Human Gene Therapy Subcommittee - 11/21-22/91 
Ms. Meyers noted that the informed consent document does not clearly state that the 
patient will not be required to pay for complications arising from injury resulting from 
the gene therapy. She added that she had drafted a statement with regard to this issue 
with the assistance of Dr. Zallen and requested that the HGTS discuss the matter as a 
future agenda item. Dr. Gellert asked the investigators if they had observed secondary 
effects on neighboring cells following ablation with ganciclovir. 
Presentation-Dr. Greenberg 
In response to Dr. Mclvor's question regarding the ability to generate T cell clones 
specific for HTV and to transduce them, Dr. Greenberg stated that the generation of 
these clones is routine in his laboratory, and there is no reason to presume that the 
clones cannot be generated and expanded. There is nothing unique about HIV proteins 
as targets that distinguishes them from any other antiviral T cell clone. The gag protein 
was chosen as the target antigen because HIV seropositive patients have easily 
detectable gag-specific CTL clones. The gag protein generates the most dominant and 
reproducible responses. In addition, gag is a relatively conserved protein as opposed to 
the envelope which is under enormous selective pressure by a variety of host 
mechanisms. Gag is more likely to be conserved than other proteins. 
In response to Dr. Mclvor's question regarding the efficiency of transduction, Dr. 
Greenberg stated that between 0.2 and 2% of the T cells are transduced and express the 
HyTK gene. Dr. Greenberg added that he has been able to transduce T cells from 
patients 100% of the time. Analogous data were presented in the murine system in 
which T cell clones express the retrovirus consistently. Dr. Greenberg said that other 
investigators have demonstrated the ability to introduce ecotropic, rather than 
amphotropic, retroviruses into murine clones. 
Dr. Greenberg presented data demonstrating that these T cell clones are human 
leukocyte antigen (HLA)-restricted and that they retain their specificity following 
transduction with the HyTK gene and selection in hygromycin. Following selection, the 
clones recognize only the autologous target expressing the gag epitope of protein. 
Regarding the levels of ganciclovir that are obtainable in vivo, he presented data 
demonstrating that at 3 micrograms per kilogram 100% of the transduced clones are 
killed; however, this concentration is relatively nontoxic to humans. 
Dr. Greenberg showed in vivo and in vitro experiments demonstrating that T cell clones 
retain their sensitivity to TK when the negative selective conditions are removed. When 
clones maintained in the presence of hygromycin were compared to selected clones 
removed from hygromycin and maintained up to six weeks in culture, both populations 
were equally sensitive to ganciclovir. 
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Recombinant DNA Research, Volume 15 
