Dicistronic polioviruses as expression vectors for foreign genes.

We have made use of certain novel genetic elements of picornaviruses termed internal ribosomal entry sites (IRES) to construct a viral RNA with the following genetic order: PV 5' NTR-EMCV IRES-PV ORF-3' NTR (PV, poliovirus; NTR, nontranslated region; EMCV, encephalomyocarditis virus; ORF, open reading frame). Transfection of this RNA into HeLa cells yielded a poliovirus (W1-PNENPO) that contained two heterologous IRES elements (type 1 IRES of PV; type 2 IRES of EMCV) in tandem. The insertion of foreign coding sequences into the genome of W1-PNENPO between the IRES elements yielded viable polioviruses with the gene order PV 5' NTR-foreign ORF-EMCV IRES-PV ORF-3' NTR. The foreign ORFs we have employed in this study included the coding region for chloramphenicol acetyltransferase (CAT), or segments of either luciferase or the HIV-1 envelope glycoprotein gp120. W1-PV/V3-3, a dicistronic poliovirus that contained HIV-1-specific sequences that included the V3 domain of gp120, was used to infect transgenic mice (PVR+) that were engineered to express the poliovirus receptor. The genetic stability of the dicistronic viruses and the HIV-1-specific immune response in PVR+ mice after infection with these novel agents are discussed.