In a boost to immunotherapy for cancer treatments, researchers have found a way to use light to guide the immune system to attack tumor cells.

In mice with melanoma on the ears, the optical control was sufficient to allow the immune system to nearly wipe out the melanoma with no toxic side effects, the study published online in the journal Nature Communications said.The method is similar to "sending light on a spy mission to track down cancer cells", said lead author Minsoo Kim, Professor at University of Rochester Medical Centre in New York. Immunotherapy is different from radiation or chemotherapy. Instead of directly killing cancer cells, immunotherapy tells the immune system to act in certain ways by stimulating T cells to attack the disease. 

Several different types of immunotherapy exist or are in development, including pills called "checkpoint inhibitors" and CAR T-cell therapy that involves removing a patient's own immune cells and altering them genetically to seek and destroy cancer cells.The problem, however, is that immunotherapy can cause the immune system to overreact or under-react, Kim said.In addition, cancer cells are evasive and can hide from killer T-cells.Aggressive tumors also suppress the immune system in the areas surrounding the malignancy (called the microenvironment), keeping T cells out.If the immune system under-reacts, currently the only way to modify it is to pump more T cells into the body.But that often unleashes a storm of toxicities that can shut down a patient's organs.Kim's laboratory focused on how to overcome the immune-suppressive environment that cancer creates.

The researchers discovered that a molecule called channelrhodopsin (CatCh), which is active in algae and is light sensitive, could be introduced to the immune system via a virus and activated to control the T- cell response to cancer.The researchers tested in mice a LED chip which could eventually be implanted in humans.The team evaluated their methods in mice with melanoma on the ears.The animals wore a tiny battery pack that sent a wireless signal to the LED chip - allowing researchers to remotely shine light on the tumor and surrounding areas, giving T cells a boost for their cancer-killing function.

The optical control allowed the immune system to nearly wipe out the melanoma with no toxic side effects, the study reported.Future studies, Kim said, would determine whether the wireless LED signal can deliver light to a tumor deep within the body instead of on the surface area, and still have the ability to stimulate T cells to attack.