Checkpoint Inhibitors — Immunotherapy for Cancer Treatment

Immune checkpoint inhibitors are monoclonal antibodies that target specific regulatory pathways used by the immune system to maintain self-tolerance. Normally, immune checkpoints—such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and its ligand (PD-L1)—prevent excessive autoimmune inflammation by acting as off-switches for T cells.

Many cancer cells hijack these checkpoints by displaying corresponding proteins on their surface, effectively disarming passing T cells and escaping destruction. Checkpoint inhibitors bind to these regulatory proteins, neutralising their inhibitory signals. This action releases the molecular brakes, allowing activated T cells to proliferate, infiltrate the tumour microenvironment, and eradicate cancer cells.

Immune checkpoint inhibitors have transformed cancer care, providing durable, long-term remissions for diseases that previously had limited options. Unlike standard chemotherapy, which attacks all rapidly dividing cells, checkpoint inhibitors stimulate a targeted immune response that can establish biological memory. Understanding these drugs helps patients anticipate distinct immune-related side effects, ensuring early communication with doctors to manage inflammation in organs like the lungs, bowel, or skin.

Before prescribing these medicines, oncologists often test tumour biopsies for specific predictive biomarkers. Common laboratory tests include immunohistochemistry (IHC) to quantify PD-L1 expression, molecular assays for microsatellite instability (MSI) or mismatch repair deficiency (dMMR), and genomic profiling to measure tumour mutational burden (TMB).

These drugs are widely utilised across diverse cancers, including advanced melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer, classic Hodgkin lymphoma, head and neck cancers, and any solid tumours demonstrating high microsatellite instability (MSI-H).

Checkpoint inhibitors are administered as intravenous infusions, either as single-agent monotherapy or combined with other immunotherapies, targeted therapies, or conventional chemotherapy. Because they stimulate immune activity, their side effects involve auto-inflammatory conditions (such as colitis, pneumonitis, or thyroiditis), which are managed promptly using corticosteroid medications rather than conventional anti-sickness drugs.