Human Gene Therapy Subcommittee - 4/5/91 
therapy. He showed data depicting the approach to fulminant leukemic transformation. 
Conventional doses of chemotherapy are used to return the patient to the indolent form 
of disease. The autologous marrow is then collected, and can be identified by the lack of 
the chromosomal abnormality characteristic of the disease. Extremely intensive therapy 
is administered to eradicate all of the systemic disease, and then the marrow is reinfused, 
with the hope that the patient remains in remission for a long period of time. 
Dr. Deisseroth said if they are restricted to patients in whom they can restore the 
indolent form of the disease rather than the restoration of normal cells, the incidence of 
durable remissions is very low. If patients are selected when the initial chemotherapy 
has produced a condition in which normal cells dominate the marrow, most of these 
patients have durable remissions of a year or more, but they too ultimately relapse. To 
improve this therapy, one has to determine the source of the cells that contribute to 
relapse. It needs to be determined whether to increase the intensity of the preparation 
of the patient for marrow transplantation, which is designed to remove all of the systemic 
cells which are leukemic, or to try to further purge the marrow. Retroviral marking is 
needed to resolve these two issues, as implementation of either one of these 
modifications of existing therapy poses potentially mortal risks to the patient. 
Dr. Deisseroth said he can achieve marking of approximately 10-20% of the marrow cell 
population. Currently, it is possible to mark 1 in 3,000 cells, which is within the 
capability of available detection assays. Data were shown depicting the frequency of 
retroviral marking and the ability to conduct PCR assays. It is possible to analyze the 
cells to determine if they are leukemic in a way that differs from Dr. Brenner's AML 
protocol. A molecular marker can be used for detecting leukemic cells, a unique 
messenger RNA that can be seen by PCR. There is also the capability of doing colony- 
by-colony analysis to determine whether each colony is leukemic and whether each 
colony has the viral marker. If the patient is relapsing from malignant cells in the 
marrow, it is expected that the blasts will be marked with the leukemia marker and the 
viral marker. Also, it can be determined how many normal cells are being marked at 
multiple sites or single sites. If the apparently normal cells are marked at a single site 
with the neo gene as well as the leukemic marker, it can be concluded that the biology 
of the disease is continuously evolving, and there is a process of continuous 
transformation from normal to abnormal. The third possibility, if there are no marked 
cells, means systemic disease is contributing to the relapse. 
Dr. Deisseroth emphasized that he can identify leukemic versus normal cells at the 
molecular level, as well as the colony level. Hopefully, this protocol will contribute to 
the resolution of the clinically important issue of source of relapse, characterization of 
the properties of normal cells, the origin of CML disease, and information of use in 
possible future gene therapy of the disease. 
Recombinant DNA Research, Volume 14 
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