Thermal cycle dideoxy DNA sequencing

Analysis of repeat units in the R2 region among different Oka varicella-zoster virus vaccine strains and wild-type strains in Germany

OBJECTIVE

The present study compared the number of R2 repeat units in six different Oka strains and in 54 varicella-zoster virus (VZV) wild-type strains isolated from patients with varicella or zoster in Germany.

METHODS

The R2 genomic region was characterized by polymerase chain reaction and sequencing methods.

RESULTS

Five VZV Oka vaccine strains showed a number of seven 42-bp units and, in one, eight repeats were found. In 11 VZV wild-type strains isolated from patients with varicella, the copy number ranged between four and eight, and in 43 strains from zoster a similar range between four and nine copies was observed. About 80% of all strains showed between five and seven repeated units. More than one third of strains revealed seven repeats like Oka.

CONCLUSIONS

The size of the R2 repeat region can also be different in single Oka vaccine strains. In German VZV wild-type strains, the R2 fragment seems to be not as variable as in Japanese wild-type strains.

Genotyping of different varicella vaccine strains

BACKGROUND

Little is known about single nucleotide polymorphism (SNP) in different lots of varicella vaccines distributed by the manufacturers. Recently, the genetic analysis of several genomic regions revealed a polymorphism in different vaccine lots of Varilrix manufactured by GlaxoSmithKline. These findings need attention since mutations in the vaccine strain could result in changes of virulence and efficacy of the vaccine.

OBJECTIVES

To identify SNPs in three varicella vaccine lots of Varilrix and to compare the results with that of Varivax as well as the published sequences of the Oka vaccine strain (V-Oka) and its parental virus (P-Oka).

STUDY DESIGN

The open reading frames (ORF) 1, 6, 10, 21, 50, 54, and 62 were analyzed by sequencing of amplified DNA fragments.

RESULTS

Wild-type nucleotides identical to that of P-Oka and/or the European wild-type reference strain Dumas and in contrast to V-Oka could be identified in ORF 1 of a Varilrix vaccine lot distributed in 1991. In the ORF 62 probably responsible for attenuation of V-Oka, this vaccine strain contained 16 SNPs which were nearly all wild-type-like. By contrast, different lots of the Varivax vaccine revealed uniform sequencing results. The vaccine Varilrix 1999 showed a high similarity to the Varivax vaccine currently available.

CONCLUSIONS

The obvious genetic diversity of different lots of the varicella vaccine Varilrix cannot be explained with the coexistence of several strain variants in the vaccine, but most likely with different seed lot preparations used for vaccine production.

B7.1 expression by the weakly immunogenic F98 rat glioma does not enhance immunogenicity

Enhanced immunogenicity has been reported following transfection of a variety of immunogenic tumors with the B7.1 co-stimulatory molecule. The purpose of the present study was to determine if transfection of a weakly immunogenic rat brain tumor, the F98 glioma, with the gene encoding B7.1 could enhance its immunogenicity. F98 cells were transfected with a plasmid containing the B7.1 gene, and stable transfectants (F98/B7.1) were obtained. Flow cytometric analysis confirmed the expression of B7.1 and MHC class I antigens on the cell surface. To investigate the effects of B7.1 expression on the tumorigenicity of the F98 glioma, Fischer rats were implanted intracerebrally with either F98 (wild-type) or F98/B7.1 transfected cells. No significant differences in survival times were noted. Mean survival times of 21.8 and 24.0 days were observed for the respective groups at a challenge dose of 103 cells. These differences in survival time were not significant. To determine if expression of B7.1 enhanced the immunogenicity of the F98 glioma, rats were vaccinated weekly for 3 weeks with 107 mitomycin C-treated F98 or F98/B7.1 cells injected subcutaneously and then challenged intracerebrally with F98 cells 1 week later. Unvaccinated animals or those that received wild-type F98 cells as a vaccine had a survival time (mean +/- s.d.) of 22.3 +/- 1.5 days following tumor challenge versus 20.0 +/- 1.7 days for rats that had been vaccinated with F98/B7.1. Although we recognize that it might be possible to design more effective vaccination regimes, nevertheless, our data indicate that transfection of the B7.1 gene into the F98 rat glioma did not enhance its immunogenicity, and that other approaches will be required.