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

β-thalassemia and Sickle Cell Disease are widespread fatal genetic diseases. None of the existing clinical treatments are resolving for all patients. So far two main strategies for the treatment are being investigated: (i) gene transfer of a normal β-globin gene; (ii) reactivation of the endogenous γ-globin gene. To date, neither approach has led to a satisfactory, commonly accepted standard of care. The δ-globin gene produces the δ-globin of the hemoglobin A2. Although low expressed, hemoglobin A2 is fully functional and could be a valid substitute of hemoglobin A in β-thalassemia disorder, as well as an antisickling agent in Sickle Cell Disease. Previous in vitro results suggested the feasibility to transcriptionally activate the human δ-globin gene promoter by inserting a Kruppel-like factor 1 binding site. We evaluate the activation of the Kruppel-like factor 1 containing δ-globin gene in vivo in transgenic mice. To evaluate the therapeutic potential we crossed the transgenic mice carrying a single copy activated δ-globin gene with a mouse model of β-thalassemia intermedia. Here we show that the human δ-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 addiction the activated δ-globin gene gives rise to a robust increase of the hemoglobin level in β-thalassemic mice, effectively improving the thalassemia phenotype. These results demonstrate, for the first time, the therapeutical potential of the δ-globin gene to treat severe hemoglobin disorders which could lead to novel approaches for the cure of β-hemoglobinopathies not involving gene addiction or reactivation.