negative. Western blot analyses of patient serum at various times after cell 
administration were all negative for evidence of exposure to virus as well. 
These studies demonstrated that gene modification of the TIL could be 
performed and that these TIL could be infused with no exposure of the patient 
to a replication competent virus. These studies provided us with valuable 
experience to perform subsequent studies of TIL modified with the gene for 
tumor necrosis factor (TNF) . These studies began on January 29, 1991 and thus 
far two patients have been treated with escalating doses of TIL transduced 
with the gene for TNF. Thus far no side effects have been seen in these two 
patients. 
2 . Interleukin-2 . 
Interleukin-2 (IL-2) is an immune mediator with a variety of immune 
modulatory effects both in vitro and in vivo (13-19). The injection of IL-2 
can mediate antitumor responses against established tumors in both the mouse 
and against established human tumors as demonstrated in our own and other 
clinical trials (see Table 3). A major activity of IL-2 is the provision of 
"helper" function by mediating the in vitro and in vivo expansion of 
immunoreactive cells bearing IL-2 receptors as a result of antigen activation. 
In an attempt to stimulate the immunogen i city of tumor cells when 
injected in vivo, Fearon et al. transfected the IL-2 gene into a poorly 
immunogenic carcinogen induced murine tumor, CT26 (20) . Whereas the 
unmodified parental tumor was highly tumorigenic the insertion of the IL-2 
gene into these tumor cells, and the resultant secretion of IL-2, eliminated 
the ability of these cells to form tumors following subcutaneous injection. 
BALB/c mice were capable of rejecting three to four orders of magnitude 
greater number of IL-2 transfected cells then the unmodified parental tumor 
cells. The immunologic nature of this tumor rejection was demonstrated by 
showing that the elimination of CD 8 positive cells in vivo resulted in the 
successful growth of these IL-2 transfected tumor cells. Further, the 
injection of these IL-2 transfected cells completely protected mice against a 
challenge two weeks later against the parental tumor. However, this immunity 
Recombinant DNA Research, Volume 15 
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