Recombinant DMA A<Jvisory Committee - 5/30-31/91 
coordinator who is able to answer any questions they may have. He underlined that all 
patients are therefore fully informed of the procedures involved as well as the risks of liver 
transplantation. 
In response to Dr. Walters' question as to whether the investigators would carry this 
experiment out without the marker gene, Dr. Ledley replied that the preclinical data on this 
point is mixed but noted that the surgeons felt they could use classical surgical methods to 
accomplish the transplant. However, he noted he felt the marker gene was important for 
verifying and confirming the success of the transplant. 
Dr. Mclvor asked what was the maximum number of human hepatocytes which had been 
transduced and what kind of transduction frequency had been seen. He also asked if Dr. 
Ledley intended to transduce 10^° cells. Dr. Ledley said that would be the case for a 50 
kilogram person, but noted that the patients they would be working with were children who 
would be in the weight range of 5-20 kilogram. Therefore, for a 10 kilogram patient they 
would transduce 2 X 10^ cells which would be comparable to the levels which were used in 
both the baboon and dog models. Dr. Woo added that in animal experiments using a human 
alpha- 1-antitrypsin stain they were able to transduce 2-3 billion hepatocytes in culture and that 
they found that approximately 20 percent stained positive for the human gene. 
Dr. McGarrity noted that there were no human hepatocellular cell lines, and he asked if 
attempts had been made to develop an immortalized cell line. Dr. Ledley said hepatocytes 
will sit in tissue culture and express hepatocyte markers for months, but that they stop dividing 
after the first 4-5 days. However, he noted this is an active area of research and that attempts 
were being made to alter the media to get these cells to continue growing. 
Dr. Kelley said he felt that for completeness sake he felt it important that Dr. Ledley should 
check out the use of dii to make sure it's not FDA-approved because this could be an 
alternative approach which could prove valuable if it were not carcinogenic or toxic in 
humans. Dr. Ledley noted that dii had only been in use for a short period but he said he 
would attempt to clarify this. 
Dr. Atlas asked for further clarification on the changes in procedures which resulted in 
improved survival of the animals after surgery. Dr. Ledley reiterated that this was a 
combination of changing the media over to Ringer's solution and phosphate-buffered saline 
as well as improvements in surgical technique. 
Dr. Mclvor asked if the investigators had ever contemplated using another virus vector, such 
as a beta-galactosidase vector, which would give improved detection. Dr. Ledley said they had 
been doing work on an alpha- 1 virus which offers some excellent prospects for the future. He 
said the issue is that the LNL6 has already received FDA approval and the investigators did 
not feel it was necessary to go to the time and expense of attempting to get another vector 
approved in light of the nature of the experiment, which is merely to test the feasibility of the 
process. However, he noted that work would continue on these other vectors and that if this 
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