These results provide the basis for the dose escalation design of this 
trial: lethally-irradiated RCC vaccine cell dose is escalated at a fixed 
range of average GM-CSF cytokine production per cell. The range of GM-CSF 
secretion chosen produces maximal systemic antitumor immune responses in the 
preclinical models. The importance of sustained, local GM-CSF production 
achieved by gene transduction is underscored by the failure of mixing soluble 
recombinant GM-CSF with non-transduced irradiated tumor vaccine cells to 
generate any measurable antitumor immunity. 
The results also underscore the importance of assessing independently 
the toxicity that may be attributable to cell dose alone from that associated 
with GM-CSF expression. If, for example, our clinical studies suggest that 
the highest dose of non-transduced cells is well tolerated, yet the highest 
dose of transduced cells is not, it may be possible to obtain maximum benefit 
from the therapy by simply reducing the proportion of transduced cells at the 
highest cell dose. 
Studies in Other Murine Tumor Models 
Several well characterized murine tumor models were used to examine the 
generality of the host response to vaccination with irradiated, GM-CSF 
expressing tumor cells. These tumors included CT26, a colon carcinoma; CMS 5, 
a fibrosarcoma; RENCA, a renal cell carcinoma; and WP 4, another fibrosarcoma. 
In these studies animals were vaccinated with irradiated wild-type tumor cells 
or with irradiated tumor cells transduced with GM-CSF. Three weeks later, the 
vaccinated animals were challenged with live, wild-type tumor cells. 
In contrast to the experience with the B16 model (Figure 1 ), irradiated 
tumor cells possessed potent immunogenic activity (Figure 3). These results 
may provide at least a partial explanation for the ability to detect the 
immunostimulatory activity of a number of cytokines in these models, but not 
in B16. 
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Recombinant DNA Research, Volume 17 
