Humoral immunity to adeno-associated virus type 2 vectors following administration to murine and nonhuman primate muscle

Adeno-associated virus (AAV) is being developed as a vector capable of conf erring long-term gene expression, which is useful in the treatment of chron ic diseases, In most therapeutic applications, it is necessary to readminis ter the vector. This study characterizes the humoral immune response to AAV capsid proteins following intramuscular injection and its impact on vector readministration. Studies of mice and rhesus monkeys demonstrated the form ation of neutralizing antibodies to AAV capsid proteins that persisted for over 1 year and then diminished, but this did not prevent the efficacy of v ector readministration. More-detailed studies strongly suggested that the B -cell response was T cell dependent. This was further evaluated with a bloc king antibody to human CD4, primatized for clinical trials, in a biological ly compatible mouse in which the endogenous murine CD4 gene was functionall y replaced with the human counterpart. Transient pharmacologic inhibition o f CD4 T cells with CD4 antibody prevented an antivector response long after the effects of the CD4 antibody diminished; readministration of vector wit hout diminution of gene expression was possible. Our studies suggest that t ruly durable transgene expression (i.e., prolonged genetic engraftment toge ther with vector readministration) is possible with AAV in skeletal muscle, although it will be necessary to transiently inhibit CD4 T-cell function t o avoid the activation of memory B cells.