The field of gene therapy still faces a challenge of the host immune response against capsid proteins. We hypothesize that our proposed immunosuppression regimen can reverse humoral and cellular responses in mice with pre-existing immunity for AAV and will allow safe microdystrophin administration and increase dystrophin expression in mice. We have developed an optimal microdystrophin (AAV9-µDysUF) that improves exhaustion and in vivo and ex vivo muscle force compared to µDys5*and GFP-injected mdx mice. Utilizing the wildtype C57BL/6 mouse, we injected them with empty AAV9 capsids to mimic pre-existing immunity in human patients. A baseline of antibody level was established. The mice were then injected with empty capsids at a dose of 1X1012 vg/kg on day 0 to induce an approximate level of anti-AAV antibodies of 150U/ml. Four weeks later, after collecting serum, the same animals (N = 6) received different immunosuppression drugs, either alone or in combination with other drugs. The immunosuppression drugs are velcade, darzalex, anti-CD20 antibody, and sirolimus. The animals were maintained in these drug regimens until day 70. We measured the anti-AAV antibody and compared group with no immunosuppression. We found a significant decrease in AAV antibody titers between no immunosuppression and animals on immunosuppression drugs. At day 70, sera from animals treated with antiCD20 antibody+sirolimus show 33%, velcade show 60%, darzalex show 60%, antiCD20 antibody+sirolimus+velcade show 88% and antiCD20 antibody+sirolimus+darzalex show 51% reduction in anti AAV9 titer respectively. This decrease in anti-AAV9 antibody is significant compared to controls. Furthermore, we plan to implement the best immunosuppression regimens for safe microdystrophin administration and increase dystrophin expression in mice. We are implementing immunomodulation strategies like an induction regimen before a high dose (1E14vg/kg), two low doses (5E13vg/kg), a maintenance regimen of anti-CD20 antibody, and sirolimus during the study to analyze which dose will provide optimal microdystrophin expression.