NEW YORK – Mayo Clinic researchers plan to begin clinical trials of a breast cancer vaccine next year to determine whether it can safely prevent the disease from occurring.
Increasingly, immunotherapies like checkpoint inhibitors and CAR-T cell therapies rely on goading the immune system to attack tumor cells and treat cancer in particular patients, and, at the same time, researchers have been studying whether vaccines could be generated that prevent cancer patients from relapsing by targeting certain features of their disease.
But one vaccine that's in the early stages of development aims to prevent all breast cancers from occurring. Priming the immune system to respond when there is an uptick in proteins that are overexpressed in breast cancers could potentially prevent tumors from occurring, according to Keith Knutson, a professor of immunology at the Mayo Clinic in Jacksonville, Florida, who is working on the project.
"We do know that having a high enough immune response will get rid of tumors — we see it all the time with new immunotherapies and antibodies that are being developed today," Knutson said.
Unlike other immunotherapies and therapeutic vaccines for cancer, this preventative vaccine's target population is healthy people and that is leading the researchers to tread carefully in how they test it.
Some cancer patients naturally have an immune response to tumor cells, and this immune response has been linked to better outcomes among those patients. For instance, a 2003 study appearing in the New England Journal of Medicine found that ovarian cancer patients whose tumors were infiltrated by T cells had both higher progression-free and overall survival rates than patients whose tumors did not harbor those immune cells.
According to Knutson, the overexpression of proteins by cancer cells triggers this immune response. In cancer cells, some proteins are expressed at very high levels. For instance, HER2 is overexpressed in about 20 percent of invasive breast cancer patients, and this can lead to a 40- to 100-fold increase in HER2 protein levels.
"It turns out that when you get that high upregulation, your immune system sees that as foreign," Knutson said. "And so, we took advantage of that idea, that concept to try to develop vaccines."
Based on this view, Mayo Clinic researchers have been developing vaccines to prevent the recurrence of breast cancer among patients previously treated for disease. Researchers there have developed a vaccine to prevent the recurrence of triple-negative breast cancer by targeting the folate receptor alpha, which is overexpressed in triple-negative disease, the safety and efficacy of which they are exploring in a clinical trial. They likewise have been examining in two trials the safety and efficacy of a vaccine targeting HER2/neu in patients who had been treated for HER2-positive breast cancer and a vaccine targeting HER2 in patients with HER2-expressing ductal carcinoma in situ.
Building on that, they are also developing a vaccine they hope will prevent all breast cancers, not just triple negative breast cancer or HER2-positive disease, by targeting six different proteins. Knutson said the trial examining this approach in patients is planned to get off the ground in 2020.
"But that's really exciting too," he said.
However, testing this type of vaccine may be challenging. Most vaccines such as ones against infectious diseases target proteins produced by those microorganisms and not ones that the human body produces on its own.This raises the worry that there could be side effects in other tissues in the body where these proteins may be expressed, though Knutson pointed out that the immune system develops tolerance for proteins under normal, lower-expression conditions.
He added that while therapies that trigger the immune system have been used in cancer patients, the risk-benefit calculation shifts when the target population is healthy people. "When you are talking about going into a healthy population, that's a different matter," he said.
This sort of approach is a new concept for the US Food and Drug Administration, Knutson noted. He said that officials at the agency have counseled him to first examine the safety and efficacy of the vaccine within breast cancer patients who have little evidence of current disease but who have a high likelihood of later recurrence. That way he could gather the data he needs about whether the vaccine leads to an immune response — as the cohort would initially have low-level disease and functioning immune systems — and the risk might be acceptable, as they could benefit from the intervention.
That's the population he said they would be focusing on for the first phase of their clinical trial, for which they hope to enroll 20 to 25 people.
For the second phase, after looking over that data with the FDA, Knutson said they would likely enroll individuals at high risk of developing breast cancer, such as women with BRCA alterations or with a family history of disease, and follow them for about five years or so, examining the rate at which women who received the vaccine developed cancer.
How this breast cancer vaccine could ultimately be used depends greatly on its safety and what Knutson and his colleagues find in their trial. He said he expects, though, that if all goes well, the vaccine would be targeted to women who are over the age of 45 — that is, women who are largely past childbearing years, as numerous proteins are also upregulated in embryos and developing fetuses — and who have an increased risk of disease.
But, as he noted, "we need data."