Bicistronic retroviral vectors were constructed containing the foot-an
d-mouth disease virus (FMDV) internal ribosome entry site (IRES) follo
wed by the coding region of beta-galactosidase (beta-gal) or therapeut
ic genes, with the selectable neomycin phosphotransferase gene under t
he control of the viral long terminal repeat (LTR) promoter, LNFX, a v
ector with a multiple cloning site 3' to foot-and-mouth disease virus
IRES, was used to construct vectors encoding rat erythropoietin (EP),
rat granulocyte colony-stimulating factor (G-CSF), human adenosine dea
minase (ADA) and beta-gal. In transduced primary rat vascular smooth m
uscle cells the cytokines were expressed at high levels, similar to th
ose obtained from vectors employing the viral LTR promoter, LNFZ, a ve
ctor encoding beta-gal, had a 10-fold increase in titer over that of L
NPoZ, a comparable vector containing the poliovirus (Po) internal ribo
some entry site, Primary canine vascular smooth muscle cells infected
with LNFZ and LNPoZ expressed similar activities of beta-gal and neomy
cin phosphotransferase (NPT), Overall, these vectors had titers betwee
n 10(6) and 2 x 10(7) c.f.u./ml, indicating that foot-and-mouth diseas
e virus IRES provides high-titer bicistronic vectors with high-level t
wo gene expression.