Transient immunomodulation allows repeated injections of AAV1 and correction of muscular dystrophy in multiple muscles

Exon-skipping AAV1-U7-associated therapy is a promising treatment for Duchenne muscular dystrophy (DMD). We have shown earlier that the newly rescued dystrophin protein is stably expressed for months in mice and dogs, and does not induce immune rejection of transduced fibers. In this study, we used the dystrophic mdx mouse as a preclinical model to characterize the immune response to the adeno- associated virus 1 (AAV1) vector, and tested the feasibility of administering multiple AAV1 injections to extend the treatment to several muscles. We found that re-injections of AAV1 vector are compromised as early as 3 days after the first injection, coincident with a rapid increase in AAV1-specific immunoglobulin M (IgM) and IgG in the serum. Adoptive transfer of immune sera confirmed the rapid appearance of an AAV1 neutralization activity, and experiments with immunoglobulindeficient (mu KO) mice proved that antibodies (Abs) are the only effectors responsible for AAV1-U7 elimination. It is important to note, however, that the AAV2 vector still generated an adverse immune response in mu KO mice. By blocking the T- B crosstalk with antiCD40 Abs and CTLA4/Fc fusion protein, we found that a mere 5 days of immunomodulation treatment was sufficient to totally abrogate the formation of anti-AAV1 Abs and to allow for the correction of muscular dystrophy in multiple muscles, provided the treatment was administered during each challenge.