the primary reconstituted animals (Lemischka et al.. 1986). In another study. 
G418-resistant CFU decreased progressively in number in secondary and tertiary 
reconstituents (Keller et al.. 1985). Using N2 containing a murine 
interleukin-3 (IL-3) gene. Wong et al (in press) have successfully infected 
mouse fetal liver cells. They have obtained evidence for infection and gene 
transfer into both CFU-C and CFU-S. and have conferred IL-3 independence upon 
infected cells. 
Vector instability in the form of deletion of gene-coding sequences has 
been reported. This appears to be related to the structure of particular 
vectors, especially when transduced cells are undergoing metabolic selection of 
a second marker gene. 
Studies by our own group: Mice reconstituted with bone marrow 
transduced by the N2 vector demonstrated stable integration of provirus after 
four months (Eglitis et al., 1985). 
C. ADA vectors in mouse bone marrow: 
Literature review: We and others (Table la and Belmont et al , 1986: 
Friedman et al.. 1985; Me Ivor et al. 1987; Williams et al.. 1986; Williams et 
al.. 1986) have attempted to transduce mouse hematopoietic cells with 
functioning human ADA vectors. Although expression of human ADA following 
infection of immortalized cells has not been difficult to achieve, there are 
only a few instances of ADA vector expression in fresh bone marrow cells. 
D 
Using a vector containing both the Neo gene and an ADA cDNA gene under the 
transcriptional control of an SV40 promoter, Belmont et al (1986) detected 
human ADA activity in murine CFU-C following selection in xylosyl arabinoside 
and deoxycoformycin. Lim et al (1986) detected ADA activity in all CFU-S which 
contained proviral DNA sequences. Their vector contained a human ADA gene 
fused to the phosphoglycerokinase gene promoter without a selectable marker 
gene present. 
[26] 
Recombinant DNA Research, Volume 12 
