Hybrid Immunity Boosts Defense Against SARS-CoV-2 Variants

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Summary

The proliferation of SARS-CoV-2 variants has placed the efficacy of extant vaccinations and the applicability of monoclonal antibody-derived therapeutics for COVID-19 in precarious positions. An investigation into the B cell and antibody response characteristics at a singular cellular level was conducted by analyzing the memory B cells of ten individuals, consisting of five naïve and five convalescent subjects inoculated with the BNT162b2 mRNA vaccine. The study involved sorting nearly 6,000 cells, revealing that over 3,000 cells synthesized monoclonal antibodies targeting the spike protein, and in excess of 400 cells neutralized the prototypical SARS-CoV-2 virus initially detected in Wuhan, China. A considerable majority of these antibodies, nearly 70%, were circumvented by the B.1.351 (Beta) and B.1.1.248 (Gamma) variants, whereas the B.1.1.7 (Alpha) and B.1.617.2 (Delta) variants affected a substantially reduced proportion. The aggregate diminution of neutralization capacity was invariably more pronounced among antibodies derived from naïve subjects. This phenomenon can be partially attributed to the presence of the IGHV2-5;IGHJ4-1 germline, exclusively identified in convalescent individuals, which engendered potent and extensively neutralizing antibodies. The findings imply that seropositive individuals, subsequent to infection or primary vaccination, will generate antibodies with heightened potency and scope, thereby facilitating superior management of emergent SARS-CoV-2 variants.

Research Criteria

The objective of this research endeavor was to scrutinize the singular cellular attributes of B cell and antibody response in subjects inoculated with the BNT162b2 mRNA vaccine. Investigators assessed the memory B cells of a cohort of ten participants, encompassing five individuals devoid of prior SARS-CoV-2 exposure and five who had recuperated from the viral infection. This inquiry aimed to elucidate the idiosyncrasies of the B cell and antibody response at an individual cellular stratum in vaccinated individuals, bearing potential ramifications for comprehending immune reactions to COVID-19 and providing insights for vaccine advancement.

Fig.1 Gating strategy of single B cells isolation by FACS. (Andreano, 2021)

Sample Type

Isolated memory B cells from 5 naïve and 5 convalescent people vaccinated with the BNT162b2 mRNA vaccine.

Result—Isolation of Neutralizing Antibodies

Researchers aimed to explore the B cell immune response by sorting single cells of antigen-specific memory B cells utilizing the SARS-CoV-2 S protein antigen encoded by mRNA vaccine as a bait. These S protein-specific cells were cultured, allowing the cells to naturally generate monoclonal antibodies (mAbs) for two weeks. Enzyme-linked immunosorbent assay (ELISA) detected mAbs produced by 65.1% of the sorted cells from seropositive participants and 40.1% from seronegative participants. A cytopathic effect-based microneutralization assay (CPE-MN) detected 411 SARS-CoV-2 neutralizing human monoclonal antibodies (nAbs), with 14.8% of S-protein-specific B cells in seropositive participants yielding nAbs. Seropositive participants showed higher percentages of nAbs neutralizing variants of concern (VoCs) than seronegative participants, with average frequencies of 80.6%, 39.4%, and 62.0% against Alpha, Beta, and Gamma variants, respectively, compared to 70.4%, 22.5%, and 43.6% in seronegative participants.

Fig.2 Identification of cross-neutralizing SARS-CoV-2 S protein-specific nAbs. (Andreano, 2021)

Result—S Protein Epitope Mapping

To delineate the S protein regions targeted by identified nAbs, researchers employed a competition assay utilizing four known antibodies—J08, S309, 4A8, and L19—which bind to distinct domains of the S protein. The nAbs were pre-incubated with the original SARS-CoV-2 S protein, followed by the addition of a mix of the four fluorophore-labeled nAbs. Using a 50% signal reduction threshold, the majority of nAbs from both seronegative and seropositive vaccinees competed with J08. Among seronegative vaccinees, the second most populous group consisted of nAbs that did not compete with any of the four labeled nAbs, while in seropositive vaccinees, S309-competing nAbs were the second most abundant. No nAbs competed with the S2-targeting L19 antibody. J08-competing nAbs, which likely bind to the receptor-binding motif, originated from several germlines, whereas S309-competing nAbs mostly derived from the IGHV2-5;IGHJ4-1 germline. Non-predominant gene families were found to be the most abundant for NTD-directed nAbs and non-competing nAbs in the assay.

Fig.3 Epitope binning and genetic characterization of competing nAbs. (Andreano, 2021)

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Reference

1. Andreano, E.; et al. Hybrid immunity improves B cells and antibodies against SARS-CoV-2 variants. Nature. 2021, 600(7889): 530-535.