In a recent study published on the bioRxiv* preprint server, researchers evaluated the impact of BNT162b2 dual messenger ribonucleic acid (mRNA) vaccination on recognition of severe acute respiratory syndrome coronavirus 2 variants of concern (VoCs) (SARS-CoV-2).
Study: Double-dose mRNA vaccination against SARS-CoV-2 progressively increases recognition of variants of concern by Spike RBD-specific memory B cells. Image credit: CKA/Shutterstock
background
Studies have reported that vaccinations against double-coronavirus disease 2019 (COVID-19) generate high titers of antibodies targeting SARS-CoV-2 S (Ab), Bmem, and T lymphocytes; however, VoCs with mutations in the SARS-CoV-2 S receptor binding domain (RBD) 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 S RBDs.
About the study
In the present study, the researchers evaluated the benefit of dual BNT162b2 vaccinations on SARS-CoV-2 VoC recognition.
Healthy, SARS-CoV-2-naive individuals (n=30) without immunologic or hematologic disease were enrolled to assess their peripheral blood B-lymphocyte subsets between February and June 2021. Samples were obtained prior to vaccination BNT162b2, 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 SARS-CoV-2 spike (S) recombinant protein RBD from the Wuhan, Gamma, and Delta strains. Neutralizing Ab (NAb) titers were assessed using 293T-ACE2 cells and SARS-CoV-2 pseudotyped viral assays. In addition, the nature of RBD-targeted Bmem was examined based on cluster of differentiation (CD) 21, 27, and 71 expression.
Enzyme-linked immunosorbent assays (ELISA) were performed to assess variant-specific S RBD antibody titers and the serum dilution required to prevent 50% of SARS-CoV-2 input values (ID50) was determined. . Flow cytometry (FC) was performed to assess Bmem counts. Immunoglobulin G (IgG) titers against the nucleocapsid protein (N) SARS-CoV-2 RBD and S RBD were assessed before and after the first and second BNT162b2 vaccinations.
results
In total, 28, 30 and 30 samples were obtained before vaccination, after three weeks of the first dose and after four weeks of the second dose, respectively. All participants remained naïve to SARS-CoV-2 throughout the study without anti-SARS-CoV-2 N antibodies. Most participants (n = 22) induced NAb after the first vaccination, and titers of NAbs after the second vaccination had IC50 values >100.
BNT162b2 dual vaccination generated robust NAb responses among all study participants. Immunoglobulin G+ (IgG+) and IgM+ RBD-targeted Bmem were generated after the first vaccination, and IgG1+ Bmem counts increased after the second vaccination. Most RBD-targeted Bmem showed binding to Delta and/or Gamma VoC, which increased significantly after the second vaccination.
The RBD-targeted Bmem compartment mainly comprised IgG1 + or IgM + cells, and in contrast, the total Bmem compartment comprised more IgG2 + cells and fewer IgG1 + cells compared to the RBD-targeted Bmem compartment.
After the second vaccination dose, Bmem populations expressing RBD-targeted IgG1, 2, and 3 were significantly expanded, although the total Bmem lymphocyte compartment was not altered.
The number of RBD-targeted IgG + Bmem was positively correlated 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 vaccination dose, absolute cell counts were identical to those observed after the first vaccine dose. Taken together, BNT162b2 vaccinations particularly affected antigen-targeted Bmem lymphocyte counts, and the production of IgG1-expressing Bmem lymphocytes was enhanced 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 baseline and post-BNT162b2 vaccination. After the first vaccine dose, 15% of anti-RBD Bmem lymphocytes were CD21lo, the proportion of which was marginally but significantly lower (reduced to 10%) four weeks after the second vaccination.
CD71 was expressed by 10% of anti-RBD Bmem lymphocytes after the first and second vaccination. In the total Bmem lymphocyte population, the results after the first and second vaccination did not differ significantly, denoting the stability of the Bmem compartment. After four weeks of vaccination, anti-RBD Bmem lymphocytes showed a natural and resting Bmem lymphocyte immunophenotype.
Anti-Wuhan S RBD-IgG titers showed partial recognition of Beta, Gamma, and Delta VoCs with more prominent reductions for Gamma and Beta VoCs than for Delta VoCs. The second dose of BNT162b2 vaccine significantly enhanced the binding of Wuhan anti-RBD antibodies to gamma and beta VoCs; however, the neutralizing potency of vaccine-induced NAbs against Gamma and Beta was lower than for Delta.
Delta RBD and Gamma RBD were recognized by 50% and 70% of RBD-targeted Bmem lymphocytes after the first and second vaccinations, respectively, and the increase in VoC-recognizing Bmem counts was largely due to elevated Bmem IgG1 + counts.
conclusion
Overall, the study findings showed that second BNT162b2 vaccination increased NAb titers and Bmem counts targeting SARS-CoV-2 RBD and that BNT162b2 dual vaccination was particularly necessary for Delta and Gamma recognition VoC. The findings indicated that the second dose of vaccine improved the counts of Bmem targeting S RBD and the affinity of Bmem to overcome VoC mutations.
*Important news
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.