CD8+ cytotoxic T cell (CTL)

CD8+ cytotoxic T cells (CTLs) are the primary effector cells of the adaptive immune system responsible for the direct elimination of malignant cells by recognizing tumor-associated antigens presented on MHC class I molecules (UniProt: P01732). In the tumor microenvironment (TME), these cells are critical for anti-tumor immunity, and their infiltration density is often used as a prognostic biomarker in various cancers (PubMed: 28125107). However, the TME is frequently immunosuppressive, leading to CTL "exhaustion" through the upregulation of inhibitory receptors such as PD-1 and CTLA-4 (Nature Reviews Immunology, 2015). Therapeutic interventions like immune checkpoint inhibitors (e.g., Pembrolizumab) aim to block these inhibitory pathways and reinvigorate the cytotoxic activity of these cells (NIH: StatPearls). Other modalities, including bispecific T-cell engagers (BiTEs) and CAR-T cell therapies, are designed to physically bridge CTLs to tumor cells or genetically engineer them for enhanced tumor recognition. While highly effective, these therapies can trigger severe systemic inflammatory responses, such as cytokine release syndrome, due to the potent effector functions of activated CTLs.

Other names

Cytotoxic T lymphocyteCTLCD8+ T cellKiller T cellCD8+ T-lymphocyte

Checkpoint inhibition, T-cell engagement, and chimeric antigen receptor (CAR) signaling.