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. CGD is an ideal target for a gene replacement therapy, since females carriers of CGD with as low as 5-10% NADPH oxidase activity are healthy. Based on our preclinical work, we initiated a Phase I/II trial in January 2004. Two X-CGD patients, 26 and 25 years old, were recruited based on their long history of recurrent and life-threatening bacterial and fungal infections. G-CSF mobilized CD34+ cells were transduced with a monocistronic gp91phox retroviral vector. The transduction efficiency was 45% for Pat.1 and 40% for Pat. 2. The number of CD34+ cells reinfused was 1.2x10e7 per kg for Pat.1 and 0.9x10e7 per kg for Pat. 2. Before reinfusion, the patients were conditioned with liposomal busulphan given i.v. at a dose of 4 mg/kg at two consecutive days, starting at day -3. The treatment was well tolerated and no adverse effects have been observed. Neutrophil counts declined to less than 100 cells per μl at day 15 post reinfusion in both patients and recovered to more than 500 cells per μl at day 30 for Pat. 1 and day 20 for Pat. 2. A significant fraction of gene marked cells has been detected in peripheral blood of both patients since day +21. Similarly, therapeutically relevant levels of ROS production have been observed. In conclusion, the protocol we have used allows for stable engraftment of gene transduced hematopoietic cells under conditions in which gene corrected cells lack a selective advantage over non-corrected cells.