Gene therapy 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. Our aim 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 α-globin 
aggregates and achieve normal levels of hemoglobin. Transgenic K562 cell lines 
and erythroid precursor cells from β(0)39-thalassemia patients were employed. 
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. First, we analyzed the effect of mithramycin on 
K562 transgenic cell lines harboring different copies of a lentiviral vector 
carrying the human β-globin gene, showing that γ-globin mRNA expression and HbF 
production can be induced in the presence of high levels of β-globin gene 
expression and HbA accumulation. We then treated erythroid progenitor cells from 
β-thalassemic patients with T9W, which expresses the human β-globin gene and 
mithramycin separately or in combination. When transduction with our lentiviral 
vector is insufficient to completely eliminate the unpaired α-globin chains, 
combination of β-globin gene transfer therapy together with fetal hemoglobin 
induction might be very efficacious to remove the excess of α-globin proteins in 
thalassemic erythroid progenitor cells.