HBB and thalassemia: Furthermore, the development of dual-function LVs combining HBB-like transgene expression with potent shRNAmiRs designed in independent studies to selectively target the mRNA of (a) BCL11A to combine de-repression of HBG with expression of HBB [54,55], (b) HBA2 to emulate an α-thalassemia carrier background [56] and (c) HBBS (βS) to reduce βS-encoding mRNA (HBB Glu6Val) in sickle cell disease patients [23,57], has paved the way for more targeted, mutation-specific gene therapy approaches to β-thalassemia.