By Kathleen Berger

There’s a groundbreaking treatment being developed at WashU Medicine for women with an extremely aggressive form of breast cancer. A small clinical trial shows promising results for patients with triple-negative breast cancer who received an investigational vaccine designed to prevent recurrence of tumors.

The phase I clinical trial was conducted at Siteman Cancer Center, based at Barnes-Jewish Hospital and WashU Medicine. The trial is the first to report results for this type of vaccine, known as a neoantigen DNA vaccine, for breast cancer patients. The study found the vaccine to be well-tolerated and the vaccine stimulated the immune system.

The study involved 18 patients diagnosed with triple-negative breast cancer that was not metastatic, meaning it had not spread to other organs. Each patient received three doses of a personalized vaccine tailored to home in on key mutations in their specific tumor and train immune cells to recognize and attack any cells bearing these mutations.

Following treatment, 14 of 18 patients showed immune responses to the vaccine. Then, after three years, 16 patients remained cancer-free. While the early-stage trial was designed to evaluate safety of the vaccine and did not include a control group to determine efficacy, the researchers analyzed historical data from patients with triple-negative breast cancer treated with the standard of care only. In that group, on average, about half of patients remained cancer-free at three years post-treatment.

In a WashU Medicine news release, the researchers said the results are better than expected. Senior author William E. Gillanders, MD, the Mary Culver Distinguished Professor of Surgery at WashU Medicine who treats patients at Siteman, continued to say, “Obviously, it’s not a perfect comparison, and we acknowledge the limitations of this type of analysis, but we are continuing to pursue this vaccine strategy and have ongoing randomized controlled trials that do make a direct comparison between the standard of care plus a vaccine, versus standard of care alone. We are encouraged by what we’re seeing with these patients so far.”

WashU Medicine researchers designed the neoantigen vaccine technology. The software development was led by computational biologists Obi Griffith, PhD, a professor of medicine, and Malachi Griffith, PhD, an associate professor of medicine, both in the Division of Oncology at WashU Medicine.

Using the technology, the researchers selected altered proteins — called neoantigens — that were made by the patients’ tumors and that were identified as most likely to trigger a strong immune response. On average, each patient’s vaccine contained 11 neoantigens specific to their tumor.

Having shown success, the researchers also hope to promote the use of this software for the design of future cancer vaccines.

In the WashU Medicine news release, Gillanders said, “We are excited about the promise of these neoantigen vaccines. We are hopeful that we will be able to bring more and more of this type of vaccine technology to our patients and help improve treatment outcomes in patients with aggressive cancers.”