Recombinant DNA Advisory Committee - 06/1-2/92 
gene marking protocols involving a total of 48 patients who will be treated either at the 
NIH or at the University of Virginia School of Medicine. 
Dr. Geiduschek stated that retrovirus mediated gene transfer will be used to transfer the 
neomycin resistance gene into the patient's bone marrow and peripheral blood derived 
stem cells. These marked cells will be reintroduced by autologous bone marrow 
transplantation or peripheral blood stem cell reimplantation. The fate of these 
genetically marked cells will be monitored. The investigators will look for the following: 
(1) short-term versus long-term persistence of the marker gene in the reconstituted 
hematopoietic system, (2) the relative contribution of the marked bone marrow and 
peripheral blood stem cells to short-term versus long-term reconstitution, (3) the 
recurrence of tumor bearing marker genes, (4) the effect of variable chemotherapy and 
peripheral stem cell mobilization regimens on gene transfer efficiency, and (5) the effect 
of different chemotherapy and radiation regimens on sustained persistence of the 
genetically marked cells in the bone marrow and systemic circulation. 
Dr. Geiduschek noted that the three clinical protocols differ in regard to the regimens 
prior to collection of the bone marrow and peripheral blood cells as well as the 
chemotherapy and radiation regimens required following cell collection and prior to their 
reintroduction. Bone marrow and peripheral blood cells will be enriched for the 
CD34( + ) subpopulation of cells. This enriched population of cells will be transduced 
with one of two retroviruses in the presence of growth factors and under optimal 
conditions for hematopoietic reconstitution. The transduction efficiency varies widely 
between tissues. 
Dr. Geiduschek stated that the data obtained with the rhesus monkey model is limited 
and requires further analysis. 
Dr. Geiduschek said that if long-term marking is not demonstrated in 6 out of the first 
10 patients receiving transduced cells, then the investigators will petition the RAC for a 
minor modification of the transduction conditions based on in vitro data. He asked Dr. 
Dunbar to expand on this point. There is no assurance that all cell types are equally 
susceptible to marking. Therefore, while positive detection of the marker gene identifies 
the source cell, the absence of the marker gene is uninformative. This marking problem 
is multiplied by the bone marrow marking procedures. Specifically, only a portion of the 
CD34( + ) selected bone marrow cells will be transduced. These transduced cells will 
then be mixed with a major portion of the unselected, untransduced marrow. 
Approximately 70% of the transplanted cells have not been fractionated. 
Dr. Geiduschek noted that the two proposed retroviral vectors, LNL6 and GINa, have 
previously been approved by the RAC. Consequently, there are no new safety concerns 
with regard to these vectors. Most of his previous concerns regarding possible retroviral 
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Recombinant DNA Research, Volume 15 
