to reconstituting irradiated mice. Even though 15-40* of the spleen colonies 
analyzed contained intact exogenous gene sequences no human ADA enzyme activity 
was detected by starch gel analysis. Further analysis of RNA from whole 
spleens failed to detect the presence of any SV40-initiated human ADA 
transcripts. In general, these findings and subsequent studies have shown that 
some foreign genes introduced by retroviral vectors will function and express 
efficiently in transformed cell lines but will not do so in the whole animal 
(see bel ow) . 
The retroviral vector, pD0L-MP10.GC20 (Choudary et al., 1986), was 
constructed by inserting a cDNA for human gl ucocerebrosidase upstream from the 
R - 
gene for Neo in a Mo-MuLV based retroviral backbone. This vector was 
subsequently used to infect type 2 Gaucher fibroblasts (GM-1260 cells) followed 
by selection for neomycin expression in G418-containing medium. The Infected 
and selected Gaucher fibroblasts produced a band of material that cross-reacted 
with a monoclonal antibody to human gl ucocerebrosidase even in the absence of 
selection. The protein produced, however, was larger than gl ucocerebrosidase 
present in normal human fibroblasts and was enzymatically Inactive. The 
inactivity was explained by a single amino acid substitution in the 
gl ucocerebrosidase cDNA used in the retroviral construct. 
p 
Of primary importance in this review are the studies using the Neo gene 
vector N2 (Armentano et al . 1987; Eglitis et al., 1985; Keller et al.. 1985; 
Humphries et al., 1986; Hock and Miller, 1986) and the vector derived from N2 
called SAX (Kantoff et al., 1986), which incorporates an SV40-promoted human 
ADA cDNA into the N2 backbone. The Neo^ gene, introduced by the N2 vector in 
human bone marrow cells in vitro , gives rise to 3 to 5% of CFU-GM and 12-20* of 
BFU-E colonies resistant to G418. The N2 vector has also been used to 
successfully infect canine bone marrow cells showing 6 to 25* G418- resistant 
CFU-GM compared to control (Kwok et al » 1986; Eglitis et al. in preparation). 
[38] 
Recombinant DNA Research, Volume 12 
