Mutations in the IL2RG gene and the ADA gene are two of the most common causes of severe combined immunodeficiency (SCID). Patients with SCID are unable to develop T-cells and as a consequence will die of infections in the first years of life. Patients with SCID are treated by hematopoietic stem cell transplantation although there are a number of retroviral/lentiviral based gene therapy clinical trials currently accruing patients. Our goal is develop a homologous recombination based approach to gene therapy for these diseases. Just as with the hemoglobinopathies we had made ZFNs to target the IL2RG and ADA genes but have found that TALENs are substantially more active and show less cytotoxicity than ZFNs and have adopted TALENs as our platform moving forward.
For the IL2RG gene we have developed a pair of TALENs and broad set of targeting constructs. Using these reagents we are achieving high rates of genome editing at the endogenous locus in cell lines and are working on optimizing the frequency of gene targeting in human CD34+ cells and their subsequent differentiation into T-cells and transplantation into NSG mice.
We have made similar progress targeting exon 1 of the human ADA gene and have a similar experimental path to the IL2RG gene.
This project is funded by the NIH/NIAID and the goal of this project, as it is with the sickle cell disease/b-thalassemia project is to develop a homologous recombination based approach to gene therapy to cure children with SCID.