SAP expressing T peripheral helper cells identify systemic lupus erythematosus patients with lupus nephritis

Abstract

IntroductionT follicular (TFH) and peripheral helper (TPH) cells have been increasingly recognized as a pathogenic subset of CD4 T cells in systemic lupus erythematosus (SLE). The SLAM Associated Protein (SAP) regulates TFH and TPH function by binding to the co -stimulatory signaling lymphocyte activation molecule family (SLAMF) receptors that mediate T cell - B cell interactions. SAP and SLAMF are critical for TPH dependent B cell maturation into autoantibody-producing plasma cells that characterize SLE pathogenesis. MethodsPeripheral blood mononuclear cells (PBMCs) were isolated using density gradient separation from whole blood. Cells were stained for cell surface markers, followed by permeabilization and staining of intracellular SAP for spectral flow cytometry analysis. Additionally, we analyzed SAP expression from renal infiltrating lupus nephritis (LN) T cells using the publicly available single-cell RNA sequencing (sc-RNA seq) Accelerated Medicines Partnership (AMP) in SLE dataset. ResultsPBMCs from 30 patients with SLE (34{+/-}10 years old, 83% female), including 10 patients with LN, were analyzed. We found an increase in total SAP-positive CD4 and CD8 T cells in SLE compared with controls (55.5{+/-}2.6 vs. 41.3{+/-}3.4, p=0.007 and 52.5{+/-}3.0 vs. 39.2{+/-}2.8, p=0.007 respectively). In CD4 T cells, the highest SAP expression was in the TPH subset. The frequency of SAP+TPH in circulation correlated with disease activity, SLE patients with renal disease had higher levels of circulating SAP+TPH that remained significant after adjusting for age, sex, race, low complements, and elevated anti-dsDNA (p=0.014). scRNA-seq data of renal infiltrating T cells identified increased SAP from LN compared with control kidney biopsy samples (p=0.03), including an expansion of SAP-positive TFH-like subsets in the LN kidneys. Increased SAP expression in LN was associated with the differential expression of SLAMF3 and SLAMF7 as well as granzyme K and EOMES. The existence of two predominant SAP-expressing subsets, the TFH-like CD4 T cells and granzyme K positive effector CD8 T cells, was verified using scRNA-seq data from a human transcriptomic atlas of fifteen major organs. ConclusionThe expansion of SAP expressing T helper cells was associated with lupus nephritis in our cohort and verified using scRNA-seq data of renal infiltrating T cells. Improved understanding of SLAM/SAP signaling can identify new therapeutic targets in LN.