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Attenuation of wild-type yellow fever virus by passage in HeLa cells
A D Barrett1, T P Monath, C B Cropp
1Department of Microbiology, University of Surrey, Guildford, U.K.
Abstract:
During the 1960s three different research groups reported that passage of wild-type yellow fever (YF) virus [strain Asibi (YF-Asibi)] in HeLa cells resulted in attenuation of the virus for monkeys so that the virus no longer caused viscerotropic disease. We have repeated and extended this observation to analyse the process of attenuation of YF virus during cell culture passage. A large plaque (LP) variant of YF-Asibi virus became attenuated for both monkeys and mice following six serial subcultures in HeLa cells (YF-Asibi-LP HeLa p6). Thus, attenuation was probably due to a genetic change in the virus population rather than to selective enrichment of a pre-existing variant of YF-Asibi-LP virus. No evidence was obtained to implicate defective interfering particles in the attenuation process. Comparison of the YF-Asibi-LP viruses before and after passage in HeLa cells, using a panel of envelope protein-reactive monoclonal antibodies (MAbs), showed that MAbs which specifically neutralize YF-Asibi-LP virus, and not YF 17D-204 vaccine virus, also neutralized YF-Asibi-LP HeLa p6. This indicated that the epitopes involved in the biological process of neutralization were not altered during attenuation. However, two MAbs that recognize envelope protein epitopes did distinguish between HeLa- and non-HeLa-passaged YF-Asibi-LP virus. One of these (MAb 117) which is YF wild-type-specific, recognized YF-Asibi-LP virus but not YF-Asibi-LP HeLa p6 virus, whereas the other (MAb411), which is YF vaccine-specific, recognized YF-Asibi-LP HeLa p6 virus but not YF-Asibi-LP virus. These results suggest that antigenic changes in the viral envelope protein may determine the relative virulence or attenuation of YF virus.
Insights
Yellow fever (YF) virus attenuation in HeLa cells likely involves genetic changes, not pre-existing variants. Antigenic alterations in the viral envelope protein may influence YF virus virulence.
Area of Science:
- Virology
- Immunology
Background:
- Wild-type yellow fever (YF) virus (strain Asibi) passage in HeLa cells was previously reported to attenuate the virus in monkeys.
- Attenuation of YF virus in cell culture is a critical process for vaccine development.
Purpose of the Study:
- To analyze the process of YF virus attenuation during cell culture passage.
- To investigate the genetic and antigenic changes associated with YF virus attenuation.
Main Methods:
- Serial subculturing of a large plaque (LP) variant of YF-Asibi virus in HeLa cells.
- Assessment of viral attenuation in monkeys and mice.
- Comparison of viral envelope protein epitopes using monoclonal antibodies (MAbs).
Main Results:
- YF-Asibi-LP virus became attenuated for monkeys and mice after six passages in HeLa cells (YF-Asibi-LP HeLa p6).
- Attenuation was likely due to genetic changes, not selection of pre-existing variants or defective interfering particles.
- Monoclonal antibody analysis revealed antigenic changes in the viral envelope protein, suggesting a role in virulence or attenuation.
Conclusions:
- Cell culture passage induces genetic and antigenic changes in YF virus, leading to attenuation.
- Antigenic modifications of the viral envelope protein are implicated in determining YF virus virulence.