Long-Term Follow-Up of Patients Treated by Gene Therapy for X-Linked Chronic Granulomatous Disease.

Chronic granulomatous disease (CGD) is a primary immunodeficiency in which phagocytic cells of affected patients have impaired antimicrobial activity due to a defect in the production of reactive oxygen species (ROS). CGD is caused by mutations in any one of four genes encoding for the subunits of the NADPH oxidase complex. Although curable by HSC transplantation, this strategy is usually limited only to patients with HLA-matched sibling or unrelated donors, as mismatched transplantation is associated with high morbidity and mortality due to graft failure and slow immune reconstitution. A therapeutic alternative for CGD patients is the genetic modification of autologous HSC. In January 2004 we initiated a Phase I/II clinical trial for X-CGD patients including conditioning with busulfan (8 mg/kg/total dose) prior to infusion of genetically modified HSC. G-CSF mobilized CD34+ cells from 2 adult patients (25 and 26 years) were transduced ex-vivo with a monocistronic gp91phox retroviral vector.

Therapeutically significant gene marking levels were detected in neutrophils of both patients with up to 60% functionally corrected phagocytes 14 months after gene therapy. This high correction resulted from an unexpected but temporarily restricted expansion of gene transduced myeloid cells in vivo. In contrast gene marking levels in B-cells has remained constant at a level of 20%, while gene marking in T-cells is below 5%. Gene marking in bone marrow was detected at levels between 30% and 40% one year after transplantation of gene modified cells. Killing assays in vitro have demonstrated antibacterial and antifungal activity in gene transduced phagocytes and both patients recovered of Staph. aureus and Aspergillus fumigatus infections after gene therapy. Our results suggest that gene therapy in combination with bone marrow conditioning is a therapeutic option for inherited diseases affecting the myeloid compartment and can be successfully used to treat CGD.