In a recent study published on the bioRxiv* preprint server, researchers assessed the impact of dual BNT162b2 messenger ribonucleic acid (mRNA) vaccination on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant-of-risk (VoC) recognition.
Study: Double-Dose SARS-CoV-2 mRNA Vaccination Progressively Increases Recognition of Alarming Variants by Spike RBD-Specific Memory B Cells. Image credit: CKA/Shutterstock
Background
Studies have reported that dual-coronavirus disease 2019 (COVID-19) vaccinations generate high titers of SARS-CoV-2 S-directed antibodies (Ab), Bmem, and T lymphocytes; however, VoCs with SARS-CoV-2 S receptor-binding domain (RBD) mutations can evade humoral immune responses.
Booster doses have been reported to enhance VoC recognition by Abs; however, it is unclear whether VoC recognition is enhanced due to higher Ab titers or due to increased Ab binding capacity to the S RBD.
About the research
In the current study, the researchers evaluated the benefit of dual BNT162b2 vaccinations on SARS-CoV-2 VoC recognition.
Healthy and untreated SARS-CoV-2 subjects (n=30) without immunologic or hematologic disease were enrolled in the study to assess their peripheral blood B-lymphocyte subsets between February and June 2021. Samples were collected before BNT162b2 vaccination, after three weeks after the first vaccination and four weeks after the second vaccination.
Serum memory B lymphocyte (Bmem) counts and Ab titers were assessed using recombinant SARS-CoV-2 spike (S) protein RBDs from the Wuhan, Gamma, and Delta strains. Neutralizing Ab (NAb) titers were assessed using 293T-ACE2 cells and SARS-CoV-2 pseudotyped virus assays. Furthermore, the nature of Bmem targeting the RBD was investigated based on the expression of cluster of differentiation (CD) 21, 27 and 71.
Enzyme-linked immunosorbent assays (ELISA) were performed to assess S variant-specific RBD antibody titers and the serum dilutions required to prevent 50% entry of SARS-CoV-2 (ID50) were determined. Flow cytometry (FC) was performed to estimate the number of Bmem. Immunoglobulin G (IgG) titers against the SARS-CoV-2 nucleocapsid (N) protein RBD and S RBD were assessed before and after the first and second BNT162b2 vaccinations.
Results
A total of 28, 30, and 30 samples were obtained before vaccination, three weeks after the first dose, and four weeks after the second dose, respectively. All participants remained SARS-CoV-2 naïve throughout the study without anti-SARS-CoV-2 N antibodies. Most participants (n=22) induced NAbs after the first vaccination, and NAb titers after the second vaccination had IC50 values >100.
Dual BNT162b2 vaccination generated strong NAb responses among all study participants. Immunoglobulin G+ (IgG+) and IgM+ RBD-directed Bmem were generated after the first vaccination, and the number of IgG1+ Bmem increased after the second vaccination. Most RBD-targeted Bmem showed binding to Delta and/or Gamma VoCs, which increased significantly after the second vaccination.
The RBD-targeted Bmem compartment is mainly composed of IgG1+ or IgM+ cells, and in contrast, the total Bmem compartment contains more IgG2+ cells and fewer IgG1+ cells than the RBD-targeted Bmem compartment.
After the second vaccination dose, the RBD-directed IgG1, 2 and 3-expressing Bmem populations expanded significantly, although the overall Bmem lymphocyte compartment was unchanged.
The number of RBD-targeted IgG+ Bmem correlated positively with RBD-targeted serum IgG after the first and second vaccinations. While two subsets of IgM+ Bmem lymphocytes (CD27+ IgM+ and CD27+ IgM+ IgD+) decreased proportionally after the second dose of vaccination, the absolute number of cells was identical to that observed after the first dose of vaccine. Taken together, BNT162b2 vaccinations notably affected the number of antigen-targeting Bmem lymphocytes, and the production of IgG1-expressing Bmem lymphocytes increased after the second BNT162b2 vaccination.
CD27 was expressed by 95% of anti-RBD and IgG-expressing Bmem lymphocytes, the proportion of which did not differ between initial and subsequent BNT162b2 vaccination. After the first dose of vaccine, 15% of anti-RBD Bmem lymphocytes were CD21lo, the proportion of which was marginally but significantly lower (down to 10%) four weeks after the second vaccination.
CD71 was expressed by 10% of anti-RBD Bmem lymphocytes after the first and second vaccinations. In the general population of Bmem lymphocytes, the results after the first and second vaccination were not significantly different, indicating stability of the Bmem compartment. After four weeks of vaccination, anti-RBD Bmem lymphocytes displayed a characteristic and quiescent Bmem lymphocyte immunophenotype.
Anti-Wuhan S RBD-IgG titers showed partial recognition of Beta, Gamma and Delta VoCs with more marked reductions for Gamma and Beta VoCs than for Delta VoCs. The second dose of BNT162b2 vaccine significantly enhanced the binding of anti-Wuhan RBD antibodies to gamma and beta VoCs; however, the neutralizing efficacy of vaccine-induced NAbs against gamma and beta was less than for delta.
Delta RBD and Gamma RBD were recognized by 50% and 70% of RBD-directed Bmem lymphocytes after the first and second vaccinations, respectively, and the increase in the number of VoC-recognizing Bmem was largely due to the increased number of IgG1+ Bmem.
Conclusion
Overall, the results of the study showed that the second vaccination with BNT162b2 increased the NAb titers and the number of Bmem targeting the SARS-CoV-2 RBD, and that the double vaccination with BNT162b2 was particularly necessary for the recognition of Delta and Gamma VoC. The findings show that the second vaccine dose improves the number of Bmem targeting the S RBD and the affinity of Bmem to overcome VoC mutations.
*Important message
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guiding clinical practice/health-related behavior or treated as established information.
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