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Immunotherapy: how these drugs work
Immunotherapy helps your own immune system find and fight cancer. Normally, immune cells called T cells have built-in brakes, called checkpoints, that keep them from attacking healthy tissue. Some cancers press on those brakes to hide. Checkpoint inhibitors release the brakes so T cells can see the cancer again. When immunotherapy works, the response can last a long time, sometimes years. Because it works through the immune system, its side effects are different from chemo. Instead of hair loss or very low blood counts, the immune system can sometimes inflame a healthy organ, like the colon, lungs, liver, thyroid, or skin. These immune-related side effects can show up weeks or months after starting, and even after treatment ends.
ℹ️ General information to help you and your loved ones talk with your care team, not medical advice. Read our disclaimer.
On this page: PD-1 blockers · PD-L1 blockers · CTLA-4 blockers · Bispecific T-cell engagers
PD-1 blockers
PD-1 is a brake on T cells. Keytruda (pembrolizumab), Opdivo (nivolumab), and Libtayo (cemiplimab) block it. They're used across lung cancer, triple-negative breast cancer, MSI-H or dMMR colorectal cancer, and more, sometimes alone and sometimes with chemo. They're given by IV every few weeks, and Keytruda and Opdivo now also come in versions injected under the skin.
PD-L1 blockers
PD-L1 is the partner protein that cancer cells use to press the PD-1 brake. Imfinzi (durvalumab) and Tecentriq (atezolizumab) block it from the other side. Imfinzi is used in lung cancer, including before and after surgery and after chemoradiation for stage III disease. Tecentriq is used in non-small cell and small cell lung cancer.
CTLA-4 blockers
CTLA-4 is a different brake that works earlier, when T cells are first being activated. Yervoy (ipilimumab) blocks it, and Imjudo (tremelimumab) works the same way. They're usually combined with a PD-1 or PD-L1 blocker. For example, Opdivo plus Yervoy is used for some lung cancers. Combinations can work better for some people, but they also cause more immune side effects.
Bispecific T-cell engagers
A bispecific antibody grabs two things at once. Imdelltra (tarlatamab) attaches to DLL3, a protein on most small cell lung cancer cells, and to CD3 on T cells, pulling them together so the T cell can attack. Because it strongly activates the immune system, the first doses are given with hospital monitoring for cytokine release syndrome (fever, low blood pressure, and chills) and nerve-related side effects.
Tests that help predict who benefits
Your team may test the tumor for PD-L1, MSI-H or dMMR (mismatch repair problems), or TMB (tumor mutational burden) to see whether immunotherapy is likely to help. Our PD-L1, MSI-H/dMMR, and TMB guides explain the results.
The side effects to know
Read our in-depth immunotherapy side effects guide. It lists every FDA-approved immunotherapy use for the cancers we cover and explains the warning signs organ by organ. Carry a wallet card saying you've had immunotherapy, and show it to any emergency doctor.
Side effect guides that may help
❓ Questions you and your loved ones can ask
- What is the goal of this treatment for me?
- How will we know if it's working?
- Which side effects should I call about right away, and what number do I call after hours?
- Which medicines, vitamins or supplements should I avoid?
- Will this affect my ability to work, drive, or care for my family?
- What will this cost me, and who can help me with coverage?
Written by the CSE Team from FDA labels and leading cancer centers. Not medical advice. · Last updated: October 15, 2026 · How we write
Sources
Last updated: October 15, 2026. We summarize these sources in our own words.