Molecular attenuation of vaccinia virus: mutant generation and animal characterization

Abstract

These studies demonstrated that the inbred BALB/c mouse strain can be optimized for the assessment of vaccinia virus virulence, growth, and spread from the site of inoculation and immune protection from a lethal vaccinia virus challenge. The studies established that manipulation of the vaccinia virus genome generated mutants exhibiting a wide range of attenuated phenotypes. The nine NYCBH vaccinia virus mutants had intracranial 50% lethal doses that ranged from 2 to >7 log1o units. The decreased neurovirulence was due to decreased replication in brain tissue. Three mutants had a decreased ability to disseminate to the lungs, brains, livers, and spleens of mice after intranasal infection. One mutant had a decreased transmission from mice infected by tail scarification to naive cage mates. Although the mutants, with one exception, grew to wild-type titers in cell culture, they showed a growth potential on the scarified skin of mice that was dramatically different from that of the wild-type virus. Consequently, all of the mutants had significantly compromised immunogenicities at low virus immunization doses compared with that of the wild-type virus. Conversely, at high immunization doses most mutants could induce an immune response similar to that of the wild-type virus. Three Wyeth vaccine strain mutants were also studied. Whereas the thymidine kinase, ribonucleotide reductase, and hemagglutinin mutants had a reduced virulence (50%o lethal dose), only the thymidine kinase mutant retained its immunogenicity.

One time intranasal vaccination with a modified vaccinia Tiantan strain MVTTZCI protects animals against pathogenic viral challenge

“…HA is found on the plasma membrane of infected cells and the envelope of extracellular virus (EEV) but is absent from intracellular mature virus (IMV), the most abundant infectious forms of infectious virions [33,34]. Several studies showed that the loss of HA is associated with the reduced virulence of vaccinia viruses [17,23,35]. For example, MVA has the major deletion III in the HA promoter region [36].…”

“…The inbred BALB/c mouse was chosen for the assessment of MVTT ZCI virulence using a previously described method [17,18]. Groups of five-week old mice were inoculated intranasally with 0, 10 4 , 10 5 or 10 6 PFU of MVTT ZCI in 20 ul of PBS.…”

“…To generate an attenuated viral variant of VTT, we sought to delete the HA gene because it is related to the attenuation of various vaccinia viruses [17,[23][24][25]. The new VTT variant named MVTT ZCI was generated after a portion of the HA gene was deleted using a homologous recombination method [26][27][28].…”

“…The inbred BALB/c mouse was chosen for the assessment of MVTT ZCI virulence using an intranasal (i.n.) inoculation model described previously by others [17,18]. As shown in Fig.…”

The attenuation of vaccinia Tian Tan strain by the removal of the viral M1L-K2L genes

“…The in vivo virulence of MVTT 2-GFP was evaluated in inbred BALB/c mice using methods as described previously (Lee et al, 1992;Betakova et al, 2000;Zhang et al, 2000). The viral virulence was first determined by the daily measurement of body weight change for a period of 10 days after the animals were inoculated with the virus via the intranasal route.…”