Laboratory adaptation of the SARS-CoV-2 Delta variant in Vero E6 cells enhances in vitro growth but attenuates human TMPRSS2-dependent fitness, pathogenicity, and transmission
- 1College of Veterinary Medicine, Northeast Agricultural University, Harbin 150030, China
- 2Key Laboratory of Jilin Province for Zoonoses Prevention and Control, State Key Laboratory of Pathogen and Biosecurity, Academy of Military Medical Sciences, Changchun 130122, China
Abstract
Laboratory propagation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for virological research, but adaptation in commonly used non-human cells with low transmembrane serine protease 2 expression may alter phenotypes relevant to biosafety and risk assessment. This study aimed to determine how serial passage in African green monkey-derived Vero E6 cells affects the growth, entry pathways, pathogenicity, and transmission of a clinical Delta strain. The parental virus was serially passaged to generate two adapted variants, which were characterized by whole-genome sequencing, replication and competition assays, spike cleavage and membrane fusion analyses, receptor binding studies, and animal experiments. The first variant acquired spike substitutions P217S, S247R, and H655Y, whereas the second acquired G261R and a six-amino-acid deletion immediately upstream of the furin cleavage site, plus non-spike mutations. Both variants replicated more efficiently than the parental virus in Vero E6, LLC-MK2, Huh-7, and HeLa cells expressing human angiotensin-converting enzyme 2 (ACE2), but not in Caco-2 cells. Their phenotypes reflected altered use of human transmembrane serine protease 2 rather than altered human ACE2 binding; they showed increased affinity for African green monkey ACE2 but unchanged affinity for the human receptor. Despite enhanced growth in vitro, both variants exhibited reduced pathogenicity and transmission in animals. These findings demonstrate that Vero E6 passage can rapidly reshape spike function and select viruses with improved cell-culture growth but impaired protease-dependent fitness in vivo, supporting rigorous genomic and phenotypic monitoring of laboratory-propagated virus stocks before use.
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BibTeX
@article{jin2026laboratory,
title = {{Laboratory adaptation of the SARS-CoV-2 Delta variant in Vero E6 cells enhances in vitro growth but attenuates human TMPRSS2-dependent fitness, pathogenicity, and transmission}},
author = {Qiushi Jin and Fang Yan and Fang Song and Tiecheng Wang and Haiyang Xiang and Bingqi Shan and Xuefeng Wang and Yuwei Gao and Xianzhu Xia},
journal = {Biosafety and health},
year = {2026},
month = sep,
doi = {10.1016/j.bsheal.2026.09.002},
url = {https://europepmc.org/article/PMC/PMC13729064},
note = {CC BY-NC-ND},
}
RIS
TY - JOUR
TI - Laboratory adaptation of the SARS-CoV-2 Delta variant in Vero E6 cells enhances in vitro growth but attenuates human TMPRSS2-dependent fitness, pathogenicity, and transmission
AU - Qiushi Jin
AU - Fang Yan
AU - Fang Song
AU - Tiecheng Wang
AU - Haiyang Xiang
AU - Bingqi Shan
AU - Xuefeng Wang
AU - Yuwei Gao
AU - Xianzhu Xia
PY - 2026
DA - 2026/09/07
JO - Biosafety and health
DO - 10.1016/j.bsheal.2026.09.002
UR - https://europepmc.org/article/PMC/PMC13729064
AB - Laboratory propagation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for virological research, but adaptation in commonly used non-human cells with low transmembrane serine protease 2 expression may alter phenotypes relevant to biosafety and risk assessment. This study aimed to determine how serial passage in African green monkey-derived Vero E6 cells affects the growth, entry pathways, pathogenicity, and transmission of a clinical Delta strain. The parental virus was serially passaged to generate two adapted variants, which were characterized by whole-genome sequencing, replication and competition assays, spike cleavage and membrane fusion analyses, receptor binding studies, and animal experiments. The first variant acquired spike substitutions P217S, S247R, and H655Y, whereas the second acquired G261R and a six-amino-acid deletion immediately upstream of the furin cleavage site, plus non-spike mutations. Both variants replicated more efficiently than the parental virus in Vero E6, LLC-MK2, Huh-7, and HeLa cells expressing human angiotensin-converting enzyme 2 (ACE2), but not in Caco-2 cells. Their phenotypes reflected altered use of human transmembrane serine protease 2 rather than altered human ACE2 binding; they showed increased affinity for African green monkey ACE2 but unchanged affinity for the human receptor. Despite enhanced growth in vitro, both variants exhibited reduced pathogenicity and transmission in animals. These findings demonstrate that Vero E6 passage can rapidly reshape spike function and select viruses with improved cell-culture growth but impaired protease-dependent fitness in vivo, supporting rigorous genomic and phenotypic monitoring of laboratory-propagated virus stocks before use.
SN - 2590-0536
SN - 2096-6962
ER -