Checkpoint Inhibitor

Checkpoint inhibitors represent monoclonal antibodies or small molecules targeting immune regulatory proteins including programmed death-1 (PD-1), programmed death ligand-1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to enhance endogenous anti-tumour immunity. These agents block inhibitory signalling pathways preventing T-cell exhaustion, thereby restoring immune surveillance against malignant cells. Mechanism of action involves disrupting ligand-receptor interactions enabling sustained T-cell proliferation, cytokine production, and effector function. Clinical efficacy varies substantially across tumour types, reflecting heterogeneous immunogenicity and baseline immune infiltration levels.

Management of checkpoint inhibitor therapy requires vigilant immune-related adverse event monitoring including colitis, hepatitis, endocrinopathy, and pneumonitis reflecting non-selective immune activation. Biomarker-directed patient selection incorporating PD-L1 expression, microsatellite instability, and tumour mutational burden increasingly enhances treatment efficacy prediction. Combination strategies with conventional chemotherapy, targeted therapeutics, or concurrent checkpoint inhibitors demonstrate synergistic anti-tumour effects in multiple settings. Resistance mechanisms including PD-1/PD-L1 axis exhaustion, immunosuppressive microenvironment expansion, and T-cell trafficking impairment continue driving development of next-generation checkpoint modulators.