Recombinant DNA Advisory Committee - 21^191 
Dr. Blaese said that there were many technical questions to be answered by the protocol. 
One question was whether routine apheresis could be performed on children repeatedly 
in order to collect sufficient numbers of cells for immunotherapy. This has proven to be 
an achievable and very simple procedure with no side effects noted that were associated 
with the collection of cells, and no anemia. Because of this success there has been no 
necessity to introduce central venous lines in order to perform apheresis on a routine 
basis. 
He noted the consistent success in culturing the T cells from peripheral blood samples 
and stimulating their proliferation, a question which had not been answered previous to 
the study. They also had reproducible ADA gene transfer and expression into these cells 
in tissue culture and that routine infusion of cultured T cells has not been limited by any 
side effects. 
Dr. Blaese said that they had been able to demonstrate the feasibility of using 
cryopreserved gene-modified cells. One child had been treated using this technique and 
that it has been demonstrated to be feasible. 
He said one of the questions which had come up in the subcommittee discussions of this 
protocol had centered on the question of the half-life of the infused cells. He presented 
data to show that the persistence of these cells could be demonstrated and was quite 
dramatic in some cases. He further added that he would present data to show that 
infusions of interleukin-2 (IL-2) are not required for long-term persistence of these cells. 
Dr. Blaese said there was limited data on the continued expression of the genes in vivo 
but that due to the protocol design of gradual escalation in cell dosages, all of the data 
are not complete. The long-term objective of the protocol was to develop improved 
patient immune function. A thorough evaluation of this would not be done until after 
the sixth infusion in patients, but that there are some preliminary data in this regard that 
he would present. 
Dr. Blaese explained the protocol in detail, noting that it is divided into three parts or 
phases. The first part calls for early reinfusion of cells within a couple of weel« to limit 
the possibility of cells losing heterogeneity by being maintained in culture for long 
periods. The second part calls for cell selection to increase the proportion of cells 
expressing the human ADA gene. And the third part of the protocol is an attempt to 
escalate the dose of cells to determine if ultimately it would be possible to use this 
therapy to replace the requirement for PEG-ADA injections in the patients. 
He presented data on the first patient showing a T cell growth curve beginning in the 
range of 50 million cells which was expanded in 1,000 fold in tissue culture over a 10-11 
day period. Dr. Blaese showed that these polyclonal T cells could be grown up very 
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Recombinant DNA Research, Volume 14 
