Recombinant DNA Advisoiy Committee - 2/10-11/92 
was observed with TK( + ) cells. Dr. Freeman then presented toxicity study data. Eighteen 
mice were injected with TK(+) cells, treated with ganciclovir, and sacrificed at days 1, 3, 
10, 17, 24, or 31 post-treatment. Tissue samples were analyzed, and no abnormalities were 
observed. 
Dr. Freeman explained that the patients eligible for the proposed study would have 
microscopic tumors and have an expected survival of 18 to 24 months. Three therapeutic 
animal models were established to mimic the human situation: (1) a mouse model with 
microscopic tumor, (2) a mouse model that has macroscopic tumor less than 1 centimeter, 
and (3) a mouse model that combines the modified cells and immunization. In mixing 
experiments, only the mice that received either 100% TK(+) cells or 50% TK( + ) and 
50% TK(-) cells demonstrated prolonged survival. Therefore, TK(+) cells must have a 
toxic effect on nearby TK(-) cells. When the treatment was initiated on the day following 
tumor challenge, survival tripled. This model is analogous to the microscopic tumors 
observed in the patient population. In the intraperitoneal tumor model, mice were found 
to develop subcutaneous tumors at the needle track site. At autopsy, no evidence of 
intraperitoneal tumor was observed, only the subcutaneous tumors. This fact may be why 
longer survival is not being observed. Based on these results, their patient population is 
confined to Stage I, II, and III ovarian carcinoma. 
Dr. Freeman detailed the results of an experiment in mice with large six-day tumors. By 
day six, the mice developed tumors that were approximately 4 millimeters in diameter. 
When treated only with ganciclovir alone, the mice survived 13 days. When mice were 
treated with 2x1 Or, lxlO 6 , or lxlO 7 TK(+) cells, prolonged survival was observed with both 
IX 10 6 and IX 10 7 cells. This data suggests that the system is functioning. Examination of 
the peritoneal cavity at autopsy demonstrated the presence of necrotic tumor within 24 
hours of receiving the modified cells. 
In conclusion, Dr. Freeman presented data on the combination of immunization and 
injection of TK( + ) cells. Mice were immunized six weeks prior to tumor challenge. Six 
days following tumor challenge, the mice were treated with TK( + ) cells and ganciclovir; a 
pronounced effect was observed. Mice survived up to 50 days following tumor challenge. 
The data presented should justify approval of the protocol because the data demonstrates 
clinical efficacy and safety, no other therapy exists for microscopic tumors, and statistically 
significant prolonged survival analogous to the patients' response has been demonstrated in 
animal models. 
Discussion 
Dr. Mclvor asked Dr. Freeman four questions: (1) What is the ratio of transduced cells to 
existing tumor cells necessary to observe prolonged survival? (2) How will the existing 
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