Human Gene Therapy Subcommittee - July 29-30, 1991 
carcinoma cell line. The tumor was injected into mice. One day later either 
unmodified or TK-modified human SKO ovarian tumor cells were injected. A long- 
term survival of 140 days was observed. When irradiated TK+ cells were injected, the 
response to ganciclovir was identical to the response observed with nonirradiated cells. 
Dr. Mclvor asked if experiments had been performed in which the irradiated and 
nonirradiated cells were compared in the absence of ganciclovir. The observed 
difference in survival is substantial, but may not be dependent on ganciclovir. Dr. 
Freeman said if the cells do not have the TX gene, they are not responsive to 
ganciclovir, and early experiments showed that the ganciclovir was found to be required 
to obtain the long-term survival. 
Dr. Kelley asked if the ratio of TK+ to TK- cells (required for the effects) had been 
improved in subsequent experiments. Dr. Freeman replied that he had not performed 
experiments that would address that issue. There is a question as to the relevancy of 
such mouse experiments to the treatment of humans. Every patient will be different, 
and the ratios required to obtain a positive result will differ as well. 
Dr. Leventhal asked how the ratios of TK+ and TK- cells will be changed if there is 
no success observed at the current levels. Dr. Freeman said ongoing experiments will 
address this issue. 
Dr. Freeman said the safety of the procedure is assured in three ways: (1) the tumor 
cells are transduced and grown in culture for extended periods of time, so that they can 
be tested for recombinant virus; (2) the cell line is already transformed, so there is no 
risk of transforming the cell line; and (3) the cells will be irradiated before infusion. 
Dr. Freeman presented data from allogeneic experiments. There was discussion about 
the location of tumor masses in the animals when they succumb to the disease. 
Dr. Neiman asked if there is any evidence that non-established primary tumors are 
sensitive to toxic ganciclovir metabolites or that these cells can incorporate small cell 
fragments. Dr. Freeman replied that this experiment has not been done. 
Dr. Erickson said that in patients with pre-existing ovarian cancer, tumor cells may 
have an extracellular matrix including fibroblasts. Do these cells phagocytose injected 
tumor cell fragments in the peritoneum? Dr. Freeman said the investigators will 
examine distribution within the patient's peritoneal cavity before treatment. 
Dr. Leventhal asked how tumor location will be assessed in the patients before they 
enter the protocol. Dr. McCune, Dr. Freeman's collaborator, said patients with 
progressive, relapsing disease will be defined by CEA, second-look laparotomy, or CT 
scans that may show small lesions. There must be evidence of residual disease, but 
Recombinant DNA Research, Volume 14 
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