Lymphocyte Gene Therapy for Mild Hunter Syndrome 
1.0 SPECIFIC AIMS 
The overall objective of this study is to evaluate the feasibility of treating Hunter syndrome 
by lymphocyte gene therapy. Peripheral blood lymphocytes (PBL) will be harvested by 
conventional apheresis. After stimulation with anti-CD3 antibody and growth in culture (with IL- 
2) for 3-1/2 days, the expanded population of T-lymphocytes will be transduced with L2SN (END 
#5370), a retrovirus vector designed for insertion and expression of the human IDS gene. The 
heterogeneous population of cells, including transduced and non-transduced cells (i.e., not 
selected with G418), will be returned to the patient by intravenous infusion. It is anticipated that 
the transduced lymphocytes will survive for several weeks, partially replenishing the deficient 
IDS enzyme, and resulting in metabolic correction. Conceptually, this approach goes beyond the 
pioneering trial of lymphocyte gene therapy for ADA deficiency: it seeks to determine if 
therapeutic numbers of cells and recombinant gene product (i.e.. enzyme) can be delivered to treat 
systemic disease. It is hoped that some of the most serious symptoms of Hunter syndrome will be 
slowed, prevented, or reversed by this treatment. Thus, the specific objectives of this clinical trial 
are: 
1.1 Enzyme "Dose" Determine the levels of IDS enzyme that are attained by infusing increasing 
"doses" of L2SN-transduced lymphocytes ranging from 5 x 10 7 cells/kg (initial dose) to 5 x 10 9 
cells (maximal feasible dose). 
1.2 Cell Survival Determine the duration of survival of these transduced cells by quantitating the 
pool of L2SN genetically-modified cells. 
1.3 Metabolic Correction Determine if monthly infusion of L2SN-transduced lymphocytes will 
accomplish metabolic correction as measured by reduction of urinary glycosaminoglycan 
excretion. 
1.4 Pathophysiology Determine if monthly infusion of L2SN- transduced lymphocytes will 
decrease liver and spleen volumes, and have any therapeutic effect upon cardiac and pulmonary 
dysfunction. 
1.5 Other Effects Determine if there are any other effects of this treatment regimen including (a) 
observation for other improvements such as decreased glycosaminoglycan in the brain as imaged 
by MRI, and (b) monitor for potential adverse reactions to treatment. 
2.0 BACKGROUND AND SIGNIFICANCE 
2.1 Overview 
Hunter syndrome (mucopolysaccharidosis type II) is a rare* X-linked recessive inborn error 
of lysosomal metabolism resulting from deficient iduronate-2-sulfatase (IDS) enzyme (reviewed in 
references 1-3). Consequent accumulation of the glycosaminoglycan substrates is clinically 
manifest as hepatosplenomegaly, skeletal abnormalities, cardiopulmonary failure and early 
demise. Patients with the "severe" form of Hunter syndrome incur progressive mental retardation 
* Estimated to occur at a frequency of 1/100,000 births (see reference 3, included in the appendix, 
for a comprehensive review). 
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