larger, unmarked population. At FDA's request. Dr. Anderson and 
his colleagues are developing criteria for deciding whether or not 
to reinfuse a specific patient's TIL. 
The G418 selection procedure is used to remove TIL that are not 
expressing the NeoR gene. If the TIL are exposed to the N2 
vector more than once, the rate of incorporation will increase. 
This also means that the multiplicity of infection (MOI) goes up, 
concomitantly increasing the risk of insertional mutagenesis. 
Dr. Mclvor concluded that the greater concern appears to be a lack 
of incorporation of the NeoR gene, as opposed to the number of 
insertions, particularly because the risk of the latter appears to 
be small. Dr. Parkman agreed that it is preferable to obtain the 
most highly representative TIL population and, therefore, to avoid 
the risks associated with G418 selection. It has been reported 
that G418 selection, although commonly performed, alters phenotypic 
characteristics in ways that have not been explained. Dr. Parkman 
applauded the investigators' consideration of this issue, to which 
Dr. Anderson replied that this type of problem underpinned the 
decision to mark only a portion of the TIL. 
Dr. Rosenberg 
Dr. Rosenberg, National Cancer Institute, explained that the 
rationale for the gene transfer procedure was to improve the TIL 
therapy in later applications by drawing correlations between 
response to treatment, and TIL characteristics and behavior. The 
current protocol is state-of-the-art but there is much to be 
learned. 
There was some general discussion of the pros and cons of looking 
at the effects of delivering a broad, heterogeneous population of 
marked TIL, vs. a narrow homogeneous sample. Dr. Rosenberg noted 
that the ideal experiment would be to administer a single clone to 
one group of patients, and another clone to a second group, etc... 
and observe the results. However, this would require a large 
number of patients and is not justified at this stage of 
development. The alternative is to begin with a heterogeneous TIL 
population. 
Dr. Anderson 
Dr. Anderson responded to written comments regarding the safety of 
the N2 vector-packaging system. There are other vectors, for 
example, LNL6, developed by Dr. Dusty Miller, Fred Hutchinson 
Cancer Research Center. There are also other packaging cell lines, 
e.g., Cre/Crp, from Dr. Richard Mulligan; Split, from Drs. Arthur 
Bank and Steven Goff, Columbia University; and a new Split from 
Dr. Martin Eglitis, Genetic Therapy, Inc. The N2 system has been 
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