Our results demonstrate that infection and integration of the retroviral 
vector SAX in primate marrow cells can be obtained under conditions which favor 
the recovery of viable cells and that expression of low levels of the gene 
products, both h-ADA and NPT enzymatic activities, can be detected for short 
periods in circulating blood and marrow cells from seme reconstituted animals. 
Although the levels of expression in the PBMC and bone marrow are low, they may 
represent moderate levels of expression on a per cell basis. It is unfortunate 
that, for logistic reasons, we do not have more complete data for animals #56 
and #57 during the critical period from 60 to 120 days. The data for animal 
#57 are summarized in Table 3. Since the limit of resolution on our Southern 
blots is approximately 1 copy in 20 cells, the negative Southern blots on days 
34, 52, and 104 for animal #57 would indicate that vector ENA was present on 
those days in less than 5% of the PBMC. The presence of neo R FNA in 28 of 3415 
cells as detected by in situ hybridization on day 127 indicates that at that 
time at least 0.8% of the cells contained vector (more may have had 
non-expressing vector ENA sequences) . The number of cells containing vector on 
day 69, when the maximum level of h-ADA was found (0.5% of endogenous monkey 
ADA activity) , is unknown. If 5% of PBMC contained vector on day 69, then 
infected cells may produce h-ADA at around 10% of endogenous monkey ADA levels 
(in addition to endogenous monkey ADA already being produced in the cell). If 
fewer than 5% of the cells contained vector on day 69, then the amount of h-ADA 
produced on a per cell basis could exceed 10%. 
It should be noted that vectors that do not express genes in one species 
may be capable of doing so in others. We have used the SAX vector to 
efficiently transfer the ADA gene into mouse hematopoietic cells but have not 
detected any ADA expression in vivo in the mouse. We are currently 
investigating whether this is a vector and/or pranoter specific phenomenon. 
Recombinant DNA Research, Volume 12 
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