Background/Purpose: T-bet⁺ B cells, known as age-associated B cells (ABCs) and/or double-negative B cells (DN), expand in various autoimmune diseases. This study aimed to clarify whether these populations of B cells serve as prognostic and/or therapeutic biomarkers for SLE in humans.

Methods: Peripheral blood from 22 active SLE patients and 10 healthy donors (HDs) was analyzed. Flow cytometry was used to enumerate T-bet+ B cells, as well as the subsets of ABCs (CD19⁺CD21^–CD11c⁺T-bet⁺) and DN (CD19⁺IgD^–CD27^–CXCR5^–T-bet⁺). All patients met the 2019 EULAR/ACR classification criteria for SLE. In addition to flow cytometry experiments, data from previously published single-cell RNA sequencing (scRNA-seq) studies, regarding 6 HDs and 11 active SLE patients, were used for a meta-analysis focusing on T-bet+ B cells, so as to allow characterization of the genes and pathways associated with the biology of ABCs/DN. Bioinformatics analysis was used to predict the effects of hydroxychloroquine, anifrolumab and fasudil  (a Rho-associated protein kinase inhibitor) on T-bet+ B cells. In order to validate the in silico predictions, 24 hour-long primary cell cultures combined with in vitro pharmacological treatments of 1 hour were performed, so as to evaluate the effects of the aforementioned 3 pharmaceutical agents on the percentages of T-bet+ B cells.

Results: T-bet+ B cells, as well as ABCs and DN, were expanded  in SLE patients. Interestingly, percentages of T-bet+ B cells and DN B cells positively correlated with the SLEDAI score of the patients. According to scRNA-seq analysis, T-bet was highly expressed in 2 specific B cell clusters with pathogenic characteristics for SLE (atypical memory B cells and activated naïve B cells). The analysis, furthermore, suggested that all three drugs of interest can target T-bet+ B cells. In line with these data, cell culture experiments confirmed that all 3 compounds can deplete T-bet+ B cells, while leaving unaffected the total numbers of lymphocytes, T cells and B cells, respectively.

Conclusion: T-bet+ B cells expand in SLE patients and associate with disease activity, thus can probably serve as an additional disease activity and severity biomarker. Circumstantial data suggest that these cells may promote disease pathogenesis and may represent a therapeutic target.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/t-bet-expressing-b-cells-as-a-putative-prognostic-and-therapeutic-biomarker-for-human-sle/