“…These studies were the basis for the development of a safer and more efficacious vectors, derived from the human immunodeficiency lentivirus (HIV) and carrying carefully designed transgene expression cassettes based on cellular promoters and regulatory elements [ 6 ]. A number of seminal clinical studies addressing primary immunodeficiencies [ 7 , 8 , 9 , 10 ], hemoglobinopathies [ 11 , 12 ], stem cell deficiencies [ 13 ] and neurometabolic diseases [ 14 , 15 , 16 , 17 ] proved the therapeutic efficacy and safety of lentiviral vectors, which eventually allowed the commercial registration of Zynteglo ® for gene therapy of β-thalassemia ( , accessed on 1 August 2021) and Libmeldi ® for metachromatic leukodystrophy (MLD) ( , accessed on 1 August 2021).…”