Tu110 - Characterizing Dysregulated B Cell Subsets in Systemic Lupus Erythematosus

Salvinaz Moutusy – Stanford University; shaghayegh Jahanbani – Stanford University; Xiaohao Wu – Stanford University; Marlayna Harris – Stanford University; Mahesh Pandit – Stanford University; Laura Sophie van Dam – Stanford University; Orr Sharp – Stanford University; Paul Utz – Stanford University; William Robinson – Stanford University

Abstract Text: Background
B cell dysregulation and production of autoantibodies against autoantigens are hallmarks of Systemic lupus erythematosus (SLE). In healthy adults, B cells with autoreactive antibodies are eliminated from the repertoire before they reach the B cell maturation stage, a mechanism that is altered in SLE.

Objectives
Investigating the dysregulated B cell subtypes in SLE compared to healthy control (HC) and characterize their transcriptional programs, antibody repertoires and their antigen specificity.

Methods
Single-cell RNA-sequencing (scRNA-seq) and BCR repertoire-sequencing of B cells from SLE (n=10) and HC (n=10). We expressed monoclonal antibodies (mAbs) encoded by dysregulated B cells in SLE (n=100) and screened their antigens specificity.

Results
scRNA-seq clustered memory B cells (mB) into CD27+ mB (IgD-CD27+CD11c-) and double negative (DN2) mB (IgD-CD27-CD11c+, Fig. 1A-D). Transcriptome analyses of SLE CD27+ mB cells revealed remarkable upregulation of cell activation and antigen processing and presentation (APC) pathways, as compared to HC (Fig. 1E-H). BCR analysis showed that the CD27+ mB and DN2s are class-switched and have increased somatic hypermutations (SHM). Characterization of mAbs encoded by expanded and dysregulated B cells in SLE identified multiple SLE B cell mAbs that stained the HEP-2 cells and bound self-antigens on antigen arrays (Fig. 2).

Conclusions
Our findings revealed subsets of dysregulated CD27+ mB cells encoding anti-nuclear autoantibodies in SLE. We demonstrate that clonally expanded autoimmune B cells are shared between CD27+ and DN2 linages. Our results suggest that CD27+ mB cells undergo cell activation, encode autoantibodies and consequently contribute to the development of pathogenic DN2 B cells.