Background: Besides PARP inhibitors and bevacizumab, there are no approved maintenance therapies after platinum based chemotherapy for patients with a platinum sensitive relapsed epithelial ovarian cancer (OC). Immune checkpoint inhibitors (ICI) as single agents have limited activity in OC. One attractive strategy is to turn OC from immunogenic “cold” to “hot” tumors via vaccination with tumor-associated antigens (TAAs). OSE2101 is a multiple-neoepitope vaccine restricted to HLA-A*02-positive patients (45% of OC patients) targeting 5 TAAs: TP53, MAGE2, MAGE3, CEA and HER2. These neo-epitopes are modified to increase both major histocompatibility complex and the T cell receptor binding affinity. The proof of concept for this approach was recently demonstrated with OSE2101 improving overall survival in a phase III trial in lung cancer progressing after ICI (Besse et al. 2021¹). The combination of OSE2101 with an ICI may most effectively harness anti-tumor immunity. Methods: TEDOVA is an international randomized open-label, phase II trial evaluating the benefit of maintenance by OSE2101 alone or in combination with PD1 inhibition (pembrolizumab) after platinum based chemotherapy in relapsed OC, previously treated with bevacizumab (if eligible) and a PARP inhibitor (if eligible). Patients (N=180) with CR/PR/SD at the end of chemotherapy are randomized (1:1:2) to: Observation/BSC (Arm A), OSE2101 alone (Arm B), or OSE2101 in combination with pembrolizumab (Arm C). Experimental treatments are continued until progression, or intolerance, for up to 2 years. The primary endpoint is progression-free survival (PFS). Secondary endpoints include overall response rate, safety, time to subsequent first or second treatment (TTST-1, TTST-2) and overall survival. 180 HLA-A*02 positive patients will be randomized. HLA-A*02 negative patients will be followed in a separate observational cohort. The sample size is calculated to provide 90% power to detect an improvement in PFS for Arm C vs Arm A with a HR of 0.57. Three one-sided Log-rank tests will be considered in a pre-defined sequence: H1: C (OSE2101+pembrolizumab) vs A (BSC); H2: C (OSE2101+pembrolizumab) vs B (OSE2101) and H3: B vs A. The type I error will be α=5%. The type II error will be β=10%. Tests will be one-sided. Status: The TEDOVA/GINECO-OV244b/ENGOT-ov58 trial is currently recruiting. Clinical trial information NCT04713514. 1. Besse B, Garcia MR, Cobo MA, Quoix E, Madroszyk A, Felip E, et al. LBA47 - Activity of OSE-2101 in HLA-A2+ non-small cell lung cancer (NSCLC) patients after failure to immune checkpoint inhibitors (IO): Final results of phase III Atalante-1 randomised trial. Annals of Oncology 2021;32(suppl_5) : S1283-S1346. Clinical trial information: NCT04713514.