How Checkpoint Inhibitor Immunotherapy Works
Cancer cells evade immune destruction by activating “checkpoint” proteins that signal immune cells to stand down. Checkpoint inhibitor drugs block these signals, allowing the immune system to recognize and attack cancer cells.
- Nivolumab (Opdivo) — blocks the PD-1 checkpoint on T cells, releasing immune suppression. Made by Bristol Myers Squibb.
- Ipilimumab (Yervoy) — blocks the CTLA-4 checkpoint, providing a complementary immune activation mechanism. Together with nivolumab, it produces a synergistic anti-tumor effect.
- Pembrolizumab (Keytruda) — also blocks PD-1; studied in mesothelioma as both monotherapy and combination with chemotherapy. Made by Merck.
CheckMate 743: The Trial That Changed Treatment
The pivotal CheckMate 743 clinical trial compared nivolumab + ipilimumab to chemotherapy (cisplatin/carboplatin + pemetrexed) as first-line therapy in 605 patients with unresectable pleural mesothelioma. Results published in 2021:
| Outcome | Nivolumab + Ipilimumab | Chemotherapy |
|---|---|---|
| Median overall survival | 18.1 months | 14.1 months |
| 2-year survival rate | 41% | 27% |
| Epithelioid cell type benefit | Modest (18.7 vs. 16.7 mo) | — |
| Non-epithelioid benefit | Strong (18.1 vs. 8.8 mo) | — |
The non-epithelioid (sarcomatoid and biphasic) survival benefit was dramatic — over double the median survival of chemotherapy — making immunotherapy the preferred first-line choice for these cell types, which respond poorly to cisplatin/pemetrexed.
Pembrolizumab (Keytruda) in Mesothelioma
Pembrolizumab has shown activity in mesothelioma clinical trials, particularly in patients with high PD-L1 expression. The KEYNOTE-158 trial showed responses in approximately 18% of pleural mesothelioma patients. Pembrolizumab is being studied in combination with chemotherapy and in the perioperative setting (around surgery). It is used in many mesothelioma clinical trials as a backbone agent.
Immune-Related Side Effects (irAEs)
Immunotherapy works by activating the immune system — which can cause it to attack healthy tissues. These immune-related adverse events (irAEs) differ from chemotherapy side effects:
| Side Effect | Organs Affected | Management |
|---|---|---|
| Immune pneumonitis | Lungs | Corticosteroids; hold immunotherapy |
| Colitis | Bowel | Corticosteroids; infliximab if severe |
| Hepatitis | Liver | Corticosteroids; hold immunotherapy |
| Endocrinopathies | Thyroid, pituitary, adrenal | Hormone replacement; usually permanent |
| Skin rash | Skin | Topical steroids; typically manageable |
| Myocarditis (rare) | Heart | Urgent corticosteroids; discontinue treatment |
IrAEs with ipilimumab tend to be more common and severe than with nivolumab alone. Any new symptoms during immunotherapy should be reported to your oncologist promptly.