in Vitro Studies 
We have obtained preliminary data in a mammary cell line that the NGW retroviral 
vector can transform these cells in vitro , as determined by anchorage independent 
growth. The NGW retroviral vector contains traditionally non-oncogemc genes (g-owth 
hormone and neo^) and promoters. We are currently investigating whether the genes 
contained within the retroviral vector or the viral LTR's are responsible for the 
transformation process. 
Non-Human Primate and Human Safety Studies 
A non-human primate model was established by Cornetta et al (34) to analyze the 
affect of amphotropic retrovirus on monkeys. Five normal or immunosuppressed 
monkeys were inoculated with amphotropic viral stock to determine adverse effects of 
amphotropic virus in monkeys. In addition, some monkeys also received virus 
producing fibroblasts. Some immunosuppressed monkeys became viremic for 
approximately three weeks, but subsequently recovered with no repeat episodes of 
viremia or adverse effects. 
To date, approximately one dozen patients have received genetically engineered 
cells with no adverse effects (17, 19, and 20). The initial studies by Rosenberg et al. 
injected genetically marked TIL cells into cancer patients. These cells were 
transduced with replication incompetent viral stock. The viral stock was monitored for 
the presence of replication competent virus, a by product of a recombination event, by 
the sensitive S+/L- assay or helper rescue assay. In addition, once transduced, the TIL 
cells were grown in vitro for almost a month and tested for replication competent virus 
in the event that a replication competent viral particle went ur detected in the viral 
stock. Growing the cells in culture for a few weeks prior to reinfusion also allows the 
opportunity to analyze the cells for an oncogenic event produced by the insertion of 
the retroviral vector near a protoncogene. The next two human gene transfer clinical 
protocols followed similar procedures. 
Recently, clinical protocols have been submitted which transduce and infuse bone 
mamow cells into a patient within a few days of the transduction process (21). These 
protocols which for technical reasoas cannot monitor the transduced cells for 
replication competent virus or an oncogenic event before reinjection are still 
considered safe since the viral stock is tested by the above described sensitive 
techniques In addition, the frequency of oncogenesis using murine retroviral vectors 
is very low. These factors are considered before an approval of the protocol in the 
context of the risk-benefit to the cancer patient. In the advanced cancer patients used 
in the last studies, the inability to monitor transduced cells long term before reinfusion 
was deemed an acceptable risk. 
Our protocol also uses advanced cancer patients, but we will be able to monitor the 
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Recombinant DNA Research, Volume 15 
