Characterization of T-bet expressing B cells in lupus patients indicates a putative prognostic and therapeutic value of these cells for the disease

To investigate whether T-bet+ B cells, as well as age-associated B cells/ABCs (CD19+CD21-CD11c+T-bet+) and double-negative B cells/DN (CD19+IgD-CD27- CXCR5-T-bet+), serve as prognostic and/or therapeutic tools for systemic lupus erythematosus (SLE) in humans. Flow cytometry was used for enumerating T-bet+ B cells and ABCs/DN subsets, found in the peripheral blood of 10 healthy donors and 22 active SLE patients. Whole blood assay cultures, combined with in vitro pharmacological treatments, were performed to evaluate the effects of hydroxychloroquine, anifrolumab and fasudil (a ROCK kinase inhibitor) on T-bet+ B cells' percentage. Moreover, previously published single-cell RNA sequencing (scRNA-seq) data were used in a meta-analysis to allow characterization of genes and pathways associated with the biology of T-bet in B cells. T-bet+ B cells displayed an expansion in SLE patients [1.47 (1.9 - 0.7) vs 10.85 (37.4 - 3.6)]. Similarly, both ABCs and DN were found to be expanded. Interestingly, percentages of T-bet+ B cells positively correlated with patients' SLEDAI scores (rs=0.55, p=0.007). Cell culture experiments conducted, revealed that all three agents tested can deplete T-bet+ B cells (without affecting the cell viability of lymphocytes, T cells and B cells). According to bioinformatics analyses, T-bet is highly expressed in two B cell clusters with pathogenic characteristics for SLE (designated as atypical memory B cells and activated naïve B cells). These clusters can be targeted for therapeutic interventions. T-bet+ B cells can serve as a putative prognostic biomarker of lupus severity. Circumstantial data suggest that these cells may promote disease pathogenesis and may represent a novel therapeutic target.