Comparative analysis of FV vectors with human α- or β-globin gene regulatory elements for the correction of β-thalassemia.

β-Globin locus control region (LCR) sequences have been widely used for the regulated expression of the human β-globin gene in therapeutic viral vectors. In this study, we compare the expression of the human β-globin gene from either the HS2/HS3 β-globin LCR or the HS40 regulatory element from the α-globin locus in the context of foamy virus (FV) vectors for the genetic correction of β-thalassemia. Both regulatory elements expressed comparable levels of human β-globin in a murine erythroleukemic line, whereas in murine hematopoietic stem cells the HS40.β vector proved more efficient in β-globin expression and correction of the β-thalassemia phenotype. Following transplantation in the Hbb(th3/+) mouse model, the expression efficiency by the two vectors was similar, whereas the HS40.β vector achieved relatively more stable transgene expression. In addition, in an ex vivo assay using CD34+ cells from thalassemic patients, both vectors achieved significant human β-globin expression and restoration of the thalassemic phenotype as evidenced by enhanced erythropoiesis and decreased apoptosis. Our data suggest that FV vectors with the α-globin HS40 element can be used as alternative but equally efficient vehicles for human β-globin gene expression for the genetic correction of β-thalassemia.