The structure of LVs used in clinical trials for β-hemoglobinopathies. The LV name is given in bold type. HS2, HS3, and HS4 are hypersensitive sites from the LCR. ΔLTR, self-inactivating LTR; β-p, β-globin promoter; E, β-globin gene enhancer; FB, FII/BEAD-A; RRE, Rev-responsive element; SA, splice acceptor; SD, splice donor.