Reviewed and edited by: Danielle Leonardo, M.D. Medical Oncologist

Mesothelioma is an especially deadly type of cancer, but immunotherapy treatments can fight it. Immunotherapy boosts the strength of your immune system to fight diseases, including mesothelioma.

One type of immunotherapy is CTLA-4 inhibitor drugs, and the best-known example is ipilimumab. CTLA-4 inhibitors can treat mesothelioma and other cancers, but it’s important to understand the pros and cons of this treatment.

What is CTLA-4?

CTLA-4 is part of your immune system, and it’s found on T-cells. T-cells are powerful and they fight harmful substances in your body. But if they aren’t kept under control, they can go too far and start attacking healthy cells. CTLA-4 helps keep T-cells under control by being an on/off switch.

CTLA-4 is a protein receptor, meaning it’s a protein that receives and attaches to things. It likes to attach to dendritic cells (another type of immune cell). When CTLA-4 receptors attach to dendritic cells, that turns the T-cell off. When CTLA-4 receptors don’t have dendritic cells attached, the T-cell stays turned on.

Cancer tumors don’t want T-cells to be on because the T-cells will attack and destroy them. So these tumors have a sneaky tactic. They release cells that attach to CTLA-4 receptors. The CTLA-4 receptors think they’re attached to dendritic cells, causing the T-cells to turn off.

When T-cells are off, they can’t fight cancer tumors like mesothelioma. So something needs to be done to keep the T-cells on. CTLA-4 inhibitors can do this.

What do CTLA-4 inhibitors do to fight mesothelioma?

CTLA-4 inhibitors work by attaching to CTLA-4 receptors. Their goal is to get to the CTLA-4 receptors before the tumor cells do.

When this happens, the tumor cells will still try to do the same thing as before: pretend to be dendritic cells and attach to CTLA-4 receptors. But this time, it won’t work. The tumor cells would like to turn off the T-cells, but the T-cells stay on, meaning they can keep attacking the cancer.

How well do CTLA-4 inhibitors work against mesothelioma?

This question is hard to answer. CTLA-4 inhibitors have shown some success against other cancers, but not as much against mesothelioma. Only a few mesothelioma studies have been done so far with very small groups of people. That’s why it’s hard to know how well this treatment works for mesothelioma.

The few studies that have been done on CTLA-4 inhibitors and mesothelioma have had mixed results. Some people had reduced tumors, but others didn’t see much of a change.

The good news is that this treatment doesn’t have to be used alone. Combining CTLA-4 inhibitors with other cancer treatments may lead to better results.

What are the side effects of CTLA-4 inhibitors?

Since CTLA-4 inhibitors stop CTLA-4 from keeping T-cells under control, the T-cells become a lot more active – and that can cause trouble.

When your immune system is too active, your body can be harmed in multiple ways. These harmful effects are called immune-related adverse events. Immune-related adverse events can affect your skin, gastrointestinal tract, liver, lungs, and endocrine glands.

The most common side effects of CTLA-4 inhibitors are:

  1. Pneumonitis (lung inflammation)
  2. Colitis (colon inflammation)
  3. Hepatitis (liver inflammation)
  4. Hypothyroidism (underactive thyroid gland)

These side effects can range from mild to severe, and since not everyone has the same side effects, they can be hard to predict. If any of these things happens to you, tell your healthcare provider right away.

CTLA-4 inhibitors are able to fight mesothelioma tumors in some patients. CTLA-4 inhibitors work by stopping tumor cells from turning off T-cells. When T-cells are on, they can destroy tumor cells.

Sometimes T-cells go too far and attack healthy cells in your body, causing side effects. But these side effects can be treated. And as scientists keep studying CTLA-4 inhibitors, they can figure out how to improve them and combine them with other treatments to fight mesothelioma.