In a recent study published on the bioRxiv * prepress server, researchers explored the virological profiles of new variants of Omicron in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Study: virological characteristics of new Omicron SARS-CoV-2 variants including BA.2.12.1, BA.4 and BA.5. Image credit: Naeblys / Shutterstock
The presence of SARS-CoV-2 spike (S) protein mutations increases the immune evasion, fusogenicity, and pathogenicity of SARS-CoV-2 variants by promoting binding of the S-receptor binding domain ( RBD) with the conversion of human angiotensin. enzyme (ACE2). The authors of the present study had previously characterized the virological characteristics of the SARS-CoV-2 Omicron BA.1 and BA.2. However, the impact of the S L452 residue mutation on the virological characteristics of the new Om.2ron variants related to BA.2 is unclear.
About the study
In the present study, the researchers extended their previous analysis by exploring the virological profiles of five new variants of Omicron related to BA.2 (BA.2.9.1, BA.2.11, BA.2.12.1, BA.4 and BA.5). ) containing L452R / M / Q mutations in their S RBD.
The sensitivity of BA.2-related Omicron variants to anti-SARS-CoV-2 humoral immunity was assessed by pseudovirus-based assays using pseudoviruses comprising S proteins from BA.2.9.1, BA.2.11, BA.2.12 .1, BA. .4 / 5 and BA.2. In addition, cell culture experiments were performed using HEK293-ACE2 / TMPRSS2 cells (human embryonic kidney 293-ACE2 / serine transmembrane protease 2), VeroE6 / TMPRSS2 cells, and airway epithelial cells. cultivated humans (Calu-3). Yeast surface visualization assays and cell-based fusion assays were also performed.
Serums were obtained from convalescent patients positive for SARS-CoV-2 unvaccinated and vaccinated (advanced infections) infected with BA.1 and BA.2. In addition, BA.2-infected hamsters and mice immunized with recombinant RBD (r) BA.2 S were used to assess the immune evasion of BA.2-related Omicron variants tested from infection-induced immunity. BA.2. The growth kinetics of the new Omicron variants tested were evaluated in vitro using recombinant strains of SARS-CoV-2, ie. WK-521 strainer and TY40-385 strainer.
The replication dynamics of BA.2-related Omicron variants were analyzed in vivo by hamsters infected with rBA.2-, rBA.2.12.1-, and rBA.4 / 5. Lung load of ribonucleic acid (RNA) SARS-CoV-2 and nucleocapsid (N) expression were assessed by quantitative reverse transcription polymerase (RT-qPCR) and immunohistochemistry (IHC) chain reaction. , respectively. In addition, the positivity of N protein was evaluated to compare the propagation efficiency of rBA.4 / 5 and BA.2. Hamster lungs were also subjected to histopathological analysis to assess the pathogenicity of BA.2.12.1 and BA.4 / 5 in vivo.
Results
BA.2 and all BA.2-related Omicron variants demonstrated resistance to positive convalescent sera for BA.1. In advanced infection sera BA.1, BA.2.9.1, BA.2.11 BA.2 showed comparative sensitivity, while BA.4 / 5 and BA.2.12.1 were 2.3 times and 1, 3 times more sensitive than BA.2. This indicated that BA.4 / 5 strains were more resistant to immunity induced by advanced BA.1 infections compared to BA.2.
Innovative BA.2 infection sera showed stronger anti-SARS-CoV-2 effects compared to convalescent BA.2 sera from unvaccinated patients. BA.2 showed three times greater resistance compared to B.1.1, indicating that BA.2 infection did not induce efficient anti-SARS-CoV-2 immunity. In contrast, BA.4 / 5 showed 1.6 times greater resistance than BA.2. In hamster and mouse sera, BA.4 / 5 evaded responses induced by BA.2 infections. The findings indicated that BA.4 / 5 was more resistant to immunity induced by BA.1 and BA.2.
In pseudovirus infectivity trials, BA.4 / 5 was 18.3 times more infectious than BA.2. Yeast surface visualization assays showed that the L452R mutation increased the ACE-2 binding affinity of BA.2 S RBD. Likewise, cell-based fusion assays showed that, compared to BA.2 S, the L452R mutation substantially increased the fusogenicity of BA.2.11 S while the S704L mutation (in BA.2.12.1) and HV69-70del, F486V and R493Q. mutations (at BA.4 / 5) resulted in a substantially lower fusogenicity. Cell culture experiments showed that BA.2.11 S and BA.4 / 5 S with L452R showed a higher fusogenicity than BA.2 S. The finding was supported by growth capacity experiments, in which the plaques formed by rBA.2.11 and rBA.4 Infections / 5 were larger than those formed by rBA.2 infections.
In growth kinetic assays, rBA.2.9.1, rBA.2.12.1, and rBA.4 / 5 replicated more efficiently compared to rBA.2 in human-induced pluripotent stem cells (iPSCs) derived from epithelial cells of the airways. The finding was consistent with SARS-CoV-2 lung RNA levels 61-fold and 34-fold higher in culture supernatants infected with rBA.2.12.1 and rBA.4 / 5, respectively, one day after infection (dpi). ). At three to five dpi, viral RNA levels in the peripheral regions of rBA-infected hamster lungs.4/5 were 5.7-fold and 4.2-fold higher compared to rBA-infected hamsters.2, respectively, indicating that rBA.4 / 5 propagates more efficiently than rBA.2. In addition, N protein positivity analysis showed more positive N cells in rBA.2.12.1 and rBA.4 / 5 infected hamster lungs compared to rBA.2 infected lungs.
In in vivo experiments, hamsters infected with rBA.2.12.1 and infected with rBA.4 / 5 weighed substantially less than hamsters infected with rBA.2. The Rpef values of rBA-infected hamsters.4 / 5 were also substantially lower compared to rBA-infected hamsters.2. This indicated that Omicron variants related to L452R / Q-bearing BA.2, especially BA.4 / 5, were more pathogenic than BA.2. The finding was supported by most histopathological changes (bronchitis, hemorrhage, and alveolar damage) with type II pneumocyte cell hyperplasia among rBA-infected hamsters.4 / 5.
Overall, the findings of the study highlighted the increased risk of L452R / M / Q-related Omicron variants with BA.2, especially BA.4 and BA.5, for general public health.
* Important news
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guided by clinical practice / health-related behavior, or treated as established information.