EP-101 STEMVAC is an investigational cancer vaccine being developed by EpiThany to treat women with human epidermal growth receptor 2 (HER2)-negative breast cancer.

The vaccine is designed to introduce cancer-associated proteins into a person to stimulate the immune system to recognize and attack the breast tumor. Because the vaccine contains multiple proteins it has the potential to treat other types of cancers as well.

How EP-101 STEMVAC works

EP-101 STEMVAC contains several different proteins, or antigens, that are expressed by breast cancer cells. Called a multi-antigen vaccine, it uses a genetic engineering technology that manipulates DNA to instruct a cell to produce the target antigens. EP-101 STEMVAC contains pieces of proteins CD-105, Yb-1, SOX2, CDH2, and MDM2, all antigens associated with cancer cells.

When a patient receives the vaccine, the immune system is exposed to the cancer-associated antigens that activate T-cells, specifically T-helper cells. T-helper cells promote the destruction of cancer cells by stimulating another type of immune cell — called the B-cells  — to produce antibodies and activate cytotoxic, or cell-killing, T-cells.

Other breast cancer treatments target the HER2 receptor, but these treatments are not an option for women with HER2-negative breast cancer or breast cancer that does not express the HER2 receptor. EP-101 STEMVAC is designed to treat these women because it stimulates the immune system to attack other breast cancer-associated proteins as well.

EP-101 STEMVAC in clinical trials

A Phase 1 clinical trial (NCT02157051) is underway to assess the safety, immunogenicity (ability to trigger an immune response), and best dose of EP-101 STEMVAC in women with advanced, HER2-negative breast cancer. The trial, located at the University of Washington, began in June 2015 and has an estimated completion date of 2022. It aims to enroll about 30 women with stage 3 or 4 HER2-negative breast cancer, and is currently recruiting participants.

In May 2017, EpiThany announced that a randomized, double-blind, placebo-controlled Phase 2 trial will be initiated to test EP-101 STEMVAC in combination with Bavencio (avelumab) as neoadjuvant therapy — treatment that aims to shrink the tumor before surgery — in women with HER2-negative breast cancer. Bavencio targets programmed death ligand 1 (PD-L1), a protein that tumor cells use to protect themselves from T-cells. Blocking PD-L1 leaves tumor cells more vulnerable to T-cell attacks.

The planned Phase 2 trial will evaluate the safety, immunogenicity, and clinical benefit of the combination therapy. It is expected to begin in early 2018 and enroll up to 84 women, who will be randomized to receive either EP-101 STEMVAC or a placebo.

Additional information

The Phase 2 trial is a collaboration between EpiThany, Pfizer, and Merck KGaA (EMD Serono in the U.S. and Canada).  Bavencio, the product of an alliance between Pfizer and Merck, was approved by the U.S. Food and Drug Administration (FDA) in March 2017 for the treatment of metastatic Merkel cell carcinoma, a rare type of skin cancer, but it has not yet been proven safe and effective to treat breast cancer.


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