CheckpointInhibition

Checkpoint inhibition refers to a class of cancer therapies that block inhibitory pathways used by the immune system to restrain T‑cell activity. These inhibitory receptors, such as cytotoxic T‑lymphocyte‑associated protein 4 (CTLA‑4) and programmed death‑1 (PD‑1), normally prevent autoimmunity by down‑regulating T‑cell responses. Tumors can exploit these checkpoints to avoid immune destruction. Antibodies that inhibit CTLA‑4 or PD‑1/PD‑L1 ligands reinstate immune surveillance, allowing cytotoxic T cells to target malignant cells.

The most widely used checkpoint inhibitors include ipilimumab (anti‑CTLA‑4), pembrolizumab, nivolumab and cemiplimab (anti‑PD‑1), and atezolizumab, durvalumab and avelumab (anti‑PD‑L1). These agents are approved for a broad range of solid tumors such as melanoma, non‑small cell lung cancer, renal cell carcinoma, urothelial carcinoma, head‑and‑neck squamous cell carcinoma, and Hodgkin lymphoma, as well as for adjuvant treatment in high‑risk melanoma and immune‑related solid organ transplant settings.

Mechanistically, CTLA‑4 blockade primarily acts in the lymphoid organs to amplify the initial T‑cell priming, whereas PD‑1 blockade functions mainly at peripheral sites, including the tumor microenvironment, to reverse T‑cell exhaustion. Combination regimens, for example CTLA‑4 plus PD‑1 inhibitors or checkpoint inhibitors with chemotherapy, radiation, or targeted therapy, have shown synergistic benefits but also increase toxicity.

Adverse events arise from immune‑related inflammation in organs such as the skin, gastrointestinal tract, liver, endocrine glands, lungs, and nervous system. Management involves corticosteroids and, when necessary, discontinuation of therapy. Ongoing research focuses on identifying predictive biomarkers, overcoming resistance mechanisms, and expanding indications to HPV‑positive cervical cancer, hepatocellular carcinoma and other malignancies.