A team of researchers has developed a vaccine in mice that they believe can be used to inoculate a person against cancer, even before tumors develop.
In a study published in the journal Cell Stem Cell on February 15, mice were treated with stem cells created from adult tissue, called induced pluripotent stem cells. These stem cells have similar properties to cancer cells, and by combining them with a small amount of bacteria in a vaccine, the team successfully activated an immune response.
A few weeks after the mice had been vaccinated this way, the researchers injected them with breast cancer cells. Some T cells — white blood cells that fight off unwanted invaders — rejected the cancer cells in the mice, as well as newly-injected stem cells without the bacteria. The researchers replicated this treatment using lung and skin cancer cells, and the vaccination worked successfully each time.
While the vaccine is far from use in people and is just now entering trials in human cells, the researchers say it provides proof that stem cells could be enlisted in the development of personalized cancer vaccines in the future. “We’re proposing to activate the immune system, to target the immune system even before cancer develops,” says Nigel Kooreman, the lead researcher and surgical resident studying stem cell immunology at the Stanford School of Medicine.
But the idea of using stem cells as a cancer vaccine is an old one. Researchers in the mid 1960’s discovered that exposure to stem cells caused the body to destroy implanted tumors. More recently, scientists have found an explanation for why this reaction occurs: stem cells and cancer cells have hundreds of similar antigens on their surfaces. This similarity is what inspired Kooreman and his team to look into how they could use stem cells to train the body to recognize and fight off cancer.
“The good thing that these guys did is that they tried several different kinds of cancer in several different strains of mice,” says John Eaton, a molecular pharmacologist at the University of Louisville, who was not involved in the study. “Different strains of mice have different immune systems, so their results imply that [the vaccine] was more generally applicable.” And since the mice were raised in sterile environments, they tend to have weaker immune systems then humans, which suggests the vaccine will be even more useful in people, Eaton says.
In 2010, the FDA approved the first cancer vaccine for advanced prostate cancer, called Provenge (sipuleucel-T). It is used once a person already has cancer, and involves removing T cells from the body, training them to respond to certain antigens on prostate cancer cells, and then returning them to the body. Stem cell vaccines would jumpstart T cells in a similar manner, Eaton says. But using stem cells means the same treatment could act on a much wider variety of cancer cells. Stem cell vaccines would also train the body to recognize multiple antigens on the same type of cancer, Eaton says. That would help the body to continue to fight off cancer even when the cancer cells mutate and lose some of the original antigens — something that the Provenge vaccine is currently unable to do.
Another advantage stem cell vaccines may have over Provenge and other immunotherapy offerings, like CAR T therapy, is that these vaccines would be used as a preventive measure before you get cancer, instead of a treatment after the fact, says Joseph Wu, one of the study authors and a molecular pharmacologist at the Stanford School of Medicine. “In the future, if you’re 70 years old, we could take your blood, make the [induced pluripotent stem] cells — which have lot of the same antigens as your future cancer cells — and then immunize you from getting cancer,” he says.
But Eaton worries that stem cell vaccines, like current immunotherapy treatments, may be expensive. CAR T leukemia therapy, for example, costs around $373,000. Despite this concern, recent analyses have shown that personalized immunotherapies are actually quite economical compared to chemotherapies, especially when patient survival, quality of life and long-term health care costs are taken into account.
The stem cell vaccine data still has to hold up in human cells and large-scale clinical trials too. The vaccine is currently being tested in human cells in petri dishes to determine if it is safe to test in people, Kooreman says. “There’s not a definitive timeline to where we could push this to clinical trials,” he says.
“I think the general approach has some legs, how far it’s going to go is anybody’s guess,” Eaton says. Getting all the way through the clinical trials to FDA approval is a long process, and often requires fine-tuning. However, Eaton is optimistic that at the very least the study will spark more research on using stem cells for cancer vaccines. “I think there’s a chance that they might work pretty well,” he says.