Ma. Adam et al., R-REGION CDNA INSERTS IN RETROVIRAL VECTORS ARE COMPATIBLE WITH VIRUS-REPLICATION AND HIGH-LEVEL PROTEIN-SYNTHESIS FROM THE INSERT, Human gene therapy, 6(9), 1995, pp. 1169-1176
Protein expression from retroviral vectors is often highest when the e
xpressed cDNA is driven by the retroviral promoter. However, the typic
al retroviral vector design places the cDNA downstream of the retrovir
al packaging signal and far from the retroviral promoter. In an attemp
t to improve protein production levels from cDNAs expressed in retrovi
ral vectors, we inserted the MyoD or the purine nucleoside phosphoryla
se (PNP) cDNAs into the R regions of both retroviral LTRs, close to th
e retroviral promoter and just upstream of the polyadenylation signal
present in each long terminal repeat (LTR). These R-region double-copy
vectors could be produced in unrearranged form, although the titer wa
s about seven-fold lower than that of typical vectors. R-region positi
oning of the MyoD cDNA resulted in five-fold higher MyoD expression co
mpared to MyoD expression in a typical vector, whereas PNP expression
was not improved. Thus, R-region double-copy vectors provide an altern
ative vector design that can improve protein expression from some cDNA
s.