Advances in the treatment of chronic granulomatous disease by gene therapy

Gene transfer into hematopoietic stem cells has been successfully used to correct immunodeficiencies affecting the lymphoid compartment. However, similar results have not been reported for diseases affecting myeloid cells, mainly due to low engraftment levels of gene-modified cells observed in unconditioned patients. Here we review the developments leading to a gene therapy approach for the treatment of Chronic Granulomatous Disease (CGD), a primary life threatening immunodeficiency caused by a defect in the oxidative antimicrobial activity of phagocytes. Although the disease can be cured by bone marrow transplantation, this treatment is only available to patients with HLA-identical sibling or matched unrelated donors. One therapeutic option for patients without suitable donor is the genetic modification of autologous hematopoietic stem cells. Although early attempts to correct CGD by gene therapy were unsuccessful, these studies demonstrated the safety and limitations of gene transfer into hematopoietic stem cells (HSC) of CGD patients using retroviral vectors. The recent development of advanced gene transduction protocols together with improved retroviral vectors, combined with low intensity chemotherapy conditioning, allowed partial correction of the granulocytic function with a significant clinical benefit in treated patients. These results may have important implications for future applications of gene therapy in myeloid disorders and inherited diseases using hematopoietic stem cells.