Various co-stimulatory TNFL/TNFR pairs, including CD40L/CD40, CD70/CD27, 4-1BBL/4-1BB, and OX40L/OX40, have gained prominence as possible targets for cancer immunotherapy, in particular with the aim of induction or (re)activation of antitumor T-cell immunity. The gene discussed is CD27; the disease is cancer.