Recombinant DNA Advisory Committee - 06/1-2/92 
adequate. Dr. Deisseroth stated that not all PCR positive cells will contribute to disease. 
CML may be a multi-step process. 
Dr. Geiduschek returned to the issue of the sensitivity limits for detection of replication 
competent virus. He summarized an earlier discussion stating that it is not possible to 
exclude the high probability that every patient, or most of the patients, will receive more 
than one replication competent virus particle in their total treatment. Dr. Deisseroth 
was asked to comment further on this issue. He suggested that since Dr. Dunbar was 
present, she may also want to comment on this issue. 
Dr. Geiduschek stated that the other issue that the investigators should address is the 
efficiency of CD34( + ) selection techniques. 
Dr. Deisseroth said that data has been submitted for publication by other investigators 
regarding CD34( + ) selection in non-leukemic patients undergoing autologous bone 
marrow transplantation; for these non-leukemic patients, hematopoietic reconstitution 
has been complete and rapid. Equivalent numbers of CD34( + ) cells have been obtained 
from leukemic patients and the DR(-) subpopulation of CD34( + ) cells has been isolated. 
It is this CD34( + )/HLA-DR(-) population of cells that has been shown to be normal 
and non-leukemic. By every criterion, these are the cells that are most competent to 
regenerate rapid hematopoietic reconstitution. However, the only way in which to prove 
this theory is to transplant these cells into humans. He reminded Dr. Geiduschek that 
there is always a reserve of cryopreserved cells available for autologous bone marrow 
transplantation in the event that engraftment does not occur. 
Dr. Geiduschek asked if the CD34( + ) selection procedure will provide these patients 
with a margin of benefit in return for the risk? Dr. Deisseroth acknowledged that the 
first step of the bone marrow fractionation process offers a large potential for benefit to 
these patients. He stated a reluctancy to introduce both fractionation steps at the same 
time. Bone marrow reconstitution from CD34( + ) fractionated cells must be 
demonstrated prior to introducing further selection procedures. This protocol is a 
systematic, step-wise plan to use retroviral marking to resolve very important therapeutic 
issues. 
Mr. Capron asked if the results of this protocol demonstrate that CML relapse is the 
result of inefficient purging of the autologous transplanted bone marrow cells, will this 
lead to more intense purging and a more stringent preparatory treatment? Dr. 
Deisseroth responded that due to the heterogeneity of this disease and the random 
somatic mutations, it is conceivable that some patients will relapse from contaminating 
marrow cells and others will relapse from systemic disease. However, these gene 
marking studies will allow for independent evaluation of the contribution of the bone 
marrow for systemic disease. Knowledge should be obtained about the relative 
Recombinant DNA Research, Volume 15 
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