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lower risks than allogeneic transplantation. The risks associated with autologous 
transplantation are from the ablative conditioning therapy. If individuals with Gaucher 
disease could be transplanted with primitive macrophage precursor cells and stem cells 
into which a functional glucocerebrosidase gene has been placed without requiring a 
dangerous ablative regimen, the risk would be greatly reduced. It is the goal of gene 
therapy to be able to modify the patients own macrophage precursor cells and return 
them to the patient without using dangerous ablative regimens. If enough of the patient’s 
macrophages could be corrected, gene therapy would be therapeutic. If enough multi- 
potential pluripotent hematopoietic stem cells were corrected, gene therapy would be 
expected to be curative, as is allogeneic bone marrow transplantation. 
1.3 Preclinical Data 
Retroviral mediated transfer of GC cDNA in rodent in vivo marrow transplant models 
Extensive studies by several investigators have demonstrated the feasibility of retroviral 
mediated gene transfer into the hematopoietic stem cells of mice (15, 16). Furthermore, 
efficient transfer of GC cDNA into a substantial fraction of murine hematopoietic stem 
cells has been accomplished using retroviral mediated gene transfer (17-20). The 
retroviral constructs utilized are similar or identical to the ones proposed to be used 
clinically in this protocol. The Gc vector is equivalent to the LG vector described by Dr. 
Karlsson (20, 25) and the L-GC vector described by Dr. Kohn (14). Efficient transfer 
requires the presence of growth factors during the transduction period; in particular, 
Stem Cell Factor (SCF), interleukin-3 (IL-3) and interleukin-6 (IL-6) have been shown 
to increase gene transfer efficiencies. The sustained long-term level of human 
glucocerebrosidase expression measured in these animals is substantially higher than 
endogenous murine enzyme levels and would therefore be expected to permit correction 
of the enzyme defect in Gaucher disease patients if similar levels were obtained in 
humans. 
Retroviral mediated transfer of GC cDNA into human hematopoietic cells 
RMGT into human colony-forming cells has advanced significantly over the efficiencies 
seen only a few years ago. Using combinations of growth factors such as interleukin- 1 
(IL-1), IL-3, IL-6, and SCF it has been possible to increase the efficiency of gene 
transfer into progenitor cells to approximately 50% or more (21-25). These efficiencies 
have been seen with a variety of retroviral vectors transferring a variety or genes. 
Moreover, the efficient transfer of GC to cells derived from patients with Gaucher 
disease has been directly demonstrated and the expression of adequate levels of gene 
product shown (13, 14). This data includes the transfer and expression of GC in 
Gaucher disease macrophage precursor cells. 
Retroviral mediated transfer of GC cDNA into human long-term marrow cultures 
Human colony-forming assessments of gene transfer are limited in their ability to 
measure the parameters of gene transfer into more primitive hematopoietic cells. To 
study earlier progenitor cells (and possibly the pluripotent stem cell), Dexter developed 
[796] 
Recombinant DNA Research, Volume 17 
