Tiny magnetic particles boost immune response to cancer in Hopkins study

Researchers activate naive T cells to fight melanoma in mice

Johns Hopkins researchers have used magnetic nanoparticles to make the immune systems in mice better at attacking a specific kind of cancer, an approach they say could represent a significant step in the fights against cancer and other deadly diseases.

In their experiments, the scientists used tiny, artificial white blood cells that they have developed to jumpstart an immune response to melanoma, a deadly skin cancer. The nanoparticles—called artificial antigen-presenting cells, or aAPCs—interact with naive T cells in the body, cells that are basically hanging out awaiting instructions on where and what to attack. This prompts a targeted immune response and also triggers the creation of new T cells.

The researchers found that the tumors in mice treated in this way stopped growing, and by the end of the experiment were about 10 times smaller than those in untreated mice.

Their findings are published online in the journal ACS Nano.

"Size was key to this experiment," says Jonathan Schneck, a professor of pathology, medicine, and oncology at the Johns Hopkins University School of Medicine's Institute for Cell Engineering. "By using small enough particles, we could, for the first time, see a key difference in cancer-fighting cells, and we harnessed that knowledge to enhance the immune attack on cancer."

The team had been working with microscale particles, which are about one one-hundredth of a millimeter across, but the particles were too large to get into some areas of a body. So they began working with much smaller nanoparticles and found them to be particularly effective in coaxing the naive T cells into action.

The magnets were used to create clusters of the nanoparticles, which led to more activation and ramped up the immune response. In the study, six of the eight mice treated with magnetic particle clusters showed no signs of tumor growth for four weeks after treatment.

"We were able to fine-tune the strength of the immune response by varying the strength of the magnetic field and how long it was applied, much as different doses of a drug yield different effects," says Karlo Perica, a graduate student in Schneck's laboratory. "We think this is the first time magnetic fields have acted like medicine in this way."

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