one viral particle in 106 vector particles. If the background 
includes defective viral particles with the same envelope proteins, 
the sensitivity of the S+/L- assay will be reduced but the 3T3 
amplification assay would be sufficient. 
Looking at the worst case scenario, Dr. Anderson explored what 
might happen if one viral particle went undetected. The TIL cells 
are poorly infectable and the virus replicates slowly so that it 
might take time to detect. In this case, PCR, with a sensitivity 
of detecting 1 infected cell in 100,000, would be used to search 
for viral genomic DNA. This technique would be used to minimize 
the chance of missing even one viral particle. 
Dr. Anderson reviewed data from experiments involving the 
intentional exposure of a monkey to replication competent virus. 
In this case, there was no detectable pathology in a monkey in whom 
viremia had been established. Dr. Mclvor noted that it may be 
difficult to determine many of the health effects without autopsy 
results. However, the monkey is being followed to this date. 
Dr. Neiman asked about assays applied after 4-6 weeks of 
maintaining TIL in culture, but just prior to reinfusion in the 
patient. For example, the 3T3 assay requires 3 weeks of culture 
and, therefore, cannot be used on cells at the same time as 
delivery to the patient. Dr. Anderson stated that the S+/L-, PCR, 
IL-2 withdrawal, and reverse transcriptase (for other viral 
contamination) assays are used. The 3T3 assay could be used on an 
aliquot for follow-up purposes. 
Dr. Mahoney asked if it is possible to use short-lived nonhuman 
primates to look at the effects of chronic retroviral infection? 
Dr. Parkman responded that the virus appears to be cleared rapidly 
in monkeys and in vitro . This can be correlated with patients to 
show that the virus is inactivated. 
Dr. Anderson explained that an experiment had been done in a monkey 
to demonstrate the absence of risk to lab workers who might be 
accidentally exposed through a finger stick. A monkey was 
intentionally exposed by the implantation of infected autologous 
fibroblasts. The result was a 2-day episode of viremia with no 
fever, and the monkey is now well and cleared of virus. Dr. Neiman 
noted that the primate complement system inactivates retroviruses 
quite effectively, but that this is not the case in chickens. 
Dr. Anderson discussed the decision of how many TIL cells to 
transduce, and at what stage in cell growth this process was 
optimized. If a small number of TIL are transduced early in the 
culture period, there are fewer mutagenic events. However, at this 
point, there is still some shifting of phenotypes, thereby creating 
a less representative population. This can be avoided by examining 
those characteristics that indicate clonal selection has taken 
place and only reinfusing those TIL which are representative of the 
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