Researchers have discovered a groundbreaking cell line that significantly improves the isolation of SARS-CoV-2, the virus responsible for the COVID-19 pandemic. The new Vero E6-TMPRSS2-T2A-ACE2 cells demonstrate a 1.6-fold increase in efficiency compared to the previously used VeroE6/TMPRSS2 cells, particularly for clinical specimens with a relatively low viral load. This advancement has far-reaching implications for understanding the evolving nature of SARS-CoV-2 and its variants, as well as for developing effective treatments and countermeasures against the virus. The findings highlight the importance of selecting the right cell culture system to accurately determine SARS-CoV-2 infectivity, a critical factor in the ongoing fight against the pandemic. SARS-CoV-2, COVID-19, Virus isolation, Cell culture
Tackling the Challenges of SARS-CoV-2 Isolation
The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has been a global health crisis of unprecedented scale. As the virus continues to evolve, with new variants emerging, the need for efficient and reliable methods to isolate and characterize the virus has become increasingly crucial. Virus isolation from clinical specimens is not only essential for laboratory diagnosis but also for obtaining live virus samples to study the properties of emerging variants.
The Importance of Cell Lines in SARS-CoV-2 Isolation
Previous studies have shown that the VeroE6/TMPRSS2 cell line, which expresses the SARS-CoV-2 receptor ACE2 and the serine protease TMPRSS2, is highly susceptible and permissive to SARS-CoV-2 infection. These cells have been widely used for isolating the virus from clinical specimens. However, the emergence of new SARS-CoV-2 variants, such as the Omicron variant, has highlighted the need for more efficient cell culture systems.
Introducing the Vero E6-TMPRSS2-T2A-ACE2 Cell Line
In this groundbreaking study, researchers have demonstrated that the Vero E6-TMPRSS2-T2A-ACE2 cell line is superior to VeroE6/TMPRSS2 cells for isolating SARS-CoV-2 from clinical specimens. These cells show a 1.6-fold increase in efficiency for SARS-CoV-2 isolation, particularly for specimens with a relatively low viral load (less than 10^6 copies/mL).
The key to the improved performance of Vero E6-TMPRSS2-T2A-ACE2 cells lies in their enhanced expression of both TMPRSS2 and ACE2. The researchers found that the expression of TMPRSS2 mRNA in these cells is approximately 100-fold higher than in VeroE6/TMPRSS2 cells. Additionally, the Vero E6-TMPRSS2-T2A-ACE2 cells display a significantly higher level of ACE2 protein expression compared to the VeroE6/TMPRSS2 line.
Increased Infectivity and Virus Titration
The researchers further investigated the infectivity of SARS-CoV-2 in the different cell lines using a pseudovirus system. They found that the infectivity of pseudoviruses bearing the spike proteins of various SARS-CoV-2 variants, including the Omicron variants, was 2- to 4-fold higher in Vero E6-TMPRSS2-T2A-ACE2 cells compared to VeroE6/TMPRSS2 cells.
Fig. 2
Moreover, the researchers observed that the viral titers of SARS-CoV-2 strains, including the ancestral, BA.5, BF.7.4.1, BF.7, XBB.1.5, and CH.1.1.3 variants, were higher when measured in Vero E6-TMPRSS2-T2A-ACE2 cells compared to VeroE6/TMPRSS2 cells. This suggests that the choice of cell line can significantly impact the determination of SARS-CoV-2 infectivity, a critical factor in understanding the virus’s behavior and developing effective countermeasures.
Implications for SARS-CoV-2 Surveillance and Research
The improved efficiency of SARS-CoV-2 isolation using the Vero E6-TMPRSS2-T2A-ACE2 cell line has far-reaching implications. It will enable researchers to more effectively isolate and characterize emerging SARS-CoV-2 variants, which is crucial for monitoring the virus’s evolution and assessing potential threats to public health.
Table 1 Comparison of SARS-CoV-2 isolation using VeroE6-TMPRSS2-T2A-ACE2 cells with that using VeroE6/TMPRSS2.
Additionally, the use of this cell line in virus titration and neutralization assays can provide more accurate and reliable data, informing the development of vaccines, therapeutics, and other interventions against COVID-19. The researchers also found that the genomes of SARS-CoV-2 isolates obtained using Vero E6-TMPRSS2-T2A-ACE2 cells were generally stable, with no specific mutations arising during the isolation process.
Exploring the Broader Implications
While the study focused on SARS-CoV-2, the findings have broader implications for the field of virology. The superior performance of the Vero E6-TMPRSS2-T2A-ACE2 cell line highlights the importance of selecting appropriate cell culture systems for accurately determining the infectivity and properties of other viruses. This principle applies not only to the ongoing efforts against COVID-19 but also to the study of emerging infectious diseases and the development of effective countermeasures.
As the scientific community continues to grapple with the challenges posed by SARS-CoV-2 and its evolving variants, the availability of this advanced cell line represents a significant advancement in our ability to understand and combat the virus. The findings of this study will undoubtedly contribute to the ongoing efforts to control the COVID-19 pandemic and pave the way for more effective strategies in the face of future viral threats.
Author credit: This article is based on research by Hitomi Kinoshita, Tsukasa Yamamoto, Yudai Kuroda, Yusuke Inoue, Kaya Miyazaki, Norio Ohmagari, Daisuke Tokita, Phu Hoang Anh Nguyen, Souichi Yamada, Shizuko Harada, Takayuki Kanno, Kenichiro Takahashi, Masumichi Saito, Kazuya Shirato, Ikuyo Takayama, Shinji Watanabe, Tomoya Saito, Hideki Ebihara, Tadaki Suzuki, Ken Maeda, Shuetsu Fukushi.
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