In vivo activation of the human δ-globin gene: the therapeutic potential in β-thalassemic mice.

beta-thalassemia and sickle cell disease are widespread fatal genetic diseases. None of the existing clinical treatments provides a solution for all patients. Two main strategies for treatment are currently being investigated: (i) gene transfer of a normal beta-globin gene; (ii) reactivation of the endogenous g-globin gene. To date, neither approach has led to a satisfactory, commonly accepted standard of care. The delta-globin gene produces the delta-globin of hemoglobin A2. Although expressed at a low level, hemoglobin A2 is fully functional and could be a valid substitute of hemoglobin A in beta-thalassemia, as well as an anti-sickling agent in sickle cell disease. Previous in vitro results suggested the feasibility of transcriptional activation of the human d-globin gene promoter by inserting a Kruppel-like factor 1 binding site. We evaluated the activation of the Kruppel-like factor 1 containing delta-globin gene in vivo in transgenic mice. To evaluate the therapeutic potential we crossed the transgenic mice carrying a single copy activated delta-globin gene with a mouse model of beta-thalassemia intermedia. We show that the human delta-globin gene can be activated in vivo in a stage-and tissue-specific fashion simply by the insertion of a Kruppel-like factor 1 binding site into the promoter. In addition the activated d-globin gene gives rise to a robust increase of the hemoglobin level in beta-thalassemic mice, effectively improving the thalassemia phenotype. These results demonstrate, for the first time, the therapeutic potential of the delta-globin gene for treating severe hemoglobin disorders which could lead to novel approaches, not involving gene addition or reactivation, to the cure of beta-hemoglobinopathies.