Human Gene Therapy Subcommittee - 11/21-22/91 
Dr. Miller said he would like to review the sequence data on a disk in order to run it 
through GenBank. 
Presentation-Dr. Nabel 
Dr. Walters called on Dr. Nabel to respond to the reviewers' comments and questions. 
Dr. Nabel presented data demonstrating the successful transduction of a melanoma cell 
line using a retroviral vector containing the gene encoding for HLA-B7. The 
transduction efficiency using the retroviral vector was approximately 100%. For 
comparison, he showed the same cell line that had been liposome-transduced with 
Vector II, which has RSV encoding HLA-B7 with the SV40 polyadenylation signal. The 
liposome-transfected cells were then co-transfected with the neomycin resistance (Neo R ). 
Transduction efficiencies ranged between 10 and 20%. 
Dr. Parkman asked how the liposomal DNA was quantitated. Dr. Nabel responded that 
the optimal method is to use Vector II, co-transfect with Neo R , and stain for P- 
galactosidase (p-gal). 
Dr. Miller asked if a true melanoma cell line was used or if it was just a primary isolate 
that had been grown in culture. Dr. Nabel explained that the melanoma tumor cells 
used in these experiments were primary isolates and that these cultures contained 
melanin, creating a black appearance. Dr. Nabel said that no delay has been observed 
in their growth; however, the cells had obviously undergone selection. Liposomal 
transfection experiments have already been performed in colon carcinoma cells 
exhibiting similar results. 
I 
As to the ambiguity of the IRB statement, the investigators sent a letter to their IRB 
clarifying that it would be melanoma, and the issue has been resolved. 
Dr. Parkman presented a scenario in which tumor biopsies would be performed on two 
patients. If the transfection rate in vitro were 10% for one patient and 0.1% for another 
patient, would the investigators be inclined to treat the patient exhibiting the higher 
tumor transfection rate? Dr. Nabel responded that since there are numerous cell 
adaptations between tumor resection and time in culture, the rate of transduction would 
not be a realistic criterion for patient selection. In fact, this scenario is one of the 
justifications for performing this trial in vivo. Dr. Nabel showed additional animal data 
in which an established MCA 106 (fibrosarcoma) leg tumor was injected with the p-gal 
vector. An identical tumor on the opposite leg was injected with Vector II containing 
the H-2K S gene. Complete tumor regression was observed with Vector II, and no 
response was observed in the control. Following treatment, the tumor recurred. When 
treatment was initiated a second time, the recurrent tumor disappeared. Dr. Nabel 
hypothesized that successful treatment is probably dependent on accessing sufficient 
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