Fast forwarding evolution – accelerated adaptation in a proofreading deficient hypermutator herpesvirus

Authors: XING, NA - Freie University; HOFLER, THOMAS - Freie University; Hearn, Cari; NASCIMENTO, MARIANA - Freie University; CAMPS PARADELL, GEORGINA - Freie University; MCMAHON, DINO - Freie University; KUNEC, DUSAN - Freie University; Cheng, Hans; TRIMPERT, JAKOB - Freie University; OSTERRIEDER, NICHOLAS - Freie University

Submitted to: Virus Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2022
Publication Date: 10/14/2022
Citation: Xing, N., Hofler, T., Hearn, C.J., Nascimento, M., Camps Paradell, G., Mcmahon, D.P., Kunec, D., Cheng, H.H., Trimpert, J., Osterrieder, N. 2022. Fast forwarding evolution – accelerated adaptation in a proofreading deficient hypermutator herpesvirus. Virus Evolution. 8(2):veac099. https://doi.org/10.1093/ve/veac099.
DOI: https://doi.org/10.1093/ve/veac099

Interpretive Summary: New mutations are the source of evolution for all species including viruses. In this study, Marek's disease virus (MDV), a serious pathogen of poultry that causes lymphomas in chicken, was engineered to produce more mutations. This "hypermutator" virus was compared to the original version under various conditions in both cultured cells and animals. We find that the hypermutator virus could more quickly adapt to new environmental conditions like different cell types or response to anti-viral drugs, and could be more easily adapted to make non-pathogenic viruses, e.g., for vaccine development. This approach shows great promise in understanding viral evolution as it should be more feasible to identify genetic changes that account for traits such evasion from vaccines or drugs. If true, this should enhance mitigation steps to control new or more virulent viral strains, such as those repeatedly observed for MDV since the 1960s.

Technical Abstract: Evolution relies on the availability of genetic diversity for fitness-based selection. However, most deoxyribonucleic acid (DNA) viruses employ DNA polymerases (Pol) capable of exonucleolytic proofreading to limit mutation rates during DNA replication. The relative genetic stability produced by high-fidelity genome replication can make studying DNA virus adaptation and evolution an intensive endeavor, especially in slowly replicating viruses. Here, we present a proofreading-impaired Pol mutant (Y547S) of Marek’s disease virus that exhibits a hypermutator phenotype while maintaining unimpaired growth in vitro and wild-type (WT)-like pathogenicity in vivo. At the same time, mutation frequencies observed in Y547S virus populations are 2–5-fold higher compared to the parental WT virus. We find that Y547S adapts faster to growth in originally non-permissive cells, evades pressure conferred by antiviral inhibitors more efficiently, and is more easily attenuated by serial passage in cultured cells compared to WT. Our results suggest that hypermutator viruses can serve as a tool to accelerate evolutionary processes and help identify key genetic changes required for adaptation to novel host cells and resistance to antiviral therapy. Similarly, the rapid attenuation achieved through adaptation of hypermutators to growth in cell culture enables identification of genetic changes underlying attenuation and virulence, knowledge that could practically exploited, e.g. in the rational design of vaccines.