A vaccine that targets cancer stem cells dramatically limits tumor growth in mice, researchers reported in April. If the technique works in humans, it could be used to train a person’s own immune system to attack and destroy the cells at the root of most cancers.
Cancer stem cells are believed to lurk in nearly every type of tumor. Like other kinds of stem cells (which can develop into many other cell types), they can divide repeatedly. Unlike other stem cells, they multiply without limit and are thought to be major drivers of cancer relapse and progression. “All you need is one leftover cancer stem cell for a tumor to come back,” says Qiao Li, an immunologist at the University of Michigan Comprehensive Cancer Center in Ann Arbor. “These cells are the really bad guys.” The goal, then, is to wipe out every one of them.
To that end, Li and his colleagues developed a vaccine that specifically targets cancer stem cells. First they exposed mouse dendritic cells, which teach other immune cells what to attack, to stem cells taken from mouse tumors. The dendritic cells then stimulated the immune system’s main fighters, called T cells, to seek out and kill cancer stem cells—something they do not normally do. Finally, Li’s team injected a group of healthy mice with a vaccine of exposed dendritic cells, followed by an injection of cancer-causing cells. Another group of mice were injected with the cancer cells alone. Forty days later, the tumors in the immunized mice were one-tenth the size of those in the animals that did not get the vaccine.
Whether this approach can shrink tumors in humans is still unknown. If it proves as effective in people as it is in mice, a vaccine could one day be given to cancer patients after surgery, radiation therapy, or chemotherapy to prevent tumors from regrowing. Currently, Li’s approach works only after a cancer is already established, but there is an even greater hope: If researchers can identify a cancer stem cell that is common to all malignancies, they might be able to develop a broad-based vaccine to prevent cancer in the first place.