Recombinant DNA Advisory Committee - 09/14-15/92 
assay exists to detect CLL progenitors. Dr. Deisseroth said that he was unaware of such 
an assay. Dr. D. Miller expressed concern about the frequency of gene marking. If the 
frequency is 0.1%, then the analysis will be difficult. Is there no method of measuring 
the frequency of marking? Dr. Deisseroth responded that since there is no technique for 
growing these progenitors, no estimate of the marking percentage can be provided. Dr. 
D. Miller inquired if PCR analysis of DNA rather than RNA would provide data 
regarding the frequency of transduction. Dr. Deisseroth said that RNA quantitation was 
chosen for PCR analysis because the sensitivity of the assay would be increased and the 
DNA could be analyzed. Dr. D. Miller noted that RNA is extremely difficult to 
quantitate, and it is difficult to estimate the number of cells. 
In response to Ms. Meyers concerns, Dr. Deisseroth stated a large number of bone 
marrow marking protocols are necessary because each type of leukemia if different, both 
in terms of biology and the questions that are addressed in each of the protocols. CML 
is a disease which results in cells that have unique cell surface changes, and these cells 
repopulate both the peripheral blood and bone marrow. There is no method for 
separating CML cell populations by differentiation antigens as is the case with CLL. 
Another reason to initiate a variety of bone marrow marking protocols is that patients 
who are eligible for bone marrow transplantation demonstrate a 10 to 30% mortality rate 
depending on whether they receive autologous or allogeneic transplantation. The 
application of gene marking to this protocol provides the opportunity to improve on 
these transplantation therapies. Most importantly, the study of hematopoietic 
reconstitution coupled with in vitro fractionation of marrow and retroviral marking 
provides important information that will lead to the initiation of therapy not only for 
hematopoietic neoplasms, but also for solid tumors and other human disease. Therefore, 
the information obtained from these marking protocols not only addresses the clinical 
problems associated with specific types of leukemia, but provides essential information 
regarding the use of bone marrow cells as a conduit through which to introduce 
therapeutic molecules into the systemic circulation. 
The importance of focusing on gene transfer in leukemia and cancer before other 
diseases is that cancer provides the clinical setting for solving the technical aspects of 
vector modification of somatic cells. Investigators can learn how to isolate early 
progenitor cells from marrow, monitor gene marking, obtain data that will yield 
immediate therapeutic implications relevant to the immediate disease, as well as prepare 
the foundation for procedures that will be necessary to provide molecules to the systemic 
circulation that can provide therapeutic benefit to patients with genetic diseases. These 
protocols set the stage for gene therapy of genetic diseases. 
Dr. Haselkorn inquired about the status of Dr. Deisseroth's previously approved 
protocols. Dr. Deisseroth said that the first approved protocol designed to establish the 
origin of relapse in CML has been initiated. Two patients have been transplanted with 
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