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Characterization of Chemically-Induced Endogenous Retroviral Particles in the CHO-K1 Cell Line
Nicholas B Mattson1, Trent J Bosma1, Yamei Gao1
1Laboratory of Retroviruses, Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Review, U.S. Food and Drug Administration, Silver Spring, MD 20993, USA.
Viruses
|November 27, 2025
Summary
This study investigated latent infectious endogenous retroviruses in CHO-K1 cells. Chemical induction activated retroviral particles, but infectivity assays confirmed no replicating retroviruses were present.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Chinese hamster ovary K1 (CHO-K1) cells constitutively produce retroviral-like particles (RVLPs) with reverse transcriptase (RT) activity.
- Previous studies reported infectious retroviruses in other rodent species, prompting investigation into CHO-K1 cells.
- Endogenous retroviruses (ERVs) can exist in latent states within host genomes.
Purpose of the Study:
- To investigate the presence of latent, infectious endogenous retroviruses (ERVs) in CHO-K1 cells.
- To determine if chemical induction can activate ERVs in CHO-K1 cells.
- To assess the infectivity of induced retroviral particles in various cell lines, including human.
Main Methods:
- Chemical induction assays using 5-iodo-2'-deoxyuridine and 5-azacytidine.
- Detection of reverse transcriptase (RT) activity using the product-enhanced RT (PERT) assay.
- Transmission electron microscopy (TEM) for retroviral particle visualization.
- Long-read and short-read high-throughput sequencing (HTS) for viral sequence analysis.
- Infectivity studies by inoculating various cell lines (human, monkey, rodent, CHO-K1) with cell-free supernatant.
Main Results:
- Chemical induction, particularly dual treatment, increased retroviral-like particle (RVLP) production and RT activity.
- Transmission electron microscopy confirmed the activation of A-type and C-type retroviral particles.
- Long-read HTS confirmed induction of A- and C-type particles in dual-drug-treated CHO-K1 cells.
- Infectivity studies showed no evidence of replicating retroviruses in inoculated cell lines, including human cells.
- Short-read HTS did not detect retroviral sequence integration in inoculated human cells.
Conclusions:
- Chemical induction successfully activated RVLPs and RT activity in CHO-K1 cells.
- Despite activation, no infectious or replicating endogenous retroviruses were detected in CHO-K1 cells.
- The study found no evidence for latent, infectious RVLPs in the CHO-K1 cell line.
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