Laboratory markers for over-attenuation of mumps vaccine virus

Isolation and Characterization of a Discrete Genetically Homogeneous Viral Subpopulation of Mumps Virus RS-12 Strain with Superior Oncolytic Potency Compared to Its Progenitor Virus

Background: Oncolytic virotherapy can serve as a novel therapeutic strategy in oncology. In this study, we aimed to evaluate the oncolytic activity of the mumps virus RS-12 strain after its adaptation to cancer cells via serial passaging. Methods: To adapt the RS-12 strain-based vaccine to cancer cells, it was passaged eight times in the HT1080 cell line and was isolated via two terminal endpoint dilutions. The genetic homogeneity of isolated cancer cell-adapted RS-12 variant was confirmed by direct sequencing of regions, encompassing four known heterogeneous genomic positions. The in vitro cytotoxic effects of viruses was assessed in two different cancer cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The apoptosis-inducing effects of the cancer cell-adapted variant and its parental virus on cancer cells were quantified by flow cytometry. Results: According to the chromatograms, the RS-12 strain vaccine seed exhibited two peaks at the genomic nucleotide positions 1591, 2417, 3774, and 12977. On the contrary, cancer cell-adapted RS-12, isolated by terminal endpoint serial dilutions, contained no viral subpopulations in these positions. A significant improvement was observed in the oncolytic potency of our cancer cell-adapted variant compared to its parental virus vaccine seed in vitro. Besides, the variant efficiently induced apoptosis in the human fibrosarcoma and adenocarcinoma cell lines. Conclusions: Considering the increased oncolytic potency and apoptosis-inducing capacity of this variant in cancer cells, it can be a promising option for future experiments.

An outbreak of mumps in a population partially vaccinated with the Rubini strain

Since 1991, 6 years after the recommendation of universal childhood triple vaccination against measles, mumps and rubella (M + M + R), Switzerland has been confronted with an increasing number of mumps cases affecting both vaccinated and unvaccinated children. The M + M + R vaccine mainly used in the Swiss population after 1986 contains the highly attenuated Rubini strain of mumps virus. We analysed an outbreak of 102 suspected mumps cases by virus isolation, determination of IgM antibodies to mumps virus in 27 acute phase sera, and verification of vaccination histories. Mumps was confirmed by virus isolation in 88 patients, of whom 72 had previously received the Rubini vaccine strain. IgM antibodies to mumps virus were detected in 24/27 acute phase serum samples. A group of 92 subjects from the same geographic area without signs of mumps virus infection served as controls. IgG antibodies to mumps virus and vaccination status were assessed in these children. The vaccination rate in these controls was 61%, with equal seropositivity for unvaccinated and Rubini-vaccinated subjects. These data support other recent reports which indicate an insufficient protective efficacy of current mumps vaccines.

[Mumps vaccines: virological basis]

The prevention of mumps virus infection relies on the application of live, attenuated mumps virus vaccines. The process of attenuation from a wildtype mumps isolate to a safe vaccine has been empirical. A lower degree of attenuation results in solid immunity but carries an increased risk of post-vaccination meningitis due to the vaccine strain. Currently used vaccine strains are highly attenuated and essentially free of vaccine strain induced disease. However, their immunogenicity may be lower than previously reported.

Rapid detection of mumps virus by the polymerase chain reaction

A procedure for detecting mumps virus in under 48 h was developed using the PCR. The sensitivity of the PCR amplification reaction and of the detection of the PCR product was significantly improved by: (i) enriching for viral template RNAs by overnight culture of the virus in Vero cells and (ii) substitution of polyacrylamide gel analysis for agarose gel electrophoresis. The technique was capable of detecting 1-20 infectious units of virus or an equivalent of 1-10 pg of mumps virus-specific plasmid DNA.

Genetic evidence for variant selection in the course of dilute passaging of mumps vaccine virus

Mumps vaccine viruses, Leningrad-3 (L-3) strain, harvested at the 8th (8P) and 38th (38P) passage levels, were compared by nucleotide sequencing of the fusion (F) and the phosphoprotein (P) genes, and for replication efficiency in cell culture. Sequencing revealed only one clear base substitution throughout the entire F gene, and no substitutions in the variable 183-nucleotide-long region of the P gene. However, the 8P virus, unlike the 38P variant, contained multiple "ambiguous" nucleotide regions, i.e., additional bases positioned at the level of the principal ones. The 38P variant replicated faster and appeared more homogeneous by its plaque character compared to the 8P virus. The results indicate that the 8P progenitor virus consisted of more than one viral variant and that one of these was selected on repeated passage due to its higher replication efficiency.

Further-attenuated measles vaccine: virus passages affect viral surface protein expression, immunogenicity and histopathology pattern in vivo

Measles vaccine viruses Leningrad-16 (L-16) and Moscow-5 (M-5, an L-16-derived clonal variant), at passage levels used for vaccination and after ten further low-multiplicity passages on quail embryo (QE) cells, were compared for (1) immunogenicity, (2) histopathological lesions induced in vivo and (3) surface protein expression within infected cells and on the virion surface. At the 10th passage, viruses evoked a poorer neutralizing antibody response in guinea pigs, induced an earlier appearance of more pronounced pathological lesions and replicated faster in Vero cells than the original viruses. H protein expression increased 1.8-2.3-fold after 10 passages of the L-16 variant, but remained virtually unaltered for the M-5 variant. F protein expression of both 10th-passage variants was 0.5-0.8 that of the original virus variants. A similar two-fold decrease in F protein expression was noted after a single virus passage in guinea pigs. The data implicate the loss of F protein as a cause of reduced immunogenicity of further attenuated measles vaccines.