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Vaccine Generates Immune Response Against Breast Cancer in Trial

A gloved hand holding a syringe and drawing up vaccine solution from a glass vial.
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Researchers in a new study describe the development of an experimental vaccine that could be used to prevent or treat an aggressive form of breast cancer, safely generating an immune response against an important driver of breast cancer growth.

“Because this was not a randomized clinical trial, the results should be considered preliminary, but the findings are promising enough that the vaccine will now be evaluated in a larger, randomized clinical trial,” explained senior author Dr. Mary “Nora” L. Disis, professor of medicine at the University of Washington and director of the Cancer Vaccine Institute.

Designing a “cancer vaccine”

The experimental vaccine was evaluated in a Phase I clinical trial to assess its safety and efficacy in a small number of patients and to see if it would generate a strong immune response to its target, human epidermal growth factor receptor (HER2).

HER2 is an important protein found on the surface of cells that regulates cell growth and division. However, in around 30% of breast cancers, HER2 is overproduced, and these “HER2-positive” cancer cells can produce hundreds of times the normal amount of HER2.

Additionally, HER2-positive breast cancers are typically more aggressive, as they are more likely to come back (recur) after treatment than other types of breast cancer. However, the overabundance of HER2 also represents a useful target for cancer treatments as this can trigger a strong immune response against the cancer cells.

Patients that produce a strong cytotoxic (cell-killing) immune response against their HER2-positive cancers typically have longer overall survival than those who don’t, and their disease is also less likely to recur.

Disis and colleagues set out to target and stimulate this anti-HER2 immune response by developing a DNA vaccine. This involves giving the patient the DNA instructions to make the target protein, rather than a protein vaccine, which either contains the protein of interest itself or parts of it.

When the DNA vaccine is injected into the patient, cells in the injection site take up the genetic material and begin to produce the encoded protein. The finished protein is presented to the immune system, which in turn stimulates a strong cytotoxic response. In this study, the vaccine was designed with the instructions for the inner part of the HER2 protein that is found within the cell, as this is more likely to induce a strong response.

Safety and efficacy in Phase I clinical trial

Sixty-six women with metastatic breast cancer (i.e., cancer that had spread to other parts of the body) participated in the Phase I clinical trial to test the vaccine. All participants had previously completed a standard course of chemotherapy which had either resulted in complete remission (all signs of their cancer had disappeared) or left only slow-growing tumors remaining in their bones.

The researchers divided the participants into three groups, each receiving three injections of either low (10 µg), intermediate (100 µg) or high doses (500 µg) of the vaccine. Additionally, all groups were given the immune-stimulating drug granulocyte-macrophage colony-stimulating factor (GM-CSF) to help induce a cytotoxic immune response.

After receiving their doses, the participants were monitored over a follow-up period ranging from 3 to 13 years (median follow-up was 10 years). The relatively long follow-up period was crucial as HER2 is found in many other healthy cell types, and researchers needed to ensure the vaccine did not result in an autoimmune reaction in which the body attacks its own normal tissues.

The results of the trial showed that the vaccine successfully generated the desired cytotoxic immune response without severe side effects. The strongest immune response occurred in patients who received the intermediate doses. Disis also notes that after 10 years, 80% of the women involved in the trial are still alive.

“The results showed that the vaccine was very safe,” Disis said. “In fact, the most common side effects that we saw in about half the patients were very similar to what you see with COVID vaccines: redness and swelling at the injection site and maybe some fever, chills and flu-like symptoms.”

Promising results for breast cancer treatment

Despite the study not being designed to assess whether the vaccine would slow or prevent cancer progression, the researchers noted how promising the results were in this regard, as around half of patients with a similar disease stage would typically die within 5 years of treatment.

“If the results of the new randomized-controlled phase II trial of the vaccine are positive, it will be a strong signal for us to rapidly move forward to a definitive phase III trial,” Disis said. “I have high hopes that we’re close to having a vaccine that can effectively treat patients with breast cancer.”

Reference: Disis ML, Guthrie KA, Liu Y, et al. Safety and outcomes of a plasmid DNA vaccine encoding the ERBB2 intracellular domain in patients with advanced-stage ERBB2-positive breast cancer: a phase 1 nonrandomized clinical trial. JAMA Oncol. 2022. doi: 10.1001/jamaoncol.2022.5143

This article is a rework of a press release issued by the University of Washington. Material has been edited for length and content.