Recombinant DNA Advisory Committee- 9/12-13/94 
that the level of IL-2 required to show clinical benefit is unknown at present. 
Investigator Response--Dr. Lyerly 
Responding to a question by Dr. Smith regarding the origin of IL-2 production. Dr. Lyerly 
said that after transducing the primary cell culture, tumor cells were purified and T cells 
were isolated by phenotypic markers. No measurable IL-2 production was observed in T 
cells. The other experiment used an irrelevant plasmid as a control for transfection, and 
no IL-2 production was obtained. Thus, it was not due to nonspecific activation of the 
residual T cells. The other types of studies in which the IL-2 gene delivery and expression 
into tumor cells is to look for intracellular IL-2 expression. Such studies are ongoing. 
Dr. Lyerly explained that the unit for expressing IL-2 production is defined as pg/ml/10 6 
cells/24 hours. Dr. Miller said that this unit is not interpre table since one cannot have 
exactly 10 6 cells in one ml. Dr. Lyerly said it refers to one ml supernatant from a tissue 
culture dish of approximately 10 6 cells. The IL-2 level is corrected for actual number of 
cells in each dish. Dr. Miller suggested leaving out the "ml" in the definition to avoid 
confusion. 
Responding to the question of IL-2 levels required for clinical response, Dr. Lyerly said 
that in animal experiments, 1,000 to 2,000 pg IL-2/ 10 6 cells/24 hours, demonstrated 
protection against tumor metastasis. Initially, the level of IL-2 production in primary 
tumor cells was 200 to 800 pg/10 6 cells/24 hours. After improving the techniques, IL-2 
levels comparable to the animal studies, i.e., 1,000 to 2,000 pg were achieved. Dr. Lyerly 
noted the problem of IL-2 production in this kind of therapy, and that was the reason for 
choosing the present vector. In these primary breast cancer cells, the production of IL-2 
was undetectable using the retroviral vectors. 
In response to Dr. Doi’s question about the optimal level of IL-2, Dr. Lyerly said that 
there has been no reported data suggesting that there is an optimal level for T cell 
immune response. TTie consensus is that the more the better, and the reasonable starting 
level would provide the protection against tumors in the mouse model. 
Dr. Miller asked about the explanation for the extremely high level of EL-2 production 
shown in one of the experiments. Dr. Lyerly said the high level, i.e., 200,000 pg/10 6 
cells/24 hours, was obtained from a human breast cancer cell line, MCF-7, which can be 
grown as a monolayer in a tissue culture dish. That level has not been achieved with 
primary tumor cells. Dr. Parkman asked what IL-2 level was used when animal 
experiments demonstrate efficacy. Dr. Lyerly said it is about 1,000 units, and it is a level 
achieved with primary tumor cells. 
Committee Motion 
Dr. Smith made a motion to approve the protocol pending review of the vector in the 
closed session. Dr. Doi seconded the motion. 
Recombinant DNA Research, Volume 20 
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