macroscopic nodule), the disease was detected in one small area in the porta hepatis. In the other 
mouse, there was one small nest of tumor cells (smaller than those shown in Figure 2F-Smythe et 
al., 1993c) adherent to the surface of the small intestine detectable only by anti-human HLA 
immunostaining. These studies have been repeated with an additional human mesothelioma line (1- 
45) with virtually identical results. 
We have extended these studies to look for a survival advantage after gene therapy (See Smythe et 
al., 1994c). Groups of animals (7 per group) were given intraperitoneal injections of 
mesothelioma and then treated with (1) vehicle alone, (2) H5.010CMV/acZ plus GCV, (3) 
H5.01 ORSV TK without GCV, or (4) H5.010RSV77< r plus GCV. Almost all animals in the first three 
groups died within 8 weeks of tumor injection (median survival between 35-51 days). In marked 
contrast, the median survival of the HSVTK/GCV group was 77 days, with 1 animal still alive at the 
time of writing (>25 weeks). Four of the H5.010RSVTK-treated animals that died were necropsied. 
Although two of the four animals had a small tumor nodule, as best as could be determined, the cause 
of death in each case appeared to be due to bowel obstruction due to adhesions and scarring. We 
postulate that this fibrosis was due to the inflammatory response associated with tumor regression. 
Obviously, bowel obstruction and fibrosis will not be a problem with intrapleural tumor. 
Established Intrapleural tumors were successfully treated in Fisher rats using the 
H5.01 ORSVTK/GCV System. We have also examined the efficacy of the HSVTK/GCV system in a 
pleural model of mesothelioma in an immunocompetant rat (see above). To this end, we first tested 
the ability of adenovirus to infect rat mesothelium. Injection of 2 x 10 10 pfu of H5.010RSV/acZ in 
a volume of 0.25 ml resulted in clear cut expression of p-gal in about 50% of the visceral and 
parietal pleural mesothelial cells with no gene transfer to the underlying lung or chest wall. We 
therefore used this virus to treat established pleural tumors created by injection of 1145 rat 
mesothelioma cells into the thoracic cavity. Injection of 2 x 10 10 pfu of HS.OICRSVTK' into the 
pleural space, five days after tumor injection, followed by intraperitoneal administation of GCV at 
50 mg/kg markedly inhibited the growth of tumor (see Figure 3 below). Injection of 
H5.010CMV/acZ had no effect on tumor growth. Tumor mass was assessed by determining the weight 
of all visible tumor. 
Figure 3 
Treatment of Rat Pleural Mesothelioma with Ad.RSVtk 
Ad.tk/GCV Sallne/GCV 
Treatment 
In summary, we have demonstrated that the H5.010RSVTK/GCV system is effective in eliminating 
tumors created by pre-transduced cells and that a strong in vivo bystander effect is present. In 
addition, we have successfully used this system to effectively treat macroscopic, established tumor 
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Recombinant DNA Research, Volume 20 
