Overview

This prospective observational cohort study investigates the subset-specific metabolic adaptation and functional remodeling of cytotoxic γδT cells in critically ill patients with and without sepsis. Emerging evidence indicates that γδT cells, as a bridge between innate and adaptive immunity, play a critical role in early anti-infection defense during sepsis. However, the functional status and underlying regulatory mechanisms of cytotoxic γδT cells in septic patients remain incompletely understood. Our preliminary single-cell transcriptomic analysis revealed that cytotoxic γδT cells from septic patients exhibit significant alterations in cytotoxicity-associated molecules (GZMB, PRF1, GNLY) and mitochondrial oxidative phosphorylation (OXPHOS) pathway genes, particularly COX6C, which correlates with cytotoxic effector molecule expression. This study aims to systematically characterize the proportion, cytotoxicity, and mitochondrial metabolic function of circulating cytotoxic γδT cells across three cohorts: healthy controls, critically ill non-septic patients, and critically ill septic patients. By integrating flow cytometry, mitochondrial function assays, and functional validation experiments, we seek to elucidate the role of COX6C-mediated mitochondrial metabolic abnormalities in cytotoxic γδT cell dysfunction, providing theoretical basis for understanding immune dysregulation in sepsis and identifying novel therapeutic targets.

Eligibility

Inclusion Criteria:

1. Healthy Control Group (NHC):
   • Age ≥ 18 years.
   • No acute or chronic major diseases.
   • Provide written informed consent.
2. Non-septic Critical Illness Group (CI-NS):
   • Age ≥ 18 years.
   • Admitted to the ICU and meeting the definition of critical illness.
   • Excluded from sepsis according to the Sepsis-3 criteria (infection + ΔSOFA ≥ 2 points).
   • Written informed consent provided by the participant or legally authorized representative.
3. Septic Critical Illness Group (CI-Sep):
   • Age ≥ 18 years.
   • Admitted to the ICU and meeting the Sepsis-3 criteria (infection + ΔSOFA ≥ 2 points).
   • Written informed consent provided by the participant or legally authorized representative.

Exclusion Criteria:

• Age \< 18 years.
• Known immunodeficiency, HIV infection, active hematologic malignancy, or history of hematopoietic stem cell or solid organ transplantation within the past 3 months.
• Receipt of T-cell-targeted immunosuppressive therapy (e.g., antithymocyte globulin, calcineurin inhibitors, mycophenolate mofetil, methotrexate, or high-dose corticosteroids \>1 mg/kg/day prednisone equivalent) before ICU admission or within 24 hours after ICU admission.
• Use of immune checkpoint inhibitors (e.g., anti-PD-1/PD-L1/CTLA-4 antibodies) within the past 6 weeks.
• Expected ICU stay \< 24 hours or imminent risk of death (moribund state).
• Pregnancy or breastfeeding.
• Active major bleeding.
• Inability to obtain informed consent.