Vaccine-derived mutation in motif D of poliovirus RNA-dependent RNA polymerase lowers nucleotide incorporation fidelity.

All viral RNA-dependent RNA polymerases (RdRps) have a conserved structural element termed motif D. Studies of the RdRp from poliovirus (PV) have shown that a conformational change of motif D leads to efficient and faithful nucleotide addition by bringing Lys-359 into the active site where it serves as a general acid. The RdRp of the Sabin I vaccine strain has Thr-362 changed to Ile. Such a drastic change so close to Lys-359 might alter RdRp function and contribute in some way to the attenuated phenotype of Sabin type I. Here we present our characterization of the T362I RdRp. We find that the T362I RdRp exhibits a mutator phenotype in biochemical experiments in vitro. Using NMR, we show that this change in nucleotide incorporation fidelity correlates with a change in the structural dynamics of motif D. A recombinant PV expressing the T362I RdRp exhibits normal growth properties in cell culture but expresses a mutator phenotype in cells. For example, the T362I-containing PV is more sensitive to the mutagenic activity of ribavirin than wild-type PV. Interestingly, the T362I change was sufficient to cause a statistically significant reduction in viral virulence. Collectively, these studies suggest that residues of motif D can be targeted when changes in nucleotide incorporation fidelity are desired. Given the observation that fidelity mutants can serve as vaccine candidates, it may be possible to use engineering of motif D for this purpose.

[Genetic Characteristics of Type 2 Vaccine-derived Poliovirus in Shanxi Province (China) in 2014].

The World Health Organization redefined the type 2 vaccine-derived poliovirus (VDPV) in 2010. To study the genetic characteristics and evolution of type 2 VDPV under this new definition, we conducted genome sequencing and analyses of type 2 VDPVs isolated from one patient with acute flaccid paralysis in Shanxi province (China) in 2014. Nucleotide sequencing revealed that the full-length of type 2 VDPV is 7439 bases encoding 2207 amino acids with no insertion or deletion of nucleotides compared with Sabin2. One nucleotide substitution identified as a key determinant of the attenuated phenotype of the Sabin 2 strain (A-G reversion at nucleotide nt 481 in the 5-end of the untranslated region) had reverted in the Shanxi type 2 VDPV. The other known key determinant of the attenuated phenotype of the Sabin 2 strain (U-->C reversion at nt2909 in the VP1 coding region that caused a Ile143Thr substitution in VP1) had not reverted in the Shanxi VDPV. The Shanxi type 2 VDPV was S2/S1 recombinant, the crossover site of which mapped to the 3-end of the 3D region (between nt 6247 and nt 6281). A phylogentic tree based on the VP1 coding region showed that evolution of the Shanxi type 2 VDPV was independent of other type 2 VDPVs detected worldwide. We estimated that the strain circulated for approximately = 11 months in the population according to the known evolution rate. The present study confirmed that the Chinese Polio Laboratory Network could discover the VDPV promptly and that it played an important part in maintenance of a polio-free China.

[Formation and identification of virus-like particles of poliovirus type I].

OBJECTIVE: To establish a method to produce virus-like particles (VLP) of poliovirus type I in Saccharomy cescerevisiae to develop potential novel recombinant vaccine against poliovirus type 1. METHODS: The genes of P1 and 3CD of poliovirus type I were optimized, synthesized and inserted into expression vector, which was further transfected into Saccharomy cescerevisiae. The extracts of yeast cells were purified by CsCl density gradient centrifugation after induction and cell lysis. RESULTS: Electrophoresis and sequencing analyses showed that the genes P1 and 3CD of poliovirus type I were successfully inserted into expression vector and encode a protein whose amino acid sequences were identical with wide-type genes of poliovirus type I. Electronic microscopy analysis showed that the VLPs of poliovirus type I could be efficiently formed in Saccharomy cescerevisiae. CONCLUSION: The VLPs of poliovirus type I could be efficiently produced by co-expression of P1 and 3CD genes in Saccharomy cescerevisiae.

Presence of cytokines in biological preparations.

In vaccines produced in eukaryote cells as well as in commercial medical preparations of leukocyte interferon a number of cytokines such as IL-1beta, IL-6 and TNF-alpha have been detected. Among the vaccines examined in this study the highest level of IL-1beta was demonstrated in inactivated hepatitis A vaccine prepared in the green monkey kidney cell line 4647, that of IL-6 in inactivated rabies vaccine produced in Syrian hamster kidney (SHK) cell culture, and that of TNF-alpha in live poliomyelitis vaccine manufactured in VERO cells. A spontaneous and poliovirus-induced capacity of cell cultures to produce cytokines was detected. The level of cytokines produced depend on the kind of cell culture and the type of virus, a more pronounced effect being generated by types 1 and 2 poliovirus as compared with type 3. The presence of highly active cytokines in virus vaccines and interferon preparations points to the necessity of investigating the influence of the presence of cytokines on the biological activity of these preparations and to the advisability of standardizing and controlling the cytokine content.

Endogenous neosynthesis vs. cross-presentation of viral antigens for cytotoxic T cell priming.

Induction of antiviral cytotoxic T lymphocytes (CTLs) has been proposed to require cross-presentation of viral antigens derived from infected extralymphatic host cells by antigen-presenting cells (APC). This postulated mechanism of cross-priming is thought to be essential for CTL responses against viruses that do not infect professional APC, e.g., because of absence of the specific virus receptor. Here, we show for the human pathogen poliovirus that naturally nonpermissive murine APC acquire viral RNA in vivo independently of the cellular virus receptor. Uptake of poliovirus or polioviral RNA initiated neosynthesis of viral antigen to an extent sufficient to prime CTLs in vivo, which were detectable 2-3 wk after infection. Our results do not only indicate that experiments studying cross-presentation and cross-priming by using potentially amplifiable or translatable materials need careful examination, but they also question the general biological importance of cross-presentation and cross-priming in antiviral CTL responses.