Abstract 1599: CD40L-dependent regulation of BIM leads to lymphoma survival and therapy resistance in protective niches

Abstract Introduction: Mantle Cell Lymphoma (MCL), an aggressive B-cell lymphoma, is tightly dependent on the microenvironment (TME) for expansion and a dynamic cellular dialogue within lymph node (LN) niches results in ecosystem corruption and tumoral resistance. Within the TME, we identified modulations of the BCL2 family, including a deep inhibition of the pro-apoptotic protein BIM. The aims of this project were to identify the molecular pathways involved in the TME-dependent regulation of BIM and to evaluate the functional consequences in tumor survival and resistance. Methods: To decipher TME-dependent molecular regulations, we performed RNA-seq and ATAC-seq of MCL and normal B cells (NBC) in culture models previously set up to mimic signals observed in the LN ecosystem (Chiron et al., Blood, 2016). Identified hits/pathways were validated by qPCR and Western Blot. To evaluate the functional consequences of BIM inhibition, we generated BIM-/- MCL cells using CRISPR/Cas9 and performed BH3-profiling, drug testing (chemo, targeted and immune-therapies), serum-free survival studies and in vivo tumor growth assays in CAM model. Results: MCL cells stimulated by CD40L (T-cell signal) recapitulated BIM regulation, which was tumor-specific. Unsupervised analysis of annotated BIM transcription factors, using RNA-seq and TOBIAS (Transcription factor Occupancy prediction By Investigation of ATAC-seq Signal) analysis, highlighted FOXO1 as a candidate for MCL-specific and CD40L-dependent regulation of BIM. FOXO1 nuclear exclusion was further observed upon CD40L stimulation. Downstream of CD40, we demonstrated activation of the AKT, ERK and NFKB pathways. The involvement of AKT and/or ERK pathways in FOXO1/BIM regulation are under investigation. Functional studies showed an increased survival of BIM-/- cells in serum-free condition and an increase tumor growth in vivo. While primary MCL cells do not survive without TME support ex vivo, BIM-/- cells derived into TME-independent cell lines, reinforcing the association between BIM expression and tumor dependence to their TME. This is also consistent with BIM deletions being enriched in MCL lines. In addition, BIM -/- cells showed reduced mitochondrial priming and resistance to therapies (chemo, targeted). In contrast, T-cell engager efficiently killed both WT and BIM -/- lines, suggesting that modern immunotherapies could overcome BIM downregulation associated resistance. Conclusions: By integrating high-throughput technologies and cutting-edge functional studies, we have identified BIM inhibition as a TME-dependent source for therapeutic resistance and tumor cell survival. Innovative therapies, such as bispecific T-cell engager, could counteract this TME-induced resistance and provide new strategies for patients with these high-risk hemopathies. Citation Format: Candice Madiot, Céline Bellanger, Christelle Dousset, Salomé Decombis, Antonin Papin, Agnès Moreau-Aubry, Benoit Tessoulin, Catherine Pellat-Deceunynck, David Chiron. CD40L-dependent regulation of BIM leads to lymphoma survival and therapy resistance in protective niches [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 1599.