Human Gene Therapy Subcommittee - 11/30/90 
functions does not excuse Dr. Cometta from providing the data within the protocol, 
rather than relying on the HGTS to somehow read the information from data 
appearing in another protocol. Dr. Cometta's data was very minimal, having data on 
one patient showing a 1% transduction. 
Dr. Epstein then said that a basic premise of this protocol is that if labeled cell 
appear in a patient at the time of relapse, this result would prove the necessity of 
purging bone marrow before reinsertion into the patient. He asked the investigators 
what outcomes would result in this determination. 
Dr. Cometta said that finding any one cell in a reinfused patient, which arose from 
the bone marrow and caused leukemia, would constitute such an outcome. 
Currently, there is mixed opinion about whether there is any benefit to purging 
marrow; and there are those who even consider that it may have some toxic effects. 
Since the efficacy of the therapy is in doubt, it will be hard to interpret the results if 
the experimental results are negative. 
Dr. Mahoney asked if data showed that re-engraftment is hampered by vector 
exposure. Dr. Cometta said there is no data in humans, and the only proof comes 
from animal data. Dr. Anderson noted that the only data concerning gene transfer 
in humans are coming from the N2/TIL experiments, and those results indicate that 
the cells are not affected by the vector. 
Dr. Parkman asked for a quantitative estimate of the number of patients with 
positive results which would be required to show that purging of the bone marrow is 
necessary. Dr. Cometta said that the proposed protocol will be a preliminary study, 
and he did not have all the answers. There is a good chance that some evidence of 
patients having relapse due to leukemia in their marrow would be found. Without 
conducting the experiment, it would continue to be a question for physicians 
performing transplants. Dr. Parkman said that if there is going to be a randomized 
assignment of purged versus unpurged marrow, then there is no need to carry out 
the study, only to perform a randomized trial. 
Dr. Cometta said he thought Dr. Parkman was attempting to interpret data not yet 
available in order to push forward the randomized trial. It would be a significant 
finding if, for example, only 1 in 100 of these patients relapsed due to the marrow. 
This expected result would provide sufficient justification to conduct this study. 
Dr. Anderson said that no matter what the numbers involved, the point of the 
deliberation was if any significant data will come out of the proposal and to judge 
the risk of the procedure to the patient in order to gain this knowledge. 
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Recombinant DNA Research, Volume 14 
