The present invention relates generally to polypeptides or nucleic acids for use in the treatment, management, retardation of progression or normalisation of development of an iduronate-2-sulfatase (IDS) deficiency and/or Mucopolysaccharidosis type II (MPS II) in an individual, wherein the polypeptides comprise iduronate-2-sulfatase (IDS) tethered to a tandem repeat of Apolipoprotein E (ApoEII) or the nucleic acids comprise an iduronate-2-sulfatase (IDS) gene sequence tethered to a tandem repeat of the Apolipoprotein E (ApoEII) gene sequence. The invention also relates to haematopoietic stem and progenitor cells (HSPCs) transduced by such nucleic acids for use in therapies.