ARSA and metachromatic leukodystrophy: Atidarsagene autotemcel (arsa-cel) is an autologous HSC post-lentiviral gene therapy ex vivo (HSC-GT) to treat presymptomatic late-infantile and early-juvenile and early-symptomatic early-juvenile MLD patients.32 CD34+ cells are harvested, engineered ex vivo with a lentiviral vector encoding human ARSA cDNA, and infused after busulfan conditioning, leading to overexpression of ASA and higher-than-normal ASA activity.