Gene therapy for chronic granulomatous disease combined with in vivo expansion of transduced hematopoietic cells.

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We have developed 'selective amplifier genes (SAGs)' which encode chimeric receptors to confer in vivo growth advantage on transduced hematopoietic cells. In this project, we investigated the feasibility of using SAGs to boost clinical benefit of gene therapy in a mouse model of X-linked chronic granulomatous disease (X-CGD). (1)A fusion receptor GcRER was constructed with the granulocyte colony-stimulating factor receptor and the estrogen-binding domain. X-CGD bone marrow cells were transduced by a retroviral vector encoding GcRER and gp91-phox, the latter of which is deficient in X-CGD. The transduced cells were reinfused into irradiated X-CGD mice for hematopoietic reconstitution. After recovery, estrogen was administered to a subset of the transplants, and the estrogen-treated animals had a significantly higher level of functionally corrected granulocytes. (2)As a second generation of SAGs, the extracellular domain of erythropoietin receptor (EpoR) was employed as a molecular switch to regulate cell growth signaling. EpoR was fused to the cytoplasmic domain of c-Mpl, and the gene for the chimera (EpoRMpl) was inserted into a retroviral vector together with the gp91-phox gene. X-CGD bone marrow cells were transduced with the vector and transplanted to X-CGD recipients as in the previous experiments. Erythropoietin administration to the recipient animals resulted in an elevation of functionally corrected granulocytes.These results indicated that SAG-mediated expansion of transduced hematopoietic cells is feasible in gene therapy for X-CGD.