July 30, 1990, Human Gene Therapy Subcommittee 
time they do not engraft. He noted this result may have to do with down-regulation of 
cell surface molecules and their ability to pass the peritoneal barrier in mice and may 
not be relevant to human engraftment. He said it had not been studied thoroughly 
because it was set aside when it was found that it did not work. 
Dr. Mulligan questioned whether the persistence was due to in vitro cultivation of the 
cells or whether the persistence was merely due to gene transfer. He said he thought the 
actual virus-producing cells have an effect on infection but do not necessarily have an 
effect on bone marrow. Dr. Bordignon agreed with Dr. Mulligan and said his data 
suggested this was the case. Dr. Mulligan asked if Dr. Bordignon had an estimate of the 
frequency of the initial fraction of cells that are infected in his experiments. Dr. 
Bordignon said that this is not known but is being studied currently. 
Dr. Mclvor asked if any ADA assays had been done on the bulk population after 
infection. Dr. Bordignon said it was between 1/5 and 1/3 of what would be expected 
with a good expression clone after 2 days of integration and expression time. 
Dr. Herschfield asked if it would be worthwhile to maintain the ADA-deficient cells 
from the patient in the presence of a level of PEG- ADA or other exogenous 
concentrations of ADA while they are in vitro or after injection into the mice. Dr. 
Bordignon said that he had done a variation of this experiment and that it did not affect 
response to antigens or PHA proliferation. Dr. Herschfield asked whether most of the 
deoxyadenosine that the cells are exposed to didn't come from degradation of DNA by 
macrophages, with red cell precursors being the source of the DNA. Having ADA 
outside the cells that are ADA deficient could allow them to function or persist for a 
longer period of time once removed from the patient. Dr. Bordignon said this was 
possible. 
Dr. Walters thanked Dr. Bordignon for his cooperation in attending the meeting and 
presenting his data. He then asked Dr. Parkman if he had any further points to make 
relative to the i.p. route of administration in light of Dr. Bordignon's data. 
Dr. Parkman said he was not comfortable with leaving the decision for instituting i.p. 
administration up to the local IRB. He thought that it should either be removed from 
the protocol altogether or that the investigators be required to return to the HGTS with 
data showing a greater level of efficacy with the i.p. as opposed to the i.v. route. 
Dr. Anderson said he did not feel this process was necessary if the investigator and all of 
the IRBs who will have to approve such a change in the protocol felt it was in the best 
interest of the patients. It would cause undue delay because of the frequency of the 
HGTS meetings. He asked for a compromise of having it come before a small subgroup 
of the subcommittee for approval similar to the "chairman's approval" of minor 
modifications in protocols. Dr. Blaese said the reason he left this option in the protocol 
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Recombinant DNA Research, Volume 14 
