Distinct dynamics of antigen-specific induction and differentiation of different CD11c⁺Tbet⁺ B-cell subsets

Background: CD11c⁺Tbet⁺ B cells are enriched in autoimmunity and chronic infections and also expand on immune challenge in healthy individuals. CD11c⁺Tbet⁺ B cells remain an enigmatic B-cell population because of their intrinsic heterogeneity. Objectives: We investigated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen-specific development and differentiation properties of 3 separate CD11c⁺ B-cell subsets—age-associated B cells (ABCs), double-negative 2 (DN2) B cells, and activated naive B cells—and compared them to their canonical CD11c⁻ counterparts. Methods: Dynamics of the response of the 3 CD11c⁺ B-cell subsets were assessed at SARS-CoV-2 vaccination in healthy donors by spectral flow cytometry. Distinct CD11c⁺ B-cell subsets were functionally characterized by optimized in vitro cultures. Results: In contrast to a durable expansion of antigen-specific CD11c⁻ memory B cells over time, both ABCs and DN2 cells were strongly expanded shortly after second vaccination and subsequently contracted. Functional characterization of antibody-secreting cell differentiation dynamics revealed that CD11c⁺Tbet⁺ B cells were primed for antibody-secreting cell differentiation compared to relevant canonical CD11c⁻ counterparts. Conclusion: Overall, CD11c⁺Tbet⁺ B cells encompass heterogeneous subpopulations, of which primarily ABCs as well as DN2 B cells respond early to immune challenge and display a pre–antibody-secreting cell phenotype.