Recombinant DNA Advisory Committee - 09/14-15/92 
He asked Dr. Schuening if he had data in his model to confirm this hypothesis. Is the 
co-culture step necessary since there is the potential of added risk? Dr. Schuening 
responded that his in vitro data suggest that the co-cultivation step is necessary. Cells 
were transduced with and without co-cultivation with producer cells and gene expression 
was monitored for six weeks. Neo R expression was much longer with the co-cultivation 
procedure. 
Dr. Walters asked for further information regarding the cause of death in one of the 
animals. Dr. Schuening said that the animal died of infectious complications, i.e., sepsis, 
resulting from the transplantation procedure. It is not unusual for animals to die in the 
early phase post transplantation because they are immunosuppressed as a result of the 
chemotherapy regimen. Dr. Walters asked how long the remaining two animals will be 
studied before sufficient data is obtained to initiate the human protocol. Dr. Schuening 
stated that all of the animals would be monitored for helper virus during their lifetime. 
However, monitoring of the marked peripheral blood cells will not be monitored for this 
period of time. A reasonable estimate is that the peripheral blood would be assayed in 
these remaining animals for one year following transplantation to demonstrate that 
pluripotent stem cells have been transduced prior to initiating the human protocol. By 
the time FDA approval is obtained, the animals will have been followed for 
approximately one year. 
As a point of clarification, Dr. Parkman explained that the actual objective of the 
protocol is to determine the most optimal cytokine for mobilizing repopulating cells in 
these patients. Other investigators have already demonstrated that lethally irradiated 
patients could be reconstituted with peripheral blood stem cells. In terms of efficacy, all 
patients are obtaining their own bone marrow; so unless there is a flaw in the 
cryopreservation process, all patients will engraft. Seventy-five percent of the stem cells 
readministered to the patient will be untransduced; therefore, the clinical impact of the 
gene marking is minimal. Dr. Geiduschek inquired if the only variable between the 
protocols submitted by Dr. Schuening is the choice of mobilizing cytokine, then explain 
the choice of different patient populations and different target tumors. Dr. Schuening 
replied that he was not entirely in agreement with the statement made by Dr. Parkman. 
Previous data does not indicate whether long-term recovery is due to the transplanted 
peripheral blood derived cells or to endogenous recovery resulting from the temporary 
support provided by these cells. This question has never been answered formally in the 
human setting. IL-3 and G-CSF are the two cytokines proposed for use in these 
protocols; however, additional protocols will be submitted in the future to examine a 
broader range of cytokines. 
Dr. Leventhal said that these protocols are not designed to answer the cytokine question, 
because they are intended to target two separate tumor populations. Why are the 
investigators looking at so many variables, i.e., different patient populations, different 
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