Cancer treatments that make the immune system attack tumor cells often stop working after a while. This is because cells (called T regulatory cells) that protect our bodies from the immune system also end up protecting our tumors. New research shows that blocking T regulatory cells with antibodies extends immunotherapy in mice implanted with human lymphoma tumors. The researchers injected tumors with a mix of these antibodies and an immune system booster called CpG and found that treating just one tumor was enough to control tumors elsewhere, too. This could help treat tumors in the central nervous system, which can be hard to reach with conventional therapies. A clinical trial of the new treatment is underway for people with colon cancer, lymphoma, or melanoma and is currently recruiting participants.