Genetic Manipulation of Hematopoietic Stem Cells 
allows identification of the stem cells by the poly- 
merase chain reaction (PGR), is especially suited 
for analysis of very small numbers of cells. A fam- 
ily of vectors carrying the bacterial gene neo have 
been constructed that are identical except for 
small variations in size, variations conveniently 
distmguished by PGR. When mixed together 
these vectors provide an array of potential 
markers that can integrate into each stem cell. 
Because each cell receives one to four vectors, 
the integration of a particular subset of the vec- 
tors provides a genetic fingerprint unique to each 
cell family. 
Preliminary results with these vectors indicate 
that we can mark the most primitive hematopoi- 
etic precursors efficiently. We plan to use this 
method to compare different culture conditions 
for stem cells. We hope to be able eventually to 
grow the stem cells in very long-term cultures. 
The retroviral vector genetic marking system 
may also prove to be highly informative in clini- 
cal bone marrow transplantation. We have under- 
taken collaborative studies with Albert Deisse- 
roth (M.D. Anderson Hospital, Houston) to 
determine whether the techniques that have been 
used to optimize gene transfer of mouse bone 
marrow stem cells can be used for human cells. 
These experiments demonstrate that consistent 
and efficient gene transfer into primitive human 
precursors is possible. After further tissue culture 
studies are performed, we plan to do genetic la- 
beling experiments in patients undergoing bone 
marrow transplant for advanced leukemia. These 
investigations will provide a novel way to investi- 
gate the origins of leukemia recurrence and the 
recuperation of the blood system following trans- 
plantation. We also hope to learn many valuable 
lessons that will contribute to the long-term goal 
of treating disease by insertion of therapeutic 
vectors. 
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