Immune checkpoint ligand

Immune checkpoint ligands (often referred to as tumor cell inhibitory ligands) are a functional class of cell surface proteins expressed by malignant cells to facilitate immune evasion by suppressing the activity of tumor-infiltrating lymphocytes (Ramsay et al., 2012). These ligands, which include molecules such as Programmed death-ligand 1 (PD-L1/CD274), B7-H3 (CD276), CD200, and HVEM (CD270), engage inhibitory receptors on the surface of T cells and Natural Killer (NK) cells, leading to functional exhaustion, reduced cytokine production, and impaired immune synapse formation (Fatah et al., 2015; Ramsay et al., 2014). In many cancers, the overexpression of these ligands correlates with poor clinical prognosis and resistance to conventional therapies (Nature Reviews Cancer, 2018). Modern immunotherapy focuses on blocking these ligand-receptor interactions using monoclonal antibodies to restore the immune system's anti-tumor effector functions (Pardoll, 2012). Clinically approved drugs such as atezolizumab, durvalumab, and avelumab specifically target the PD-L1 ligand, while other candidates under development target additional members of this class, such as B7-H3 and CD47, to overcome resistance in 'cold' tumors (FDA, 2024; ClinicalTrials.gov). This field remains a primary focus of oncology research, aiming to expand the efficacy of checkpoint blockade to a broader range of solid and hematological malignancies.

Other names

Tumor cell inhibitory ligandsTumor-associated inhibitory ligandsCo-inhibitory ligandsT-cell inhibitory ligandsImmune-suppressive ligands

Monoclonal antibodies target these ligands to block their interaction with inhibitory receptors on immune cells (such as PD-1, TIGIT, or BTLA). By preventing the binding of tumor-expressed ligands to these receptors, the drugs interrupt the 'off' signals that suppress T-cell and Natural Killer (NK) cell activity, thereby restoring the immune system's ability to recognize and destroy malignant cells (Pardoll, 2012; Ramsay et al., 2012).