Lymphocyte Gene Therapy for Mild Hunter Syndrome 
and die in childhood, while those with the "mild" form experience only the other somatic disease 
and survive to age 30 - 40 years. Conventional therapy is limited to palliative procedures (e.g., 
repair of carpal tunnel syndrome, herniorrhaphy, tracheotomy) which have virtually no impact 
upon the ultimate lethality of the disease. 
Allogeneic bone marrow transplantation (BMT) for patients with mucopolysaccharidosis 
diseases has been shown to provide a continuous source of enzyme and produces metabolic 
correction in many tissues (detailed below) as evidenced by reduction of urinary 
glycosaminoglycan excretion, disappearance of lysosomal inclusions in the liver, and amelioration 
of respiratory disease. However, several factors limit the application of BMT including the high 
morbidity and mortality of the procedure, lack of histocompatible donors, and tremendous cost of 
treatment ($200,000 - $1,000,000 per patient). 
These limitations now motivate exploration of alternate therapeutic modalities. A 
straightforward approach would be to combine the proven effectiveness of ex vivo lymphocyte 
gene therapy utilizing the LXSN-based retroviral vector system, and the encouraging results of 
bone marrow transplantation for somatic features of Hunter syndrome (Fig. 1). Predinical studies 
(see Preliminary Studies, below) suggest that retroviral-mediated insertion and expression of the 
human IDS gene in hematopoietic cells will prove to be a feasible, safe, and efficacious means of 
treating patients with mild Hunter syndrome. 
Fig.l 
Lymphocyte Gene Therapy for Mild Hunter Syndrome 
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