Immune checkpoint inhibitors
Antibodies that release the brakes on T cells (PD-1, PD-L1, CTLA-4) so the immune system attacks the cancer; the price is autoimmune-type side effects.
What they are
Intravenous antibodies against PD-1 (pembrolizumab, nivolumab, cemiplimab), PD-L1 (atezolizumab) and CTLA-4 (ipilimumab). They are used in melanoma, lung cancer, kidney cancer, head and neck cancer, Hodgkin lymphoma and tumours with mismatch-repair deficiency, among others.
Mechanism of action
T cells carry inhibitory receptors that normally prevent autoimmunity. Tumours exploit them: PD-L1 on tumour cells switches off PD-1-positive T cells inside the tumour, and CTLA-4 limits T-cell priming in lymph nodes. Blocking these checkpoints lets T cells stay active and kill tumour cells, but it can also break tolerance to normal tissues.
Target: T-cell checkpoints PD-1, PD-L1 and CTLA-4
Drugs in this class
- PembrolizumabAn anti-PD-1 antibody that reactivates T cells against many cancers, including melanoma, lung cancer and any tumour…Programmed cell death protein 1 (PD-1) on T cells
- NivolumabAn anti-PD-1 antibody used in melanoma, lung, kidney, head and neck and liver cancer and Hodgkin lymphoma, alone or…Programmed cell death protein 1 (PD-1) on T cells
- IpilimumabAnti-CTLA-4 antibody for melanoma, often with nivolumab. It causes more immune toxicity (colitis, hypophysitis) than…Cytotoxic T-lymphocyte antigen 4 (CTLA-4)
- AtezolizumabAn anti-PD-L1 antibody for lung cancer (including small cell), liver cancer with bevacizumab, and melanoma; adverse…Programmed death-ligand 1 (PD-L1) on tumour and immune cells
- CemiplimabAn anti-PD-1 antibody for advanced cutaneous squamous cell carcinoma, basal cell carcinoma after hedgehog inhibitors…Programmed cell death protein 1 (PD-1) on T cells
- Nivolumab/relatlimabTwo checkpoint antibodies in one infusion: nivolumab blocks PD-1, relatlimab blocks LAG-3. Used in advanced melanoma…PD-1 (nivolumab) and LAG-3 (relatlimab) on T cells
- DurvalumabHuman anti-PD-L1 antibody that releases the brake on T cells. For lung, bladder, biliary, liver and other cancers…Programmed death-ligand 1 (PD-L1) on tumour and immune cells
Others in the class
- durvalumab
- avelumab
- dostarlimab
- tremelimumab
Test yourself
Think of the answer, then tap the question to see it.
A patient on pembrolizumab develops several watery stools a day with abdominal pain. What is the likely cause and the key treatment?
Immune-mediated colitis; the drug is withheld and systemic corticosteroids are started according to severity.
Where does CTLA-4 blockade act, compared with PD-1 blockade?
CTLA-4 blockade boosts T-cell priming in lymph nodes; PD-1/PD-L1 blockade reactivates T cells inside the tumour.
Which endocrine problems should be looked for during checkpoint inhibitor treatment?
Hypo- or hyperthyroidism, hypophysitis, adrenal insufficiency and type 1 diabetes.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Pembrolizumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); Ipilimumab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.