Profiling the B cell immune response elicited by vaccination against the respiratory virus SARS-CoV-2

Abstract

B cells play a fundamental role in host defenses against viral infections. Profiling the B cell response elicited by SARS-CoV-2 vaccination, including the generation and persistence of antigen-specific memory B cells, is essential for improving the knowledge of vaccine immune responsiveness, beyond the antibody response. mRNA-based vaccines have shown to induce a robust class-switched memory B cell response that persists overtime and is boosted by further vaccine administration, suggesting that memory B cells are critical in driving a recall response upon re-exposure to SARS-CoV-2 antigens. Here, we focus on the role of the B cell response in the context of SARS-CoV-2 vaccination, offering an overview of the different technologies that can be used to identify spike-specific B cells, characterize their phenotype using machine learning approaches, measure their capacity to reactivate following antigen encounter, and tracking the maturation of the B cell receptor antigenic affinity.

Keywords: B cell ELISpot; BCR repertoire; COVID-19 vaccines; SARS-CoV-2; computational flow cytometry; memory B cells; respiratory virus.

Figure 1

Workflow for the identification of vaccine-induced spike-specific B cells. Schematic representation of different technologies to detect antigen-specific B cells in blood samples collected from SARS-CoV-2 vaccinated subjects. PBMC can be used for multiparametric flow cytometry analysis labelling cells with the fluorescent antigen as probe to identify rare antigen-specific B cells. Computational flow cytometry can be then applied to explore and visualize multiparametric flow cytometry data (fcs files) using specific tools and algorithms. Effector function of spike-specific memory B cells can be measured in PBMC by B-cell ELISpot technique upon in vitro restimulation of cells. High-throughput bulk RNA sequencing of BCR heavy-chain genes can be performed on whole blood to unravel the dynamics of the BCR repertoire.

Figure 2

Schematic gating strategy for the identification of spike-specific B cells. (A) Examples of different strategies that can be used for selecting the parent subset of B cells to be analyzed for the presence of spike-specific B cells. Starting from CD19⁺ B cells gated among live, singlet cells a, it can be selected the not-naïve B cells by excluding the IgD⁺CD27^- cells b; the CD19⁺CD20⁺ c, switched MBC (IgD^-IgM^-, d, and the CD19^-/low CD20^- cells c CD38^highCD27⁺ plasmablasts e. (B) Identification of antigen-specific-B cells using two fluorescent labelled spike proteins f, the full spike versus the RBD domain only g or versus the spike protein of a viral variant (var1, h).