Abstract A019: <i>Ex vivo</i> modeling of immune interactions to improve immunotherapeutic efficacy in follicular lymphoma

Abstract Introduction Follicular lymphoma (FL), the second most common non-Hodgkin lymphoma, is virtually incurable with existing therapies. Emerging immune-based treatments like CD3xCD20 bispecific antibodies (BsAbs) have demonstrated promising activity in first line with complete remission rates exceeding 80%. However, relapses are common, often presenting with more resistant or transformed disease (PMID: 39349431, 41371238, PMC10429717). A critical imperative is to define mechanisms of in vivo resistance to BsAbs and identify biologically informed combination partners capable of overcoming them. To that end, we seek to develop in vitro co-culture models that recapitulate interactions between FL and T cells, as with existing models (PMID: 38402619), as well as tumor associated macrophages (MФ), which have been implicated in FL treatment response, proliferation, and transformation (PMID: 38194685, 26272216). These models will serve as tractable platforms for mechanistic interrogation and preclinical investigation of BsAbs in combination with candidate immunomodulators like Bruton’s tyrosine kinase inhibitors (BTKi).Methods FL cell lines WSU-FSCCL and SC-1 expressing luciferase and mCherry (FmC) were used in co-cultures. Peripheral blood mononuclear cells were isolated from healthy donors and patients with FL. CD3+ T cells were immunomagnetically isolated and activated ex vivo. Monocytes were differentiated using MCSF into MФ and polarized to pro-tumoral-like phenotypes. FmC FL lines were co-cultured with T cells and MФ in 1:1 and 1:4 effector-to-target (E:T) ratios, respectively. T cell-mediated cytotoxicity was evaluated by luminescence, while MФ phagocytosis was measured by flow cytometry, luminescence and Incucyte. Relevant concentrations of epcoritamab (epco) and glofitamab (glofit) were used for treatment with and without Ibrutinib (Ibr) and Zanubrutinib (Zanu). Results Preliminary findings indicate that tumor susceptibility to BsAbs is influenced by lymphoma cell line genetics, T cell functional states, and presence or absence of BTKi. Epco and glofit in the presence of T cells led to 20% viability of WSU and 70% viability of SC-1, over 56 hours. However, incubation of FL cells with Ibr or Zanu prior to the addition of T cells and epco led to better tumor control compared to BsAbs or BTKi alone. Phagocytosis using MФ and tumor cells, regardless of BTKi presence, manifested a peak of phagocytosis within 4 hours, with SC-1 being more susceptible to phagocytosis (18%), compared to WSU-FSCCL (5.5%). Future Directions Ongoing work focuses on incorporating patient-derived tumor cells, autologous T cells, and myeloid cells to establish more biologically fidelitous models for therapeutic susceptibility testing and response predictions. Citation Format: Ioulia Vogiatzi, Uday Aditya Sarkar, Irabelle Labomarel, Emily Sumpena, Olivia Hoffman, Laura Beckmann, Reid Merryman, Philippe Armand, Erin Parry, Paolo Ghia, Mark Murakami. Ex vivo modeling of immune interactions to improve immunotherapeutic efficacy in follicular lymphoma [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr A019.