In vivo selection of genetically modified erythroid cells using a jak2-based cell growth switch

Cell-based therapies have potential widespread applications in clinical medicine, and methods for controlling the fate of transplanted cells are needed. We have previously described a means for directing the growth of genetically modified cells in vivo using a derivative of the thrombopoietin receptor, mpl, that is reversibly activated by a drug called a chemical inducer of dimerization (CID). Since Jak2 participates in signaling from a number of different cytokine receptors (including mpl), we tested whether direct activation of the JH1 domain of Jak2 would broaden the repertoire of hematopoietic lineages responsive to the CID. While the engineered Jak2 induced a significant rise in genetically modified red cells, as we have observed previously with mpl, it lacked mpl's ability to expand genetically modified platelets and failed to expand genetically modified granulocytes, B cells, or T cells. These findings identify a signaling molecule other than mpl that can function as a cell growth switch in vivo and demonstrate that signaling molecules used for in vivo selection need not be confined to receptors. The erythroid-restricted growth response suggests that CID-activated Jak2 may be well suited to gene therapy applications in sickle cell anemia or beta-thalassemia.