Abstract PR001: Interpretation of patient-specific ex vivo immunotherapy response for ovarian cancer
Authors: Ceton Lieke , Koedoot Esmee , Sijsenaar Timothy , Garcia Marta Montero , Grillet Fanny , van der Valk Jurrian , Weber Klaus , Schoenauer Roman , Hufnagel Katrin , Schmidt Ronny , Stroh Nadine , Boekhoff Henning , de Kroon Cor , van Altena Anne , van der Meer Dieudonné , Vader Willemijn , Ottevanger Nelleke , Kroep Judith 
Published: December 2023

Background: Immunotherapies have shown great benefits, including durable clinical responses. However, the overall response rate remains low and it is challenging to select sensitive patients upfront. Patient-derived ex vivo tumor tissues with preserved tumor microenvironment (TME) represent the ideal model for patient-specific testing of immunotherapy sensitivities. This study aims to confirm that patient-specific ex vivo immunotherapy responses are matched by the presence of relevant immune components.

Material & Methods: Ascites of 84 patients with predominantly primary high grade ovarian carcinoma was collected between 2019 and 2023 in the Netherlands (IRB P18.032). Fresh tumor clusters with TME were seeded and exposed to six immunotherapies and the superantigen Staphylococcus aureus (SEA) as positive control. Tumor killing and immune cell proliferation were measured using 3D imaging. Ex vivo tumor sensitivity was classified on percentage and statistical significance of tumor killing. Immunohistochemical staining (IHC) for immune cell markers (CD3, CD68) (n=40) and proteomics analyses (n=26) were performed prior to drug exposure.

Results: SEA response was observed in 52% (44/84). Differential patient response profiles were observed, with 30% of the patients tissues displaying highly significant sensitivity for at least one of the therapies tested. Clustering the patients based on pathology scores uncovered four distinct groups: 1) CD68-/CD3-, 2) CD3-/CD68+, 3) CD3+/CD68+ and 4) CD3++/CD68++. Clustering and regression analysis demonstrated a significant correlation of increased CD3 and CD68 expression to ex vivo SEA sensitivity (p-value &lt; 0.05). Protein biomarker analysis supported these results, reporting significantly higher levels of chemokines and interleukins in SEA responders. Finally, different immune checkpoint inhibitors demonstrated distinct protein abundance profiles consistent with their mode of action.

Conclusion: This study reports classification and characterization of patient-specific sensitivity to 6 immunotherapies in 84 ovarian cancer patients enabled by a robust image-based ex vivo 3D tumor testing platform. The results demonstrate a positive relationship between the ex vivo sensitivity to immune-stimulatory compounds and the presence of functional immune components in the patient's TME. This confirms the interpretability of 3D ex vivo tumor testing for classification of patient-specific immune responses. Discussion: We previously demonstrated the predictive value of the platform by correlation of ex vivo sensitivity to clinical chemotherapy responses of ovarian cancer patients. Assay feasibility was also established for NSCLC, mesothelioma and bladder cancer. The two-week timeline enables its application in clinical practice. Quantifying ex vivo immunotherapy sensitivity will facilitate improved patient stratification for standard of care and novel treatments. Clinical trials are currently ongoing to establish the correlation of the assay with patients' response to immunotherapy.

Citation Format: Lieke Ceton, Esmee Koedoot, Timothy Sijsenaar, Marta Montero Garcia, Fanny Grillet, Jurrian van der Valk, Klaus Weber, Roman Schoenauer, Katrin Hufnagel, Ronny Schmidt, Nadine Stroh, Henning Boekhoff, Cor de Kroon, Anne van Altena, Dieudonné van der Meer, Willemijn Vader, Nelleke Ottevanger, Judith Kroep. Interpretation of patient-specific ex vivo immunotherapy response for ovarian cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr PR001.