin G (IgG) production and cytokines. Interestingly, exogenous gene expression significantly improved after multiple administrations of AAV vector in vivo. Our study generates a reliable and effective method for repeated dosing of AAV vectors that is needed on gene therapy.