Recombinant DMA Advisory Committee - 5/30-31/91 
with making this a suggestion, rather than a requirement. 
Dr. Deisseroth said that Dr. Mclvor also brought up the question of whether the investigators 
knew whether they were marking normal cells or not. He noted that he had presented data 
showing the colonies that grew from normal marrow after exposure to the virus were at very 
low level and the level now of marking in normal cells is a lot lower at the analytical level 
than it is at the leukemic level. But he said there was no reason to expect that if one were 
to purify those normal progenitors from normal marrow that it would not be possible to see 
same frequency of marldng. He emphasized that the immediate objective of the study is not 
to study normsil marrow, but rather to determine the origin of relapse. He said in the next 
phase of trying to follow the purification of the normal stem cell this would be an objective, 
but he noted that this was not now before the committee. He said this was of interest to the 
investigators and that they would continue to address it over the next months and years and 
when they have collected data relevant to these questions they would return to the RAC with 
another protocol. 
Dr. Deisseroth said he would be happy to, in consonance with Dr. Mclvor's suggestion, include 
a flow chart in the protocol to list the exact sequence of events. He added that they were 
planning on using quantitative laser confocal microscopy to quantitate the copy number of 
trans genomes in the cell. He presented a slide depicting the algorithm for interpreting the 
results of the experiment. He said that clearly one possible outcome of the marking would 
be that the blasts would be marked at multiple DNA sites and this would indicate that a 
polyclonal relapse had occurred which probably had arisen from the marrow. However, if the 
blasts were marked at a single site, that would mean that a single cell had arisen from the 
marrow which is dominating the relapse population and could have multiple interpretations. 
He noted that one such possible interpretation would be that a second mutation was acquired 
following the marking which conferred a selective advantage on this cell, and he felt this 
would be an interpretable result. However, if none of them are marked, then this would leave 
the interpretation up in the air. He noted that Dr. Leventhal had suggested that different 
results may be seen in different patients and he said he agreed with this and that he did not 
expect to see homogeneous pattern of response in all patients. However, he noted that unless 
a cell acquires another mutation after marking which gives it a selective advantage over all 
other cells he would expect to see a polyclonal relapse, provided a sufficient number of cells 
are in the marrow at the time of marking. So he said he felt there was no way to predict the 
outcome short of performing the experiment. 
Dr. Leventhal suggested doing a marrow at one week would allow the investigators to find out 
if their whole technical set-up had worked and at least give them the knowledge that they 
were able to reinfuse the cells and find them. She said this would be a lot to know in terms 
of interpreting later results. 
Dr. Deisseroth agreed with her and said that in fact he planned on doing this. He added that 
he would include an algorithm in the protocol which would be specifically directed at all the 
time points at which measurements would be done. 
Recombinant DNA Research, Volume 14 
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