Written by Karen Selby, RN | Medically Reviewed By Dr. Rupesh Kotecha | Edited By Walter Pacheco | Last Update: February 2, 2024

What is WT1?

A cancer vaccine is an immunotherapy drug that trains the body’s immune system to recognize and fight cancer cells.

doctor administering vaccine to patient

WT1 is a protein made by the Wilms Tumor 1 gene. It is found in higher amounts on many types of cancer cells, including mesothelioma cells. This makes it a good immunohistochemical marker for mesothelioma. Doctors look for WT1 and other markers during mesothelioma diagnosis.

A 2021 study showed that 70-95% of mesotheliomas have this protein and lung adenocarcinomas do not. But, it does not distinguish between hyperplastic mesothelium and mesothelioma.

WT1 Vaccine Fast Facts

  • Targets a protein overexpressed by mesothelioma cells
  • Stimulates the immune system to attack cancer cells
  • Meant to be combined with other treatments
  • Generic form galinpepimut-S awaiting a phase III clinical trial

The chemical markers of cancer are also known as antigens. For years, researchers have explored the potential of cancer-related antigens in immunotherapy.

In 2009, the National Cancer Institute (NCI) looked at 75 antigens to determine which one could help in immunotherapy. After scoring 75 antigens, they showed WT1 should have the highest priority in immunotherapy research.

Part of the reason is that a vaccine based on WT1 could work on many types of cancer. Certain cancers overexpress WT1. They include pleural mesothelioma, myeloid leukemia, multiple myeloma and ovarian cancer.

The WT1 cancer vaccine in development is called galinpepimut-S. The company Sellas Life Sciences is developing it based on research that began at the Memorial Sloan Kettering Cancer Center.

How Does the WT1 Vaccine Work?

Galinpepimut-S works as an immunostimulant. It is a synthetic peptide vaccine made out of molecules similar to those in the WT1 protein. When the body’s immune system learns to recognize the vaccine as a foreign invader, the immune system also learns to attack any cell overexpressing the WT1 protein.

The WT1 cancer vaccine is meant to be given along with other cancer treatments. After doctors have removed tumors from the body through conventional therapies, the cancer vaccine could enable the body’s immune system to kill any remaining cancer cells.

Researchers believe the body’s immune system would then also be able to target cancer cells if they return.

Galinpepimut-S in Mesothelioma Clinical Trials

A phase II clinical trial of adjuvant (postoperative) galinpepimut-S ended in 2021. It involved 41 pleural mesothelioma patients. It prompted the U.S. Food and Drug Administration (FDA) to grant galinpepimut-S orphan-drug status for mesothelioma.

Orphan-drug designation encourages the development of treatments for rare diseases through tax incentives, grants and waivers that reduce development costs. Companies also receive the exclusive rights to develop the drug for a period of time.

In the trial, doctors first eliminated as much cancer as possible from patients’ bodies through surgery and chemotherapy. Then they gave the experimental group of patients the WT1 vaccine to try to prevent tumors from regrowing.

Both groups received two special medicines to help the vaccine work better. The names of these medicines are GM-CSF and Montanide.

The experimental group went a median of 10.1 months without cancer recurrence, versus 7.4 months for the control group.

Median survival was 22.8 months for the patients who received the vaccine, compared to 18.3 months for patients who did not receive the vaccine. However, the phase II trial was too small to show a statistically significant difference in treatment outcomes.

The side effects of galinpepimut-S were mild, so the study did confirm the treatment’s safety.

The FDA has given permission for Sellas Life Sciences to do a special experiment called a phase III clinical trial. This type of trial will test how well the vaccine works on mesothelioma in more people. Other phase II trials in combination with other drugs are underway for mesothelioma.

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