In tests in mice, the devices induced remission, prevented growth and spread of cancers, and increased survival times.

The immune system is a powerful frontline of defense against pathogens and illnesses, but a class of immune cells called regulatory T cells (Tregs) have the job of ensuring that it doesn't mistakenly attack the body's healthy cells. Unfortunately, one of cancer's nefarious tricks is to hijack this process and use it to protect itself from the immune system.

This makes Tregs an intriguing target for treatment, and in previous studies scientists have found ways to reprogram Tregs into cancer-killing immune cells. However, while reducing Treg levels can help make cancers more vulnerable, if done system-wide it runs the risk of triggering autoimmune complications. So in the new work, the UCLA team developed a new method for clearing out Tregs only in the area immediately around a tumor.

The end result is a device they call a SymphNode, which is essentially a biodegradable sponge about the size of an eraser on the end of a pencil. This is made of a hydrogel-like material called alginate, and loaded up with drugs that not only blocks Tregs but summons other anti-cancer T cells. When a SymphNode is implanted right next to a tumor, it gets to work releasing its drug payload.

The team tested the system in mice with breast cancer and melanoma, with impressive results across the board. The SymphNode shrank tumors in 80% of those with breast cancer, and prevented metastasis in 100% of cases. The device even stopped the growth of a second tumor elsewhere in the body. Untreated control mice, meanwhile, all died within a few weeks, after their cancers spread to their brains and lymph nodes.