Recombinant DNA Advisory Committee - 2/10-11/92 
There is a question if these vesicles might be as effective at killing the primary tumor as 
administering whole TK( + ) cells. Data from one animal experiment to the contrary 
should not be the basis for dismissing this concept entirely. Two mechanisms have been 
proposed, one is direct cell-to-cell killing and the other is an immune response stimulated 
by TK( + ) dying cells. He noted an experiment that demonstrated little or no tumoricidal 
effect in irradiated and nude mice. This study would suggest that the observed effect is a 
result of an immune system response. This result is still unresolved. The investigators 
have not provided much additional information since submission of the original protocol. 
Review-Dr. Geiduschek 
Dr. Geiduschek stated that the RAC originally sent the protocol back to Dr. Freeman for 
consideration of five specific points: (1) improve the animal model so that it has some 
relevance to the malignancy seen in patients; (2) examine the animal model for the tumor- 
specificity of cytotoxic T lymphocytes (CTL); (3) demonstrate the efficacy of the proposed 
treatment by measuring the tumor burden in patients and state whether this assessment 
will be conducted by laparoscopy, imaging techniques, or both; (4) refine safety tests; and 
(5) eliminate every reference to cancer vaccine in the patient consent form. The 
investigator submitted a supplemental appendix to address these points. This appendix 
includes new experimental data as well as old data previously considered by the RAC. 
Dr. Geiduschek summarized the protocol stating that it involves three steps: (1) 
introduction of the HSV-TK gene into a human ovarian cancer cell line; (2) 
intraperitoneal injection of these cells into the patients; and (3) treatment of the patients 
with ganciclovir. There are two proposed mechanisms of the effect observed with this 
treatment. The first proposed mechanism is that ganciclovir treatment specifically kills the 
peritoneally introduced HSV-TK cells, and that these cells then release apoptotic vesicles 
which effect killing of the patient's tumor. The second mechanism is that the apoptotic 
vesicles generated in situ are especially effective in presenting antigen to the immune 
system, and the killed HSV-TK cells elicit an immune response directed at the tumor. 
Dr. Geiduschek then described the supplemental appendix submitted by Dr. Freeman. 
Figures 1 through 7 are data previously seen by the RAC. Figure 8 illustrates the results 
of one experiment that demonstrated that the vesicle containing supernatant fraction 
cannot prolong survival in tumor bearing mice whereas whole cells can prolong survival. 
Figure 9 is data on the prolongation of survival of mice with six-day tumors that received 
irradiated HSV-TK cells. These mice die an average of eight days later than the untreated 
mice. This result might indicate that very large doses of irradiated, ganciclovir treated 
HSV-TK cells can reduce, but not eradicate, solid tumors. New data on the uptake of 
material from ganciclovir treated cells by ganciclovir resistant cells was submitted as 
fluorescent micrographs. Dr. Geiduschek said that he was surprised that this protocol was 
[336] 
Recombinant DNA Research, Volume 15 
