Novel role of T cells to induce development of proliferative plasmablasts in systemic lupus erythematous

Abstract While research on human SLE and mouse models of lupus have focused on mechanisms of B cell tolerance loss, these efforts have been complicated by multiple networks of immune regulatory genes, thereby impeding current understanding of the development of autoantibody producing B cells in SLE. We applied an unsupervised single cell RNA-seq (scRNA-seq) approach to determine the network and pathways-associated with the development of plasmablasts (PBs) in SLE. PBs were isolated as CD19+CD21−IgD−CD27hiCD38hi cells from PBMCs of SLE patients (n=3). A high-throughput scRNA-seq was carried out using a droplet-based 10x Chromium approach (~ 2,000 cells per sample). We identified two populations of PBs based on the expression of MKI67 encoding for Ki67, a nuclear protein associated with cellular proliferation. Representative genes elevated in MKI67+ PBs included cell cycle related genes as well as TNFR2. Gene ontology analysis further suggest that TNFR2+ B cells expressed increased levels of genes that are associated with cell cycle G1/S transition, DNA synthesis and elongation, and replication. Flow cytometry analysis identified TNFR2+ B cells as a population of antibody secreting cells expressing higher levels of CD86, CD11c, and CD38 but lower levels of CD20. As both CD86 and CD11c poise B cells to receive T-cell help, our studies suggest that T-cell stimulation enables development of cycling PBs in SLE. The strong association of TNFR2 with cell cycle genes in PBs suggest that blockade of TNFR2 may be a novel strategy to inhibit PB proliferation and differentiation.