Abstract 5810: Distinct mechanisms of CD28 and 4-1BB costimulation in glofitamab combination therapies for relapsed/refractory non-Hodgkin lymphoma (R/R NHL)

Abstract Background: Two recent Phase I studies (NCT04077723, NCT05219513) investigated CD19-targeted 4-1BB or CD28 costimulatory bispecifics combined with glofitamab in patients with R/R NHL, showing added efficacy benefit but with distinct response dynamics (Hutchings et al; Dickinson et al, ASH 2024). While both costimulators are designed to enhance the anti-tumor effects of T-cell engagers, we present, for the first time, key differences in the mechanisms and response profiles of CD28 and 4-1BB costimulation in these combinations. Methods: Exploratory biomarker analyses included 28 indolent and aggressive NHL patients treated with RO7443904 (CD19-CD28) and 99 with englumafusp alfa (CD19-4-1BBL) on Cycle 2 (C2) Day 8, after completion of glofitamab step-up dosing, followed by administration on the same day as glofitamab from C3 onwards (Q3W) for a fixed duration of 12 cycles. Peripheral immune profiling was done by flow cytometry, and gene expression and mutational profile of the tumors were characterized by mRNA- and targeted DNA-sequencing. On-treatment pharmacodynamic changes were compared to historical glofitamab data from NCT03075696 (n=140). The cross-trial comparisons were adjusted for differences in baseline characteristics and sample size. Results: Compared to glofitamab monotherapy, both costimulators boosted and sustained peripheral T-cell activation and proliferation, with 4-1BB primarily expanding HLA-DR+ CD8 cells (1.5-fold), indicating prolonged activation, and CD28 boosting CD4/CD8 proliferation (2-fold). Additionally, 4-1BB further increased both effector and central memory CD8 cells (1.5-fold), while CD28 selectively expanded effector memory CD8 cells (1.5-fold) relative to glofitamab alone. Both costimulators limited PD1+ T-cell expansion in a dose-dependent manner, with 4-1BB mainly affecting Temra cells and CD28 targeting effector memory cells. Complete responses occurred independently of recurrent mutations (e.g. TP53, CREBBP, B2M) or cell-of-origin. However, tumor-infiltrating conventional dendritic cells (cDCs) were linked to response to 4-1BB and immunosuppressive macrophages were linked to lack of response to CD28, as determined by gene expression profiling of pre-treatment biopsies. Conclusion: Our findings reveal distinct mechanisms of CD28 and 4-1BB costimulation with glofitamab, which may explain their different response dynamics. Specifically, 4-1BB promotes a sustained and prolonged immune response, while CD28 triggers rapid T-cell activation and proliferation. Moreover, 4-1BB appears to bypass macrophage suppression, and benefits from cDC-mediated antigen presentation and CD8 T-cell priming. These effects mirror those observed in second-generation CAR T-cell therapies and provide insight into how these off-the-shelf costimulators may be utilized based on tumor biology. Citation Format: Koorosh Korfi, Zhiwen Jiang, Sabine Wilson, Ailsa Christiansen, Wilfred Leung, Katharina Lechner, Natalie Dimier, Philip Knuckles, Kat Reyskens, Iva Lelios, Annika Blank, Alexandra Epp, Sylvia Herter, Johannes Sam, Paolo Caimi, Lorenzo Falchi, Roch Houot, Fritz Offner, Harriet Walter, Herve Ghesquieres, Guillaume Cartron, William Townsend, Giuseppe Gritti, Francesc Bosch, Michael Dickinson, Carmelo Carlo-Stella, Martin Hutchings, Franck Morschhauser. Distinct mechanisms of CD28 and 4-1BB costimulation in glofitamab combination therapies for relapsed/refractory non-Hodgkin lymphoma (R/R NHL) [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 5810.