Human Gene Therapy Subcommittee - 11/30/90 
cells containing the neomycin resistance gene demonstrated a higher plating 
efficiency than normal progenitor cells. Dr. Brenner said that these differences in 
plating efficiency were observed with normal cells, but that it had not been shown to 
inhibit transduction in malignant clones but rather was due to a technical problem in 
the transduction techniques that were employed. 
Mr. Capron asked if this selective advantage was taken into account in Dr. Brenner's 
calculation of transduction efficiency. Dr. Brenner said that it was assumed that the 
cells to be used in the protocol will steadily grow with or without the neomycin 
resistance gene. Therefore, the selective advantage is not included in the 
calculations. 
Dr. Brenner said that they will attempt to look at whether or not AML is a 
pluripotent stem cell disorder. If AML is a result of insertion sites being the same 
in pluripotent malignant progenitors as in normal progenitors, then attempts to treat 
AML using intensified chemotherapy and autologous BMT may founder, because of 
an inability to selectively remove malignant progenitors, and may force an increased 
emphasis on allogeneic transplantation. However, if the insertion sites are different 
in these two populations, the difference would allow for identification of malignant 
pluripotent stem cells from normals by inverted PCR analysis. 
Dr. Brenner said the protocol was least likely to answer whether or not the marker 
gene incorporates early uncommitted pluripotent progenitor cells. This 
determination would allow for discovery of the mechanism by which autologous 
marrow repopulates. An experiment was described in which selected and non- 
selected colonies of progenitor cells from 4 patients with AML in remission were 
transduced and assayed, and it was shown that a proportion of the committed 
progenitor cells could be transduced. However, none of the early colony types were 
identified. This result could be either because it reflects transduction of an early 
progenitor or because transduction of committed progenitors takes time to develop. 
Dr. Brenner also said that there was no evidence that mixing non-transduced and 
transduced bone marrow together would prove toxic to the non-transduced bone 
marrow. Experiments to demonstrate this result had been carried out in four bone 
marrows to date. 
Dr. Ihle said that he would address the question of animal models for this type of 
study. The most important point was that there were no spontaneous animal models 
for AML, and the model used in the past has been that of retroviral-induced 
myeloid leukemia in mice. A major problem in using this model was the fact that 
viruses are highly immunogenic. Consequently, it is not possible simply to mix the 
[402] 
Recombinant DNA Research, Volume 14 
