Abstract 3996: Organoids and immune cells co-culture for evaluating the efficacy of enfortumab vedotin and pembrolizumab combination therapy

Significant therapeutic progress have been made for advanced bladder cancer (BC) particularly with the combination of Enfortumab Vedotin (EV) and the pembrolizumab (anti-PD1). This combination has shown a manageable safety profile and superior outcomes compared to chemotherapy, leading to FDA approval for patients with advanced BC. In clinical settings, decisions regarding PD1 immunotherapy are guided by PDL1 expression levels on tumor cells. We selected two organoid models (F659 and BLOU_191) out of 18 from our biobank based on their PDL1 and nectin-4 expression. An additional organoid model (F659R) with acquired-resistance to EV was also included. The objectives of this study were to highlight the advantages of a co-culture system, which combines organoids and immune cells, to evaluate the efficacy of EV and pembrolizumab combination. Furthermore, leveraging recent developments, effectiveness of this therapy was assessed in a context of EV resistance. Transcriptome sequencing of our biobank enabled the identification of mRNA levels expression for PDL-1 and nectin-4. Peripheral blood mononuclear cells (PBMCs) from healthy donors were introduced into organoid cultures at varying effector-to-target (E:T) ratios. Co-cultures were treated with pembrolizumab (200 nM) and EV (from 0.3 to 3 µg/mL), both individually and in combination. Organoid viability was assessed using the CellTiter-Glo® assay at intervals ranging from 48 to 96 hours post-treatment. The efficacy of the combination therapy was then compared to the effects of each compound alone. We have assessed the responses of the three models to pembrolizumab and EV, and correlated treatment efficacy with PDL1 and nectin-4 expression levels, respectively. Results demonstrated that pembrolizumab efficacy was related to PDL1 expression in organoid models, while EV efficacy did not show a strict correlation with nectin-4 expression. Indeed, despite its high Nectin-4 expression, BLOU_191 presented only a low response to EV. In co-culture systems using the EV-responsive organoid model (F659), the combination of EV and pembrolizumab exhibited significant 20% enhanced efficacy compared to the individual treatments whereas it did not in the low-responder model (BLOU_191). In the resistant model, neither EV nor pembrolizumab exhibited significant efficacy when used alone, and their combination did not enhance these effects. The co-culture system involving organoids and PBMCs demonstrated its utility in evaluating the combination of pembrolizumab and EV. Notably, this study highlighted a critical finding: while the combination has shown superiority over current treatment options, it does not overcome resistance to EV. Overall, this co-culture system is highly adaptable to other immunotherapeutic agents and presents a valuable tool for developing novel therapies, particularly in addressing resistance to EV. Citation Format: Anne-Sophie Bajeot, Céline Rouget, Nadège Bidan, Claire Béraud, Sarah Péricart, Xavier Gamé, Mathieu Roumiguié, Philippe Lluel, Emilie Decaup. Organoids and immune cells co-culture for evaluating the efficacy of enfortumab vedotin and pembrolizumab combination therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3996.