CD34 and X-linked adrenoleukodystrophy: One attempt to improve the clinical therapeutic options and decrease mortality is the execution of ex vivo ABCD1 gene replacement in CD34-positive HSPCs in 17 ALD boys with early stage brain disease using a lentivector (Lenti-D) (NCT01896102; NCT03852498; Cartier et al., 2009; Eichler et al., 2017).