Implant raises cellular army to attack cancer

Implants that sit in the body and reprogram a person's immune cells could be used to treat a range of infectious diseases and even cancer. In a trial on mice with an aggressive melanoma that usually kills within 25 days, the new treatment saved 90% of the group.

Because cancer cells originate within the body, the immune system usually leaves them alone. Therapies exist that involve removing immune cells from the body before priming them to attack malignant tissue and injecting them back into a patient.

Results are not encouraging, though - more than 90% of re-injected cells die before they can have any effect, says David Mooney of Harvard University.

Mooney and colleagues have now developed a technique that directs the immune system from within the body - a method that is more efficient and potentially cheaper too.

Search and destroy

Their breakthrough involves implanting cylinders of an FDA-approved biodegradable polymer into the body. The implants release a particular variety of the cell-signalling molecules called cytokines - a sort of molecular perfume that is irresistible to a certain kind of immune-system messenger cell.

These dendritic cells are attracted into the pores of Mooney's implant, where they are exposed to antigens - the molecular signatures of the cancer, bacterium or virus being treated - and a danger-signal chemical derived from bacterial DNA.

This alert signal makes the dendritic cells flee to the nearest lymph node, where they meet up with the immune system's "killer" T-cells and program them to hunt down the invading cells.

Strength in numbers

In tests, the researchers implanted cylinders with a diameter of 8.5 millimetres into mice and two weeks later injected the animals with highly aggressive melanoma cells.

Mice implanted with 'blanks' - cylinders lacking any chemical additives - developed large tumours within 18 days and had to be euthanised. However, 90% of the mice given the full treatment were cured.

"There have not been any reports of the traditional [external] dendritic cell activation having survival rates at the levels we find with our materials for the cancer model we used," says Mooney.

He suspects this is because the implants can recruit and activate very large numbers of dendritic cells. "It is a continuous process - dendritic cells are attracted to the device, take up the [cancer] antigen and [the warning signal] … and then they can leave," says Mooney. "New cells are continuously arriving while activated cells are leaving."

The team thinks modified versions of the material could be effective against a range of cancers and infectious diseases. These might also help reprogram the immune system to combat autoimmune diseases such as type 1 diabetes, caused by immune cells destroying insulin-producing cells in the pancreas.