Recombinant DNA Advisory Committee - 12/3-4/92 
Other Comments 
Dr. Parkman asked about the patient eligibility criteria. Dr. Leventhal responded that 
patients will possess Stage IV breast cancer. Dr. Parkman addressed the issue of 
possible tumor cell transduction. Immunohistochemical staining can detect 
approximately 1 in 10 5 tumor cells. If patients demonstrate no detectable tumor cells by 
this method at the time of biopsy and at the time of ABM harvest, then the likelihood of 
tumor cells being transduced is extremely low. Clinically, disease reoccurs at the site of 
previous bulk disease. 
Dr. Parkman stated that the optimal method for detecting MDR-1 gene expression is to 
grow the transduced cell population in the presence of a selective agent and then to 
perform PCR on the individual resistant clones. Double marking will distinguish 
endogenous MDR-1 expression from MDR-1 expression based on the differences in 
ribonucleic acid (RNA) length. 
Dr. Doi asked if a high level MDR-1 expression is essential to the success of this 
protocol and whether the investigators plan to modify the level of expression. Are there 
in vitro experiments that could be performed that would provide information regarding 
expression, i.e., the in vitro maintenance an expansion of MDR-1 transduced 
hematopoietic cells. He inquired how long ABM cells would have to survive in vivo to 
provide a therapeutic effect during high dose chemotherapy. 
Mr. Barton said that since the purpose of this study is to permit the use of a more 
intense chemotherapy regimen in the event of relapse, the risk versus benefit section of 
the informed document should be expanded to more thoroughly address this issue. 
Dr. Post asked about the number of transduced cells that will be administered to these 
patients. Since the cells will be enriched by several logs due to the CD34( + ) selection, 
what is the level of sensitivity of the immunohistochemical staining? 
Dr. D. Miller explained that the proposed vectors are similar to LNL6 and GINa with 
the addition of the MDR-1 gene. However, human complementary DNA (cDNA) will 
be used instead of murine cDNA. What are the differences between human and mouse 
cDNA with regard to drug sensitivity? Some of the supporting data for this protocol was 
derived from murine experiments using a vector different from those being proposed for 
this study. How does the vector used for the animal experiments compare to the vector 
proposed for the human study? Will the investigators introduce additional cDNA 
mutations to reduce inappropriate splicing? 
Recombinant DNA Research, Volume 16 
[539] 
