SLAMF4 orchestrates the cytotoxic response of CD4 + T cells in rheumatoid arthritis

This study aimed to assess whether signaling lymphocytic activation molecule family receptors (SLAMFs) are involved in the shaping of the pathological response of CD4 T cells in rheumatoid arthritis (RA). Peripheral blood (PB) and synovial fluid (SF) mononuclear cells from RA patients were freshly isolated. In RA, we used a multi-modal approach to determine the involvement of numerous subpopulations of CD4 T cells expressing SLAMFs. Experimentally, multiple flow cytometry panels, RNA sequencing and ex vivo stimulations were used. Analyses involved high-dimensional unsupervised clustering of flow cytometry data and pathway enrichment analyses of transcriptomic data. In PB of RA patients with active disease, SLAMF4 effector memory T cells (Tem) represented the only overrepresented subpopulation of CD4 T cells expressing SLAMFs. This positive correlation between RA activity and SLAMF4 Tem was restricted to those co-expressing the intracellular molecule SAP and the tissue-homing receptor CCR5. Gene Set Enrichment Analysis of RNA-sequencing data reveals that SLAMF4 CCR5 Tem display a cytotoxicity-related gene signature. Moreover, based on the differential expression of cytotoxicity markers (GPR56, CX3CR1, granzyme-B, perforin and granulysin), unsupervised clustering of flow cytometry data identified distinct subpopulations of PB cytotoxic Tem. Among them, only SLAMF4 SAP CCR5 Tem (Cytotox-F4 Tem) were correlated with RA activity. Remarkably, Cytotox-F4 Tem emerged as the only cytotoxic population of CD4 T cells (CD4 CTLs) present in SF of patients with active disease. This study emphasizes that Cytotox-F4 Tem represent a significant CD4 CTL subpopulation involved in RA, suggesting that their inhibition represent a promising therapeutic interest.