Immunotherapy unleashes the power of the immune system to fight cancer. However, for some patients, immunotherapy doesn't work, and new research may help explain why. When immune cells called T lymphocytes infiltrate malignant tumors, the genetic program of those T cells and the developmental path they then follow, may affect their response to immunotherapy and predict overall patient survival, according to a new study. The results overturn the prevailing model of immune responses in melanoma and present different therapeutic approaches.