Polio is (still) not dead: Vaccine vectors, antiviral drugs, pathogenesis, and unexpected mutants

The results presented here are divided among four projects: (I) candidate AIDS vaccine, (II) Ribavirin is an RNA virus mutagen, (III) Poliovirus receptor (PVR) transgenic mice, and (IV) Novel poliovirus mutants. In project I, we provide the first report of protection against a vaginal challenge with a highly virulent SIV using a vaccine vector. We constructed new poliovirus vaccine vectors using Sabin 1 and 2 vaccine strain viruses, from which we generated a series of SabRV-SIV viruses containing SIV (simian immunodeficiency virus) gag, pol, env, nef, and tat in overlapping fragments. Two cocktails of poliovirus vectors (SabRV1-SIV and SabRV2-SIV) were then inoculated in a prime-boost regimen to vaccinate seven macaques. All seven vaccinated macaques, and twelve control macaques, were then challenged vaginally with highly pathogenic uncloned SIV_mac251. Strikingly, 4 of 7 vaccinated animals exhibited substantial protection against the vaginal SIV challenge. All twelve control monkeys became SIV+. These results demonstrate the efficacy of SabRV as a potential human vaccine vector to prevent AIDS, and that a vaccine vector cocktail expressing an array of defined antigenic sequences can be an effective vaccination strategy in an outbred population. In project II, we demonstrate that the important broad spectrum antiviral drug ribavirin (currently used to treat hepatitis C infections among others) is an RNA virus mutagen. We describe a molecular test of the error catastrophe theory and demonstrate that ribavirin's full antiviral activity is exerted through lethal mutagenesis of the viral genetic material. We conclude that mutagenic ribonucleosides may be an important new class of anti-RNA virus agents. In project III, we constructed a PVR transgenic mouse susceptible to a mucosal route of poliovirus infection. In project IV, we describe the discovery of two interesting independent sets of poliovirus mutants. One set of mutants contains novel manganese dependent RNA dependent RNA polymerases, and the other set of mutants is resistant to brefeldin A. Brefeldin A was the only anti-poliovirus compound for which no escape mutants were known. It has been presumed that the virus could not become resistant to brefeldin A because the drug targets a cellular host protein, not the virus directly.