POINTS TO CONSIDER 
Scientific Abstract 
Protocol: Use of double marking with retroviral vectors to determine rate of reconstitution of 
untreated and cytokine expanded CD34+ selected marrow cells in patients undergoing autologous 
bone marrow transplantation 
SCIENTIFIC ABSTRACT 
Autologous BMT in is frequently used as consolidation or salvage therapy in pediatric 
malignancy to allow administration of intensive chemotherapy where hemopoietic suppression 
would otherwise be dose limiting. This increased dose of chemotherapy and radiation therapy 
may allow a higher proportion of patients to be cured than would be possible with conventional 
therapy. One of the major causes of morbidity after autograft is the risk of infection and bleeding 
during the period of pancytopenia which follows the administration of ablative chemotherapy. 
One way of improving autologous stem cell rescue is therefore to shorten the period of aplasia 
which follows the procedure and thereby reduce the morbidity and mortality. A second 
improvement would be to harvest as few stem cells as possible. One way to achieve both these 
aims is by expanding committed and uncommitted progenitor cells ex vivo. 
We and other investigators have evaluated the ability of growth factors to expand CD34 enriched 
marrow cells ex-vivo and noted little expansion of the most primitive cell populations (appendix 
A). While growth factor treated marrow may therefore produce earlier engraftment, its capacity 
to produce long term reconstitution remains unknown. There is a concern that the use of more 
extensive growth factor combinations, whose activities reached further back in hemopoiesis, 
would differentiate rather than expand or maintain true stem cells. If so, such marrow would 
produce earlier reconstitution but at the expense of being unable to contribute to long term 
engraftment 
The ideal of ex vivo expansion is to increase both committed and non-committed progenitor cells 
thereby accelerating initial engraftment and ensuring sustained reconstitution. An acceptable 
alternative is simply to exp^d committed progenitor cells to reduce the period of post transplant 
aplasia provided sufficient pluripotent stem cells were retained in an undifferentiated state to 
permit long term recovery. Gene marking of marrow ex vivo allows determination of whether 
adequate numbers of stem cells remain in vivo. In this study we plan to use genetic marking of 
marrow ex vivo with two distinct vectors to compare the subsequent in vivo reconstitution of two 
aliquots of CD34 selected marrow - one treated and one unmanipulated. This protocol will 
therefore answer questions about the feasibility of accelerating hemopoietic reconstitution and the 
impact of such action on uncommitted progenitor cells. It will be a generic processing and 
transduction protocol for patients receiving autologous BMT for pediatric malignancy. 
[ 486 ] 
Recombinant DNA Research, Volume 19 
