Rational Design of Genetically Stable, Live-Attenuated Poliovirus Vaccines of All Three Serotypes: Relevance to Poliomyelitis Eradication

Abstract

The global eradication of poliomyelitis caused by wild-type virus is likely to be completed within the next few years, despite immense logistic and political difficulties, and may ultimately be followed by the cessation of vaccination. However, the existing live-attenuated vaccines have the potential to revert to virulence, causing occasional disease, and viruses can be shed by immunocompromised individuals for prolonged periods of time. Moreover, several outbreaks of poliomyelitis have been shown to be caused by viruses derived from the Sabin vaccine strains. The appearance of such strains depends on the prevailing circumstances but poses a severe obstacle to strategies for stopping vaccination. Vaccine strains that are incapable of reversion at a measurable rate would provide a possible solution. Here, we describe the constructions of strains of type 3 poliovirus that are stabilized by the introduction of four mutations in the 5 noncoding region compared to the present vaccine. The strains are genetically and phenotypically stable under conditions where the present vaccine loses the attenuating mutation in the 5 noncoding region completely. Type 1 and type 2 strains in which the entire 5 noncoding regions of Sabin 1 and Sabin 2 were replaced exactly with that of one of the type 3 strains were also constructed. The genetic stability of 5 noncoding regions of these viruses matched that of the type 3 strains, but significant phenotypic reversion occurred, illustrating the potential limitations of a rational approach to the genetic stabilization of live RNA virus vaccines.Poliomyelitis is caused by poliovirus, a member of the picornavirus family that occurs in three serotypes such that immunity to one serotype does not protect against the other two.

Dengue virus type 3 vaccine candidates generated by introduction of deletions in the 3′ untranslated region (3′-UTR) or by exchange of the DENV-3 3′-UTR with that of DENV-4

“…This is a new strategy for attenuation of a flavivirus, although chimeric live oral poliovirus vaccines have been generated by swapping the 5' UTR of a modified Sabin type 3 strain with that of type 1 and 2 in an effort to increase genetic stability [39]. In addition, Markoff and colleagues previously constructed chimeric West Nile virus/DENV-2 viruses with swaps confined to the 3' terminal stem loop structure that were found to be attenuated for replication in tissue culture [40].…”

An Attenuated Strain of Enterovirus 71 Belonging to Genotype A Showed a Broad Spectrum of Antigenicity with Attenuated Neurovirulence in Cynomolgus Monkeys

“…Several strategies have been proposed for attenuation and stabilization of the phenotype of PV (4,9,12,15,22,32,38). However, in general, attenuated PV strains exhibit impaired virus growth, even in cells cultured in vitro.…”

Multiple Independent Emergences of Type 2 Vaccine-Derived Polioviruses during a Large Outbreak in Northern Nigeria

“…Virus was grown to high titers in RD cell monolayers at 37.0°C, and infectivity yields were measured by plaque assays (70) on L20B cells incubated at 37.0°C and 39.5°C (73).…”

“…Higher virus yields at elevated temperatures may facilitate person-to-person transmission by increasing the amount of infectious virus excreted by febrile individuals. Sabin 2, all 25 VDPV2 isolates tested, and MEF-1 grew to high titers (8.23 to 9.42 log 10 PFU/ml) in RD cells incubated at 37.0°C when measured by plaque assays on L20B cells also incubated at 37.0°C (Table 5) (73,91). However, when cells were incubated at 39.5°C for plaque assays, the efficiency of plating of Sabin 2 on L20B cells dropped Ն6,000-fold, whereas that of MEF-1 was largely unaltered.…”