Gene therapy and fetal hemoglobin induction

Gene therapy is one of the strategy to correct the lack of β-globin synthesis in human hematopoietic stem cells (HSC) derived from β-thalassemia patients. In a recent manuscript, Breda et al. described a very interesting novel vector (T9W-Ank) carrying, in addition to the therapeutic β-globin gene, an ankirin isulator. These authors found that insertion of an ankyrin insulator leads to higher, potentially therapeutic levels of human β-globin through a novel mechanism that links the rate of transcription of the transgenic β-globin mRNA during erythroid differentiation with polysomal binding and efficient translation (1). However, the use of lentiviral vector carrying a therapeutic β-globin gene might fall short in achieving a complete reversion of the β-thalassemic phenotype due to current limitations in vector design and myeloablative regimen. Following gene transfer all or a large proportion of erythroid cells might express suboptimal levels of β-globin, impairing the therapeutic potential of the treatment. The aim of the present study was to evaluate whether, in absence of complete reversion of the β-globin phenotype upon gene transfer, it is possible to use fetal hemoglobin induction to eliminate the residual -globin aggregates and achieve normal levels of hemoglobin. Gene therapy was performed with the lentiviral vector T9W. Induction of fetal hemoglobin was obtained using mithramycin. Levels of mRNA and hemoglobins were determined by qRT-PCR and HPLC. Erythroid progenitor cells from -thalassemic patients were treated with T9W, which expresses the human -globin gene, and mithramycin, separately or in combination. When transduction with the T9W lentiviral vector is insufficient to completely eliminate the unpaired -globin chains, combination of -globin gene transfer therapy together with fetal hemoglobin induction was found very efficacious to remove the excess of -globin-proteins in thalassemic erythroid progenitor cells. The real clinical in vivo benefit, in our opinion, might be assayed in humanized transgenic mice mimicking thalassemia, in which HbF can be induced, the gene therapy is possible and the data obtained informative