Cytotoxic Response of CD4⁺ T Cells Orchestrated by SLAMF4 in Rheumatoid Arthritis

This study aimed to assess whether signaling lymphocytic activation molecule family receptors (SLAMFs) are involved in the shaping of the pathologic response of CD4⁺ T cells in rheumatoid arthritis (RA).

Peripheral blood (PB) and synovial fluid (SF) mononuclear cells from patients with RA were freshly isolated. In RA, we used a multimodal approach to determine the involvement of numerous subpopulations of CD4⁺ T cells expressing SLAMFs. Experimentally, multiple flow cytometry panels, RNA sequencing, and stimulations were used. Analyses involved high-dimensional unsupervised clustering of flow cytometry data and pathway enrichment analyses of transcriptomic data.

In PB of patients with RA with active disease, SLAMF4⁺ effector memory CD4⁺ 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 coexpressing the intracellular molecule SLAM-associated protein (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^high SAP⁺ CCR5⁺ Tem (Cytotox-F4^high Tem) were correlated with RA activity. Remarkably, Cytotox-F4^high 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^high Tem represent a significant CD4⁺ CTL subpopulation involved in RA, suggesting that their inhibition represent a promising therapeutic interest.