Recombinant DMA Advisory Committee - 6/9-10/94 
Dr. Smith asked whether there is the potential for toxicity resulting from high levels of 
CEA and anti-CEA antibodies in the blood. Have these toxicity issues been adequately 
addressed in animal experiments? 
Dr. Parkman expressed concern about the immune response to CEA and 
immunoprotection of syngeneic CEA expressing tumors in the murine model. The RAC 
has always required that one consistent criterion for approving any human gene transfer 
protocol is to demonstrate immunoprotection against a preexisting tumor in an animal 
model. The preclinical studies submitted by the investigator has not adequately 
demonstrated immunoprotection. The antitumor effects observed in mice resulted from 
vaccine administration initiated 7 days after the CEA bearing colon carcinoma cells were 
transplanted. The antitumor effect should be demonstrated on tumors that have been 
established for a longer period such as 21 days or more. Another important concern is 
that the human CEA antigen was used in a murine model. The rationale for the 
proposed study is to break immune tolerance by immunization with the CEA antigen. 
The preclinical murine experiments in which immune responses were demonstrated 
against human CEA. Human CEA is a foreign antigen to mice and may induce an 
immune response by acting as a hapten, a co-stimulator; therefore, the preclinical 
experiments are irrelevant. 
Dr. Haselkorn asked the investigators to elaborate on an experiment reported by 
investigators at the Memorial Sloan-Kettering Cancer Institute in which antibody 
responses to antigens associated with adenocarcinomas were induced by injection of 
human subjects with chemically treated bovine mucin. Dr. Doi inquired about the level 
of transgene expression, noting that an expression level of less than 1% is very low. 
Dr. Parkman asked the investigators why immunization with plasmid DNA-CEA is 
expected to be superior to CEA expressed by the vaccinia vector currently under 
investigation by Dr. Schlom. He noted that Dr. Schlom's vaccinia vector protocol would 
not have been exempt from RAC review according to the RAC's revised definition of 
Footnote V-21, exempt vaccines. Dr. Wivel explained that Dr. Schlom's study was 
initiated before the RAC revised Footnote V-21. 
Dr. Post said that the data obtained from the vaccinia-CEA trial should answer the 
question of whether human CEA can break tolerance and induce an immune response. 
The investigator has maintained that naked DNA injected into muscle is not integrated 
within the cell chromosomes, yet CEA has been shown to be persistently expressed for 
an extended period. Have sensitive experiments been performed to determine the exact 
percentage of DNA integration? Dr. Parkman asked whether the investigator has access 
to the data obtained from Dr. Schlom's vaccinia vector trial and whether the use of 
Cytoxan in that trial is important in breaking the immune tolerance by eliminating 
suppressor cells. 
Investigator Responses-Drs. Curiel and Lobuglio 
In response to Dr. Haselkorn's concerns. Dr. Curiel stated that the muscle cells are 
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Recombinant DNA Research, Volume 19 
