Characterization of a double avirulent mutant of rabies virus and its potency as a vaccine, live or inactivated

Reactions of beta-propiolactone with nucleobase analogues, nucleosides, and peptides: implications for the inactivation of viruses

β-Propiolactone is often applied for inactivation of viruses and preparation of viral vaccines. However, the exact nature of the reactions of β-propiolactone with viral components is largely unknown. The purpose of the current study was to elucidate the chemical modifications occurring on nucleotides and amino acid residues caused by β-propiolactone. Therefore, a set of nucleobase analogues was treated with β-propiolactone, and reaction products were identified and quantified. NMR revealed at least one modification in either deoxyguanosine, deoxyadenosine, or cytidine after treatment with β-propiolactone. However, no reaction products were found from thymidine and uracil. The most reactive sides of the nucleobase analogues and nucleosides were identified by NMR. Furthermore, a series of synthetic peptides was used to determine the conversion of reactive amino acid residues by liquid chromatography-mass spectrometry. β-Propiolactone was shown to react with nine different amino acid residues. The most reactive residues are cysteine, methionine, and histidine and, to a lesser degree, aspartic acid, glutamic acid, tyrosine, lysine, serine, and threonine. Remarkably, cystine residues (disulfide groups) do not react with β-propiolactone. In addition, no reaction was observed for β-propiolactone with asparagine, glutamine, and tryptophan residues. β-Propiolactone modifies proteins to a larger extent than expected from current literature. In conclusion, the study determined the reactivity of β-propiolactone with nucleobase analogues, nucleosides, and amino acid residues and elucidated the chemical structures of the reaction products. The study provides detailed knowledge on the chemistry of β-propiolactone inactivation of viruses.

Studies on the structures and antigenic properties of rabies virus glycoprotein analogues produced in yeast cells

We investigated two forms (designated as yGI and yGII) of rabies virus glycoprotein (G) analogues produced in the G cDNA-transfected yeast cells. Molecular weights of yGI and yGII were estimated as 66 and 56 kDa, respectively, according to their relative mobility in SDS-PAGE. Although being produced in large amounts, yGI was present mostly in insoluble forms and hardly extractable with non-ionic detergents. The yGI reacted with polyclonal anti-G antibodies, but did not react with our conformational epitope-specific anti-G monoclonal antibodies (G-MAbs). No protective immunity was induced by yGI in guinea pigs nor in mice. On the other hand, yGII was Triton-soluble, but was only small in amount (at most 1% of total G proteins) and was shown to lack the cytoplasmic domain. The yGII, however, reacted with the G-MAbs and induced protective immunity in guinea pigs as well. When the G-cDNA was expressed in animal cells in culture, a single form (about 66 kDa) of G protein was produced, which displayed similar behaviors as seen in its reactivity with the MAbs and intracellular distribution as seen in the virus-infected cells. These results suggest that most G protein molecules were not processed normally in yeast cells, resulting in abnormal folding and multimer formation, while only a small fraction were occasionally folded normally to have conformational epitopes but were mostly deprived of the C-terminal portion.

A study of the effect of chemical inactivants on the epitopes of Rift Valley fever virus glycoproteins using monoclonal antibodies

A panel of 23 monoclonal antibodies (mAbs) was used to study the effect of formalin, beta propriolactone (BPL) and binary ethylenimine (BEI) on the epitopes of the Rift Valley fever virus glycoproteins. After the initial inactivation period BEI had very little adverse affect on the epitopes whereas BPL significantly altered seven and formalin partially changed the conformation or accessibility of most of the epitopes. The epitopes of all of the inactivated antigens showed a reduced activity against the specific mAbs over a six month storage period.

Oral immunization of foxes with avirulent rabies virus mutants

SAG1, a rabies virus strain bearing one mutation which abolishes virulence for adult animals, was constructed from the SADBern strain of rabies virus which has previously been used as live vaccine for oral immunization of foxes. SAG1 also bears an antigenic mutation which serves as an additional marker of the strain. Studies on mice and four species of wild rodents showed that SAG1 is totally avirulent whereas SADBern is still pathogenic after intracerebral, intramuscular or oral inoculation and thus could cause cases of rabies. Trials of oral vaccination performed on foxes with SAG1 indicate that it is as effective as SADBern. The SAG1 strain represents a significant progress in the search for an efficient and safe live rabies for the oral immunization of wild animals.

Immunogenic and protective properties of rabies virus glycoprotein expressed by baculovirus vectors

The gene encoding the glycoprotein of rabies virus (G protein, CVS strain) has been cloned and inserted into the baculovirus transfer vector pAcYM1 derived from the nuclear polyhedrosis virus of Autographa californica (AcNPV). The gene was placed under the control of the AcNPV polyhedrin promoter and expressed to high levels by the derived recombinant virus using a Spodoptera frugiperda cell line. It has been established that the antigenic characteristics of the protein were conserved by comparison with those of the native glycoprotein of rabies virions. The immunogenicity of the expressed product was also demonstrated. Intraperitoneal or intramuscular injection of G antigen conferred protection to mice and was associated with the induction of high titers of neutralizing antibodies. The availability of large quantities of antigenically and immunogenically reactive rabies G protein may make feasible crystallographic studies and the safe preparation of a low cost subunit vaccine for the disease.

Antigenic site II of the rabies virus glycoprotein: structure and role in viral virulence

Twelve monoclonal antibodies neutralizing the CVS strain of rabies virus were used to characterize antigenic site II of the viral glycoprotein. Nineteen antigenic mutants resistant to neutralization by some of these antibodies were selected; some continued to normally or partially bind the antibody, whereas others did not. Mutations conferring resistance to neutralization by site II-specific monoclonal antibodies were localized into two clusters, the first between amino acids 34 and 42 (seven groups of mutants) and the second at amino acids 198 and 200 (three groups of mutants). Two intermediate mutations were identified at positions 147 and 184. Four mutations resulted in reduced pathogenicity after intramuscular inoculation of the virus in adult mice. One of the mutants, M23, was 300 times and the others were 10 to 30 times less pathogenic than CVS. In three cases the attenuated phenotype was related to an important modification of antigenic site II, whereas the other known antigenic sites were unchanged.