PD-1 activation mitigates lupus nephritis by suppressing hyperactive and heterogeneous PD-1⁺CD8⁺ T cells

Rationale: Programmed cell death protein 1 (PD-1)-expressing CD8⁺ T cells are typically associated with exhaustion in cancer and infections, but their role in autoimmune diseases, particularly lupus nephritis (LN), remains less understood. Understanding the characteristics and functions of PD-1⁺CD8⁺ T cells in LN could help identify novel therapeutic strategies. Methods: We analyzed the abundance and phenotypes of PD-1⁺CD8⁺ T cells in LN patients and NZB/W F1 mice. Single-cell RNA sequencing (scRNA-seq) was used to delineate subsets and TCR clonal diversity in PD-1⁺CD8⁺ T cells in NZB/W F1 mice. The therapeutic efficacy of a PD-L1 Fc fusion protein on kidney pathology and proteinuria in NZB/W F1 mice was evaluated. In addition, the inhibitory mechanism of PD-1 in CD8⁺ T cells were further explored using RNA-seq, q-PCR, flow cytometry, and Western blot. Results: PD-1⁺CD8⁺ T cells were enriched in LN patients and NZB/W F1 mice, exhibiting elevated activation markers and cytotoxic molecules compared to PD-1^- cells. scRNA-seq identified seven distinct subsets with diverse effector functions and robust TCR clonal expansion in the kidney of NZB/W F1 mice with severe disease. PD-L1 Fc treatment reduced kidney damage and proteinuria in NZB/W F1 mice, which correlated with decreased frequencies of PD-1⁺CD8⁺ and IFN-γ⁺CD8⁺ T cells. Mechanistically, PD-L1 Fc inhibited Stat1 phosphorylation, T-bet expression, and IFN-γ production in CD8⁺ T cells. Conclusion: These findings show that PD-1⁺CD8⁺ T cells in LN are hyperactive, clonally expanded, and contribute to disease progression. Targeting the PD-1/PD-L1 pathway with PD-L1 Fc effectively reduced kidney pathology in a murine model of LN, underscoring the potential of modulating PD-1 signaling as a treatment strategy for LN.