Scientists are reporting good success -- at least in mice -- from a whole new approach to fighting cancer that uses an implant to teach the immune system to attack tumours.

The tiny implant, placed under the skin, releases tumour-specific antigens to reprogram the immune system to attack and kill cancer cells,.

Scientists reporting this week in the journal Science Translational Medicine say the implants have worked well to eradicate melanoma skin cancer tumours in mice.

"This work shows the power of applying engineering approaches to immunology," says the study leader, David J. Mooney, a professor of Bioengineering in Harvard's School of Engineering and Applied Sciences.

The new plastic implants appear to be both more effective and less cumbersome than injectable cancer vaccines that are currently in clinical trials.

Those "vaccines" remove immune cells from the body, reprogram them to attack malignant tissues, and return them to the body. However, more than 90 per cent of re-injected cells die before having any effect, experiments have shown.

The implants developed by Mooney's group are made of an FDA-approved biodegradable polymer that release cytokines, powerful recruiters of immune-system messengers called dendritic cells.

These cells enter the implant, where they are exposed to antigens specific to the type of tumour being targeted. The dendritic cells then "report" to nearby lymph nodes, where they direct the immune system's T cells to hunt down and kill tumour cells.

"Inserted anywhere under the skin -- much like the implantable contraceptives that can be placed in a woman's arm -- the implants activate an immune response that destroys tumour cells," Mooney says.

The objective of Mooney's study wasn't to cure the mice of melanoma, although the researchers did observe "complete regression of distant and established melanoma tumours." But they believe their study did show that the concept of the implantable vaccines works and therefore provides "a template for future vaccine design."

In recent years, cancer vaccines have excited a lot of interest in cancer research. The hope is that they will have advantages over conventional cancer surgery and chemotherapy, since they target only cancer cells without damaging other tissues.

As well, there is even hope the vaccines can generate permanent resistance against cancerous cells, providing durable protection against relapse.

Mooney says the implant-based vaccine recruits several types of dendritic cells that direct destructive immune responses, creating an especially potent anti-tumour response.

"This approach is able to simultaneously upregulate the destructive immune response to the tumour while downregulating the arm of the immune system that leads to tolerance," Mooney says.

Earlier this year, researchers in the U.S. released the results of a study on an experimental vaccine that helps to fight prostate cancer.

With that vaccine, doctors collected dendritic cells from patients with advanced prostate cancer, mixed them with a protein found on most prostate cancer cells, and then injected the vaccine back into patients.

Those taking the vaccine lived, on average, four months longer than those who didn't receive the vaccine. While that may not sound long, that's still longer than the results offered by the chemotherapy drug that's currently the only treatment approved for late-stage prostate cancer.