Study: Effects of prior infection with SARS-CoV-2 on the B cell receptor repertoire response during vaccination. Image credit: Cinefootage Visuals/Shutterstock
Record
Characterization of B cell responses to coronavirus disease 2019 (COVID-19) vaccines from prior exposure to SARS-CoV-2 will deepen understanding of the potential use of B cell memory by vaccines. Higher rates of somatic hypermutations (SHM) have been reported in response to natural SARS-CoV-2 infections but not to vaccinations, indicative of different B cell receptor (BCR) responses to natural infections. Shared (or public) SARS-CoV-2 clonotypes have been reported among different individuals, indicative of evolutionary convergence in repertoires. The authors of the present study previously reported that anti-SARS-CoV-2 S titers in response to SARS-CoV-2 vaccinations are higher among seropositive individuals (with a prior history of COVID-19) than seronegative individuals (without a prior history of COVID -19 ). However, the impact of prior exposure to SARS-CoV-2 on BCR repertoire immune responses to COVID-19 vaccinations is unclear.
About the study
In the present study, the researchers extended their previous analysis by comparatively assessing the BCR repertoires of HIV-positive and HIV-negative individuals to assess the impact of prior COVID-19 history on B cell responses to the Pfizer SARS-CoV-2 mRNA vaccine. They also investigated potential elicitation of public BCR clonotype by the vaccine. Four HIV-negative and five HIV-positive healthcare workers (HCWs) were enrolled in the study. Previous exposure to SARS-CoV-2 was confirmed by polymerase chain reaction (PCR) and occurred one to two months before the start of the study. Blood samples were obtained before vaccination and after 21 days of vaccination, after which sera and PBMCs (peripheral blood mononuclear cells) were used for antibody (Ab) titer and BCR sequencing, respectively. Grafting analyzes were performed to assess variable (V) gene usage, heavy chain complementarity determining region 3 (HCDR3) lengths, SHM rates, clonality and convergence. Fluorescent flow cytometry (FC)-based assays were performed to determine Ab titers against SARS-CoV-2 spike (S) protein subunits 1 (S1) and 2 (S2), nucleocapsid (N) protein, and receptor binding domain (RBD), with secondary Abs for immunoglobulin G (IgG), IgA and IgM isotypes. BCR sequences containing the IgG isotype were analyzed for frequency of gene family variable (IGHV) usage, and V gene usage was assessed for IgM or IgA. IgG repertoire divergence in response to vaccination was assessed using species richness, Simpson’s diversity index and Shannon’s diversity index. Preexisting IgG repertoire clones and the 50 most abundant IgG clones were further analyzed. IgG clonal expansion (from previous infection) in response to vaccination was assessed and characterized using V gene usage, SHM length, and HCDR3 of 28 confluent clones shared among all study participants. The COVID Ab database was queried to determine whether the convergent and expanded clones identified in the study had previously been identified as SARS-CoV-2-specific clones.
Results
Vaccine-induced expanded IgG clonotypes had shorter HCDR3 lengths, and expanded clonotypes had higher SHM rates for HIV-positive individuals. Public clonotypes (n=28) were identified in all individuals with higher SHM and lower HCDR3 than other clonotypes, indicative of convergent evolution due to vaccination regardless of prior exposure to SARS-CoV-2. Serum titers of IgG, IgM, and IgA isotypes to SARS-CoV-2 S1, S2, RBD, and NP were detected with the lowest and highest titers for IgA and IgG, respectively, and Ab titers were highest among HIV-positive individuals at baseline . Three weeks after vaccination, seropositive IgG titers against S1, S2 and NP continued to be greater than seronegative titers. However, anti-S RBD IgG titers were identical. Anti-S2 IgM titers were greater among seropositive subjects, whereas IgG titers against RBD, NP and S1, RBD did not differ between serotypes. However, IgA titers did not differ significantly between serotypes for any SARS-CoV-2 antigen. HCDR3 length distribution, global BCR isotype and IGHV usage were not altered by vaccination. IgM isotypes showed the highest frequency among serotypes (seropositive 67%, seronegative: 62%). IgG BCR sequences used IGHV3 at the highest frequency. V gene usage frequency and HCDR3 lengths for IgM and IgA in BCR sequences were not statistically different between serotypes after 21 days of vaccination. BCR SHM rates increased after vaccination among HIV-positive individuals and decreased among HIV-negative individuals. Comparison of IgG SHM rates at the two time points showed no difference in the fraction of clones with either <2 mutations or ≥2 mutations between groups. However, SHM rates were greater for IgG sequences with ≥2 mutations among seronegative individuals at both time points. BCR SHM rates in IgA increased significantly after three weeks of vaccination among seropositives, but showed no significant difference among seronegative subjects after vaccination. SHM patterns for IgM and IgG were similar. At the second time point, seropositive BCR clones showed greater Shannon diversity and species richness than seronegative ones. Both serotypes had preexisting clonotypes that expanded after vaccination. However, the repertoires were dominated by new clones. Minimal overlap was observed between the 50 most abundant IgG clonotypes 21 days post-vaccination and clones of any isotype at baseline. The V gene usage of the 50 most abundant clones did not differ significantly from others in serotypes. HCDR3 lengths were significantly shorter in the top 50 BCR clones in the serotypes and shorter than in other clones. SHM rates were greater among seropositive top 50 clones and other clones than their seronegative counterparts. The queried clonotypes showed three matches to the COVID-19 Ab database. Clones #34727 and #13327 matched S-B8 and Fab-368 Ab, respectively, and both could neutralize SARS-CoV-2. Clone #8269 matched multiple Ab targets but did not neutralize SARS-CoV-2.
conclusion
In conclusion, based on the study findings, subjects with a prior history of COVID-19 had higher Ab titers after the first SARS-CoV-2 vaccination.
