Results of this phase I/II study provide the first clinical data on the safety, tolerability, and antitumor activity of mRNA-2416, a first-in-class lipid nanoparticle-encapsulated mRNA encoding human OX40L for intratumoral injection, alone and in combination with durvalumab in patients with relapsed/refractory solid tumor malignancies and ovarian cancer. The gene discussed is TNFSF4; the disease is ovarian cancer.