Gene delivery using AAV8 in vivo for disease stabilization in a bimodal gene therapy approach for the treatment of ADA-deficient SCID

Abstract Adenosine deaminase (ADA) deficiency is an inborn error of metabolism affecting multiple systems and causing severe combined immunodeficiency. We tested intravenous administration of recombinant adeno-associated virus (AAV) 2/8-ADA vector in ADA-deficient neonate and adult mice or as part of a bimodal approach comprised of rAAV treatment at birth followed by infusion of lentiviral vector (LV) modified lineage-depleted bone marrow cells at 8 weeks. ADA-/- mice treated with 10e12 or 10e13 gc/kg rAAV and ERT for 30 days were rescued from the lethal pulmonary insufficiency, surviving out to 180 days without further treatment. rAAV VCN was highest in liver, lung, and heart and was associated with near-normal ADA activity and thymocyte development. In the bimodal approach rAAV-mediated ADA expression supported survival during the four weeks before infusion of the LV modified bone marrow cells and during the engraftment period. Conditioning prior to infusion may have resulted in the replacement of rAAV marked cells in marrow and liver, with LV VCN 100-1000-fold higher in hematopoietic tissue compared to rAAV VCN and was associated with immune cell reconstitution. In conclusion, a bimodal approach may be an alternative for patients without reliable access to ERT before receiving a stem cell transplant or gene therapy.