5. What functional characteristics of the TIL 
define their ability to localize tumor or 
distant sites? 
6. Is there a correlation between localization, 
function and clinical efficacy? 
Dr. Blaese said the protocol calls for labeling TIL with the 
retroviral vector N2 containing the Neo* (neomycin resistance) 
gene. Investigators will label less than 50 percent of the 
patient's harvested TIL population so that removal of cells for 
retroviral marking will not interfere with the therapeutic 
process. The N2-transduced TIL will be reinfused at the time of 
standard therapy. They will then biopsy tumor nodules and other 
tissues at intervals and measure the vector presence by detection 
of the inserted gene. These biopsied samples will then be 
cultured and the TIL regrown with the Neo B gene to recover cells 
infused initially for analysis of their functional phenotype and 
correlation to response to treatment. 
Dr. Blaese explained that an advantage of using such marker genes 
would be that they provide properties that exogenous labels 
cannot provide for answering many of the questions stated above. 
Further, a gene label would not leach away from the original cell 
as is the case with many radioactive labels. Also, radioactive 
labels are lost as soon as a cell dies and do not become 
sequestered or reutilized marking other cells or tissues. The 
genetic label is not diluted out as TIL proliferate in the 
patient with continued administration of IL-2. The gene marker 
should permit specific recovery of the marked cells at a later 
date, thus permitting recharacterization of cells after they have 
spent variable periods of time in the patient. 
Dr. Blaese explained the methods for performing the cell culture 
and infusion in detail. He described experiments that had been 
performed using the N2 retroviral vector which demonstrated that 
the marker gene could be introduced into human TIL and expressed 
at a useful level. 
Dr. Blaese said the N2 vector had been introduced into TIL 
populations obtained from 15 patients, including 6 patients in 
whom the entire procedure being proposed, short of reinfusion, 
had been followed. The results of this experiment showed an 
infection efficiency of approximately 10 percent. The 
introduction of the vector; selection in G418 medium, a neomycin 
analog; and the presence of the marker gene, did not interfere 
with the capacity of the cell for normal growth compared to the 
regular TIL population in these patients. 
[242] 
Recombinant DNA Research, Volume 13 
