The Phase 1 ALISON trial evaluates safety, efficacy and immunogenicity of vididencel in patients with high-grade mutation agnostic serous ovarian cancer (HGSOC). Mendus and academic collaborators from the University Medical Center Groningen (UMCG) presented data at ASCO 2025 demonstrating that in the majority of patients vididencel treatment resulted in immune responses against one or more tumor antigens frequently upregulated in HGSOC and that these responses were associated with higher stable disease rates. Vididencel was found to be safe and effective, with the intradermal injection-site cutaneous reaction being the principal side effect and no adverse events above grade 2.

At week 22 from start of vididencel treatment, 10 patients participating in the ALISON trial had stable disease and 7 had progressive disease, with all patients still alive. Stable disease rates were highest (67%) in patients with vididencel-induced immune responses (VIR) as compared to patients without VIR (40%). Updated survival data until March 2025 showed that 7 patients continued to have stable disease and 10 patients had developed progressive disease at a median follow-up of 19 months, with 10 patients still alive. Stable disease was associated with vididencel-induced immune responses, with VIR observed in 6 out of 7 of the patients with stable disease. Furthermore, two patients with VIR were reported to have stable disease for more than 3 years.

“We are thankful for the collaboration with the UMCG investigators with a special interest in immune-oncology treatment strategies and appreciate the opportunity to present the ALISON trial data for the first time at ASCO,” said Mendus CMO Tariq Mughal. “High-grade serous ovarian cancer is associated with a poor prognosis and sadly remains difficult to be treated in the precision oncology era. Our current findings suggest that our active immunotherapy approach with vididencel improves tumor-directed immune responses in this high-risk cohort. Longer term follow-up data, in particular survival, will enhance our understanding of the disease and the potential benefit of vididencel treatment for women diagnosed with this hard-to-treat life-threatening malignancy.”

“At the UMCG Department of Obstetrics and Gynecology, we are constantly seeking for more effective and safer methods to treat gynecological cancers” said Professor Marco de Bruyn, Head of the Immuno-oncology research group at UMCG. “The data presented at ASCO demonstrate that vididencel has the potential to induce immune responses against antigens previously shown to be relevant for HGSOC, combined with a strong safety profile. Together with Mendus we plan to further decipher the immune signatures, tumor characteristics and other potential mechanisms associated with improved clinical outcome following vididencel treatment.”

Mendus and UMCG have engaged in a research and clinical development collaboration since 2019. The collaboration comprises the single-center Phase 1 ALISON trial with vididencel in HGSOC and a preclinical research program to develop novel immunotherapies for gynecological cancers, including therapies based on tumor-infiltrating lymphocytes. Enrolment and week 22 analysis has been completed for all 17 participants of the ALISON trial. Long-term follow-up to assess potential survival benefit of vididencel treatment is ongoing. A next read-out of the trial based on 2-year follow-up is anticipated in the fourth quarter of 2025.

Please see below for details of the abstract presented at ASCO during the Gynecologic Cancer poster session on Sunday June 1, 2025, 9am-12pm CDT.

Abstract title: Successful induction of tumor-directed immune responses in high grade serous ovarian cancer patients after primary treatment using a whole tumor cell vaccine

Authors: Annegé Vledder, Hester van Zeeburg, Koen Brummel, Anneke Eerkens, N. van Rooij, Annechien Plat, Jeroen Rovers, Marco de Bruyn, Hans Nijman

Abstract Nr: 5566