MtUl 1 
nf ill I 
short. Overall there appears to be no advantage to 
marrow purging in AML with only a modest potential 
benefit in ALL (10,13,14,17,29,32,37,38). Taken 
together, these data suggests that improving the 
preparative regimen, rather than marrow purging, 
may be important in increasing patient survival and 
decreasing relapse after AuBMT for AML. If the 
cause (s) of leukemic relapse after AuBMT can be 
resolved, new transplantation protocols can be 
studied to decrease the relapse rate after AuBMT. 
One approach to determining the cause of disease 
relapse would be to mark the transplanted cells 
used for AuBMT. At present there are no reliable 
clinical procedures for long-term marking of 
autologous cells in vivo . Radionuclides have been 
extensively evaluated as labels, but their in vivo 
use is limited by either rapid decay or radiation 
exposure (39,40). In addition, the loss, 
reutilization, or sequestration of label by cells 
not related to the original labelled cells is a 
significant problem for long-term in vivo studies. 
We propose to use retroviral-mediated gene transfer 
(RMGT) to mark autologous cells since retroviral 
vectors are extremely well suited to labelling 
autologous cells. Retroviral vectors have the 
following advantages: (1) they insert stably into 
the target cell genome; (2) the label dies with the 
cell, it is not lost or sequestered; (3) if the 
cell divides, all of its progeny also contain the 
marker; (4) very sensitive methods of vector 
detection, namely the polymerase chain reaction, 
exist which can detect approximately 1 in 10 5 cells 
containing the vector; (5) if a selectable marker 
gene is used, it may be possible to select out 
marked cells from a population of cells which do 
not contain the vector; and (6) RMGT is a simple 
technical procedure which does not expose the 
marked cell to toxic compounds or radioactivity 
which might alter the function of the marked cells. 
RMGT has been used extensively in vitro in many 
types of cells including leukemia cell lines and 
bone marrow. Human leukemic cell lines are easily 
transduced with retroviral vectors with an 
efficiency of 10-60% using the transduction 
protocol proposed in this study (41-43) . RMGT has 
also been used extensively in mice syngeneic bone 
marrow transplantation with stable integration and 
expression of exogenous genes (44-50) . Drs. 
[470] 
Recombinant DNA Research, Volume 15 
