Thus, the central question is the relevance of an NGS signal. Using a different

approach, NGS transcriptome analysis is used as a readout in infectivity assays to

detect viral replication in infected cells, indicating the presence of live virus in the

tested material [42]. Transcriptomics analysis identified viral RNAs only synthe-

sized during cell infection. Metabolic labeling of newly synthesized RNA has also

been used to unambiguously and specifically detect virus replication in permissive

cell lines [43].

According to these approaches, the transcriptome generated by NGS can not

only be used to detect and identify virus sequences, but also to be used assign them

to non-viable or viable/replicative, eliminating false positive signals.

Alternatively, new genetic-engineering technologies can be also used to modify

or disrupt the activity of endogenous and extraneous viruses in cell lines. A genome

editing technology has been used to disrupt in CHO cells, an active retrovirus C

element, and completely suppress the release of RNA‐loaded viral particles [44].

CHO cells have been made resistant to MVM infection by altering genes involved

in cell-surface sialylation [45].

4.5

CONCLUSIONS

Cell lines are essential for vaccine manufacturing. For live-attenuated or inactivated

viral vaccines, cell lines have been developed to allow viral replication.

Because cell cultures and raw materials can harbor adventitious agents, the viral

safety assessment of cell lines and eukaryotic expression systems represents a key

step in the choice of cell line for vaccine manufacture. Measures to prevent con-

tamination by adventitious agents include the use of cell-culture media devoid of

animal-derived components.

Numerous analytical methods are also part of control strategy to mitigate con-

tamination by adventitious agents. Novel technologies are complementing or re-

placing existing conventional methods, such as those based on NGS, and have

enabled the improved characterization of cell lines. The genetic engineering of cell

lines to prevent potential contamination by adventitious agents is also a promising

approach. These improvements will further contribute to safety of vaccines.

ACKNOWLEDGMENTS

All authors conceptualized the manuscript and contributed equally to the book

chapter. All authors have read and agreed to the published version of the chapter.

Competing financial interests: all authors are employees of the GSK group of com-

panies. Trademarks used in the article are the property of their respective owners.

REFERENCES

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Jan. 2003.

[2] I. Jordan and V. Sandig, “Matrix and backstage: cellular substrates for viral vac-

cines,” Viruses, vol. 6, no. 4, pp. 1672–1700, Apr. 2014.

Cell lines for vaccine production

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