By recruiting the immune system to combat tumor cells, immunotherapy has improved survival rates, offering hope to millions of cancer patients. However, only about one in five people responds favorably to these treatments.
With a goal of understanding and addressing immunotherapy’s limitations, researchers at Washington University School of Medicine in St Louis have found that the immune system can be its own worst enemy in the fight against cancer. In a new study in mice, a subset of immune cells — type 1 regulatory T cells, or Tr1 cells — did its normal job of preventing the immune system from overreacting but did so while inadvertently restraining immunotherapy’s cancer-fighting power.
“Tr1 cells were found to be a heretofore unrecognized obstacle to immunotherapy’s effectiveness against cancer,” said senior author Robert D. Schreiber, PhD, the Andrew M. and Jane M. Bursky Distinguished Professor in the Department of Pathology & Immunology, and director of the Bursky Center for Human Immunology & Immunotherapy at Washington University School of Medicine. “By removing or circumventing that barrier in mice, we successfully reenergized the immune system’s cancer-fighting cells and uncovered an opportunity to expand the benefits of immunotherapy for more cancer patients.”
The study is available in Nature.
Cancer vaccines represent a new approach to personalize cancer immunotherapy. Aimed at the mutant proteins specific to a patient’s tumor, such vaccines induce killer T cells to attack tumor cells while leaving healthy cells unharmed. Schreiber’s group previously showed that more effective vaccines also activate helper T cells, another immune cell type, that recruit and expand additional killer T cells to destroy the tumors. But when they tried to add increased amounts of the helper T cell target to supercharge the vaccine they found they generated a different type of T cell that inhibited rather than promoted tumor rejection.
“We tested the hypothesis that by increasing helper T cell activation we would induce enhanced elimination of the sarcoma tumors in mice,” said first author Hussein Sultan, PhD, an instructor in pathology & immunology. So he injected groups of tumor bearing mice with vaccines that activated killer T cells equally while triggering a different degree of helper T cell activation.