224. A Gene Therapy Clinical Study of a Patient with X-Linked Chronic Granulomatous Disease

Abstract

BACKGROUND: X-linked Chronic granulomatous disease (X-CGD) is a primary immunodeficiency disease characterized by failure of the nicotinamide adenine dinucleotide phosphate enzyme system in phagocytes to produce reactive oxygen species (ROS). This disorder derives from defects in the CYBB gene encoding gp91phox and leads to recurrent infection and hyper-inflammation, occasionally represented by CGD-associated colitis (CGD colitis). Hematopoietic stem cell transplantation (HSCT) is the only curative therapy for X-CGD, and in Europe and America, gene therapy clinical trials have been performed to patients who have no HLA-matched donor. To assess the safety and efficacy of hematopoietic stem cell gene therapy, we commenced a retroviral gene therapy clinical study using a busulfan-based preconditioning treatment regimen for CGD patients. METHODS AND PATIENT: The patient was a 27-year- old man with X-CGD. His condition was complicated by refractory subcutaneous abscess, fungal lung disease, lymphadenitis and CGD colitis, and he did not have an appropriate HLA-matched donor for HSCT. Granulocyte colony-stimulating factor -mobilized CD34+ stem cells were transduced with an MFGS-based retrovirus vector encoding the therapeutic gene of CYBB ex vivo, and infused back to the patient after busulfan-based preconditioning. Clinical and biochemical assessments were performed to evaluate the safety and efficacy of retrovirus gene therapy. RESULTS: After engraftment of 6.5×106/kg of CD34+ cells including 76% of gp91phox expressing cells, the gene-modified phagocytes appeared in peripheral blood after day +14. Dihydrorhodamine (DHR) flow cytometry assay demonstrated that the 2.3% of neutrophils in peripheral blood produced ROS, and a vector insert copy number was 2.63 per DHR+ neutrophil at day +95. His clinical symptoms of subcutaneous abscess and CGD colitis improved at almost the same time. The retrovirus insertion site of gene-modified peripheral blood cells revealed that there was no evidence of abnormal growth of clones with MDS-EVI1, SETBP1 or PRDM16 integrants at day +63. At day +182, gene marking of peripheral blood decreased to about 0.1% of neutrophils. PCR quantification of vector gene marking showed a vector insert copy number of 0.17 and 0.04 per neutrophil at day +95 and day +182, respectively. A vector insertion copy of bone marrow cells was 0.08 per marrow cell at day +183, suggesting that a reduction of gene-modified CD34+ stem cells would cause a decrease of gp91phox expressing phagocytes in peripheral blood. CONCLUSION: The therapeutic gene itself does not confer a growth advantage on the transduced cells in CGD, which would impact on the long-term gene marking and the withdrawal of clonal expansion. As other studies have reported that residual ROS production could contribute to the survival of CGD patients, the presence of gene-modified ROS-producing phagocytes led to the improvement of severe infection in our patient.