More recently, another ADA vector similar to the SAX vector has been 
developed and used for gene transfer in human ADA-deficient skin fibroblasts 
(Palmer et al.. 1987). This vector, designated LNSAL, was contructed by 
inserting an SV40-promoted human ADA cDNA downstream from the Neo R gene in N2. 
The ADA(-) human diploid skin fibroblasts (HDF) after infection were capable of 
metabolizing exogenous deoxyadenosine in the culture medium at a much greater 
rate than the ADA(-)HDF cells which had not been infected with the LNSAL 
vector. The authors stated that this vector produced the typical ADA isozyme 
pattern on starch gels. 
Successful gene transfer using retroviral vectors has been reported for a 
human^j -anti trypsin fc^AT) cDNA into mouse fibroblasts (Garver et al.. 1987). 
This vector was contructed by inserting an SV40-promoted human AT cDNA 
p 
downstream from the Neo gene in the N2 vector in the same way that the SAX ADA 
vector was produced. The AT vector. pN2-FAT, was used to infect NIH 3T3 
cells which subsequently produced o^AT-specific mRNA transcripts and secreted a 
protein recognized by an antibody to human AT. 
Mo-MuLV based vectors have been used to transfer the gene coding for human 
purine nucleoside phosphoryl ase (PNP) or human ADA along with the gene encoding 
human HPRT (Mclvor et al.. 1987)). These double expression vectors have an 
HPRT gene as a selectable marker under the transcriptional control of the viral 
LTR upstream from either the PNP or ADA sequences controlled by promoter 
elements derived from the mouse metal 1 othionein (MT) gene. The production of 
human-mouse hybrid PNP isozymes was demonstrated in the viral producer cell 
line, and low but detectable levels of human PNP were found in infected cells 
when analyzed by isoelectric focusing. Similar analysis demonstrated 
production of human ADA after infection of cultured mouse cells with the 
HPRT/ADA vector even though Southern blot analysis indicated that the long MT 
[ 40 ] 
Recombinant DNA Research, Volume 12 
i 
