Restricted TCR Diversity and Expansion of CD177⁺CD8⁺ and TLR4⁺CD4⁺T Cell Subsets in Septic Shock-Associated...

Sepsis-induced immunosuppression contributes to poor outcomes in sepsis patients, yet the mechanisms underlying T cell dysfunction remain incompletely understood. We integrated single-cell RNA sequencing (scRNA-seq), paired single-cell T cell receptor sequencing (scTCR-seq), bulk RNA sequencing (RNA-seq), and flow cytometry to characterize CD8⁺ and CD4⁺ T cells in septic shock-associated immunosuppression. Patients showed reduced T cell receptor (TCR) clonotype diversity in CD4⁺ T cells but not CD8⁺ T cells, with restricted clonality correlating with disease severity and lymphopenia. Integrative analyses revealed the expansion of two disease-associated subsets: (1) CD177⁺CD8⁺ T cells, enriched for interleukin-17 (IL-17) signaling with hyperexpanded clonotypes, and (2) TLR4⁺CD4⁺ T cells, enriched for phagocytosis- and lysosome-related programs with restricted clonality. Both subsets expressed high levels of S100A8, S100A9, and S100A12, correlating positively with severity scores and systemic inflammation. These findings provided single-cell resolution evidence that clonal restriction of CD4⁺ T cells is a hallmark of septic immunosuppression. Our study depicted a single-cell atlas linking CD4⁺ clonal restriction and the expansion of pathogenic T cell subsets to outcome, highlighting TCR clonality as a biomarker of immune competence and CD177⁺CD8⁺ and TLR4⁺CD4⁺ T cells as candidate therapeutic targets in septic shock-associated immunosuppression.