Human Gene Therapy

Pompe disease can be treated effectively, if immune tolerance to enzyme replacement therapy (ERT) with acid α-glucosidase (GAA) is present. An adeno-associated virus (AAV) vector containing a liver-specific regulatory cassette to drive GAA expression (AAV-LSPhGAA) established immune tolerance in GAA knockout (KO) mice, whereas ubiquitous expression with AAV-CBhGAA provoked immune responses. Therefore, we investigated the hypothesis that immune tolerance induced by hepatic-restricted expression was dominant. AAV-LSPhGAA and AAV-CBhGAA were administered singly or in combination to groups of adult GAA-KO mice, whereas AAV-LSPhGAA induced immune tolerance even in combination with AAV-CBhGAA. The dual vector approach to GAA expression improved biochemical correction of GAA deficiency and glycogen accumulations at 18 weeks, and improved motor function testing including wirehang and grip-strength testing. The greatest efficacy was demonstrated by dual vector administration, when both vectors were pseudotyped as AAV8. T cells from mice injected with AAV-LSPhGAA failed to proliferate at all following an immune challenge with GAA and adjuvant, whereas mock-treated GAA-KO mice mounted a vigorous T cell proliferation. Unlike AAV-LSPhGAA, AAV-CBhGAA induced selective cytokine and chemokine expression in the liver and spleen following the immune challenge. AAV-CBhGAA transduced dendritic cells and expressed high-level GAA, whereas AAV-LSPhGAA failed to express GAA in dendritic cells. The level of transduction in liver was much higher following dual AAV8 vector administration at 18 weeks, in comparison with either vector alone. Dual vector administration failed to provoke antibody formation in response to GAA expression with AAV-CBhGAA; however, hepatic-restricted expression from dual vector expression did not prevent antibody formation following a strong immune challenge with GAA and adjuvant. The relevance of immune tolerance to gene therapy in Pompe disease indicates that hepatic expression might best be combined with non-hepatic expression, achieving the benefits of ubiquitous expression in addition to evading deleterious immune responses.