Detailed characterization of BA.2 and BA.1 variants

In a recent study published in the journal NatureThe researchers evaluated the pathogenicity and infectivity of the coronavirus 2 (SARS-CoV-2) Omicron BA.2 variant of severe acute respiratory syndrome in hamsters and mice.

With the advent of Omicron BA.1, BA.2, and BA.1.1 strains, there is growing concern about a decline. Effectiveness of Coronavirus disease 2019 (COVID-19) vaccine. This has accelerated the development of antiviral agents and monoclonal antibodies (mAbs) and expanded the therapeutic environment for COVID-19.

..study: Characterization and antiviral susceptibility of SARS-CoV-2 Omicron / BA.2... Image credit NIAID

About research

In this study, researchers evaluated the pathogenicity and infectivity of BA.2 in hamsters and mice in comparison to SARS-CoV-2 D614G WA1 / 2020 D614G, beta, and Omicron BA.1 variants.

BA.2 variants such as HP353, NCD1288, TY40-385, HP354 were isolated on Vero E6 /.TMPRSS2 (Transmembrane serine protease 2) Cell line. The TY40-385 and NCD1288 isolates were obtained from Indian travelers arriving in Japan, while the HP354 and HP353 isolates were obtained from Japanese residents.

BALB / c mice were inoculated with 10 intranasally^Five Plaque forming unit (PFU) of BA.1 or BA.2. Subsequently, changes in their weight and lung function were assessed. Their Rpef and Penh values ​​were measured by whole body plethysmography (WBP) to identify lung changes. In addition, mouse lung and turbinate tissues were subjected to histopathological analysis. there Hybridization, immunohistochemical analysis, and their cytokine and chemokine levels were evaluated.

Similar analyzes were performed on transgenic K18 mice and hamsters expressing human angiotensin converting enzyme 2 (hACE2) for comparative evaluation of D614G, beta, BA.1 and BA.2 variants. In addition, microcomputer tomography (micro CT) analysis and next-generation sequencing (NGS) were performed.

BA.2 neutralization was assessed by the Focus Decreased Neutralization Test (FRNT) among COVID-19 convalescent and BNT162b2 vaccinated individuals, with titers of D614G, Delta, BA.1, and BA.1.1 variants. It was compared with the one. In addition, an FRNT assay using SARS-CoV-2 infected hamster antisera was performed to evaluate the antigenic properties of the three Omicron variants. The therapeutic effects of antiviral agents on mAbs and BA.1 and BA.2 approved by the Food and Drug Administration (FDA) were also evaluated.

result

Two days after infection (dpi), BALB / c mice infected with BA.1 and BA.2 had significantly higher Penh and lower Rpef values ​​in beta-infected individuals, as opposed to body weight and respiration. No change in functionality was seen. mouse. Lung BA.2 titer (6.9 log)_Ten PFU / g) was higher than BA.1 titer (6.4 log)_Ten PFU / g). At 5 dpi, the BA.2 titer of the lung was reduced by a factor of 33 compared to BA.1 at 5 dpi. Nevertheless, the turbinate BA.1 and BA.2 titers remained the same.

Histopathological analysis showed minimal inflammatory infiltration into the alveoli and bronchiole / bronchiole-peripheral spaces of BA.1 and BA.2 infected mice. there Hybridization analysis revealed the presence of SARS-CoV-2 ribonucleic acid (RNA) in the alveoli and bronchiolic epithelium of BA.1 and BA.2 infected mice.Immunohistochemical analysis showed a similar distribution of SARS-CoV-2 antigen RNA of mice infected with BA.1 or BA.2. Analysis showed comparable BA.1 and BA.2 infectivity, albeit lower than beta.

Compared to BA.1-infected mice, BA.2-infected mice express inflammatory chemokines and cytokines such as interleukin-1 beta (IL-1β), interferon gamma (IFN-ꓬ), and macrophages. Has increased significantly. Inflammatory protein-1 beta (MIP-1β). However, the expression of inflammation is significantly lower than that of beta infection, indicating a low replication capacity of BA.2.

At 3 dpi, K18 mice expressing hACE2 showed significantly lower BA.1 and BA.2 titers and lung and turbinate RNA than the D614G titer. BA.2-induced expression of chemokines and cytokines [IL-1β, MIP-1α, and tumor necrosis factor-alpha (TNF-α)] It was higher than that induced by BA.1, but lower than that induced by D614G. This indicates that BA.1 and BA.2 are less pathogenic than D614G.

Syrian hamsters did not show any difference in body weight or respiratory function when inoculated with 10.³ Or 10^Five PFU dose of SARS-CoV-2 strain. At 3dpi and 10³ The BA.1 titers of inoculation, turbinate and lung were substantially higher than the BA.2 titers.However, at 10 o’clock^Five The inoculation volume and lung titers of BA.1 and BA.2 were similar. In addition, no significant differences were detected in hamsters infected with BA.1 and BA.2. there Hybridization, histopathological analysis, and immunohistochemical analysis. The findings show that BA.1 and BA.2 are equally pathogenic.

Micro-CT analysis showed pathological changes in the lungs, such as pneumonia, between BA.1 and BA.2-infected hamsters, with the highest CT severity score among BA.2-infected hamsters. .. NGS analysis showed that BA.1 predominates in the lungs and turbinates of hamsters at both doses.

All 10-inoculated K18 transgenic hamsters (including M51 cell line)³ The D614G PFU died at 5 dpi, but most BA.1 and BA.2 infected hamsters survived. The BA.2 titer of the lung was 100-fold and 10,000-fold lower than the corresponding BA.1 and D614G titers, respectively. However, all strains showed comparable titers in the turbinate.

FRNT analysis showed that BNT162b2 vaccination resulted in a more significant reduction in BA.1 and BA.1.1 titers compared to BA.2 titers. Vaccinated people infected with Delta have a high 50% FRNT (FRNT)₅₀) Value for delta, but FRNT is low₅₀ Value for 3 Omicron strains.Vaccinated vaccinated with Omicron showed FRNT₅₀ 2.9 to 3.6 times lower than Delta for Omicron strains.

Hamster antisera produced against the Omicron strain showed significantly lower FRNT₅₀ Titers for D614G and Delta stocks. In addition, the neutralization of BA.1.1 and BA.1 was observed to be 17.4 times and 11.7 times lower, respectively, compared to BA.2. This indicates that BA.2 is antigenically different from the D614G, Delta, BA.1 and BA.1.1 strains.

Among the mAbs, COV2-2196 / COV2-2130, S309, and REGN10987 / REGN10933 inhibited SARS-CoV-2 replication in the lungs in BA.2-infected hamsters. Among the antiviral drugs, all significantly reduced the BA.2 titer of the lungs. In addition, S-217622 reduced the BA.2 titer of the turbinate.

Overall, the findings showed that the pathogenicity and infectivity of BA.2 was comparable to BA.1 but lower than other SARS-CoV-2 mutants.