CTLA-4 is a protein that plays an important role in the immune system. It helps keep the immune system in check by regulating T cells. Ipilimumab (Yervoy) and tremelimumab are two immune checkpoint inhibitor drugs that block CTLA-4 to allow T cells to find and fight cancers such as mesothelioma.
Cytotoxic T-lymphocyte-associated protein 4, or CTLA-4, is a protein on the surface of T cells that functions as an immune checkpoint. It affects how T cells recognize cancer cells.
T cells attack foreign invaders such as viruses and cancer cells.
CTLA-4 prevents T cells from attacking healthy parts of the body, but it can also prevent T cells from identifying and killing cancer cells.
Drugs that block CTLA-4 are called immune checkpoint inhibitors. These drugs have the potential to help people live longer with mesothelioma cancer.
French researchers discovered CTLA-4 in 1987. Nearly a decade later, scientists at the University of California, Berkley realized the role of CTLA-4.
The protein acts as a break, stopping T cells from attacking cancer cells. Researchers call this breaking mechanism an immune checkpoint.
Immune checkpoints work like on and off switches, activating or deactivating the parts of the immune system.
When activated, CTLA-4 downregulates the immune system by stopping T cells from finding cancer cells.
Scientists have developed drugs to block and deactivate CTLA-4 — a process commonly called a CTLA-4 blockade — which allows T cells to find and attack cancer cells. These drugs are known as immune checkpoint inhibitors.
Two checkpoint inhibitor drugs work against CTLA-4: Yervoy and tremelimumab.
Yervoy is FDA approved to treat late-stage melanoma. Tremelimumab is not FDA approved, but in 2015 it received orphan drug designation to treat mesothelioma.
Both of these anti-CTLA-4 mesothelioma drugs have helped people live longer with the cancer through clinical trials.
Most of the mesothelioma clinical trials involving Yervoy and tremelimumab combine them with immune checkpoint inhibitors that target other proteins. Studies show that targeting PD-1and CTLA-4 together increases effectiveness.
Mesothelioma researchers are using the combination approach because it has proven more effective in melanoma treatment. For example, when used alone, about 11 percent of melanoma patients respond to Yervoy.
When anti-PD-1 drug nivolumab (Opdivo) is added to Yervoy, about 61 percent of melanoma patients respond.
Researchers found that adding Opdivo to Yervoy increases the response rate in mesothelioma patients. In 2017, French researchers announced a significant improvement in response rates at the 2017 ASCO Annual Meeting.
Approximately 42.6 percent of mesothelioma patients responded to Yervoy alone, while 51.9 percent responded to Yervoy combined with Opdivo.
These results justified a phase III trial of Yervoy and Opdivo in mesothelioma patients, which began in 2017.
Less research is available on tremelimumab than Yervoy, but preliminary results show further research is warranted. For example, two Italian studies featured in the journal Expert Review of Anticancer Therapy reported tremelimumab temporarily stopped cancer growth in roughly half of mesothelioma participants.
One involves combining tremelimumab with surgery.
Another is testing the drug against a placebo.
A third is combining tremelimumab with durvalumab (Imfinzi).
Clinical trials suggest that Yervoy and tremelimumab are effective for some people with mesothelioma. Further research is necessary to determine which mesothelioma patients may benefit the most from immune checkpoint inhibitors that target CTLA-4.
Additional research is also required to see which drug combinations work best among people with mesothelioma.
Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators. Read More